Volume of ankle dorsiflexors and plantar flexors determined with stereological techniques

How mechanics of individual muscle-tendon units define knee and ankle joint function in health and cerebral palsy-a narrative review

This study reviews the relationship between muscle-tendon biomechanics and joint function, with a particular focus on how cerebral palsy (CP) affects this relationship. In healthy individuals, muscle size is a critical determinant of strength, with muscle volume, cross-sectional area, and moment arm correlating with knee and ankle joint torque for different isometric/isokinetic contractions. However, in CP, impaired muscle growth contributes to joint pathophysiology even though only a limited number of studies have investigated the impact of deficits in muscle size on pathological joint function. As muscles are the primary factors determining joint torque, in this review two main approaches used for muscle force quantification are discussed. The direct quantification of individual muscle forces from their relevant tendons through intraoperative approaches holds a high potential for characterizing healthy and diseased muscles but poses challenges due to the invasive nature of the technique. On the other hand, musculoskeletal models, using an inverse dynamic approach, can predict muscle forces, but rely on several assumptions and have inherent limitations. Neither technique has become established in routine clinical practice. Nevertheless, identifying the relative contribution of each muscle to the overall joint moment would be key for diagnosis and formulating efficient treatment strategies for patients with CP. This review emphasizes the necessity of implementing the intraoperative approach into general surgical practice, particularly for joint correction operations in diverse patient groups. Obtaining in vivo data directly would enhance musculoskeletal models, providing more accurate force estimations. This integrated approach can improve the clinicians' decision-making process and advance treatment strategies by predicting changes at the muscle and joint levels before interventions, thus, holding the potential to significantly enhance clinical outcomes.

A longer Achilles tendon moment arm length is not associated with superior hopping performance

Variability in musculoskeletal and lower leg structure has the potential to influence hopping height. Achilles tendon moment arm length and plantarflexor muscle strength can influence ankle joint torque development and, consequently, hopping performance. While most studies have examined the connection of the Achilles tendon moment arm with hopping performance including the resting length, in this study we attempted to explore how the changes in Achilles tendon moment arm are related to hopping performance. Therefore, the purpose of this study was to test for correlations between foot and lower leg muscle structure parameters (i.e., muscle mass, volume, cross-sectional area and Achilles tendon moment arm length) and hopping height performance in relation to changes in Achilles tendon moment arm length. Eighteen participants (10 males 8 female) performed repetitive bilateral hopping on a force platform while sagittal plane kinematics of the lower leg were recorded. Additionally, maximal isometric plantarflexion was measured. To obtain structural parameters of the lower leg, the right lower leg of each participant was scanned with magnetic resonance imaging. The cross-sectional areas of the Achilles tendon, soleus, lateral and medial gastrocnemius were measured, while muscle volumes, muscle mass, and Achilles tendon moment arm length were calculated. Contrary to our initial assumption, longer Achilles tendon moment arm did not result in superior hopping performance. Interestingly, neither maximal isometric plantarflexion force nor muscle size correlated with repetitive bilateral hopping performance. We can assume that the mechanical characteristics of the tendon and the effective utilization of the stored strain energy in the tendon may play a more important role in repetitive hopping than the structural parameters of the lower leg.

Using a Standing Heel-Rise Test as a Predictor of Ankle Muscle Strength in the Elderly

The senior population is at increased risk of falling due to a reduction in ankle muscle strength. Evaluating the strength of the ankle muscles in older adults is of paramount importance. The purpose of this study was to formulate an equation to estimate ankle muscle strength by utilizing the basic physical characteristics of the subject and the variables related to their ability to perform the standing heel-rise test (SHRT). One hundred and thirty-two healthy elderly participants (mean age 67.30 ± 7.60) completed the SHRT and provided demographic information. Ankle plantar flexor (PF) muscle strength was evaluated using a push-pull dynamometer. Multiple regression analysis was utilized to develop a prediction equation for ankle PF muscle strength. The study revealed that the ankle PF strength equation was derived from variables including the power index of the SHRT, gender, age, calf circumference, and single-leg standing balance test. The equation exhibited a strong correlation (r = 0.816) and had a predictive power of 65.3%. The equation is represented as follows: ankle PF strength = 24.31 - 0.20(A) + 8.14(G) + 0.49(CC) + 0.07(SSEO) + 0.20(BW/t-SHRT). The equation had an estimation error of 5.51 kg. The strength of ankle PFs in elderly individuals can be estimated by considering demographic variables, including gender, age, calf circumference, single-leg standing balance test, and the power index of the SHRT. These factors were identified as significant determinants of ankle PF strength in this population.

W' reconstitution rate at different intensities above critical torque: the role of muscle size and maximal strength

NEW FINDINGS

What is the central question of this study? Do muscle size, maximal force and exercise intensity influence the recovery time constant for the finite impulse above critical torque (τ_IET' )? What is the main finding and its importance? Muscle size and maximal strength have different influences on the parameters of the hyperbolic torque-time to task failure relationship. Greater muscle size and maximal strength, as well as exercise at an intensity of 60% MVC, prolong τ_IET' during intermittent isometric exercise.

ABSTRACT

Muscle perfusion and O₂ delivery limitations through muscle force generation appear to play a major role in defining the hyperbolic torque-time to task failure (T_lim ) relationship. Therefore, we aimed to determine the influence of muscle size and maximal strength on the recovery time constant for the finite impulse above critical torque (τ_IET' ). Ten men participated in the study and performed intermittent isometric tests until task-failure (T_lim ) for the knee-extensors (KE) (35% and 60% maximal voluntary contraction (MVC)) and plantar flexors (PF) (60% MVC). The τ_IET' was determined for each of these T_lim tests using the IET'_BAL model. The IET' (9738 ± 3080 vs. 2959 ± 1289 N m s) and end-test torque (ET)(84.5 ± 7.1 vs. 74.3 ± 12.7 N m) were significantly lower for PF compared to KE (P < 0.05). Exercise tolerance (T_lim ) was significantly longer for PF (239 ± 81 s) than KE (150 ± 55 s) at 60% MVC, and significantly longer for KE at 35% MVC (641 ± 158 s) than 60% MVC. The τ_IET' was significantly faster at 35% MVC (641 ± 177 s) than 60% MVC (1840 ± 354 s) for KE, both of which were significantly slower than PF at 60% MVC (317 ± 102 s). This study showed that τ_IET' during intermittent isometric exercise is slower with greater muscle size and maximal strength.

Assessment of muscle volume using magnetic resonance imaging (MRI) in football players after hamstring injuries

Muscle injuries of the hamstrings are among the most frequent in football and a main cause for significant time away from training and competition. The purpose of this study was to prospectively evaluate the loss of muscle volume in recreational football players three and six weeks after initial trauma. We hypothesized that significant muscle volume loss occurs within 6 weeks after the initial injury event. Twenty recreational football players (mean-age=25 ± 4years; mean-height=181 ± 8cm; mean-weight=81 ± 10kg) with type3a (minor partial muscle tear) and type3b (moderate partial muscle tear) injuries were included. Muscle volume was determined using established methods for the hamstrings and the quadriceps femoris muscle within 3 days and after 3 and 6 weeks following the initial injury. The injured hamstrings lost 6.5% (mean=64 cm³(95%CI=31-98 cm³), p<0.001), the healthy hamstrings lost 2.1% (mean=21 cm³(3-44 cm³),p=0.096) of muscle volume after six weeks. The quadriceps in the injured leg lost 3.8% (mean=78 cm³(51-104 cm³), p<0.001) and 4.5% (83 cm³ (45-121 cm³), p<0.001) in the healthy leg. Muscle volume loss inversely correlated with activity levels in the healthy leg for the quadriceps (r=0.96 (0.90-0.98); R²=0.92; p<0.001) and the hamstrings (r=0.72 (0.40-0.88); R²=0.51; p<0.001), as well as the quadriceps in the injured leg (r=0.70 (0.37-0.87); R²=0.49; p<0.001), but not the injured hamstrings. Muscle volume ratio of hamstrings to quadriceps in the control limb was 0.52 ± 0.06 and 0.53 ± 0.06 in the injured leg. The rehabilitation period of six weeks did not have a relevant negative or a positive effect on ratios. Significant muscle volume loss in the upper thigh occurs in recreational soccer players within three, and within six weeks after a hamstring injury and lies between 2% and 7%.Highlights This study found that significant muscle volume loss occurs within six weeks after sustaining hamstring muscle group injuries.Additionally, most of the non-professional football players in the present study demonstrated low hamstring-to-quadriceps volume ratios in both the injured, as well as the heathy leg. Low hamstring-to-quadriceps volume ratios may provide an opportunity to focus on muscle hypertrophy strategies to help reduce the risk for muscle imbalances and thus future injury.After three weeks of resting, reduced training activity, compared to the training activity before the injury, seems to be sufficient to preserve 99% of the remaining muscle volume in the quadriceps and as well as the healthy hamstrings. The number of training-minutes correlates statistically significant inversely with the muscle volume lost in a rehabilitation period.

Bilateral quadriceps and hamstrings muscle volume asymmetries in healthy individuals

Determining the magnitude of quadriceps and hamstring muscle volume asymmetries in healthy individuals is a critical first step toward interpreting asymmetries as compensatory or abnormal in pathological populations. The purpose of this study was to determine the magnitude of whole and individual muscle volume asymmetries, quantified as right-left volume differences, for the quadriceps and hamstring muscles in a young and healthy population. Twenty-one healthy individuals participated: Eleven females age = 22.6 ± 2.9 years and 10 males age = 23.2 ± 3.4 years. Whole muscle group and individual muscle volume asymmetries were quantified within the context of absolute measurement error using a 95% Limits of Agreement approach. Mean muscle asymmetries ranged from -3.0 to 6.0% for all individual and whole muscle groups. Whole muscle group 95% limits of agreements represented ±11.4% and ±8.8% volume asymmetries for the hamstrings and quadriceps, respectively. Individual muscle asymmetry 95% limits of agreements ranged from ∼ ± 11-13% for the vastii muscles while the biceps femoris short-head (±33.5%), long-head (±20.9%), and the rectus femoris (±21.4%) displayed the highest relative individual asymmetries. Individual muscle asymmetries exceeded absolute measurement error in 70% of all cases, with 26% of all cases exceeding 10% asymmetry. Although whole muscle group asymmetries appear to be near the 10% assumed clinical threshold of normality, the greater magnitude of individual muscle asymmetries highlights the subject- and muscle-specific variability in volume asymmetry. Future research is warranted to determine if volume asymmetry thresholds exist that discriminate between healthy and pathological populations. Statement of Clinical Significance: Muscle volume asymmetries displayed in healthy individuals provide a reference for interpreting asymmetries in pathological populations. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:963-970, 2018.

Do longus capitis and colli really stabilise the cervical spine? A study of their fascicular anatomy and peak force capabilities

BACKGROUND

Longus capitis and colli are proposed to play a role in stabilising the cervical spine, targeted in clinical and research practice with cranio-cervical flexion. However, it is not clear if these muscles are anatomically or biomechanically suited to a stabilising role.

OBJECTIVES

To describe the fascicular morphology of the longus capitis and colli, and estimate their peak force generating capabilities across the individual cervical motion segments.

STUDY DESIGN

Biomechanical force modelling based on anatomical data.

METHODS

Three-part design including cadaveric dissection (n = 7), in vivo MRI muscle volume calculation from serial slices in young healthy volunteers (n = 6), and biomechanical modelling of the peak force generating capacities based on computed tomography scans of the head and neck.

RESULTS

Longus capitis and colli are small muscles spanning multiple cervical motion segments. Bilateral peak flexion torque estimates were higher in the upper cervical spine (0.5 Nm), and unlikely to affect motion below the level of C5 (<0.2 Nm). Peak shear estimates were negligible (<20 N), while peak compression estimates were small (<80 N).

CONCLUSIONS

These data highlight the complex anatomy and small force capacity of longus capitis and colli, and have implications for their function. In particular, the small peak compression forces indicate that these muscles have a limited capacity to contribute to cervical stability via traditional mechanisms. This implies that the mechanism(s) by which cranio-cervical flexion exercises produce clinical benefits is worth exploring further.

Determination of contraction-induced changes in elbow flexor cross-sectional area for evaluating muscle size-strength relationship during contraction

The aims of this study were to determine contraction-induced changes in the elbow flexor cross-sectional area (CSA) and to examine whether the maximal CSA during a high-intensity contraction is more closely related to the strength than that at rest in the elbow flexors. Fourteen young male subjects participated in this study. The elbow flexor CSAs were measured at sites from 1 cm proximal to 6 cm distal to the reference site (60% of the upper arm length from the acromial process of the scapula to the lateral epicondyle of the humerus) (every 1 cm; 8 sampling sites) using magnetic resonance imaging, at rest and during 10, 20, 40, 60, and 80% of maximal voluntary contraction (MVC) of isometric elbow flexion. The elbow flexor CSA changed greatly during low-intensity contractions, and this contraction-induced change was small over 60%MVC. Compared with at rest, greater CSA around the muscle belly and smaller CSA in the distal portion of the elbow flexors were found in contracted conditions. The MVC strength was significantly correlated with the maximal CSAs at rest and each contraction level, but stepwise multiple regression analysis selected only that during 80%MVC as a significant contributor for estimating the MVC strength. These results suggest that, in the elbow flexors, the contraction-induced change in the CSA reaches its peak under high contractile level and that the maximal CSA during 80%MVC is more closely related to the MVC strength than that at rest.

Estimation of gastrocnemius muscle volume using ultrasonography in children with spastic cerebral palsy

PURPOSE

This study aimed to investigate useful parameters for estimating gastrocnemius (GCM) muscle volume (MV) using ultrasonography (US) and anthropometry in children with spastic cerebral palsy (CP).

MATERIALS AND METHODS

Eighteen legs from nine children with spastic CP aged 2 to 6 years were investigated in this study. Tibial length (TL) of each leg was measured and muscle thickness (MT) and anatomical cross-sectional area (aCSA) of GCM muscles were assessed using US. The volume of the GCM was measured by magnetic resonance imaging (MRI) scans. The relationship of TL, MT, and aCSA with MV measured by MRI was investigated. Simple and multiple regression analyses were performed to establish muscle volume prediction equations.

RESULTS

Resting MT, aCSA, and TL were highly related to MV of both medial and lateral head of GCM determined by MRI. The MV prediction equation based on simple regression analysis resulted in r² values ranging from 0.591 to 0.832 (p<0.05). The r² values were higher using aCSA as independent variable than using MT. The MV prediction equation based on multiple regression analysis resulted in r² values ranging from 0.779 to 0.903 (p<0.05). However, the relatively high standard error of the estimate values ranged from 18.0-33.6% on simple regression and 15.5-25.6% on multiple regression. The contribution of aCSA was higher than that of MT for predicting MV of GCM.

CONCLUSION

Our study demonstrated the suitability of US assessment of aCSA and MT combined with TL for estimating MV of GCM in children with spastic CP and showed that aCSA is more useful parameter than MT.

Plantar flexor moment arm and muscle volume predict torque-generating capacity in young men

Muscle volume is known to correlate with maximal joint torque in humans, but the role of muscle moment arm in determining maximal torque is less clear. Moderate correlations have been reported between maximal isometric knee extensor torque and knee extensor moment arm, but no such observations have been made for the ankle joint. It has been suggested that smaller muscle moment arms may enhance force generation at high rates of joint rotation, but this has not yet been observed for ankle muscles in vivo. The purpose of the present study was to correlate plantar flexor moment arm and plantar flexor muscle volume with maximal plantar flexor torque measured at different rates of plantar flexion. Magnetic resonance imaging was used to quantify the plantar flexor moment arm and muscle volume of the posterior compartment in 20 healthy young men. Maximal plantar flexor torque was measured isometrically and at three plantar flexion speeds using an isokinetic dynamometer. Plantar flexor torque was significantly correlated with muscle volume (0.222 < R(2) < 0.322) and with muscle moment arm at each speed (0.323 < R(2) < 0.494). While muscle volume was strongly correlated with body mass and stature, moment arm was not. The slope of the torque-moment arm regression line decreased as the rate of joint rotation increased, indicating that subjects with small moment arms experienced smaller reductions in torque at high speeds. The findings of this study suggest that plantar flexor moment arm is a determinant of joint strength that is at least as important as muscle size.

Muscle strength and its relationship with skeletal muscle mass indices as determined by segmental bio-impedance analysis

PURPOSE

Despite increasing interest in bio-impedance analysis (BIA) for estimation of segmental skeletal muscle mass (SMM), published results have not been entirely convincing. Furthermore, a better understanding of the relationship between muscle strength and SMM will be useful in interpreting outcomes of physical/training interventions particularly in groups with diverse body sizes (e.g. men vs women). This study aimed to measure SMM in the upper body (upper extremity and torso), to determine its correlation with muscle strength and to examine the effects of gender on muscle strength-muscle mass relationship.

METHODS

Segmental (upper extremity and torso) SMM and muscle strength in five distinct shoulder planes (forward flexion, abduction in scapular plane, abduction in coronal plane, internal and external rotation) were measured in 45 healthy participants (22 males, 23 females) with mean age 30.3 years. Statistical analysis included independent t tests, Pearson correlation, and multiple regression analysis.

RESULTS

Men and women differed significantly in body mass (BMI: 25.9 ± 4.3 vs 23 ± 3.6) and SMM (p < 0.01). A strong relationship correlation was found between the five shoulder strength measurements and upper extremity SMM (r = 0.66-0.80, p < 0.01), which was not affected by gender. There was a significant gender difference (p < 0.01) in absolute shoulder strength, but not after normalisation to the SMM.

CONCLUSION

BIA-estimated SMM of upper extremity and torso was highly correlated with upper extremity (shoulder) strength independent of gender. SMM may, therefore, be useful for the normalisation of muscle strength allowing size-independent comparisons of muscle strength in individuals with diverse physical characteristics.

Strength and size ratios between reciprocal muscle groups in the thigh and lower leg of male collegiate soccer players

This study investigated the strength and size ratios between reciprocal muscle groups in the thigh and lower leg of soccer players. In 11 male collegiate soccer players and 21 male non-soccer players, the joint torques developed during isometric maximal voluntary contractions of the knee extensors (TQ(KE)) and flexors (TQ(KF)), plantar flexors (TQ(PF)) and dorsiflexors (TQ(DF)) were determined using a dynamometer. The muscle volumes of the same muscles (i.e. MV(KE), MV(KF), MV(PF) and MV(DF)) were determined by magnetic resonance imaging. There were no significant differences in any of the joint torques or muscle volumes between soccer and non-soccer players. TQ(KE)/TQ(KF) was significantly lower for soccer players than for non-soccer players. On the other hand, no significant difference in TQ(PF)/TQ(DF) was found between soccer and non-soccer players. MV(KE)/MV(KF) and MV(PF)/MV(DF) for soccer players were not significantly different from those for non-soccer players. Additionally, there were no significant correlations between MV(KE)/MV(KF) and TQ(KE)/TQ(KF) and between MV(PF)/MV(DF) and TQ(PF)/TQ(DF) of soccer players. Thus, the strength ratios appear not to be affected by the size ratios between the knee extensors and flexors and between the plantar flexors and dorsiflexors in soccer players.

Kinesio taping and the circulation and endurance ratio of the gastrocnemius muscle

CONTEXT

Kinesio Tex tape is a therapeutic tape that is applied with the Kinesio-taping (KT) method and is theorized to increase circulation and subsequently improve muscle function. However, little research has been conducted to determine how KT affects performance.

OBJECTIVE

To determine the effect of KT on muscular endurance ratio, blood flow, circumference, and volume of the gastrocnemius muscle.

DESIGN

Randomized controlled clinical trial.

SETTING

Research laboratory. Patients or Other Participants: Sixty-one healthy, active people (23 men, 38 women; age = 19.99 ± 8.01 years, height = 169.42 ± 23.62 cm, mass = 71.53 ± 36.77 kg) volunteered to participate. They were assigned randomly to 1 of 3 groups: treatment KT, sham KT, and control.

INTERVENTION(S)

Tape was applied based on group assignment. The treatment KT group received the ankle-tape technique as described in the KT manual. The sham KT group received 1 strip of Kinesio Tex tape around the circumference of the proximal gastrocnemius muscle. The control group did not receive tape application.

MAIN OUTCOME MEASURE(S)

The dependent variables were blood flow in blood perfusion units, volume of water displacement in milliliters, circumference of the gastrocnemius muscle in centimeters, and endurance ratio in joules measured before, 24 hours after, and 72 hours after the intervention. Separate repeated-measures analyses of variance were conducted for each dependent variable.

RESULTS

We found no group-by-test day interaction for endurance ratios (F(4,116) = 1.99, P = .10). Blood flow, circumference, and volume measurements also yielded no differences among groups (F(2,58) range, 0.02-0.51; P > .05) or test days (F(2,116) range, 0.05-2.33; P > .05).

CONCLUSIONS

We found KT does not enhance anaerobic muscle function measured by endurance ratio. The KT also did not affect circulation or volume of the gastrocnemius muscle in a healthy population.

Reliability of ultrasound to measure morphology of the toe flexor muscles

Background

Measuring the strength of individual foot muscles is very challenging; however, measuring muscle morphology has been shown to be associated with strength. A reliable method of assessing foot muscle atrophy and hypertrophy would therefore be beneficial to researchers and clinicians. Thus, the aim of this study was to evaluate the test-retest intra-observer reliability of ultrasound to measure the morphology of the primary toe flexor muscles.

Method

The abductor hallucis, flexor hallucis brevis, flexor digitorum brevis, quadratus plantae and abductor digiti minimi muscles in the foot, and the flexor digitorum longus and flexor hallucis longus muscles in the shank were assessed in five males and five females (mean age = 32.1 ± 10.1 years). Muscles were imaged using a GE Venue 40 ultrasound (6-9 or 7.6-10.7 MHz transducer) in a random order, and on two occasions 1-6 days apart. Muscle thickness and cross-sectional area were measured using Image J software with the assessor blinded to muscle and day of scan. Intraclass correlation coefficients (ICC) and limits of agreement were calculated to assess day-to-day repeatability of the measurements.

Results

The method was found to have good reliability (ICC = 0.89-0.99) with limits of agreement between 8-28% of the relative muscle size.

Conclusion

The protocol described in this paper showed that ultrasound is a reliable method to measure morphology of the toe flexor muscles. The portability and advantages of ultrasound make it a useful tool for clinical and research settings.

Reliability and validity of a MR-based volumetric analysis of the intrinsic foot muscles

PURPOSE

To describe a semi-automated program that will segment subcutaneous fat, muscle, and adipose tissue in the foot using MR imaging, determine the reliability of the program between and within raters, and determine the validity of the program using MR phantoms.

MATERIALS AND METHODS

MR images were acquired from 19 subjects with and without diabetes and peripheral neuropathy. Two raters segmented and measured volumes from single MR slices at the forefoot, midfoot, and hindfoot at two different times. Intra- and inter-rater correlation coefficients were determined. Muscle and fat MR phantoms of known volumes were measured by the program.

RESULTS

Most ICC reliability values were over 0.950. Validity estimates comparing MR estimates and known volumes resulted in r(2) values above 0.970 for all phantoms. The root mean square error was less than 5% for all phantoms.

CONCLUSION

Subcutaneous fat, lean muscle, and adipose tissue volumes in the foot can be quantified in a reliable and valid way. This program can be applied in future studies investigating the relationship of these foot structures to functions in important pathologies, including the neuropathic foot or other musculoskeletal problems.

Importance and challenges of measuring intrinsic foot muscle strength

BACKGROUND

Intrinsic foot muscle weakness has been implicated in a range of foot deformities and disorders. However, to establish a relationship between intrinsic muscle weakness and foot pathology, an objective measure of intrinsic muscle strength is needed. The aim of this review was to provide an overview of the anatomy and role of intrinsic foot muscles, implications of intrinsic weakness and evaluate the different methods used to measure intrinsic foot muscle strength.

METHOD

Literature was sourced from database searches of MEDLINE, PubMed, SCOPUS, Cochrane Library, PEDro and CINAHL up to June 2012.

RESULTS

There is no widely accepted method of measuring intrinsic foot muscle strength. Methods to estimate toe flexor muscle strength include the paper grip test, plantar pressure, toe dynamometry, and the intrinsic positive test. Hand-held dynamometry has excellent interrater and intrarater reliability and limits toe curling, which is an action hypothesised to activate extrinsic toe flexor muscles. However, it is unclear whether any method can actually isolate intrinsic muscle strength. Also most methods measure only toe flexor strength and other actions such as toe extension and abduction have not been adequately assessed. Indirect methods to investigate intrinsic muscle structure and performance include CT, ultrasonography, MRI, EMG, and muscle biopsy. Indirect methods often discriminate between intrinsic and extrinsic muscles, but lack the ability to measure muscle force.

CONCLUSIONS

There are many challenges to accurately measure intrinsic muscle strength in isolation. Most studies have measured toe flexor strength as a surrogate measure of intrinsic muscle strength. Hand-held dynamometry appears to be a promising method of estimating intrinsic muscle strength. However, the contribution of extrinsic muscles cannot be excluded from toe flexor strength measurement. Future research should clarify the relative contribution of intrinsic and extrinsic muscles during intrinsic foot muscle strength testing.

Methodological issues related to thickness-based muscle size evaluation

The purpose of this study was to highlight the issues related to thickness-based muscle size evaluation that is commonly done in field studies. The cross-sectional area, thickness (the vertical distance from the upper end of the elbow flexors to that of the humerus) and width (the horizontal distance from the left to the right end of the elbow flexors) of the elbow flexors at levels from the reference site (60% of the upper arm length from the acromial process of the scapula to the lateral epicondyle of the humerus) to 5 cm distal to it were determined in 11 young men using magnetic resonance imaging, both at rest and during isometric elbow flexion at 30% of maximal voluntary contraction. During 30% of maximal voluntary contraction, the thickness increased but the width decreased at each measurement site compared with those at rest. This was possibly due to difference in muscle slackness between both conditions. The correlation coefficients between the thickness and cross-sectional area for the elbow flexors were significantly lower at rest (r=0.551-0.856) than during 30% of maximal voluntary contraction (r=0.711-0.922). The present findings indicate that the thickness-based muscle size measurement at rest includes errors owing to the slackness of the resting muscles.

Magnetic resonance imaging measurement reproducibility for calf muscle and adipose tissue volume

PURPOSE

To describe a new semiautomated method for segmenting and measuring the volume of the muscle, bone, and adipose (subcutaneous and intermuscular) tissue in calf muscle compartments using magnetic resonance (MR) images and determine the intrarater and interrater reproducibility of the measures.

MATERIALS AND METHODS

Proton-density weighted MR images were acquired from the right calf of 21 subjects. Three raters segmented and measured the volumes of bones, adipose tissue, and five individual muscle compartments. Two raters repeated the segmentations. The intra- and interrater reproducibility of the measures (intraclass correlation coefficients; ICC) were determined using generalizability theory.

RESULTS

All ICC values were greater than 0.96. The average standard error of the mean (SEM) of all measures was 1.21 cm(3) and none were greater than 2.3 cm(3) . Essentially all variation (≥97% for all measures) was due to subject differences, indicating low error in the measurements.

CONCLUSION

The volumetric measurements for the bones, adipose tissue, and muscle in each of the compartments using MRI were highly reproducible. MRI can provide quantitative, reproducible volumetric measures of bone, adipose tissue, and individual muscle compartments in the calf. We believe these methods can be used to quantify specific muscle or adipose volumetric measures for other clinical or research purposes.

Calibration of cross-sectional images measured by an ultrasound-based muscle evaluation system

The quantification of muscle volume can be used to estimate muscular strength. Therefore, we developed a flexible measuring system for muscle volume using ultrasonog-raphy. In the measuring process, subjects are not required to perform any muscular contraction, so it is completely safe and particularly suitable for elderly people. The ultrasound probe is installed on a mechanical arm, and continuously scans fragmental images along the body surface. The measured images are then composed into a wide area cross-sectional image. However, the muscle area measured by our system was slightly smaller than that measured by MRI. because the ultrasound probe contacted the body surface with a little pressure during the measurement. The strain then decreases the total image size and its circumference. This paper introduces our developed system and proposes a new calibration method for the muscle area in the thigh based on its circumference.

Development of an equation to predict muscle volume of elbow flexors for men and women with a wide range of age

The present study examined the age-related changes in muscle thickness (MT) and volume (MV) of elbow flexors and developed a prediction equation of the MV based on the MT applicable to men and women with a wide range of age. The MT and MV were determined from a single ultrasonographic image and multiple magnetic resonance imaging scans, respectively, in 72 men and 75 women aged 19-77 year. As a result of examining the age-MT and age-MV relationships by calculation of partial correlation coefficients with the control variable of gender, MV was decreased with aging whereas the corresponding decline in MT was not significant. The subjects were randomly separated into either a validation (38 men and 42 women) or a cross-validation (34 men and 33 women) group, and a multiple regression equation to estimate MV using not only MT but also upper arm length (L), age and gender as independent variables [MV (cm(3)) = 60.8 x MT (cm) + 6.48 x L (cm) - 0.709 x age (year) + 51.4 x gender (0 women, 1 men) - 187.4] was validated and cross-validated. Thus, the prediction equation for MV of elbow flexors newly developed was shown to be applicable to men and women with a wide range of age.

Atrophy of foot muscles in diabetic patients can be detected with ultrasonography

OBJECTIVE

To establish a bedside test with ultrasonography for evaluation of foot muscle atrophy in diabetic patients.

RESEARCH DESIGN AND METHODS

Thickness and cross-sectional area (CSA) of the extensor digitorum brevis muscle (EDB) and of the muscles of the first interstitium (MILs) were determined in 26 diabetic patients and in 26 matched control subjects using ultrasonography. To estimate the validity, findings were related to the total volume of all foot muscles determined at magnetic resonance imaging (MRI-FM(vol)). Furthermore, the relations of ultrasonographic estimates to nerve conduction, sensory perception thresholds, and clinical condition were established.

RESULTS

In diabetic patients, the ultrasonographic thickness of EDB (U-EDB(t)) was (means +/- SD) 6.4 +/- 2.1 vs. 9.0 +/- 1.0 mm in control subjects (P < 0.001), the thickness of MIL (U-MIL(t)) was 29.6 +/- 8.3 vs. 40.2 +/- 3.6 mm in control subjects (P < 0.001), and the CSA of EDB (U-EDB(CSA)) was 116 +/- 65 vs. 214 +/- 38 mm(2) in control subjects (P < 0.001). The MRI-FM(vol) was directly related to U-EDB(t) (r = 0.77), U-MIL(t) (r = 0.71), and U-EDB(CSA) (r = 0.74). U-EDB(t) and U-MIL(t) were thinner in neuropathic than in nonneuropathic diabetic patients (5.8 +/- 2.1 vs. 7.5 +/- 1.7 mm [P < 0.05] and 28.3 +/- 8.8 vs. 35.6 +/- 4.3 mm [P < 0.03], respectively).

CONCLUSIONS

Atrophy of intrinsic foot muscles determined at ultrasonography is directly related to foot muscle volume determined by MRI and to various measures of diabetic neuropathy. Ultrasonography seems to be useful for detection of foot muscle atrophy in diabetes.

Calf muscle volume estimates: implications for botulinum toxin treatment?

An optimal botulinum toxin dose may be related to the volume of the targeted muscle. We investigated the suitability of using ultrasound and anthropometry to estimate gastrocnemius and soleus muscle volume. Gastrocnemius and soleus muscle thickness was measured in 11 cadaveric human legs, using ultrasound. Lower leg length was tape-measured. Muscle volume was determined by water displacement of the dissected muscles. Simple and multiple regression analyses, using muscle thickness and lower leg length as independent variables, were performed to establish muscle volume prediction equations from the muscle volume measured by water displacement. Validating the equations based on simple regression analyses resulted in a correlation (r2) of 0.373 and 0.518 (P < 0.047), and a standard error of the estimate of 24.4 cm3 (11.7% of the measured mean muscle volume) and 33.2 cm3 (12.7%) for the gastrocnemius and soleus muscles, respectively. The corresponding values for the multiple regression analyses were an r2 of 0.497 and 0.650 (P < 0.017), and a standard error of the estimate of 21.9 cm3 (10.5%) and 28.4 cm3 (10.8%) for the gastrocnemius and soleus muscles, respectively. It seems possible to estimate the volume of individual plantar flexor muscles using ultrasound and anthropometry. This possibility should be investigated further in living humans.

Segmentation of fascias, fat and muscle from magnetic resonance images in humans: the DISPIMAG software

Segmentation of human limb MR images into muscle, fat and fascias remains a cumbersome task. We have developed a new software (DISPIMAG) that allows automatic and highly reproducible segmentation of lower-limb MR images. Based on a pixel intensity analysis, this software does not need any previous mathematical or statistical assumptions. It displays a histogram with two main signals corresponding to fat and muscle, and permits an accurate quantification of their relative spatial distribution. To allow a systematic discrimination between muscle and fat in any subject, fixed boundaries were first determined manually in a group of 24 patients. Secondly, an entirely automatic process using these boundaries was tested by three operators on four patients and compared to the manual approach, showing a high concordance.

Myotendinous plasticity to ageing and resistance exercise in humans

The age-related loss of muscle mass known as senile sarcopenia is one of the main determinants of frailty in old age. Molecular, cellular, nutritional and hormonal mechanisms are at the basis of sarcopenia and are responsible for a progressive deterioration in skeletal muscle size and function. Both at single-fibre and at whole-muscle level, the loss of force exceeds that predicted by the decrease in muscle size. For single fibres, the loss of intrinsic force is mostly due to a loss in myofibrillar protein content. For whole muscle, in addition to changes in neural drive, alterations in muscle architecture and in tendon mechanical properties, exemplified by a reduction in tendon stiffness, have recently been shown to contribute to this phenomenon. Resistance training can, however, cause substantial gains in muscle mass and strength and provides a protective effect against several of the cellular and molecular changes associated with muscle wasting and weakness. In old age, not only muscles but also tendons are highly responsive to training, since an increase in tendon stiffness has been observed after a period of increased loading. Many of the myotendinous factors characterizing ageing can be at least partly reversed by resistance training.

Atrophy of foot muscles: a measure of diabetic neuropathy

OBJECTIVE

Diabetic neuropathy is a length-dependent process that leads to reduced muscle strength and atrophy of leg muscles in some patients. We hypothesized that intrinsic foot muscles are atrophied in diabetic neuropathy and that the degree of atrophy is a measure of motor dysfunction closely related to the neuropathic process.

RESEARCH DESIGN AND METHODS

Consecutive cross-sectional magnetic resonance images of the nondominant foot were obtained for stereological determination of the total volume of the intrinsic foot muscles (VFM) in 23 long-term diabetic patients with (n = 15) and without (n = 8) chronic neuropathy and in 23 matched healthy nondiabetic control subjects. Based on clinical examination, nerve conduction studies, and quantitative sensory examination, a neuropathy rank-sum score was calculated for each patient.

RESULTS

Total VFM was 86 +/- 52, 165 +/- 34, and 168 +/- 42 cm3 in neuropathic patients, nonneuropathic patients, and healthy control subjects, respectively (P < 0.001). There was a close inverse relationship between the neuropathy rank-sum score and the VFM (r = -0.75, P < 1 x 10(-5)).

CONCLUSIONS

Total volume of the foot muscles is halved in patients with diabetic neuropathy. Atrophy of foot muscles is closely related to the severity of neuropathy and reflects motor dysfunction.

Structure and function of the ankle dorsiflexor muscles in young and moderately active men and women

The aim was to investigate determinants of ankle dorsiflexor muscle (DF) strength and size in moderately active young men and women (n = 30; age 20-31 yr). Concentric (Con) and eccentric (Ecc) strength were measured isokinetically. Magnetic resonance imaging was used to determine the muscle cross-sectional area (CSA). Multiple biopsies were obtained from the tibialis anterior muscle to determine total numbers, areas (Area I and II) and proportions (Prop I and II) of type I and II fibers, respectively, and relative contents of myosin heavy chain (MHC) isoforms MHC1, MHC2a, and MHC2x. Women had lower Con and Ecc strength (24 and 27%; P < 0.01), smaller CSA (19%; P < 0.001), lower Ecc DF specific strength (strength/CSA) (10%; P < 0.01), and smaller Area I and Area II (21 and 31%; P < 0.01) than men. Prop I, MHC1, estimated total number of fibers, and Con DF specific strength were similar for both sexes. Con DF strength was up to 72% determined by CSA and Prop I, and Ecc DF strength was up to 81% determined by CSA, Prop I, and sex; variables other than CSA explained at most 9%. Body weight and fiber areas explained >50% of the variation in CSA. In conclusion, CSA was the predominant determinant of DF strength, CSA was to a great extent determined by the body weight and the sizes of muscle fibers, and sex differences in Ecc specific strength require further study.

Organogenesis of lung and kidney in Thoroughbreds and ponies

Equine lung and kidney organogenesis has not previously been examined with the use of unbiased stereological techniques. The present study examined healthy (control) pony and Thoroughbred lungs and kidneys to establish baseline data of organ development from before birth until maturity at age 3-18 years. Whole left lungs and kidneys were collected from 45 equine postmortem examinations (34 Thoroughbred, 11 pony). Stereological techniques were used to estimate whole kidney, cortex and medulla volume, total glomerular number and volume-weighted mean glomerular volume, lung volume, total terminal bronchiolar duct ending number and total gas exchange surface area. Lungs were demonstrated to be more developed at birth in ponies compared with Thoroughbreds. Thoroughbreds showed continued lung development after birth, a unique micromorphogenic postnatal development. Kidneys were developed equally in ponies and Thoroughbreds. This study has provided data on the baseline development of the equiune lung and kidney which can be used in further studies to examine whether the development of these organs is affected by specific illnesses.

Muscle volume is a major determinant of joint torque in humans

Muscle force (MF) is linearly related to physiological cross-sectional area (CSA), which is obtained from muscle volume (MV) divided by fibre length. Taking into account the fact that joint torque (TQ) is determined by MF multiplied by the moment arm, the maximal TQ would be a function of MV. This proposition was tested in the present study by investigating the relationship between MV and TQ for elbow flexor (EF) and extensor (EE) muscles of 26 males. The MVs of EF and EE were determined from a series of muscle CSA by magnetic resonance imaging (MRI), and pennation angle (theta) and FL by ultrasonography (US). Maximal isometric TQ was measured at right angle of elbow joint for EF and EE. There was a highly significant correlation between MV and TQ both for EF and EE (r=0.95 and 0.96 respectively) compared with that between muscle CSA and TQ, suggesting the dependence of TQ on MV. Furthermore, prediction equations for MV (MVULT) from muscle thickness (MT) measured by US was developed with reference to MVMRI by the MRI on 26 subjects, and the equations were applied to estimate MV of healthy university students (CON; 160 males) and sports athletes (ATH; 99 males). There were significant linear relationships between MVULT and TQ both for EF (r=0.783) and EE (r=0.695) for all subjects (n=259). The MVULT was significantly higher in ATH (by 32% for EF and 33% for EE, respectively) than in CON. Similarly, significantly greater TQ was observed in ATH (by 35% for EF, 37% for EE, respectively). The theta for EE showed no difference between both groups (17.8 degrees for CON and 17.5 degrees for ATH). On the other hand, the TQ to MV ratio were identical for CON and ATH. The results reveal that the muscle volume of the upper arm is a major determinant of joint torque (TQ), regardless of athletic training.

Validity of estimating limb muscle volume by bioelectrical impedance

The present study aimed to investigate the validity of estimating muscle volume by bioelectrical impedance analysis. Bioelectrical impedance and series cross-sectional images of the forearm, upper arm, lower leg, and thigh on the right side were determined in 22 healthy young adult men using a specially designed bioelectrical impedance acquisition system and magnetic resonance imaging (MRI) method, respectively. The impedance index (L(2)/Z) for every segment, calculated as the ratio of segment length squared to the impedance, was significantly correlated to the muscle volume measured by MRI, with r = 0.902-0.976 (P < 0.05). In these relationships, the SE of estimation was 38.4 cm(3) for the forearm, 40.9 cm(3) for the upper arm, 107.2 cm(3) for the lower leg, and 362.3 cm(3) for the thigh. Moreover, isometric torque developed in elbow flexion or extension and knee flexion or extension was significantly correlated to the L(2)/Z values of the upper arm and thigh, respectively, with correlation coefficients of 0.770-0.937 (P < 0.05), which differed insignificantly from those (0.799-0.958; P < 0.05) in the corresponding relationships with the muscle volume measured by MRI of elbow flexors or extensors and knee flexors or extensors. Thus the present study indicates that bioelectrical impedance analysis may be useful to predict the muscle volume and to investigate possible relations between muscle size and strength capability in a limited segment of the upper and lower limbs.

Ageing, muscle properties and maximal O(2) uptake rate in humans

This paper asks how the decline in maximal O(2) uptake rate (VO(2),max) with age is related to the properties of a key muscle group involved in physical activity - the quadriceps muscles. Maximal oxygen consumption on a cycle ergometer was examined in nine adult (mean age 38.8 years) and 39 elderly subjects (mean age 68.8 years) and compared with the oxidative capacity and volume of the quadriceps. VO(2),max declined with age between 25 and 80 years and the increment in oxygen consumption from unloaded cycling to VO(2),max (delta VO(2)) in the elderly was 45 % of the adult value. The cross-sectional areas of the primary muscles involved in cycling - the hamstrings, gluteus maximus and quadriceps - were all lower in the elderly group. The quadriceps volume was reduced in the elderly to 67 % of the adult value. Oxidative capacity per quadriceps volume was reduced to 53 % of the adult value. The product of oxidative capacity and muscle volume - the quadriceps oxidative capacity - was 36 % of the adult value in the elderly. Quadriceps oxidative capacity was linearly correlated with delta VO(2) among the subjects with the slope indicating that the quadriceps represented 36 % of the VO(2) increase during cycling. The decline in quadriceps oxidative capacity with age resulted from reductions in both muscle volume and oxidative capacity per volume in the elderly and appears to be an important determinant of the age-related reduction in delta VO(2) and VO(2),max found in this study.