Managing Lower Limb Muscle Reinjuries in Athletes: From Risk Factors to Return-to-Play Strategies

Muscle injuries and subsequent reinjuries significantly impact athletes, especially in football. These injuries lead to time loss, performance impairment, and long-term health concerns. This review aims to provide a comprehensive overview of the current understanding of muscle reinjuries, delving into their epidemiology, risk factors, clinical management, and prevention strategies. Despite advancements in rehabilitation programs and return-to-play criteria, reinjury rates remain alarmingly high. Age and previous muscle injuries are nonmodifiable risk factors contributing to a high reinjury rate. Clinical management, which involves accurate diagnosis, individualized rehabilitation plans, and the establishment of return-to-training and return-to-play criteria, plays a pivotal role during the sports season. Eccentric exercises, optimal loading, and training load monitoring are key elements in preventing reinjuries. The potential of artificial intelligence (AI) in predicting and preventing reinjuries offers a promising avenue, emphasizing the need for a multidisciplinary approach to managing these injuries. While current strategies offer some mitigation, there is a pressing need for innovative solutions, possibly leveraging AI, to reduce the incidence of muscle reinjuries in football players. Future research should focus on this direction, aiming to enhance athletes' well-being and performance.

Regional differences in behaviors of fascicle and tendinous tissue of the biceps femoris long head during hamstring exercises

The biceps femoris long head (BFLH) gains its properties from internal elements (fascicles and tendinous tissues) which behaviors remain poorly understood across BFLH regions and dynamic tasks. The aim of this study was to assess the in vivo behaviors of fascicles and tendinous tissue in the proximal and distal regions of BFLH during different dynamic knee and hip tasks. Twenty males performed the Nordic hamstring exercise (NHE) (n = 9) and Romanian deadlift (RDL) (n = 11). Activation of the BFLH was assessed using surface electromyography signals. Ultrasound images of BFLH and kinematic data were used to estimate the interaction between fascicle and tendinous tissue. The fascicles changed less in length (p < 0.05) and contributed less to BFLH length change (p < 0.05) in NHE with higher activation (p < 0.05) relative to RDL. The higher pennation angle changes of BFLH were found in distal region compared to proximal region in both tasks (p < 0.05), while the activation of distal region was higher than activation of proximal region in NHE (p < 0.05). The BFLH length change was primarily contributed by the tendinous tissue during dynamic resistance tasks, and was contributed less by fascicles which operated more isometrically in knee-dominant NHE with higher activation relative to hip-dominant RDL. Regional differences in pennation angle change and activation during dynamic tasks suggest potential regional differences in the mechanical function of BFLH, warranting further investigation.

Influence of ultrasound machine settings on quantitative measures derived from spatial frequency analysis of muscle tissue

BACKGROUND

Ultrasound is a powerful tool for diagnostic purposes and provides insight into both normal and pathologic tissue structure. Spatial frequency analysis (SFA) methods characterize musculoskeletal tissue organization from ultrasound images. Both sonographers in clinical imaging and researchers may alter a minimized range of ultrasound settings to optimize image quality, and it is important to know how these small adjustments of these settings affect SFA parameters. The purpose of this study was to investigate the effects of making small adjustments in a typical default ultrasound machine setting on extracted spatial frequency parameters (peak spatial frequency radius (PSFR), Mmax, Mmax%, and Sum) in the biceps femoris muscle.

METHODS

Longitudinal B-mode images were collected from the biceps femoris muscle in 36 participants. The window depth, foci locations, and gain were systematically adjusted consistent with clinical imaging procedures for a total of 27 images per participant. Images were analyzed by identifying a region of interest (ROI) in the middle portion of the muscle belly in a template image and using a normalized two-dimensional cross-correlation technique between the template image and subsequent images. The ROI was analyzed in the frequency domain using conventional SFA methods. Separate linear mixed effects models were run for each extracted parameter.

RESULTS

PSFR was affected by modifications in focus location only (p < 0.001) with differences noted between all locations. Mmax% was influenced by the interaction of gain and focus location (p < 0.001) but was also independently affected by increasing window depth (p < 0.001). Both Mmax and Sum parameters were sensitive to small changes in machine settings with the interaction of focus location and window depth (p < 0.001 for both parameters) as well as window depth and gain (p < 0.001 for both) influencing the extracted values.

CONCLUSIONS

Frequently adjusted imaging settings influence some SFA statistics. PSFR and Mmax% appear to be most robust to small changes in image settings, making them best suited for comparison across individuals and between studies, which is appealing for the clinical utility of the SFA method.

The effects of hip- vs. knee-dominant hamstring exercise on biceps femoris morphology, strength, and sprint performance: a randomized intervention trial protocol

BACKGROUND

The hamstrings are an important muscle group that contribute to horizontal force during sprint acceleration and are also the most injured muscle group in running-based sports. Given the significant time loss associated with hamstrings injury and impaired sprinting performance following return to sport, identifying exercises that drive adaptations that are both protective of strain injury and beneficial to sprint performance is important for the strength and conditioning professional. This paper describes the study protocol investigating the effects of a 6-week training program using either the hip-dominant Romanian deadlift (RDL) or the knee-dominant Nordic hamstring exercise (NHE) on hamstring strain injury risk factors and sprint performance.

METHODS

A permuted block randomized (1:1 allocation) intervention trial will be conducted involving young, physically-active men and women. A target sample size of 32 will be recruited and enrolled participants will undergo baseline testing involving extended-field-of-view ultrasound imaging and shear wave elastography of the biceps femoris long head muscle, maximal hamstrings strength testing in both the RDL and NHE, and on-field sprint performance and biomechanics. Participants will complete the 6-week training intervention using either the RDL or NHE, according to group allocation. Baseline testing will be repeated at the end of the 6-week intervention followed by 2 weeks of detraining and a final testing session. The primary outcome will be regional changes in fascicle length with secondary outcomes including pennation angle, muscle cross sectional area, hamstring strength, and maximal sprint performance and biomechanics. An exploratory aim will determine changes in shear wave velocity.

DISCUSSION

Despite extensive research showing the benefits of the NHE on reducing hamstring strain injury risk, alternative exercises, such as the RDL, may offer similar or potentially even greater benefits. The findings of this study will aim to inform future researchers and practitioners investigating alternatives to the NHE, such as the RDL, in terms of their effectiveness in reducing rates of hamstring strain injury in larger scale prospective intervention studies.

TRIAL REGISTRATION

The trial is prospectively registered on ClinicalTrials.gov (NCT05455346; July 15, 2022).

Skeletal Muscle Assessment Using Quantitative Ultrasound: A Narrative Review

Ultrasound (US) is an important imaging tool for skeletal muscle analysis. The advantages of US include point-of-care access, real-time imaging, cost-effectiveness, and absence of ionizing radiation. However, US can be highly dependent on the operator and/or US system, and a portion of the potentially useful information carried by raw sonographic data is discarded in image formation for routine qualitative US. Quantitative ultrasound (QUS) methods provide analysis of the raw or post-processed data, revealing additional information about normal tissue structure and disease status. There are four QUS categories that can be used on muscle and are important to review. First, quantitative data derived from B-mode images can help determine the macrostructural anatomy and microstructural morphology of muscle tissues. Second, US elastography can provide information about muscle elasticity or stiffness through strain elastography or shear wave elastography (SWE). Strain elastography measures the induced tissue strain caused either by internal or external compression by tracking tissue displacement with detectable speckle in B-mode images of the examined tissue. SWE measures the speed of induced shear waves traveling through the tissue to estimate the tissue elasticity. These shear waves may be produced using external mechanical vibrations or internal "push pulse" ultrasound stimuli. Third, raw radiofrequency signal analyses provide estimates of fundamental tissue parameters, such as the speed of sound, attenuation coefficient, and backscatter coefficient, which correspond to information about muscle tissue microstructure and composition. Lastly, envelope statistical analyses apply various probability distributions to estimate the number density of scatterers and quantify coherent to incoherent signals, thus providing information about microstructural properties of muscle tissue. This review will examine these QUS techniques, published results on QUS evaluation of skeletal muscles, and the strengths and limitations of QUS in skeletal muscle analysis.

Hamstring Strain Injury in Athletes

Hamstring strain injury (HSI) may result in considerable impairment, activity limitation, and participation restriction, including time lost from competitive sports. This CPG includes sports-related overloading and overstretching injuries to myofascial or musculotendinous structures in any combination of the 3 hamstring muscles (the semitendinosus, semimembranosus, and biceps femoris). J Orthop Sports Phys Ther 2022;52(3):CPG1-CPG44. doi:10.2519/jospt.2022.0301.

Effect of knee joint angle on individual hamstrings morphology quantified using free-hand 3D ultrasonography

Exercise responses and injury rates differ between individual hamstrings and this may be linked with their morphology. The aim of this study was to compare muscle length and tendon dimensions between the individual hamstrings at two knee joint angles using free hand three-dimensional ultrasound (3D US). Muscle-tendon length and distal tendon cross-sectional area (CSA), volume, length and echogenicity of biceps femoris long (BFlh) and short (BFsh) head, semimembranosus (SM) and semitendinosus (ST) of 16 individuals were measured using free-hand 3D US at 0° (full extension) and 45° of knee flexion. ST showed the greatest length than all muscles and BFsh the lowest (p < 0.05). No difference was observed between SM and BFlh length (p > 0.05). Of the four muscles, ST tendon was longer, with less volume and CSA but greater echogenicity than the other tendons. In contrast, SM and BFlh showed shorter tendons and lower echogenicity but a greater volume and CSA than ST (p < 0.05). Muscle and tendon lengthened from 45° to 0° knee flexion angle (p < 0.05) but this change was not statistically different between individual hamstrings (p > 0.05). Freehand 3D US indicated that hamstring muscle length and distal tendon dimensions differ between individual hamstrings. All muscles and tendons lengthened as the knee was extended but this change was similar for all individual hamstrings.

Reliability of Distal Hamstring Tendon Length and Cross-sectional Area Using 3-D Freehand Ultrasound

The objective of this study was to investigate the reliability of distal hamstring tendon morphology using freehand 3-D ultrasound (US). Freehand 3-D US scans were acquired for 16 young males and females, in two sessions, spaced a week apart. The length, volume, cross-sectional area (CSA) and echo intensity (EI) of the semitendinosus (ST), biceps femoris long and short head and semimembranosus (SM) tendons were acquired. Measurements of the CSA and EI were obtained from three sites along each tendon. The intra-class correlation coefficients ranged from 0.88-0.99 of the examined variables, indicating high test-retest reliability. In addition, the minimal detectable change (MDC) ranged from 0.255-3.766 mm (MDC% of the mean: 0.406%-12.558%) for hamstring tendon length, from 0.036-0.077 mL (MDC%: 1.548%-3.178%) for tendon volume, from 0.512-1.948 mm² (MDC%: 0.702%-3.586%) for CSA and from 0.898-2.586 au (MDC%: 1.145%-3.325%) for EI. Of the four hamstring tendons, ST had the greatest length (141.587 ± 10.701 mm) and EI (94.637 ± 5.536 au), while SM had the greatest volume (3.056 ± 0.421 mL) and CSA (115.277 ± 16.442 mm²) relative to other tendons. Freehand 3-D US appears to be a reliable tool for the evaluation of hamstring distal tendon morphology; hence, its use for in vivo evaluation of tendon properties is promising.

Changes in Biceps Femoris Long Head Fascicle Length after 10-d Bed Rest Assessed with Different Ultrasound Methods

PURPOSE

This study aimed to investigate the changes in fascicle length (Lf) of biceps femoris long head (BFlh) after 10 d of bed rest (BR) by comparing four different ultrasound (US) methods.

METHODS

Ten healthy men participated in 10-d BR. Before (BR0) and after (BR10) the BR period, BFlh Lf values were obtained using 1) extended-field-of-view (EFOV) technique, 2) the manual linear extrapolation (MLE) method, and 3) two trigonometric equations (equations A and B) from a single US image.

RESULTS

After BR10, decreased Lf values were observed by EFOV (P < 0.001; Hedges' g = 0.29) and MLE (P = 0.0082; g = 0.22) methods, but not with equations A and B. Differences between equation A and the other US methods were detected at both time points. The percentage of changes in Lf between BR0 and BR10 was influenced by the US methods applied, with difference detected between the changes measured by EFOV and the ones estimated by equation A (P = 0.04; g = 0.53). Bland-Altman analyses revealed relevant average absolute biases in Lf between EFOV and other methods at both time points (range BR0-BR10: MLE, 0.3-0.37 cm (3.4%-4.32%); equation B, 0.3-0.48 cm (3.24%-5.41%); equation A, 2.44-2.97 cm (24.05%-29.2%)). A significant correlation (r = 0.83) in percentage of change in Lf values was observed only between EFOV and MLE.

CONCLUSIONS

We showed that four distinct US methods lead to different results in the assessment of BFlh Lf changes after a short-term period of unloading. The implementation of EFOV technique (or alternatively MLE) to assess Lf changes in BFlh during longitudinal studies is warranted.

Effects of Nordic hamstring exercise combined with glider exercise on hip flexion flexibility and hamstring passive stiffness

Eccentric training proved to be effective in hamstring injury prevention; however, little is known about effects of eccentric hamstring training at long muscle length on hamstring flexibility. Hence, the aim was to evaluate the effect of eccentric training at long muscle lengths on flexibility and passive properties of the hamstring muscles. 34 physically active young adults were randomized to either the control or intervention group (6 weeks of eccentric hamstring training at long muscle length; control group resumed with their usual activities). Maximal passive hip flexion range of motion (ROM), passive hamstring stiffness, shear modulus and tendon length of the biceps femoris long head (BFlh) were measured pre- and post-intervention. A significant time × group effect was observed for maximal passive hip ROM. Post-hoc testing revealed a significant increase in the intervention group (+11.2%; p < 0.001; d = 1.55). Additionally, a significant time effect was shown for shear modulus in a relaxed position (p < 0.001). No significant interaction was shown for other parameters. Results indicate that eccentric hamstring training at long muscle length elicits large gains in hamstring flexibility, which are most likely not related to changes in passive hamstring stiffness or BFlh distal tendon length.

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.

Spatial-frequency Analysis of the Anatomical Differences in Hamstring Muscles

Spatial frequency analysis (SFA) is a quantitative ultrasound method that characterizes tissue organization. SFA has been used for research involving tendon injury, but may prove useful in similar research involving skeletal muscle. As a first step, we investigated if SFA could detect known architectural differences within hamstring muscles. Ultrasound B-mode images were collected bilaterally at locations corresponding to proximal, mid-belly, and distal thirds along the hamstrings from 10 healthy participants. Images were analyzed in the spatial frequency domain by applying a two-dimensional Fourier Transform in all 6.5 × 6.5 mm kernels in a region of interest corresponding to the central portion of the muscle. SFA parameters (peak spatial frequency radius [PSFR], maximum frequency amplitude [Mmax], sum of frequencies [Sum], and ratio of Mmax to Sum [Mmax%]) were extracted from each muscle location and analyzed by separate linear mixed effects models. Significant differences were observed proximo-distally in PSFR (p = .039), Mmax (p < .0001), and Sum (p < .0001), consistent with architectural descriptions of the hamstring muscles. These results suggest that SFA can detect regional differences of healthy tissue structure within the hamstrings-an important finding for future research in regional muscle structure and mechanics.

Regional Differences in Biceps Femoris Long Head Stiffness during Isometric Knee Flexion

This study sought to investigate whether the stiffness of the biceps femoris long head differs between proximal and distal regions during isometric knee flexion at different contraction intensities and muscle lengths. Twelve healthy individuals performed knee flexion isometric contractions at 20% and 60% of maximum voluntary isometric contraction, with the knee flexed at 15 and 45 degrees. Muscle stiffness assessment was performed using ultrasound-based shear wave elastography. Proximal and distal regions of the biceps femoris long head were assessed. Biceps femoris long head muscle showed a greater stiffness (i) in the distal region, (ii) at higher contraction intensity, and (iii) at longer muscle length. The proximal-to-distal stiffness ratio was significantly lower than 1 (i.e., heterogenous) at lower contraction intensity regardless of the muscle length. However, this was not observed at higher contraction intensity. This study is the first to show heterogeneity in the active stiffness of the biceps femoris long head. Given the greater incidence of injury at the proximal region of biceps femoris long head, this study opens new directions for future research. Additionally, the present study results indicate that studies assessing muscle stiffness at one single muscle region should be interpreted with caution.

Sports-related lower limb muscle injuries: pattern recognition approach and MRI review

Muscle injuries of the lower limbs are currently the most common sport-related injuries, the impact of which is particularly significant in elite athletes. MRI is the imaging modality of choice in assessing acute muscle injuries and radiologists play a key role in the current scenario of multidisciplinary health care teams involved in the care of elite athletes with muscle injuries. Despite the frequency and clinical relevance of muscle injuries, there is still a lack of uniformity in the description, diagnosis, and classification of lesions. The characteristics of the connective tissues (distribution and thickness) differ among muscles, being of high variability in the lower limb. This variability is of great clinical importance in determining the prognosis of muscle injuries. Recently, three classification systems, the Munich consensus statement, the British Athletics Muscle Injury classification, and the FC Barcelona-Aspetar-Duke classification, have been proposed to assess the severity of muscle injuries. A protocolized approach to the evaluation of MRI findings is essential to accurately assess the severity of acute lesions and to evaluate the progression of reparative changes. Certain MRI findings which are seen during recovery may suggest muscle overload or adaptative changes and appear to be clinically useful for sport physicians and physiotherapists.

Differences in Lower Limb Strength and Structure After 12 Weeks of Resistance, Endurance, and Concurrent Training

PURPOSE

To investigate strength and structural adaptations after 12 weeks of resistance, endurance cycling, and concurrent training.

METHODS

Thirty-two healthy males undertook 12 weeks of resistance-only (RT; n = 10), endurance-only (END; n = 10), or concurrent resistance and endurance training (CONC; n = 12). Biceps femoris long head (BFlh) architecture, strength (3-lift 1-repetition maximum), and body composition were assessed.

RESULTS

Fascicle length of the BFlh reduced 15% (6%) (P < .001) and 9% (6%) (P < .001) in the END and CONC groups postintervention, with no change in the RT group (-4% [11%], P = .476). All groups increased BFlh pennation angle (CONC: 18% [9%], RT: 14% [8%], and END: 18% [10%]). Thickness of the BFlh increased postintervention by 7% (6%) (P = .002) and 7% (7%) (P = .003) in the CONC and RT groups, respectively, but not in the END group (0% [3%], P = .994). Both the CONC and RT groups significantly increased by 27% (11%) (P < .001) and 33% (12%) (P < .001) in 3-lift totals following the intervention, with no changes in the END cohort (6% [6%], P = .166). No significant differences were found for total body (CONC: 4% [2%], RT: 4% [2%], and END: 3% [2%]) and leg (CONC: 5% [3%], RT: 6% [3%], and END: 5% [3%]) fat-free mass.

CONCLUSIONS

Twelve weeks of RT, END, or CONC significantly modified BFlh architecture. This study suggests that conventional resistance training may dampen BFlh fascicle shortening from cycling training while increasing strength simultaneously in concurrent training. Furthermore, the inclusion of a cycle endurance training stimulus may result in alterations to hamstring architecture that increase the risk of future injury. Therefore, the incorporation of endurance cycling training within concurrent training paradigms should be reevaluated when trying to modulate injury risk.

Intra-session and inter-rater reliability of spatial frequency analysis methods in skeletal muscle

Spatial frequency analysis (SFA) is a quantitative ultrasound (US) method originally developed to assess intratendinous tissue structure. This method may also be advantageous in assessing other musculoskeletal tissues. Although SFA has been shown to be a reliable assessment strategy in tendon tissue, its reliability in muscle has not been investigated. The purpose of this study was to examine the reliability of spatial frequency parameter measurement for a large muscle group within a healthy population. Ten participants with no history of lower extremity surgery or hamstring strain injury volunteered. Longitudinal B-mode images were collected in three different locations across the hamstring muscles. Following a short rest, the entire imaging procedure was repeated. B-mode images were processed by manually drawing a region of interest (ROI) about the entire muscle thickness. Four spatial frequency parameters of interest were extracted from the image ROIs. Intra- and inter-rater reliabilities of extracted SFA parameters were performed. Test-retest reliability of the image acquisition procedure was assessed between repeat trials. Intraclass correlation coefficients showed high intra- and inter-rater reliability (ICC(3,1) > 0.9 for all parameters) and good to moderate test-retest reliability (ICC(3,1) > 0.50) between trials. No differences in parameter values were observed between trials across all muscles and locations (p > 0.05). The high reliability metrics suggest that SFA will be useful for future studies assessing muscle tissue structure, and may have value in assessing muscular adaptations following injury and during recovery.

Biceps Femoris Long-Head Architecture Assessed Using Different Sonographic Techniques

PURPOSE

To assess the repeatability of, and measurement agreement between, four sonographic techniques used to quantify biceps femoris long head (BFlh) architecture: (i) static-image with linear extrapolation; extended field-of-view (EFOV) with linear ultrasound probe path (linear-EFOV), using either (ii) straight or (iii) segmented analyses; and (iv) EFOV with nonlinear probe path and segmented analysis (nonlinear-EFOV) to follow the complex fascicle trajectories.

METHODS

Twenty individuals (24.4 ± 5.7 yr; 175 ± 0.8 cm; 73 ± 9.0 kg) without history of hamstrings strain injury were tested in two sessions separated by 1 h. An ultrasound scanner coupled with 6-cm linear probe was used to assess BFlh architecture in B-mode.

RESULTS

The ultrasound probe was positioned at 52.0% ± 5.0% of femur length and 57.0% ± 6.0% of BFlh length. We found an acceptable repeatability when assessing BFlh fascicle length (ICC3,k = 0.86-0.95; SEM = 1.9-3.2 mm) and angle (ICC3,k = 0.86-0.97; SEM = 0.8°-1.1) using all sonographic techniques. However, the nonlinear-EFOV technique showed the highest repeatability (fascicle length ICC3,k = 0.95; fascicle angle, ICC3,k = 0.97). The static-image technique, which estimated 35.4% ± 7.0% of the fascicle length, overestimated fascicle length (8%-11%) and underestimated fascicle angle (8%-9%) compared with EFOV techniques. Also, the rank order of individuals varied by approximately 15% between static-image and nonlinear-EFOV (segmented) when assessing the fascicle length.

CONCLUSIONS

Although all techniques showed good repeatability, absolute errors were observed using static-image (7.9 ± 6.1 mm for fascicle length) and linear-EFOV (between 3.7 ± 3.0 and 4.2 ± 3.7 mm), probably because the complex fascicle trajectories were not followed. The rank order of individuals for fascicle length and angle were also different between static-image and nonlinear-EFOV, so different muscle function and injury risk estimates could likely be made when using this technique.

Sonographic landmarks in hamstring muscles

The ultrasound examination of hamstrings inspires respect due to the connective complexity of their structures, particularly for sonographers who are not used to this kind of study. Therefore, it is important to know the specific ultrasound reference points that facilitate the location of the hamstring structures, dividing them into four areas of interest: (a) tendinous origin of the hamstring, (b) the proximal half, (c) distal and medial half, and (d) distal and lateral half. The origin of the hamstrings is found at the level of the ischial tuberosity. Here, the connective structures under study are the common tendon and the semimembranosus tendon, together with the muscle fibers more proximal to the semitendinosus, which can also be assessed through ultrasound locating the ischial tuberosity. The proximal half of the thigh consists of a characteristic structure made up by the common tendon, the sciatic nerve and the semimembranosus tendon, enabling to define the biceps femoris and the semitendinosus, respectively. To identify the distal and medial section, the volumetric relationship between the ST and SM muscle masses is used, where it is also possible to identify the three muscles in the knee that make up the pes anserine. To identify the distal and lateral sections, the sciatic nerve pathway is followed until identifying both heads of the biceps femoris. These four areas of interest, with their specific landmarks, show a tuning fork that enables the comprehensive study of hamstrings through ultrasound.

Ultrasound Elastographic Measurement of Sciatic Nerve Displacement and Shear Strain During Active and Passive Knee Extension

There is current need for objective measures of sciatic nerve mobility in patients with sciatic-type pain. The objective of the study was to assess the feasibility and reliability of ultrasound elastography to quantify sciatic nerve displacement and shear strain at the sciatic nerve-hamstring muscle interface during active and passive knee extension-flexion exercises performed while sitting in healthy people. Ultrasound elastography showed excellent intrarater within-session reliability for assessing sciatic nerve displacement and sciatic nerve-hamstring muscle interface shear strain during active knee extension-flexion exercises. These findings will inform similar future work conducted in patients with sciatic-type pain.

Ultrasonographic Measurement of the Biceps Femoris Long-Head Muscle Architecture

OBJECTIVES

Biceps femoris long-head architectural assessment using ultrasonography (US) has not been previously described in detail for both acquisition (image capture) and digitization (image measurement) processes, and the effect of the US window width is unknown. This study aimed to describe the reliability and test-retest minimum detectable difference of US-based biceps femoris architectural measurements.

METHODS

Muscle length was determined by marking the muscle-tendon junction distances. Sonograms were acquired with a 6-cm image width and cropped for a 3-cm width in 3 assessments (n = 20 adults). Intra- and inter-rater reliability rates were determined for both image (3- and 6-cm widths) acquisition and digitizing processes separated and together (within session) for the biceps femoris fascicle length, fascicle angle, and muscle thickness measurements using intraclass correlation coefficients (ICCs) and Pearson (r) correlation coefficients.

RESULTS

Muscle length was measured with high intra-rater (ICC = 0.93; r = 0.92) and inter-rater (ICC = 0.90; r = 0.90) reliability. Intra-rater (coefficient of variation, 0.2%-1.8%) and inter-rater (ICC = 0.79-0.99; r = 0.80-0.99) digitizing reliability rates were high. High intra-rater (ICC = 0.79-0.95; r = 0.79-0.95) and moderate-to-high inter-rater (ICC = 0.51-0.92; r = 0.70-0.93) session reliability rates were found for all architectural parameters for 6- and 3-cm images (intra-rater ICC = 0.77-0.93; r = 0.79-0.93; inter-rater ICC = 0.63-0.98; r = 0.90-0.98). The inter-rater session reliability rates for both image acquisition and digitizing processes were higher for 6-cm images (ICC = 0.65-0.86; r = 0.67-0.87) than 3-cm images (ICC = 0.28-0.93; r = 0.67-0.93). The minimum detectable differences for the 6-cm images were 8.4 mm, 1.5 °, and 1.6 mm for fascicle length, fascicle angle, and muscle thickness, respectively.

CONCLUSIONS

Ultrasonography can be used to reliably assess midmuscle architecture of the biceps femoris muscle when the same rater performs image acquisition and digitization.

Region-dependent hamstrings activity in Nordic hamstring exercise and stiff-leg deadlift defined with high-density electromyography

Recent studies suggest region-specific metabolic activity in hamstring muscles during injury prevention exercises, but the neural representation of this phenomenon is unknown. The aim of this study was to examine whether regional differences are evident in the activity of biceps femoris long head (BFlh) and semitendinosus (ST) muscles during two common injury prevention exercises. Twelve male participants without a history of hamstring injury performed the Nordic hamstring exercise (NHE) and stiff-leg deadlift (SDL) while BFlh and ST activities were recorded with high-density electromyography (HD-EMG). Normalized activity was calculated from the distal, middle, and proximal regions in the eccentric phase of each exercise. In NHE, ST overall activity was substantially higher than in BFlh (d = 1.06 ± 0.45), compared to trivial differences between muscles in SDL (d = 0.19 ± 0.34). Regional differences were found in NHE for both muscles, with different proximal-distal patterns: The distal region showed the lowest activity level in ST (regional differences, d range = 0.55-1.41) but the highest activity level in BFlh (regional differences, d range = 0.38-1.25). In SDL, regional differences were smaller in both muscles (d range = 0.29-0.67 and 0.16-0.63 in ST and BFlh, respectively) than in NHE. The use of HD-EMG in hamstrings revealed heterogeneous hamstrings activity during typical injury prevention exercises. High-density EMG might be useful in future studies to provide a comprehensive overview of hamstring muscle activity in other exercises and high-injury risk tasks.

Adaptation of a MR imaging protocol into a real-time clinical biometric ultrasound protocol for persons with spinal cord injury at risk for deep tissue injury: A reliability study

BACKGROUND

High strain in soft tissues that overly bony prominences are considered a risk factor for pressure ulcers (PUs) following spinal cord impairment (SCI) and have been computed using Finite Element methods (FEM). The aim of this study was to translate a MRI protocol into ultrasound (US) and determine between-operator reliability of expert sonographers measuring diameter of the inferior curvature of the ischial tuberosity (IT) and the thickness of the overlying soft tissue layers on able-bodied (AB) and SCI using real-time ultrasound.

MATERIAL AND METHODS

Part 1: Fourteen AB participants with a mean age of 36.7 ± 12.09 years with 7 males and 7 females had their 3 soft tissue layers in loaded and unloaded sitting measured independently by 2 sonographers: tendon/muscle, skin/fat and total soft tissue and the diameter of the IT in its short and long axis. Part 2: Nineteen participants with SCI were screened, three were excluded due to abnormal skin signs, and eight participants (42%) were excluded for abnormal US signs with normal skin. Eight SCI participants with a mean age of 31.6 ± 13.6 years and all male with 4 paraplegics and 4 tetraplegics were measured by the same sonographers for skin, fat, tendon, muscle and total. Skin/fat and tendon/muscle were computed.

RESULTS

AB between-operator reliability was good (ICC = 0.81-0.90) for 3 soft tissues layers in unloaded and loaded sitting and poor for both IT short and long axis (ICC = -0.028 and -0.01). SCI between-operator reliability was good in unloaded and loaded for total, muscle, fat, skin/fat, tendon/muscle (ICC = 0.75-0.97) and poor for tendon (ICC = 0.26 unloaded and ICC = -0.71 loaded) and skin (ICC = 0.37 unloaded and ICC = 0.10).

CONCLUSION

A MRI protocol was successfully adapted for a reliable 3 soft tissue layer model and could be used in a 2-D FEM model designed to estimate soft tissue strain as a novel risk factor for the development of a PU.