Skeletal muscle architecture and aging: A comparison of ultrasound techniques and an assessment of intrarater reliability

OBJECTIVE

To assess intrarater reliability of ultrasound-determined measurements of skeletal muscle characteristics across different measurement outcomes, imaging techniques, and age groups.

METHODS

2D ultrasound images (B-mode) of the quadriceps were obtained from young (26 ± 4 year, n = 8 M, 8 F) and older (70 ± 7 year, n = 7 M, 5 F) adults on two occasions, separated by 6 ± 3 days. With participants in both standing and supine postures, images were collected from five anatomical sites along the anterior (two sites) and lateral (three sites) compartments of the thigh corresponding to 56%, 39%, and 22% (lateral only) of femur length. Images were analysed for muscle thickness, pennation angle, and echogenicity. Intraclass correlation coefficients (ICC) were used to assess reliability.

RESULTS

Muscle thickness values were higher (p < 0.05) on images collected in the stand versus supine posture only for muscles of the anterior compartment, independent of age. Echogenicity values were higher (p < 0.05) in the vastus intermedius on images collected in the supine versus stand posture only in older adults. Pennation angle values were not impacted by imaging posture (p > 0.05). ICC values for thickness, echogenicity, and pennation angle were generally higher for analyses conducted on images collected in the supine versus stand posture. Imaging posture generated a greater difference in ICC values in the lateral versus anterior muscles and in older versus younger participants.

CONCLUSION

Our findings suggest that participant posture during imaging impacts the absolute values and intrarater reliability of ultrasound-determined muscle characteristics in a muscle-specific fashion, and this effect is greater in older compared to younger individuals.

Acute fatigue-induced alterations in hamstring muscle properties after repeated Nordic hamstring exercises

This study aimed to investigate the impact of the Nordic hamstring exercises (NHE) on acute fatigue-induced alterations in the mechanical and morphological properties of hamstring muscles. The second aim was to define the blood flow and perfusion after NHE in recreational active volunteers. Twenty-two individuals volunteered to participate in the study. This study investigated fatigue outcomes: rate of perceived exertion (RPE) scale and average force generated during NHE; mechanical properties (stiffness); morphological properties (thickness, pennation angle, and fascicle length), and vascularity index (VI) of the semitendinosus (ST) and biceps femoris long head (BFLH) at baseline, immediately post-exercise and 1-h post-exercise. The NHE fatigue procedure consisted of six bouts of five repetitions. The results showed an increase in thickness and pennation angle of BFLH and ST immediately post-exercise and a decrease in thickness and pennation angle of BFLH and ST 1-h post-exercise. While the fascicle length of BFLH and ST decreased immediately post-exercise and increased 1-h post-exercise. The VI for two muscles increased immediately post-exercise and after 1-h post-exercise. Moreover, we found a relationship between RPE and average force, that is, as RPE increased during NHE, average force decreased. In conclusion, eccentric NHE exercises significantly and acutely affect BFLH and ST. The NHE fatigue protocol significantly affected the mechanical and morphological properties of BFLH and ST muscles, changing their thickness, fascicle length, pennation angle, and VI.

Reliability of assessing skeletal muscle architecture and tissue organization of the gastrocnemius medialis and vastus lateralis muscle using ultrasound and spatial frequency analysis

Introduction

The purpose of this study was to investigate inter- and intra-rater reliability as well as the inter-rater interpretation error of ultrasound measurements assessing skeletal muscle architecture and tissue organization of the gastrocnemius medialis (GM) and vastus lateralis (VL) muscle.

Methods

The GM and VL of 13 healthy adults (22 ± 3 years) were examined thrice with sagittal B-mode ultrasound: intraday test-retest examination by one investigator (intra-rater) and separate examinations by two investigators (inter-rater). Additionally, images from one investigator were analysed by two interpretators (interpretation error). Muscle architecture was assessed by muscle thickness [MT], fascicle length [FL], as well as superior and inferior pennation angle [PA]. Muscle tissue organization was determined by spatial frequency analysis (SFA: peak spatial frequency radius, peak -6 dB width, PSFR/P6, normalized peak value of amplitude spectrum [Amax], power within peak [PWP], peak power percent). Reliability of ultrasound examination and image interpretation are presented as intraclass correlation coefficient (ICC), test-retest variability, standard error of measurement as well as bias and limits of agreement.

Results

GM and VL demonstrated excellent ICCs for inter- and intra-rater reliability, along with excellent ICCs for interpretation error of MT (0.91-0.99), showing minimal variability (<5%) and SEM% (<5%). Systematic bias for MT was less than 1 mm. For PA and FL poor to good ICCs for inter- and intra-rater reliability were revealed (0.41-0.90), with moderate variability (<12%), low SEM% (<10%) and systematic bias between 0.1-1.4°. Tissue organization analysis indicated moderate to good ICCs for inter- and intra-rater reliability. Notably, Amax and PWP consistently held the highest ICC values (0.77-0.87) across all analyses but with higher variability (<24%) and SEM% (<18%), compared to lower variability (<9%) and SEM% (<8%) in other tissue organization parameters. Interpretation error of all muscle tissue organization parameters showed excellent ICCs (0.96-0.999) with very low variability (≤1%) and SEM% (<2%), except Amax & PWP (TRV%: <6%; SEM%: <7%).

Conclusion

Our findings demonstrated excellent inter- and intra-rater reliability for MT. However, agreement for PA, FL, and SFA parameters was not as strong. Additionally, MT and all SFA parameters exhibited excellent agreement for inter-rater interpretation error. Therefore, the SFA seems to offer the possibility of objectively and reliably evaluating ultrasound images.

Architectural anatomy of the human tibialis anterior presents morphological asymmetries between superficial and deep unipennate regions

The tibialis anterior muscle plays a critical role in human ambulation and contributes to maintaining the upright posture. However, little is known about its muscle architecture in males and females. One hundred and nine physically active males and females were recruited. Tibialis anterior muscle thickness, pennation angle, and fascicle length were measured at rest in both unipennate regions of both legs using real-time ultrasound imaging. A linear mixed model was used with muscle thickness, pennation angle, or fascicle length as the dependent variables. All models were carried out with and without total leg lean mass and shank length as covariates. Causal mediation analysis was computed to explore the effect of muscle thickness on the relationship between fascicle length and pennation angle. There were no significant differences between dominant and nondominant legs regarding muscle architecture. Muscle thickness and pennation angle were greater in the deep than the superficial unipennate region in males (1.9 mm and 1.1°, p < 0.001) and women (3.4 mm and 2.2°, p < 0.001). However, the fascicle length was similar in both regions for both sexes. The differences remained significant after accounting for differences in leg lean mass and shank length. In both regions, muscle thickness was 1-3 mm greater in males and superficial pennation angle 2° smaller in females (both, p < 0.001). After accounting for leg lean mass and shank length, sex differences remained for muscle thickness (1.6 mm, p < 0.05) and pennation angle (3.4°, p < 0.001) but only in the superficial region. In both regions, leg lean mass and shank-adjusted fascicle length were 1.4 mm longer in females than males (p < 0.05). The causal mediation analysis revealed that the estimation of fascicle length was positive, suggesting that a 10% increase in muscle thickness would augment the fascicle length, allowing a 0.38° pennation angle decrease. Moreover, the pennation angle increases in total by 0.54° due to the suppressive effect of the increase in fascicle length. The estimated mediation, direct, and total effects were all significantly different from zero (p < 0.001). Overall, our results indicate that the architectural anatomy of the tibialis anterior shows sexual dimorphism in humans. Tibialis anterior presents morphological asymmetries between superficial and deep unipennate regions in both sexes. Lastly, our causal mediation model identified a suppressive effect of fascicle length on the pennation angle, suggesting that increments in muscle thickness are not always aligned with increments in fascicle length or the pennation angle.

Ultrasonographic measurements of fascicle length overestimate adaptations in serial sarcomere number

Ultrasound-derived measurements of muscle fascicle length (FL) are often used to infer increases (chronic stretch or training) or decreases (muscle disuse or aging) in serial sarcomere number (SSN). Whether FL adaptations measured via ultrasound can truly approximate SSN adaptations has not been investigated. We casted the right hindlimb of 15 male Sprague-Dawley rats in a dorsiflexed position (i.e., stretched the plantar flexors) for 2 weeks, with the left hindlimb serving as a control. Ultrasound images of the soleus, lateral gastrocnemius (LG), and medial gastrocnemius (MG) were obtained with the ankle at 90° and full dorsiflexion for both hindlimbs pre and post-cast. Following post-cast ultrasound measurements, legs were fixed in formalin with the ankle at 90°, then muscles were dissected and fascicles were teased out for measurement of sarcomere lengths via laser diffraction and calculation of SSN. Ultrasound detected an 11% increase in soleus FL, a 12% decrease in LG FL, and an 8-11% increase in MG FL for proximal fascicles and at full dorsiflexion. These adaptations were partly reflected by SSN adaptations, with a 6% greater soleus SSN in the casted leg than the un-casted leg, but no SSN differences for the gastrocnemii. Weak relationships were observed between ultrasonographic measurements of FL and measurements of FL and SSN from dissected fascicles. Our results showed that ultrasound-derived FL measurements can overestimate an increase in SSN by ∼5%. Future studies should be cautious when concluding a large magnitude of sarcomerogenesis from ultrasound-derived FL measurements, and may consider applying a correction factor. NEW FINDINGS: What is the central question of this study? Measurements of muscle fascicle length via ultrasound are often used to infer changes in serial sarcomere number, such as increases following chronic stretch or resistance training, and decreases with ageing: does ultrasound-derived fascicle length accurately depict adaptations in serial sarcomere number? What is the main finding and its importance? Ultrasound detected an ∼11% increase in soleus fascicle length, but measurements on dissected fascicles showed the actual serial sarcomere number increase was only ∼6%; therefore, measurements of ultrasound-derived fascicle length can overestimate serial sarcomere number adaptations by as much as 5%.

Adaptations in athletic performance and muscle architecture are not meaningfully conditioned by training free-weight versus machine-based exercises: Challenging a traditional assumption using the velocity-based method

BACKGROUND

Although the superior effectiveness of free-weight over machine-based training has been a traditionally widespread assumption, longitudinal studies comparing these training modalities were scarce and heterogeneous.

OBJECTIVE

This research used the velocity-based method to compare the effects of free-weight and machine-based resistance training on athletic performance and muscle architecture.

METHODS

Thirty-four resistance-trained men participated in an 8-week resistance training program allocated into free-weight (n = 17) or machine-based (n = 17) groups. Training variables (intensity, intraset fatigue, and recovery) were identical for both groups, so they only differed in the use of a barbell or specific machines to execute the full squat, bench press, prone bench pull, and shoulder press exercises. The velocity-based method was implemented to accurately adjust the planned intensity. Analysis of covariance and effect size (ES) statistics were used to compare both training modalities on a comprehensive set of athletic and muscle architecture parameters.

RESULTS

No between-group differences were found for any athletic (p ≥ 0.146) and muscle architecture (p ≥ 0.184) variable. Both training modalities significantly and similarly improved vertical jump (Free-weight: ES ≥ 0.45, p ≤ 0.001; Machine-based: ES ≥ 0.41, p ≤ 0.001) and lower limb anaerobic capacity (Free-weight: ES ≥ 0.39, p ≤ 0.007; Machine-based: ES ≥ 0.31, p ≤ 0.003). Additionally, the machine-based group meaningfully enhanced upper limb anaerobic power (ES = 0.41, p = 0.021), whereas the free-weight group significantly improved the change of direction (ES = -0.54, p = 0.003) and 2/6 balance conditions analyzed (p ≤ 0.012). Changes in sprint capacity (ES ≥ -0.13, p ≥ 0.274), fascicle length, and pennation angle (ES ≤ 0.19, p ≥ 0.129) were not significant for either training modality.

CONCLUSION

Adaptations in athletic performance and muscle architecture would not be meaningfully influenced by the resistance modality trained.

Influence of Pennation Angle and Muscle Thickness on Mechanomyographic Amplitude-Torque Relationships and Sex-Related Differences in the Vastus Lateralis

This study examined potential sex-related differences and correlations among the pennation angle (PA), muscle thickness (MT), and mechanomyographic amplitude (MMG_RMS)-torque relationships of the vastus lateralis (VL) in 11 healthy males and 12 healthy females. The PA and MT of the VL were quantified with ultrasound. Participants performed an isometric muscle action of the knee extensors that linearly increased to 70% of maximal strength followed by a 12 s plateau. MMG was recorded from the VL. Linear regression models were fit to the log-transformed MMG_RMS-torque relationships to calculate b terms (slopes) for the linearly increasing segment. MMG_RMS was averaged during the plateau. Males exhibited greater PA (p < 0.001), MT (p = 0.027), b terms (p = 0.005), and MMG_RMS (p = 0.016). The b terms were strongly (p < 0.001, r = 0.772) and moderately correlated (p = 0.004, r = 0.571) with PA and MT, respectively, while MMG_RMS was moderately correlated with PA (p = 0.018, r = 0.500) and MT (p = 0.014, r = 0.515). The greater mechanical behavior of individuals possessing a larger PA and MT of the VL may reflect increased cross-bridge activity within the muscle fibers. Additionally, PA may help explain sex-related differences in MMG_RMS between sexes.

Correlations Between Hamstring Muscle Architecture, Maturation, and Anthropometric Measures in Academy Soccer Players

PURPOSE

Muscle architecture is associated with motor performance and muscle injury. While muscle architecture and knee-flexor eccentric strength change with growth, the influence of anthropometric measures on these properties is rarely considered. This study aimed to investigate the relationship between hamstring muscle architecture and knee-flexor eccentric strength with anthropometric measurements.

METHODS

Sixty male footballers (16.6 [1.05] y) from the U16, U17, and U19 teams of an elite soccer club were included in this study. Fascicle length, pennation angle, and muscle thickness of the biceps femoris long head (BFlh) and semimembranosus muscles were measured in both legs using ultrasound. Knee-flexor eccentric strength, height, body mass, leg length, femur length, and peak height velocity (PHV) were measured within 1 week of the ultrasound images. A stepwise regression and 1-way analysis of variance tests were used to evaluate the effects of age, maturity, and anthropometric measurements on muscle properties.

RESULTS

Variance within BFlh and semimembranosus muscle thickness (r < .61), semimembranosus pennation angle (r < .58), and knee-flexor eccentric strength (r = .50) were highly related to body mass. We observed no significant correlations between muscle architecture and age (P > .29). However, moderately greater BFlh muscle thickness was shown for the post-PHV compared with the PHV group (effect size ± 90% CI: 0.72 ± 0.49).

CONCLUSIONS

In conclusion, weak correlations between muscle architecture and anthropometric measurements suggest that other factors (ie, genetics, training regimen) influence muscle architecture. The moderate effect of maturity on BFlh muscle thickness strongly suggests post-PHV hypertrophy of the BFlh muscle. Our results confirmed previous findings that eccentric knee-flexor strength is influenced by body mass.

Effect of two eccentric hamstring exercises on muscle architectural characteristics assessed with diffusion tensor MRI

OBJECTIVES

To evaluate the effect of a Nordic hamstring exercise or Diver hamstring exercise intervention on biceps femoris long head, semitendinosus and semimembranosus muscle's fascicle length and orientation through diffusion tensor imaging (DTI) with magnetic resonance imaging.

METHODS

In this three-arm, single-center, randomized controlled trial, injury-free male basketball players were randomly assigned to a Nordic, Diver hamstring exercise intervention or control group. The primary outcome was the DTI-derived fascicle length and orientation of muscles over 12 weeks.

RESULTS

Fifty-three participants were included for analysis (mean age 22 ± 7 years). Fascicle length in the semitendinosus over 12 weeks significantly increased in the Nordic-group (mean [M]: 20.8 mm, 95% confidence interval [95% CI]: 7.8 to 33.8) compared with the Control-group (M: 0.9 mm, 95% CI: -7.1 to 8.9), mean between-groups difference: 19.9 mm, 95% CI: 1.9 to 37.9, p = 0.026. Fascicle orientation in the biceps femoris long head over 12 weeks significantly decreased in the Diver-group (mean: -2.6°, 95% CI: -4.1 to -1.0) compared with the Control-group (mean: -0.2°, 95% CI: -1.4 to 1.0), mean between-groups difference: -2.4°, 95% CI: -4.7 to -0.1, p = 0.039.

CONCLUSION

The Nordic hamstring exercise intervention did significantly increase the fascicle length of the semitendinosus and the Diver hamstring exercise intervention did significantly change the orientation of fascicles of the biceps femoris long head. As both exercises are complementary to each other, the combination is relevant for preventing hamstring injuries.

Muscle Architecture, Morphology, and Mechanical and Functional Properties of Biceps Femoris Long Head in Professional Soccer Players with a Prior Healed Injured Hamstring

OBJECTIVE

The aim of the present study was to compare the fascicle length, pennation angle, muscle thickness and stiffness of the biceps femoris long head, and eccentric hamstring strength between injured dominant limbs, injured non-dominant limbs, uninjured dominant limbs and uninjured non-dominant legs in previously injured players, and between dominant and non-dominant legs in uninjured elite soccer players.

MATERIALS AND METHODS

Twenty elite soccer players participated in this study. Ultrasound imaging and MyotonPRO were used to determine the morphological and mechanical properties of the biceps femoris long head. Isokinetic and Nordic hamstring exercises were used to assess eccentric hamstring strength.

RESULTS

Previously injured players showed substantially lower fascicle length and muscle thickness, and significantly higher biceps femoris long head stiffness than uninjured players, without differences between limbs.

CONCLUSION

The morphological and mechanical properties of elite soccer players with hamstring injury history were different from those in uninjured players. The lack of differences between limbs showed that these values are characteristics of individual players that must be considered in the design of programs to prevent BFlh injury.

Automated Method for Tracking Human Muscle Architecture on Ultrasound Scans during Dynamic Tasks

Existing approaches for automated tracking of fascicle length (FL) and pennation angle (PA) rely on the presence of a single, user-defined fascicle (feature tracking) or on the presence of a specific intensity pattern (feature detection) across all the recorded ultrasound images. These prerequisites are seldom met during large dynamic muscle movements or for deeper muscles that are difficult to image. Deep-learning approaches are not affected by these issues, but their applicability is restricted by their need for large, manually analyzed training data sets. To address these limitations, the present study proposes a novel approach that tracks changes in FL and PA based on the distortion pattern within the fascicle band. The results indicated a satisfactory level of agreement between manual and automated measurements made with the proposed method. When compared against feature tracking and feature detection methods, the proposed method achieved the lowest average root mean squared error for FL and the second lowest for PA. The strength of the proposed approach is that the quantification process does not require a training data set and it can take place even when it is not possible to track a single fascicle or observe a specific intensity pattern on the ultrasound recording.

Effects of growth on muscle architecture of knee extensors

This study aimed to investigate the effects of growth on the muscle architecture of knee extensors. The present study included 123 male children and adolescents. The muscle thicknesses of the rectus femoris (RF) and vastus intermedius (VI), and pennation angles and fascicle lengths of RF were measured in three regions using ultrasonography technique at rest. The relative muscle thickness was calculated by dividing the absolute muscle thickness by body mass^1/3 . The years from age at peak height velocity were estimated for each participant, and used as a maturity index. The maturity index was significantly correlated with the relative muscle thicknesses of RF and VI in all regions. The slope of the relationship between the maturity index and the relative muscle thickness did not differ significantly between muscles within the same region or between regions within the individual muscles. The fascicle length and pennation angle of RF were significantly correlated with the absolute muscle thickness in all regions. In the proximal RF region, the coefficient of correlation between the muscle thickness and fascicle length was significantly greater than that between the muscle thickness and pennation angle. The present results showed that growth changes in muscle thickness were uniform between and within RF and VI. Our findings suggest that growth changes in the muscle thickness of RF depend on the increases in both pennation angle and fascicle length, but their contributions to the growth of muscle thickness differ among muscle regions.

Effects of post-activation potentiation on mechanical output and muscle architecture during electrically-induced contractions in plantar flexors

This study investigated the effects of post-activation potentiation (PAP) on the force output and muscle architecture in plantar flexor muscles. The mechanical response to a single electrical stimulus (twitch), and to two (doublet) and three (triplet) stimuli (10-ms inter-pulse interval) was measured before and after a 6-s maximal voluntary contraction (MVC). Ultrasound imaging was used to measure fascicle length and pennation angle of the gastrocnemius medialis at rest and during the electrically-induced contractions. Immediately after the conditioning MVC, twitch peak force [+40%] and its maximal rate of force development [+57%] and relaxation [+62%] were greater than before the MVC (p<0.001). The PAP extent was lesser for the doublet than for the twitch and for the triplet than for the doublet (p<0.05). Whereas none of the architectural parameters changed at rest, fascicle shortening and increase in pennation angle during contractions were greater after than before the conditioning MVC, with a greater extent (p<0.001) during the twitch (+28% and +58%, respectively) compared with the doublet (+16% and +36%) and the triplet (+12% and +14%). Overall, our results indicate that the effect of the conditioning MVC on mechanical output and muscle architecture decreased from the twitch to the triplet in PF muscles. The decreased PAP observed during doublet and triplet compared to twitch, indicate that the benefit of this mechanism to the enhancement of muscle performance become progressively less effective during successive muscle activation.

Effect of the Knee and Hip Angles on Knee Extensor Torque: Neural, Architectural, and Mechanical Considerations

This study examined the influence of knee extensors' hip and knee angle on force production capacity and their neuromuscular and architectural consequences. Sixteen healthy men performed sub-maximal and maximal voluntary isometric contractions (MVIC) of knee extensors with four different combinations of the knee and hip angles. Muscle architecture, excitation-contraction coupling process, muscular activity, and corticospinal excitability were evaluated on the vastus lateralis (VL) and rectus femoris (RF) muscles. MVIC and evoked peak twitch (Pt) torques of knee extensors increased significantly (p < 0.05) by 42 ± 12% and 47 ± 16% on average, respectively, under knee flexed positions (110° flexion, 0° = full extension) compared to knee extended positions (20° flexion) but were not different between hip positions (i.e., 0° or 60° flexion). Knee flexion also affected VL and RF muscle and fascicle lengths toward greater length than under knee extended position, while pennation angle decreased for both muscles with knee flexion. Pennation angles of the VL muscle were also lower under extended hip positions. Alternatively, no change in maximal muscle activation or corticospinal activity occurred for the VL and RF muscles across the different positions. Altogether these findings evidenced that MVIC torque of knee extensors depended particularly upon peripheral contractile elements, such as VL and RF muscle and fascicle lengths, but was unaffected by central factors (i.e., muscle activation). Furthermore, the hip position can affect the pennation angle of the VL, while VL muscle length can affect the pennation angle of the RF muscle. These elements suggest that the VL and RF muscles exert a mutual influence on their architecture, probably related to the rectus-vastus aponeurosis.

Comparison Between High- and Low-Intensity Static Stretching Training Program on Active and Passive Properties of Plantar Flexors

The purpose of this study was to compare two static stretching (SS) training programs at high-intensity (HI-SS) and low-intensity (LI-SS) on passive and active properties of the plantar flexor muscles. Forty healthy young men were randomly allocated into three groups: HI-SS intervention group (n = 14), LI-SS intervention group (n = 13), and non-intervention control group (n = 13). An 11-point numerical scale (0–10; none to very painful stretching) was used to determine SS intensity. HI-SS and LI-SS stretched at 6–7 and 0–1 intensities, respectively, both in 3 sets of 60 s, 3×/week, for 4 weeks. Dorsiflexion range of motion (ROM), gastrocnemius muscle stiffness, muscle strength, drop jump height, and muscle architecture were assessed before and after SS training program. The HI-SS group improved more than LI-SS in ROM (40 vs. 15%) and decreased muscle stiffness (−57 vs. −24%), while no significant change was observed for muscle strength, drop jump height, and muscle architecture in both groups. The control group presented no significant change in any variable. Performing HI-SS is more effective than LI-SS for increasing ROM and decreasing muscle stiffness of plantar flexor muscles following a 4-week training period in young men. However, SS may not increase muscle strength or hypertrophy, regardless of the stretching discomfort intensity.

Gastrocnemius Muscle Architecture in Elite Basketballers and Cyclists: A Cross-Sectional Cohort Study

Eccentric and concentric actions produce distinct mechanical stimuli and result in different adaptations in skeletal muscle architecture. Cycling predominantly involves concentric activity of the gastrocnemius muscles, while playing basketball requires both concentric and eccentric actions to support running, jumping, and landing. The aim of this study was to examine differences in the architecture of gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) between elite basketballers and cyclists. A trained sonographer obtained three B-mode ultrasound images from GM and GL muscles in 44 athletes (25 basketballers and 19 cyclists; 24 ± 5 years of age). The images were digitized and average fascicle length (FL), pennation angle (θ), and muscle thickness were calculated from three images per muscle. The ratio of FL to tibial length (FL/TL) and muscle thickness to tibial length (MT/TL) was also calculated to account for the potential scaling effect of stature. In males, no significant differences were identified between the athletic groups in all parameters in the GM, but a significant difference existed in muscle thickness in the GL. In basketballers, GL was 2.5 mm thicker (95% CI: 0.7-4.3 mm, p = 0.011) on the left side and 2.6 mm thicker (95% CI: 0.6-5.7 mm, p = 0.012) on the right side; however, these differences were not significant when stature was accounted for (MT/TL). In females, significant differences existed in the GM for all parameters including FL/TL and MT/TL. Female cyclists had longer FL in both limbs (MD: 11.2 and 11.3 mm), narrower θ (MD: 2.1 and 1.8°), and thicker muscles (MD: 2.1 and 2.5 mm). For the GL, female cyclists had significantly longer FL (MD: 5.2 and 5.8 mm) and narrower θ (MD: 1.7 and 2.3°) in both limbs; no differences were observed in absolute muscle thickness or MT/TL ratio. Differences in gastrocnemius muscle architecture were observed between female cyclists and basketballers, but not between males. These findings suggest that participation in sport-specific training might influence gastrocnemius muscle architecture in elite female athletes; however, it remains unclear as to whether gastrocnemius architecture is systematically influenced by the different modes of muscle activation between these respective sports.

Effects of Muscle Architecture on Eccentric Exercise Induced Muscle Damage Responses

There is a need to investigate the role of muscle architecture on muscle damage responses induced by exercise. The aim of this study was to determine the effect of muscle architecture and muscle length on eccentric exercise-induced muscle damage responses. Eccentric exercise-induced muscle damage was performed randomly to the elbow flexor (EF), knee extensor (KE), and knee flexor (KF) muscle groups with two week intervals in 12 sedentary male subjects. Before and after each eccentric exercise (immediately after, on the 1^st, 2^nd, 3^rd, and 7^th days) range of motion, delayed onset muscle soreness, creatine kinase activity, myoglobin concentration and isometric peak torque in short and long muscle positions were evaluated. Furthermore, muscle volume and pennation angle of each muscle group was evaluated before initiating the eccentric exercise protocol. Pennation angle and muscle volume was significantly higher and the workload per unit muscle volume was significantly lower in the KE muscles compared with the KF and EF muscles (p < 0.01). EF muscles showed significantly higher pain levels at post-exercise days 1 and 3 compared with the KE (p < 0.01-0.001) and KF (p < 0.01) muscles. The deficits in range of motion were higher in the EF muscles compared to the KE and KF muscles immediately after (day 0, p < 0.01), day 1 (p < 0.05-0.01), and day 3 (p < 0.05) evaluations. The EF muscles represented significantly greater increases in CK and Mb levels at day 1, 3, and 7 than the KE muscles (p < 0.05-0.01). The CK and Mb levels were also significantly higher in the KF muscles compared with the KE muscles (p < 0.05, p < 0.01 respectively). The KF and EF muscles represented higher isometric peak torque deficits in all the post-exercise evaluations at muscle short position (p < 0.05-0.001) compared with the KE muscle after eccentric exercise. Isometric peak torque deficits in muscle lengthened position was significantly higher in EF in all the post-exercise evaluations compared with the KE muscle (p < 0.05-0.01). According to the results of this study it can be concluded that muscle structural differences may be one of the responsible factors for the different muscle damage responses following eccentric exercise in various muscle groups.

Muscle Fibre Architecture of Thoracic and Lumbar Longissimus Dorsi Muscle in the Horse

Simple Summary

As the longissimus dorsi muscle is the largest muscle in the equine back, it has great influence on the stability of the spine and facilitates proper locomotion. In general, muscle function is determined by its specific intramuscular architecture. However, only limited three-dimensional metrical data are available for the inner organisation of the equine longissimus dorsi muscle. The thoracic and lumbar longissimus muscles of five formalin-fixed cadaveric horse backs of different ages and body types were dissected layerwise from cranial to caudal. Three-dimensional coordinates along individual muscle fibre bundles were digitised from the origin to the insertion and 3D models were created using imaging software and computed tomography. The muscle was divided into functional compartments and morphometric parameters (muscle fascicle length, pennation angles, muscle volume and the physiological cross-sectional area (PCSA)) were determined. Fascicle length showed the highest values in the thoracic region and decreased from cranial to caudal, while in most caudal compartments, fascicle length was less than 50% of the fascicle length in thoracic compartments. The pennation angles differ between compartments. In the cranial compartment, fascicles almost run parallel to the horizontal plane (mean angle 0°), while in the caudal compartment, the angles increase up to a mean angle of 38°. In the sagittal plane, the pennation angles varied from parallel (0°) in cranial compartments to 0–22° in the caudal compartments. The muscle volume ranged from 1350 cm³ to 4700 cm³ and PCSA from 219 cm² to 700 cm². This study lays the anatomical basis for a biomechanical model to simulate muscle function.

Abstract

As the longissimus dorsi muscle is the largest muscle in the equine back, it has great influence on the stability of the spine and facilitates proper locomotion. The longissimus muscle provides support to the saddle and rider and thereby influences performance in the horse. Muscular dysfunction has been associated with back disorders and decline of performance. In general, muscle function is determined by its specific intramuscular architecture. However, only limited three-dimensional metrical data are available for the inner organisation of the equine longissimus dorsi muscle. Therefore, we aimed at investigating the inner architecure of the equine longissimus. The thoracic and lumbar longissimus muscles of five formalin-fixed cadaveric horse backs of different ages and body types were dissected layerwise from cranial to caudal. Three-dimensional coordinates along individual muscle fibre bundles were recorded using a digitisation tool (MicroScribe^®), to capture their origin, insertion and general orientation. Together with skeletal data from computed tomography (CT) scans, 3D models were created using imaging software (Amira). For further analysis, the muscle was divided into functional compartments during preparation and morphometric parameters, such as the muscle fascicle length, pennation angles to the sagittal and horizontal planes, muscle volume and the physiological cross-sectional area (PCSA), were determined. Fascicle length showed the highest values in the thoracic region and decreased from cranial to caudal, with the cranial lumbar compartment showing about 75% of cranial fascicle length, while in most caudal compartments, fascicle length was less than 50% of the fascicle length in thoracic compartments. The pennation angles to the horizontal plane show that there are differences between compartments. In most cranial compartments, fascicles almost run parallel to the horizontal plane (mean angle 0°), while in the caudal compartment, the angles increase up to a mean angle of 38°. Pennation angles to the sagittal plane varied not only between compartments but also within compartments. While in the thoracic compartments, the fascicles run nearly parallel to the spine, in the caudal compartments, the mean angles range from 0–22°. The muscle volume ranged from 1350 cm³ to 4700 cm³ depending on body size. The PCSA ranged from 219 cm² to 700 cm² depending on the muscle volume and mean fascicle length. In addition to predictable individual differences in size parameters, there are obvious systemic differences within the muscle architecture along the longissimus muscle which may affect its contraction behaviour. The obtained muscle data lay the anatomical basis for a specific biomechanical model of the longissimus muscle, to simulate muscle function under varying conditions and in comparison to other species.

Automatic Measurement of Pennation Angle from Ultrasound Images using Resnets

In this study, an automatic pennation angle measuring approach based on deep learning is proposed. Firstly, the Local Radon Transform (LRT) is used to detect the superficial and deep aponeuroses on the ultrasound image. Secondly, a reference line are introduced between the deep and superficial aponeuroses to assist the detection of the orientation of muscle fibers. The Deep Residual Networks (Resnets) are used to judge the relative orientation of the reference line and muscle fibers. Then, reference line is revised until the line is parallel to the orientation of the muscle fibers. Finally, the pennation angle is obtained according to the direction of the detected aponeuroses and the muscle fibers. The angle detected by our proposed method differs by about 1° from the angle manually labeled. With a CPU, the average inference time for a single image of the muscle fibers with the proposed method is around 1.6 s, compared to 0.47 s for one of the image of a sequential image sequence. Experimental results show that the proposed method can achieve accurate and robust measurements of pennation angle.

Chronic Adaptations of the Posterior Rotator Cuff in Professional Pitchers

BACKGROUND

Because of the large forces and high frequency of throwing, the upper extremity experiences repetitive stresses that lead to acute and chronic adaptations. While the importance of pennation angle and muscle thickness as predictors of muscle force production has been shown in other populations and other joints, there has been little research done that examines these variables in the shoulders of baseball players.

PURPOSE

(1) To examine the chronic effect pitching has on the rotator cuff muscle architecture (pennation angle and muscle thickness) in healthy professional baseball pitchers, and (2) to examine the correlation between muscle architecture and clinical measures of strength and range of motion (ROM).

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Twenty-eight healthy professional pitchers were recruited during the 2019 spring training. Internal rotation (IR) and external rotation (ER) strength were measured with a handheld dynamometer and IR and ER ROM were measured with an inclinometer. A diagnostic ultrasound machine was utilized to capture images of humeral retroversion, as well as the pennation angle and muscle thickness of the infraspinatus and teres minor muscles. ImageJ software was used to quantify the pennation angle and muscle thickness.

RESULTS

There were no significant differences between the dominant and nondominant arms for ER or IR strength. Also, no pennation angle and muscle thickness differences were found between the dominant and nondominant arms. A weak positive relationship between infraspinatus muscle thickness (superficial and total) and ER strength (P = .016, R = 0.287 and P = .009, R = 0.316) and a moderate negative relationship between soft tissue glenohumeral internal rotation deficit (GIRD) and the bilateral difference of the teres minor deep pennation angle (R = -0.477, P = .008) were observed. No other significant relationships were noted.

CONCLUSION

Our results are contrary to current literature as we expected to see a stronger dominant arm, with a larger pennation angle and greater muscle thickness. Interestingly, we found that ER strength was positively related to only the thickness of the infraspinatus muscle, and that soft tissue GIRD was positively related to only the side-to-side adaptation of the pennation angle within the deep portion of the teres minor. This suggests that when posterior shoulder tightness occurs, specifically the architecture of the teres minor muscle is involved. However, the organization to which these players belonged has a very extensive training protocol throughout the year that emphasizes bilateral training during a large majority of the exercises. Therefore, the results may not be generalizable to all professional players.

longissimus thoracis et lumborum) Associated with Muscle Fiber Pennation Angle and Their Relationships with Pork Loin Quality

The influence of muscle architecture on muscle fiber characteristics and meat quality has not been fully elucidated. In the present study, muscle fiber characteristics on the chop surface of pork loin (M. longissimus thoracis et lumborum, LTL), pennation angle degree, and meat quality were evaluated to understand the pork LTL architecture and its relationship with the loin chop quality. Muscle fiber pennation degree ranged from 51.33° to 69.00°, resulting in an ellipse-shaped muscle fiber on the surface of pork loin chop. The cross-sectional area (CSA) on the sections cut vertical to the muscle length (M-Vertical) was considerably larger (p<0.05) than that on the sections cut vertical to the muscle fiber orientation (F-Vertical) regardless of the fiber type. Pennation angle is positively correlated with CSAs of F-Vertical (p<0.05) and with Warner-Bratzler shear force (r=0.53, p<0.01). Besides the shear force, lightness and pH were positively correlated with the fiber composition and CSA of IIX fiber (p<0.05); however, the redness, yellowness, drip loss, and cooking loss were not correlated with the pennation angle and muscle fiber characteristics on the chop surface (p>0.05). These observations might help us in better understanding pork loin architecture and the relationship between the pennation angle, muscle fiber characteristics, and meat quality of pork loin chop.

Surgical repair of the supraspinatus: architectural changes in the muscle pre- and postoperatively

INTRODUCTION

Shortening of the tendon and muscle is recognised as a strong predictor for surgical failure of supraspinatus tendon tears. Changes in muscle architecture following repair have not been thoroughly investigated. We aimed to compare the architecture of the supraspinatus pre- and postoperatively.

METHODS

We recruited eight participants with full-thickness supraspinatus tears. Images of the supraspinatus were captured preoperatively (pre-op) and postoperatively at one (post-op1), three (post-op2) and six (post-op3) months in relaxed and contracted states (0° and 60° glenohumeral abduction). Fibre bundle length (FBL), pennation angle (PA) and muscle thickness (MT) were quantified. Self-reported function, and maximal isometric abduction and external rotation strengths were assessed.

RESULTS

Mean FBL increased from pre-op to post-op1 (p = 0.001) in the relaxed state and from pre-op to post-op2 (p = 0.002) in the contracted state. Decrease in FBL was observed from post-op2 to post-op3 in the relaxed state. Mean PA decreased from pre-op to post-op1 (p < 0.001) in the relaxed state, but increased from post-op2 to post-op3 in both relaxed (p = 0.006) and contracted (p = 0.004) states. At post-op3, external rotation (p = 0.009) and abduction (p = 0.005) strengths were greater than at post-op2. Overall function increased by 47.67% from pre-op to post-op3.

CONCLUSION

Lengthening of the supraspinatus occurs with surgery, altering the length-tension relationship of the muscle, which can compromise muscle function and lead to inferior surgical outcomes. These findings may guide clinicians to optimise loads, velocities and shoulder ranges for effective postoperative rehabilitation.

Effects of eccentric training at long-muscle length on architectural and functional characteristics of the hamstrings

Hamstring strain injuries during sprinting or stretching frequently occur at long-muscle length. Yet, previous research has mainly focused on studying the effectiveness of eccentric hamstring strengthening at shorter muscle length on hamstring performance, morphology, and hamstring strain injury risk factors. Here, we evaluated the effects of 6-week eccentric hamstring training at long-muscle length on functional and architectural characteristics of the hamstrings. Healthy and injury-free participants (n = 40; age 23.7 ± 2.5 years) were randomly assigned to control or intervention group. Training intervention consisted of 12 sessions with two eccentric hamstring exercises in a lengthened position. Outcome measures included isokinetic and isometric knee flexion peak torque, Nordic hamstring exercise peak torque, voluntary activation level, and countermovement jump performance. Ultrasonography was used to determine muscle thickness, pennation angle, and fascicle length of biceps femoris long head (BFlh). A significant time × group interaction effect was observed for all measured parameters except countermovement jump performance and muscle thickness. The training intervention resulted in increased concentric and eccentric knee flexion peak torque at 60°/s (d = 0.55-0.62, P = .02 and .03) and concentric peak torque at 180°/s (d = 0.99, P = .001), increased isometric knee flexion peak torque (d = 0.73, P = .008) and Nordic hamstring exercise peak torque (d = 1.19, P < .001), increased voluntary activation level (d = 1.29, P < .001), decreased pennation angle (d = 1.31, P < .001), and increased fascicle length (d = 1.12, P < .001) of BFlh. These results provide evidence that short-term eccentric hamstring strengthening at long-muscle length can have significant favorable effects on various architectural and functional characteristics of the hamstrings.

Differential changes in muscle architecture and neuromuscular fatigability induced by isometric resistance training at short and long muscle-tendon unit lengths

We evaluated the effects of differential muscle architectural adaptations on neuromuscular fatigue resistance. Seven young males and six females participated in this study. Using a longitudinal within-subject design, legs were randomly assigned to perform isometric training of the tibialis anterior (TA) three times per week for 8 wk at a short (S-group) or long muscle-tendon unit length (L-group). Before and following training, fascicle length (FL) and pennation angle (PA) of the TA were assessed. As well, fatigue-related time course changes in isometric maximal voluntary contraction (MVC) torque and isotonic peak power (20% MVC resistance) were determined before, immediately after, and 1, 2, 5, and 10 min following task failure. The fatiguing task consisted of repeated maximal effort isotonic (20% MVC resistance) contractions over a 40° range of motion until the participant reached a 40% reduction in peak power. Although there was no clear improvement in neuromuscular fatigue resistance following training in either group (P = 0.081; S-group: ∼20%; L-group: ∼51%), the change in neuromuscular fatigue resistance was related positively to the training-induced increase in PA (∼6%, P < 0.001) in the S-group (r = 0.739, P = 0.004) and negatively to the training-induced increase in FL (∼4%, P = 0.001) in the L-group (r = -0.568, P = 0.043). Both groups recovered similarly for MVC torque and peak power after the fatiguing task as compared with before training. We suggest that the relationships between the changes in muscle architecture and neuromuscular fatigue resistance depend on the muscle-tendon unit lengths at which the training is performed.NEW & NOTEWORTHY Eight weeks of isometric training at a long or short muscle-tendon unit length increased and did not change fascicle length, respectively. The "width" of the torque-angle relationship plateau became broader following isometric training at the long length. Despite marked differences in muscle architecture and functional adaptations between the groups, there was only a small-magnitude improvement in neuromuscular fatigue resistance, which was surprisingly negatively related to increased fascicle length in the long length-training group.

Review of the methods used for calculating physiological cross-sectional area (PCSA) for ecological questions

This review examines literature that used physiological cross-sectional area (PCSA) as a representative measure of an individual muscle's maximal isometric force production. PCSA is used to understand the muscle architecture and how a trade-off between muscle force and muscle contractile velocity reflect adaptations of the musculoskeletal system as a reflection of functional demands. Over the decades, methods have been developed to measure muscle volume, fascicle lengths, and pennation angle to calculate PCSA. The advantages and limitations of these methods (especially the inclusion/elimination of pennation angle) are discussed frequently; however, these method descriptions are scattered throughout the literature. Here, we reviewed and summarised the different approaches to collecting and recording muscle architectural properties to subsequently calculate PCSA. By critically discussing the advantages and limitations of each methodology, we aim to provide readers with an overview of repeatable methods to assess muscle architecture. This review may serve as a guide to facilitate readers searching for the appropriate techniques to calculate PCSA and measure muscle architecture to be applied in ecomorphology research. RESEARCH HIGHLIGHTS: Discuss the theories behind PCSA in a synthesised review to inform researchers about PCSA methodology.

The Influence of Maturity Status on Muscle Architecture in School-Aged Boys

PURPOSE

To determine the differences in muscle architecture of the lower limb in pre-peak height velocity (PHV), circa-PHV, and post-PHV boys.

METHOD

Muscle architecture variables from both the gastrocnemius medialis (GM) and vastus lateralis (VL) were derived from ultrasonographic images in 126 school-aged boys. One-way analysis of variance using Bonferroni post hoc comparisons was employed to determine between-group differences, and effect sizes were calculated to establish the magnitude of these differences.

RESULTS

All muscle architecture variables showed significant small to large increases from pre-PHV to post-PHV, excluding GM fascicle length (d = 0.59-1.39; P < .05). More discrete between-group differences were evident as GM and VL muscle thickness, and physiological thickness significantly increased between pre-PHV and circa-PHV (d > 0.57; P < .05); however, only the VL muscle thickness and physiological thickness increased from circa-PHV to post-PHV (d = 0.68; P < .05). The post-PHV group also showed larger GM pennation angles than the circa-PHV group (d = 0.59; P < .05).

CONCLUSION

The combined results showed that maturation is associated with changes in muscle morphology. These data quantify that the maturity-related changes in muscle architecture variables provide a reference to differentiate between training-induced adaptations versus changes associated with normal growth and maturation.

Impact of Nutritional Status on Muscle Architecture in Elerly Patients Hospitalized in Internal Medicine Wards

Nutritional alterations are highly prevalent in older rather than adult hospitalized patients. In these subjects, a loss of physical performance is dependent on the impairment of muscle architecture. This study aimed to investigate the association between the nutritional status and muscle architecture in elderly patients hospitalized in internal medicine wards. 68 aged patients admitted in internal medicine wards were consecutively enrolled and stratified in three groups based on the Mini Nutritional Assessment (MNA) score: well-fed (WF), at risk of malnutrition (RM), and malnourished (M). Biochemical indices and anthropometric parameters were sampled at hospital admission. Furthermore, all patients were assessed at admission and after 7 days of hospitalization for muscle strength (hand-grip test), mass (bioimpedentiometry), and architecture (ultrasonography of vastus lateralis). At hospital admission, M patients showed lower percentage of fat free mass and muscle mass with respect to WF and RM. Furthermore, M group presented with lower muscle thickness and pennation angle, as compared to WF and RM. At admission, the MNA score was positively related to the pennation angle and muscle strength. Multivariate linear regression analysis showed that the nutritional status at admission was the only significant factor influencing pennation angle. Finally, during the first 7 days of hospitalization, a decrease of pennation angle occurred in all the groups studied. We conclude that malnutrition at admission is associated with impaired muscle architecture in elderly patients hospitalized in internal medicine wards. Moreover, muscle architecture is impacted by early hospitalization, irrespective of nutritional status.

Tensiomyography Derived Parameters Reflect Skeletal Muscle Architectural Adaptations Following 6-Weeks of Lower Body Resistance Training

Measurement of muscle specific contractile properties in response to resistance training (RT) can provide practitioners valuable information regarding physiological status of individuals. Field based measurements of such contractile properties within specific muscle groups, could be beneficial when monitoring efficacy of training or rehabilitation interventions. Tensiomyography (TMG) quantifies contractile properties of individual muscles via an electrically stimulated twitch contraction and may serve as a viable option in the aforementioned applications. Thus, aims of this study were; (i) to investigate the potential use of TMG to quantify training adaptations and differences, in response to exercise specific lower limb RT; and (ii) investigate any associations between TMG parameters and accompanying muscle architectural measures. Non-resistance trained male participants (n = 33) were randomly assigned to 1 of 3 single-exercise intervention groups (n = 11 per group); back squat (BS), deadlift (DL), or hip thrust (HT). Participants completed a 6-week linearized training program (2× per week), where the assigned exercise was the sole method of lower body training. Pre- and post-intervention testing of maximal dynamic strength was assessed by one repetition maximum (1RM) of BS, DL, and HT. Radial muscle belly displacement (Dm) and contraction time (Tc) were obtained via TMG from the rectus femoris (RF) and vastus lateralis (VL) pre- and post-intervention, alongside muscle architectural measures (pennation angle and muscle thickness). All three groups displayed significant increases all 1RM strength tests (p < 0.001; pη2 = 0.677-0.753). Strength increases were accompanied by significant overall increases in RF muscle thickness (p < 0.001, pη2 = 0.969), and pennation angle (p = 0.007, pη2 = 0.220). Additionally, an overall reduction in RF Dm (p < 0.001, pη2 = 0.427) was observed. Significant negative relationships were observed between RF Dm and pennation angle (p = 0.003, r = -0.36), and with RF Dm and muscle thickness (p < 0.001, r = -0.50). These findings indicate that TMG is able to detect improved contractile properties, alongside improvements in muscle function within an untrained population. Furthermore, the observed associations between Dm and muscle architecture suggest that TMG contractile property assessments could be used to obtain information on muscle geometry.

Contralateral seventh cervical nerve transfer can affect the pennation angle of the lower limb in spastic hemiplegia patients: An observational case series study

INTRODUCTION

We previously reported transferring seventh cervical (C7) nerve from unaffected side to affected side in patients with spastic hemiplegia due to chronic cerebral injury, to improve function and reduce spasticity of paralyzed upper limb. In the clinics, some patients also reported changes of spasticity in their lower limb, which could not be detected by routine physical examinations. Pennation angle of muscle can indirectly reflect the condition of spasticity. The purpose of this study was to evaluate whether this upper limb procedure may affect spasticity of lower limb, using ultrasonography to detect changes of muscle pennation angle (PA).

METHODS

Twelve spastic hemiplegia patients due to cerebral injury including stroke, cerebral palsy, and traumatic brain injury, who underwent C7 nerve transfer procedure, participated in this study. B-mode ultrasonography was used to measure PA of the gastrocnemius medialis (GM) muscle at rest preoperatively and postoperatively. The plantar load distribution of the lower limbs was evaluated using a Zebris FDM platform preoperatively and postoperatively.

RESULTS

The PA of the GM was significantly smaller on the affected side than that of unaffected side before surgery. On the affected side, the postoperative PA was significantly larger than preoperative PA. On the unaffected side, the postoperative PA was not significantly different compared to preoperative PA. The postoperative plantar load distribution of the affected forefoot was significantly smaller than preoperative load distribution, which was consistent with ultrasonography results.

CONCLUSIONS

This study indicates that C7 nerve transfer surgery for improving upper limb function can also affect muscle properties of lower limb in spastic hemiplegia patients, which reveals a link between the upper and lower limbs. The interlimb interactions should be considered in rehabilitation physiotherapy, and the regular pattern and mechanism need to be further studied.

Effects of Rest Position on Morphology of the Vastus Lateralis and Its Relationship with Lower-Body Strength and Power

Ultrasonography of the lower body typically encompasses supine rest due to fluid shifts affecting tissue size and composition. However, vastus lateralis (VL) examination is completed in the lateral recumbent position, and this positional change may influence morphology and its ability to predict function. This study aimed to examine the effect of position on VL morphology and its relationship with lower-body performance. Cross-sectional area (CSA), muscle thickness (MT), pennation angle (PA), echo intensity (UnCorEI), subcutaneous adipose tissue thickness (SFT), and echo intensity corrected for SFT (CorEI) were assessed in 31 resistance-trained males (23.0 ± 2.1 yrs; 1.79 ± 0.08 m; 87.4 ± 11.7 kg) immediately after transitioning from standing to supine (IP), after 15 min of standing (ST), and after 15 min of rest in three recumbent positions: supine (SUP), dominant lateral recumbent (DLR), non-dominant lateral recumbent (NDLR). Participants also completed unilateral vertical jumps, isometric/isokinetic tests, and a one-repetition maximum leg press. CSA, MT, PA, and SFT were greater in ST compared to NDLR, DLR, and SUP (p < 0.05). CSA, UnCorEI, and CorEI were different between recumbent positions; however no differences were observed for MT, PA, and SFT. Different magnitudes of relationships were observed between muscle morphological characteristics measured after rest in different positions and performance variables. Muscle morphology in IP generally appears to be the best predictor of performance for most variables, although utilizing the NDLR and DLR positions may provide comparable results, whereas morphology measured in ST and SUP provide weaker relationships with physical performance. IP also requires less time and fewer requirements on the technician and subject, thus researchers should consider this positioning for VL examination.

The correlation of muscle thickness and pennation angle assessed by ultrasound with sarcopenia in elderly Chinese community dwellers

Background: Sarcopenia is typically defined as the loss of muscle mass, strength and low physical performance with aging. Ultrasound is a safe and easy method for evaluating muscle mass and quality by muscle thickness (MT) and pennation angle (PA), respectively. Although the positive correlations between MT and muscle mass and handgrip strength were observed, the relationship between MT, PA and physical performance remains unclear.

Purpose: This study aimed to investigate the correlation of aforementioned ultrasound parameters with muscle mass, muscle strength and physical performance and explore the utility of ultrasound in predicting sarcopenia.

Patients and methods: A total of 265 elderly Chinese community dwellers were included. MT of both forearm and lower leg as well as PA of gastrocnemius was assessed by ultrasound. Muscle mass was assessed by dual-energy X-ray absorptiometry. Muscle strength was measured by a Jamar hand dynamometer. Physical performance was assessed by the Short Physical Performance Battery (SPPB).

Results: Anterior radial MT in men and regional MTs except posterior fibula in women were negatively correlated with the age. No significant correlation was observed between PA and the age in both genders. Posterior tibial MT and posterior fibula MT were positively correlated with the relative appendicular skeletal muscle mass in men and women, respectively. Anterior ulnar MT was positively correlated with grip strength in both genders. Moreover, gastrocnemius medialis PA showed a positive association with gait speed and SPPB in women but not in men.

Conclusion: A combination of posterior fibula MT, anterior ulnar MT and gastrocnemius medialis PA measured by muscle ultrasound is helpful for the assessment of sarcopenia in Chinese elderly women. In addition, a combination of posterior tibial MT and anterior ulnar MT measured by muscle ultrasound is helpful for the assessment of sarcopenia in Chinese elderly men.

Change in the pennation angle of the supraspinatus muscle after rotator cuff tear repair

BACKGROUND

The pennation angle is an important architectural and functional feature of pennate muscles. The purpose of this study was to investigate the change in the pennation angle of the supraspinatus muscle after rotator cuff tear repair.

MATERIALS AND METHODS

The study included 68 patients who underwent arthroscopic rotator cuff repair and magnetic resonance imaging. The size of the tear was measured under arthroscopic visualization. The pennation angle of the supraspinatus both preoperatively and postoperatively and the integrity of the repaired cuff were determined by magnetic resonance imaging.

RESULTS

The preoperative pennation angle was significantly greater with enlargement of the tear size (P < .0001, analysis of variance). The retear rate was 29% in patients with medium tears and 59% in patients with large or massive tears. No retear was noted in patients with partial and small tears. The retear rate was 90.9% when the preoperative pennation angle was 20° or greater and was 12.3% when this angle was 19° or less, and the risk ratio for retear was 7.4 when this angle was 20° or greater. For repair-type tears, comparison between the preoperative and postoperative pennation angles showed a significant decrease in the mean value from 11.8° ± 3.7° to 9.9° ± 3.0° in the medium tear group (P = .007, paired t test) but no significant difference in the large or massive tear group (from 15.1° ± 7.0° to 13.3° ± 5.8°) (P = .33). For retear-type tears, no significance was found between groups.

CONCLUSION

The preoperative pennation angle is directly correlated with the tear configuration and could be one of the prognostic factors for postoperative cuff integrity. To restore the pennation angle, primary repair is more appropriate in smaller rotator cuff tears than in medium-sized tears.

Maturity status effects on torque and muscle architecture of young soccer players

This study investigated the effects of maturity status on knee extensor torque and vastus lateralis architecture of young soccer players. Thirty-four males aged 13-18 years were divided into two groups: pubescent (PUB, n = 15) and postpubescent (POSP, n = 19). Torque by angle interaction was established for absolute [F(2.649, 84.771) = 9.066, p < 0.05] and relative to body mass [F(2.704, 86.533) = 4.050, p < 0.05] isometric torque with the POSP group showing greater values. Muscle volume torque-angle relationship was similar between groups. Absolute, relative to body mass, and relative to muscle volume concentric and eccentric torque-velocity relationship showed a non-significant interaction but a significant group effect in favour the POSP group for absolute and concentric torque relative to body mass. Torque-angle and torque-velocity relationship normalized by body mass allometric exponents showed a non-significant interactions and group effects. Muscle thickness (3.6 ± 0.6 vs. 3.8 ± 0.6 cm), fascicle length (8.3 ± 1.4 vs. 8.9 ± 1.6 cm) and pennation angle (15.0 ± 2.3 vs. 14.3 ± 3.2 degrees) was similar between PUB and POSP groups, respectively. Maturity status did not show a significant effect on muscle architecture and on isometric and dynamic torques when allometrically normalized.

Supersonic Shear Imaging Elastography in Skeletal Muscles: Relationship Between In Vivo and Synthetic Fiber Angles and Shear Modulus

OBJECTIVES

To verify a relationship between the pennation angle of synthetic fibers and muscle fibers with the shear modulus (μ) generated by Supersonic shear imaging (SSI) elastography and to compare the anisotropy of synthetic and in vivo pennate muscle fibers in the x₂ -x₃ plane (probe perpendicular to water surface or skin).

METHODS

First, the probe of Aixplorer ultrasound scanner (v.9, Supersonic Imagine, Aix-en-Provence, France) was placed in 2 positions (parallel [aligned] and transverse to the fibers) to test the anisotropy in the x₂ -x₃ plane. Subsequently, it was inclined (x₁ -x₃ plane) in relation to the fibers, forming 3 angles (18.25 °, 21.55 °, 36.86 °) for synthetic fibers and one (approximately 0 °) for muscle fibers.

RESULTS

On the x₂ -x₃ plane, μ values of the synthetic and vastus lateralis fibers were significantly lower (P < .0001) at the transverse probe position than the longitudinal one. In the x₁ -x₃ plane, the μ values were significantly reduced (P < .0001) with the probe angle increasing, only for the synthetic fibers (approximately 0.90 kPa for each degree of pennation angle).

CONCLUSIONS

The pennation angle was not related to the μ values generated by SSI elastography for the in vivo lateral head of the gastrocnemius and vastus lateralis muscles. However, a μ reduction with an angle increase in the synthetic fibers was observed. These findings contribute to increasing the applicability of SSI in distinct muscle architecture at normal or pathologic conditions.

Sex-Related Responses to Eccentric-Only Resistance Training in Knee-Extensors Muscle Strength and Architecture

PURPOSE

The present study aimed to investigate whether or not eccentric-only training induced different sex-related adaptations in vastus lateralis muscle architecture and knee extensors strength.

METHODS

Thirteen healthy women and 13 healthy men were recruited. Vastus lateralis pennation angle, fascicle length, and muscle thickness, as well as knee extensors eccentric, isometric, and concentric peak torque and one-repetition maximum (1RM) were measured. Both women and men underwent a unilateral iso-load knee-extension eccentric-only training with 120% of the concentric 1RM, consisting of 4 sets × 10 repetitions twice a week for a total of 8 weeks.

RESULTS

Pennation angle increased in women (+ 14%, 95% CI [10, 17], effect size [ES] = 1.54) but not in men (+ 5%, 95% CI [-1, 11], ES = 0.28), while fascicle length increased in both women (+ 7%, 95% CI [4, 10], ES = 1.02) and men (+ 12%, 95% CI [8, 16], ES = 1.82) and muscle thickness increased in women (+ 13%, 95% CI [8, 18], ES = 1.11) and men (+ 11%, 95% CI [7, 15], ES = 0.89). In both women and men, eccentric (18%, 95% CI [11, 25], ES = 0.96, and 16%, 95% CI [9, 22], ES = 0.82, respectively), isometric (17%, 95% CI [11, 23], ES = 0.53, and 17%, 95% CI [10, 24], ES = 0.62), concentric (12%, 95% CI [7, 16], ES = 0.49, and 9%, 95% CI [5, 13], ES = 0.42) peak torque and 1RM (10%, 95% CI [6, 14], ES = 0.53, and 10%, 95% CI [5, 15], ES = 0.50) similarly increased after the intervention.

CONCLUSIONS

This study showed that the adaptations in strength are not sex-dependent, but the increases in pennation angle only in women suggest that the changes in muscle architecture may depend on sex.

Shifting gears: dynamic muscle shape changes and force-velocity behavior in the medial gastrocnemius

When muscles contract, they bulge in thickness or in width to maintain a (nearly) constant volume. These dynamic shape changes are tightly linked to the internal constraints placed on individual muscle fibers and play a key functional role in modulating the mechanical performance of skeletal muscle by increasing its range of operating velocities. Yet to date we have a limited understanding of the nature and functional implications of in vivo dynamic muscle shape change under submaximal conditions. This study determined how the in vivo changes in medial gastrocnemius (MG) fascicle velocity, pennation angle, muscle thickness, and subsequent muscle gearing varied as a function of force and velocity. To do this, we obtained recordings of MG tendon length, fascicle length, pennation angle, and thickness using B-mode ultrasound and muscle activation using surface electromyography during cycling at a range of cadences and loads. We found that that increases in contractile force were accompanied by reduced bulging in muscle thickness, reduced increases in pennation angle, and faster fascicle shortening. Although the force and velocity of a muscle contraction are inversely related due to the force-velocity effect, this study has shown how dynamic muscle shape changes are influenced by force and not influenced by velocity.NEW & NOTEWORTHY During movement, skeletal muscles contract and bulge in thickness or width. These shape changes play a key role in modulating the performance of skeletal muscle by increasing its range of operating velocities. Yet to date the underlying mechanisms associated with muscle shape change remain largely unexplored. This study identified muscle force, and not velocity, as the mechanistic driving factor to allow for muscle gearing to vary depending on the contractile conditions during human cycling.

Influence of Joint Angle on Residual Force Enhancement in Human Plantar Flexors

Compared to pure isometric contractions, isometric muscle force at a given length is larger when the eccentric contraction is conducted before the isometric contraction. This phenomenon is widely known as residual force enhancement, and has been confirmed consistently in isolated muscle experiments. The purpose of this study was to confirm whether residual force enhancement also occurs in human plantar flexors and to examine its joint angle dependence. Eleven men participated in this study. Isometric joint torque was measured in a Control trial (pure isometric contraction) and Residual force enhancement (RFE) trial (isometric contraction after eccentric contraction) at plantar flexion 0° (Short condition) and dorsiflexion 15° (Long condition). Fascicle length and pennation angle of the medial gastrocnemius were measured simultaneously to evaluate the influence of architectural parameters on isometric joint torque. Isometric joint torque observed in the Short condition was not significantly different between the Control and RFE trials (Control: 42.9 ± 8.0 Nm, RFE: 45.1 ± 8.4 Nm) (p = 0.200). In contrast, significant differences in isometric joint torque were observed in the Long condition between Control and RFE trials (Control: 40.5 ± 9.3 Nm, RFE: 47.1 ± 10.5 Nm) (p = 0.001). Fascicle length and pennation angle were not different between Control and RFE trials in the Short and Long conditions. Isometric joint torque was larger when eccentric contraction was conducted before isometric contraction while architectural differences were not observed, indicating that residual force enhancement occurs in human plantar flexors. However, the influence of residual force enhancement may be limited in dorsiflexed positions because the magnitude of residual force enhancement is considered to be prominent in the descending limb (long muscle length condition) and small in the ascending limb (short muscle length condition) where human plantar flexors operate in plantar flexed positions.

Force Depression in Plantar Flexors Exists Equally in Plantar Flexed and Dorsiflexed Regions

Isometric muscle force attained during isometric contractions decreases after active shortening compared to that attained during purely isometric contractions. This phenomenon is called residual force depression. The aim of this study was to examine whether residual force depression occurs in human plantar flexors in both plantar flexed and dorsiflexed region. In addition, the magnitude of fascicle shortening was evaluated because not only muscle force but also fascicle shortening during active shortening are considered to affect force depression. Eleven male subjects were recruited. All muscle contractions were evoked by muscle belly-electrical stimulation. In the reference trials, isometric plantar flexion (PF) was performed at 0° and 15° of PF. In the residual force depression trials, the following two contractions were conducted: (1) muscles were activated isometrically at 15° of dorsiflexion, then actively shortened to 0° of PF (long condition) and (2) muscles were activated isometrically at 0° of PF, then actively shortened to 15° of PF (short condition). Isometric joint torque obtained 4.9 s after the onset of contraction was compared between the reference and residual force depression trials at the same joint angle to calculate the magnitude of residual force depression. At the same time point, fascicle length and pennation angle were obtained from ultrasonographic images to examine whether the muscle architecture affected residual force depression. As a result, residual force depression was confirmed in both the long and short length conditions (long: 87.1 ± 9.1%, short: 92.1 ± 7.8%) while the magnitude was not different (p = 0.182). The fascicle length and pennation angle were not different between the reference and residual force depression trials (p = 0.291–0.906). These results indicate that residual force depression occurs in the physiological range of motion in the human plantar flexors, and this phenomenon is not related to muscle architecture. In addition, joint angle dependence of the residual force depression was not observed between long and short muscle length conditions.

Stretch training induces unequal adaptation in muscle fascicles and thickness in medial and lateral gastrocnemii

This study compared adaptations in fascicle lengths, pennation angles, and muscle thickness of the lateral and medial gastrocnemii in response to 6 weeks of stretch training. The nondominant plantar flexors of 11 males were stretched five times per week for 6 weeks and compared with the contralateral leg and a nonstretched control group of 10 males. During stretch training, instantaneous electromyography was utilized to ensure passive muscle stretch. At baseline, week three, week six and 1 week after the conclusion of stretch training, ultrasound was used to measure fascicle lengths, pennation angles, muscle thickness of the lateral gastrocnemius and medial gastrocnemius, and Achilles tendon thickness and length. Plantar flexion torque was measured, and voluntary activation was assessed. Muscle thickness increased 5.6% after 6 weeks of stretch training (P=.009). The fascicles in the lateral gastrocnemius lengthened to a greater extent than the medial. Overall, fascicles lengthened 25% (P<.001) in the muscle tendon junction and 5.1% (P<.001) in the muscle belly. Pennation angles were unchanged in the medial gastrocnemius but decreased in the lateral gastrocnemius 7.1% (P=.02). There was no change in maximal voluntary contraction, voluntary activation, tendon length, or thickness. This study demonstrates that stretch training is a viable modality to alter muscle architecture of the human gastrocnemius through lengthening of muscle fascicles, decreasing pennation angles, and increasing muscle thickness, albeit adaptations are unequal between the lateral and medial heads.

Hamstring Architectural and Functional Adaptations Following Long vs. Short Muscle Length Eccentric Training

Most common preventive eccentric-based exercises, such as Nordic hamstring do not include any hip flexion. So, the elongation stress reached is lower than during the late swing phase of sprinting. The aim of this study was to assess the evolution of hamstring architectural (fascicle length and pennation angle) and functional (concentric and eccentric optimum angles and concentric and eccentric peak torques) parameters following a 3-week eccentric resistance program performed at long (LML) vs. short muscle length (SML). Both groups performed eight sessions of 3–5 × 8 slow maximal eccentric knee extensions on an isokinetic dynamometer: the SML group at 0° and the LML group at 80° of hip flexion. Architectural parameters were measured using ultrasound imaging and functional parameters using the isokinetic dynamometer. The fascicle length increased by 4.9% (p < 0.01, medium effect size) in the SML and by 9.3% (p < 0.001, large effect size) in the LML group. The pennation angle did not change (p = 0.83) in the SML and tended to decrease by 0.7° (p = 0.09, small effect size) in the LML group. The concentric optimum angle tended to decrease by 8.8° (p = 0.09, medium effect size) in the SML and by 17.3° (p < 0.01, large effect size) in the LML group. The eccentric optimum angle did not change (p = 0.19, small effect size) in the SML and tended to decrease by 10.7° (p = 0.06, medium effect size) in the LML group. The concentric peak torque did not change in the SML (p = 0.37) and the LML (p = 0.23) groups, whereas eccentric peak torque increased by 12.9% (p < 0.01, small effect size) and 17.9% (p < 0.001, small effect size) in the SML and the LML group, respectively. No group-by-time interaction was found for any parameters. A correlation was found between the training-induced change in fascicle length and the change in concentric optimum angle (r = −0.57, p < 0.01). These results suggest that performing eccentric exercises lead to several architectural and functional adaptations. However, further investigations are required to confirm the hypothesis that performing eccentric exercises at LML may lead to greater adaptations than a similar training performed at SML.

Fiber orientation measurements by diffusion tensor imaging improve hydrogen-1 magnetic resonance spectroscopy of intramyocellular lipids in human leg muscles

Twelve healthy subjects underwent hydrogen-1 magnetic resonance spectroscopy ([Formula: see text]) acquisition ([Formula: see text]), diffusion tensor imaging (DTI) with a [Formula: see text]-value of [Formula: see text], and fat-water magnetic resonance imaging (MRI) using the Dixon method. Subject-specific muscle fiber orientation, derived from DTI, was used to estimate the lipid proton spectral chemical shift. Pennation angles were measured as 23.78 deg in vastus lateralis (VL), 17.06 deg in soleus (SO), and 8.49 deg in tibialis anterior (TA) resulting in a chemical shift between extramyocellular lipids (EMCL) and intramyocellular lipids (IMCL) of 0.15, 0.17, and 0.19 ppm, respectively. IMCL concentrations were [Formula: see text], [Formula: see text], and [Formula: see text] in SO, VL, and TA, respectively. Significant differences were observed in IMCL and EMCL pairwise comparisons in SO, VL, and TA ([Formula: see text]). Strong correlations were observed between total fat fractions from [Formula: see text] and Dixon MRI for VL ([Formula: see text]), SO ([Formula: see text]), and TA ([Formula: see text]). Bland-Altman analysis between fat fractions (FFMRS and FFMRI) showed good agreement with small limits of agreement (LoA): [Formula: see text] (LoA: [Formula: see text] to 0.69%) in VL, [Formula: see text] (LoA: [Formula: see text] to 1.33%) in SO, and [Formula: see text] (LoA: [Formula: see text] to 0.47%) in TA. The results of this study demonstrate the variation in muscle fiber orientation and lipid concentrations in these three skeletal muscle types.

Measurement of muscle architecture concurrently with muscle hardness using ultrasound strain elastography

BACKGROUND

The B-mode ultrasound image that can measure muscle architecture is displayed side by side with the ultrasound strain elastogram that can assess muscle hardness. Consequently, muscle architecture can be measured concurrently with muscle hardness using ultrasound strain elastography.

PURPOSE

To demonstrate the measurement of muscle architecture concurrently with muscle hardness using ultrasound strain elastography.

MATERIAL AND METHODS

Concurrent measurements of muscle architectural parameters (muscle thickness, pennation angle, and fascicle length) and muscle hardness of the medial gastrocnemius were performed with ultrasound strain elastography. Separate measurements of the muscle architectural parameters were also performed for use as reference values for the concurrent measurements. Both types of measurements were performed twice at 20° dorsiflexion, neutral position, and 30° plantar flexion.

RESULTS

Coefficients of variance of the muscle architectural parameters obtained from the concurrent measurements (≤7.6%) were significantly higher than those obtained from the separate measurements (≤2.4%) (all P < 0.05). Intraclass correlation coefficients of the architectural parameters were lower in the concurrent measurements (≥0.74) than in the separate measurements (≥0.97). However, there were no significant differences in any muscle architectural parameters between the concurrent and separate measurements (all P > 0.05).

CONCLUSION

The use of ultrasound strain elastography for the concurrent measurement of muscle architecture and muscle hardness is feasible.

Correlation between architectural variables and torque in the erector spinae muscle during maximal isometric contraction

This study analysed whether a significant relationship exists between the torque and muscle thickness and pennation angle of the erector spinae muscle during a maximal isometric lumbar extension with the lumbar spine in neutral position. This was a cross-sectional study in which 46 healthy adults performed three repetitions for 5 s of maximal isometric lumbar extension with rests of 90 s. During the lumbar extensions, bilateral ultrasound images of the erector spinae muscle (to measure pennation angle and muscle thickness) and torque were acquired. Reliability test analysis calculating the internal consistency (Cronbach's alpha) of the measure, correlation between pennation angle, muscle thickness and torque extensions were examined. Through a linear regression the contribution of each independent variable (muscle thickness and pennation angle) to the variation of the dependent variable (torque) was calculated. The results of the reliability test were: 0.976-0.979 (pennation angle), 0.980-0.980 (muscle thickness) and 0.994 (torque). The results show that pennation angle and muscle thickness were significantly related to each other with a range between 0.295 and 0.762. In addition, multiple regression analysis showed that the two variables considered in this study explained 68% of the variance in the torque. Pennation angle and muscle thickness have a moderate impact on the variance exerted on the torque during a maximal isometric lumbar extension with the lumbar spine in neutral position.

Comparison of twice refocused spin echo versus stimulated echo diffusion tensor imaging for tracking muscle fibers

PURPOSE

To compare the precision of measuring the pennation angle and fiber length in the vastus lateralis (VL) using two distinctly different diffusion tensor imaging (DTI) sequences.

MATERIALS AND METHODS

We imaged the thigh of 10 normal subjects on a 3T magnetic resonance (MR) imager with twice refocused spin echo (TRSE) and stimulated echo (STEAM) DTI-MRI techniques. Both techniques took the same total acquisition time and employed the same diffusion weighting and gradient directions. Using the diffusion tensor images produced by each sequence, muscle fiber bundles were tracked from the aponeurosis by following the first eigenvector of the diffusion tensor. From these tracks we calculated the pennation angle and fiber length.

RESULTS

The STEAM acquisition resulted in significantly higher signal-to-noise ratio (SNR), lower apparent diffusion coefficient (ADC), higher fractional anisotropy (FA) values, and longer fibers than TRSE. Although no difference in the pennation angle between the two acquisitions was found, the TRSE sequence had a significantly greater within-subject dispersion in the pennation angle of tracked fibers, which may indicate a reduction in the coherence of fiber bundles.

CONCLUSION

DTI of muscle using a STEAM acquisition resulted in significant improvements in the SNR and FA, resulting in tracking a larger number of muscle fiber bundles over longer distances and with less within-subject dispersion.

Association between ultrasound measurements of muscle thickness, pennation angle, echogenicity and skeletal muscle strength in the elderly

The increase of elderly in our society requires simple tools for quantification of sarcopenia in inpatient and outpatient settings. The aim of this study was to compare parameters determined with musculoskeletal ultrasound (M-US) with muscle strength in young and elderly patients. In this prospective, randomised and observer blind study, 26 young (24.2 ± 3.7 years) and 26 old (age 67.8 ± 4.8 years) patients were included. Muscle thickness, pennation angle and echogenicity of all muscles of musculus quadriceps were measured by M-US and correlated with isometric maximum voluntary contraction force (MVC) of musculus quadriceps. Reproducibility of M-US measurements as well as simple and multiple regression models were calculated. Of all measured M-US variables the highest reproducibility was found for measurements of thickness (intraclass correlation coefficients, 85-97%). Simple regression analysis showed a highly significant correlation of thickness measurements of all muscles of musculus quadriceps with MVC in the elderly and in the young. Multiple regression analysis revealed that thickness of musculus vastus medialis had the best correlation with MVC in the elderly. This study showed that measurement of muscle thickness, especially of musculus vastus medialis, by M-US is a reliable, bedside method for monitoring the extent of sarcopenia.

Relationship of moderate and low isometric lumbar extension through architectural and muscular activity variables: a cross sectional study

BACKGROUND

No study relating the changes obtained in the architecture of erector spinae (ES) muscle were registered with ultrasound and different intensities of muscle contraction recorded by surface EMG (electromyography) on the ES muscle was found. The aim of this study was analyse the relationship in the response of the ES muscle during isometric moderate and light lumbar isometric extension considering architecture and functional muscle variables.

METHODS

Cross-sectional study. 46 subjects (52% men) with a group mean age of 30.4 (±7.78). The participants developed isometric lumbar extension while performing moderate and low isometric trunk and hip extension in a sitting position with hips flexed 90 degrees and the lumbar spine in neutral position. During these measurements, electromyography recordings and ultrasound images were taken bilaterally. Bilaterally pennation angle, muscle thickness, torque and muscle activation were measured. This study was developed at the human movement analysis laboratory of the Health Science Faculty of the University of Malaga (Spain).

RESULTS

Strong and moderate correlations were found at moderate and low intensities contraction between the variable of the same intensity, with correlation values ranging from 0.726 (Torque Moderate - EMG Left Moderate) to 0.923 (Angle Left Light - Angle Right Light) (p < 0.001). This correlation is observed between the variables that describe the same intensity of contraction, showing a poor correlation between variables of different intensities.

CONCLUSION

There is a strong relationship between architecture and function variables of ES muscle when describe an isometric lumbar extension at light or moderate intensity.

Changes in muscle architecture induced by low load blood flow restricted training

In order to ascertain whether differing structural mechanisms could underlie blood flow restricted training (BFRT) and high intensity training (HIT), this study had two aims: (i) to gain an insight into the acute variations of muscle architecture following a single bout of two different volumes of BFRT, and (ii) to compare these variations with those observed after HIT. Thirty-five young men volunteered for the study and were randomly divided into three groups: BFRT low volume (BFRT LV), BFRT high volume (BFRT HV) and traditional high intensity resistance training (HIT). All subjects performed a bilateral leg extension exercise session with a load of 20% of one repetition maximum (1RM) in the BFRT groups, whereas the load of the HIT group was equivalent to an 85% of their 1RM. Before and immediately after the exercise bout, ultrasound images were taken from the rectus femoris (RF) and the vastus lateralis (VL). All groups increased their RF (p < 0.001) and VL (p < 0.001) muscle thickness, while the increases in pennation angle were larger in HIT as compared to BFRT LV (p = 0.013) and BFRT HV (p = 0.037). These results support the hypothesis that acute muscle cell swelling may be involved in the processes underlying BFRT induced muscle hypertrophy. Furthermore, our data indicate differing structural responses to exercise between BFRT and HIT.

Changes in muscular pennation angle after crenotherapy

Muscular architecture involves the organization of fibres in the muscle and is one of the most important factors of muscular function. Studies have demonstrated an association with muscular architecture and contraction, with an increase of the pennation angle in muscles. The aim of the study was to evaluate the change of muscular pennation angle after therapy with warm thermal water (crenotherapy).

PARTICIPANTS

45 amateur athletes undertaking different sporting activities;

GROUP A

30 runners;

GROUP B

15 swimmers. All the athletes underwent muscular ultrasound and clinical examination before and after the 10 sessions of the thermal protocol. At baseline the groups showed different values of pennation angle (group A = 19.1° ± 3.8° vs group B = 16.7° ± 2.4°; p=0.05). Following the thermal therapy protocol, significant variation of pennation angle was detected at rest in Group A which had significantly lower values than before the treatment (17.5° ± 2.9°; p=0.01). No differences were detected in group B.

CONCLUSIONS

thermal therapy induced the greatest effect on runners (Group A) as pennation angle at rest was significantly lower after the period of crenotherapy and this variation may be as a result of a smaller muscular contracture.

Repeatability of DTI-based skeletal muscle fiber tracking

Diffusion tensor imaging (DTI)-based muscle fiber tracking enables the measurement of muscle architectural parameters, such as pennation angle (theta) and fiber tract length (L(ft)), throughout the entire muscle. Little is known, however, about the repeatability of either the muscle architectural measures or the underlying diffusion measures. Therefore, the goal of this study was to investigate the repeatability of DTI fiber tracking-based measurements and theta and L(ft). Four DTI acquisitions were performed on two days that allowed for between acquisition, within day, and between day analyses. The eigenvalues and fractional anisotropy were calculated at the maximum cross-sectional area of, and fiber tracking was performed in, the tibialis anterior muscle of nine healthy subjects. The between acquisitions condition had the highest repeatability for the DTI indices and the architectural parameters. The overall inter class correlation coefficients (ICC's) were greater than 0.6 for both theta and L(ft) and the repeatability coefficients were theta < 10.2 degrees and L(ft) < 50 mm. In conclusion, under the experimental and data analysis conditions used, the repeatability of the diffusion measures is very good and repeatability of the architectural measurements is acceptable. Therefore, this study demonstrates the feasibility for longitudinal studies of alterations in muscle architecture using DTI-based fiber tracking, under similar noise conditions and with similar diffusion characteristics.