Reliability of Ultrasound Shear Wave Elastography for Evaluating Psoas Major and Quadratus Lumborum Stiffness: Gender and Physical Activity Effects

OBJECTIVE

We aimed to assess the reliability of quantifying psoas major (PM) and quadratus lumborum (QL) stiffness with ultrasound shear wave elastography (SWE), and to explore the effects of gender and physical activity on muscle stiffness.

METHODS

Fifty-two healthy participants (18-32 y) were recruited. To determine reliability, 29 of them underwent repeated SWE measurements of PM and QL stiffness by an operator on the same day. The intra-class correlation coefficients (ICC3,1), standard error of measurement (SEM) and minimal detectable change with 95% confidence interval (MDC95) were calculated. The rest participants underwent a single measurement. Two-way MANCOVA was conducted for the effects of gender and physical activity on muscle stiffness.

RESULTS

The observed reliability for PM (ICC3,1 = 0.89-0.92) and QL (ICC3,1 = 0.79-0.82) were good-to-excellent and good, respectively. The SEM (kPa) was 0.79-1.03 and 1.23-1.28, and the MDC95 (kPa) was 2.20-2.85 and 3.41-3.56 for PM and QL, respectively. After BMI adjustment, both gender (PM: F = 10.15, p = 0.003; QL: F = 18.07, p < 0.001) and activity level (PM: F = 5.90, p = 0.005; QL: F = 6.33, p = 0.004) influenced muscle stiffness. The female and inactive groups exhibited higher stiffness in both muscles.

CONCLUSION

SWE is reliable for quantifying the stiffness of PM and QL. Female and physical inactivity may elevate PM and QL stiffness, underscoring the importance of accounting for these factors in muscle stiffness investigations. Larger prospective studies are needed to further elucidate their effects.

Is muscle stiffness a determinant for range of motion in the leg muscles?

Previous training studies with comprehensive stretching durations have reported that an increase in range of motion (ROM) can be related to decreases in muscle stiffness. Therefore, the purpose of this study was to analyze the association between the passive muscle stiffness of three muscle groups (triceps surae, quadriceps, hamstrings) to the respective joint ROM. Thirty-six healthy male soccer players volunteered in this study. After a standardized warm-up, the muscle stiffness was tested via shear wave elastography in six muscles (gastrocnemius medialis and lateralis, rectus femoris, semitendinosus, semimembranosus, and biceps femoris long head). The hip extension, hip flexion, and ankle dorsiflexion ROM were also assessed with a modified Thomas test, a sit and reach test, and a standing wall push test, respectively. We found significant moderate to large correlations between hip flexion ROM and muscle stiffness for the semimembranosus (rP = -0.43; P = 0.01), biceps femoris long head (rP = -0.45; P = 0.01), and overall hamstring stiffness (rP = -0.50; P < 0.01). No significant correlations were found for triceps surae (rP = -0.12; P = 0.51 to 0.67) and rectus femoris muscle stiffness (rP = 0.25; P = 0.14) with ankle dorsiflexion and hip extension ROM, respectively. We conclude that muscle stiffness is an important contributor to hip flexion ROM, but less important for hip extension or ankle joint ROM. Additional contributors to ROM might be tendon stiffness or stretch/pain tolerance.

Changes in passive hamstring stiffness after primary anterior cruciate ligament reconstruction: A prospective study with comparison of healthy controls

BACKGROUND

The mechanical properties of knee flexors muscles contribute to reducing anterior cruciate ligament loading. This case-control study evaluated the passive knee flexors stiffness after primary anterior cruciate ligament reconstruction with comparison of healthy controls.

METHODS

After anterior cruciate ligament reconstruction, 88 participants (24.5 [8.6] years, 56,8% males) had two isokinetic tests at 4 and 8 postoperative months with measurement of the passive resistive torque of knee flexors and extensors/flexors strength. In the control group, 44 participants (24.5 [4.3] years, 56,8% males) had one visit with the same procedures. Passive knee flexors stiffness was calculated as the slope of the passive torque-angle curve on the last 10° of knee extension (Nm/°). We investigated the impact of timing and type of surgery (autograft and combined meniscus repair) and persistent knee extension deficits on knee flexors stiffness.

FINDINGS

At 4 and 8 postoperative months, passive knee flexors stiffness was lower on the operated limb than on the non-operated limb (P < 0.001) but both limbs had significant lower values than controls (P < 0.001). Stiffness was positively correlated with knee flexors strength (P < 0.010), and knee flexors stiffness at 4 months was lower in individuals who underwent surgery <6 months from injury (P = 0.040). Knee extension deficit or the type of surgery did not have a significant influence on knee flexors stiffness.

INTERPRETATION

Similarly to neuromuscular factors that are traditionally altered after anterior cruciate ligament reconstruction, evaluating passive knee flexors stiffness changes over time could provide supplementary insights into postoperative muscle recovery.

Acute effects of static stretching on passive stiffness in older adults: A systematic review and meta-analysis

BACKGROUND

Static stretching has been demonstrated to improve the health of older adults. One of its goals is to decrease passive stiffness of the muscle-tendon unit (MTU) and/or muscles. Decreased passive stiffness in older adults could increase the range of motion and movement efficiency. Herein, we conducted a meta-analysis of the acute effects of static stretching on passive stiffness in older adults as well as a meta-analysis of differences in these effects between older and young adults.

BACKGROUND

PubMed, Web of Science, and EBSCO were searched for studies published before June 28, 2023. Manual searches were performed to identify additional studies. All included studies were critically reviewed by five authors. Meta-analyses of muscle and tendon injuries were performed using a random effect model. Of 4643 identified studies, 6 studies were included in the systematic review.

RESULTS

The main meta-analysis in older adults showed that static stretching could decrease the passive stiffness of the MTU or muscles (effect size, 0.55; 95 % confidence interval, 0.27 to 0.84; p < 0.01; and I2 = 0.0 %). Moreover, for the comparison between young and old adults, three studies were included in the meta-analysis. The results revealed no significant difference in the effects of static stretching interventions on stiffness between older and young adults (effect size, 0.136; 95 % confidence interval, -0.301 to 0.5738; p = 0.541; and I2 = 17.4 %). Static stretching could decrease the passive stiffness of the MTU and/or muscles in older adults to a small magnitude, and the effects were comparable between older and young adults.

Morphological and mechanical characteristics of the intrinsic and extrinsic foot muscles under loading in individuals with flat feet

BACKGROUND

The intrinsic and extrinsic foot softtissue structures that apply force and support the medial longitudinal arch (MLA) have been implicated in the development of flat feet. However, the relationship between the changes in MLA height under increasing load and the morphological and mechanical properties of individual intrinsic and extrinsic foot soft tissue structures is not fully understood.

RESEARCH QUESTION

To examine the morphological and mechanical characteristics of the foot soft tissue structures in flat feet when subjected to loading.

METHODS

This study consisted of two studies focusing on the extrinsic foot muscles (10 normal feet/11 flat feet) and intrinsic foot muscles (14 normal feet/13 flat feet). Images of the extrinsic and intrinsic foot muscles and plantar fascia (PF) under 10%, 50%, and 90% body weight conditions were obtained using ultrasound-based shear-wave elastography.

RESULTS

The cross-sectional area (CSA) of the peroneus brevis was larger in the flat-foot group than in the normal-foot group under all loading conditions. The CSAs of the intrinsic foot muscles (abductor hallucis, flexor digitorum brevis, and quadratus plantae) and thickness of the PF in the flat-foot group decreased significantly with increasing load. As for mechanical characteristics, the stiffness of the flexor digitorum longus and abductor hallucis was higher in the flat-foot group than in the normal group under high loading conditions. In addition, flat feet with greater flexibility tended to exhibit a greater decrease in PF thickness and smaller increase in stiffness.

SIGNIFICANCE

Excessive stretching of the intrinsic foot muscles and PF occurs in flat feet, and excessive contraction of the flexor digitorum longus may counteract the excessive lowering of the foot arch. Therefore, it is necessary to promote the contraction of the intrinsic foot musculature in feet with greater flexibility of the MLA during loading.

Physically Active Adults with Low Back Pain do not Demonstrate Altered Deadlift Mechanics: A Novel Application of Myotonometry to Estimate Inter-Muscular Load Sharing

Background

Rehabilitation clinicians that work with physically active populations are challenged with how to safely return patients back to performing deadlift movements following low back injury. Application of reliable and valid tests and measures to quantify impairments related to low back pain (LBP) enhances clinical decision making and may affect outcomes. Myotonometry is a non-invasive method to assess muscle stiffness which has demonstrated significant associations with physical performance and musculoskeletal injury.

Hypothesis/Purpose

The purpose of this study was to compare the stiffness of trunk (lumbar multifidus [LM] and longissimus thoracis [LT]) and lower extremity (vastus lateralis [VL] and biceps femoris [BF]) muscles between individuals with and without LBP during the lying, standing, and deadlifting body positions.

Study Design

Cross-sectional cohort comparison.

Methods

Muscle stiffness measures were collected in the VL, BF, LM, and LT muscles with participants in lying (supine and prone), standing, and the trap bar deadlift position. Separate analyses of covariance were conducted to compare absolute and relative muscle stiffness between the groups for each muscle and condition.

Results

Sixty-eight participants (41 female, 21.3 years, 34 LBP) volunteered for the study. Within the deadlift condition there was a significantly greater increase in the percent-muscle stiffness change in the VL (p = .029, 21.9%) and BF (p = .024, 11.2%) muscles in the control group than in the LBP group. There were no differences in percent-muscle stiffness changes for the standing condition nor were there any absolute muscle stiffness differences between the two groups for the three conditions.

Conclusion

No differences in muscle stiffness were identified in the lying, standing, or deadlifting conditions between participants with and without LBP. Differences in percent stiffness changes were noted between groups for the deadlift position, however the differences were modest and within measurement error. Future studies should investigate the utility of myotonometry as a method to identify LBP-related impairments that contribute to chronic and/or recurrent low back injury.

Level of Evidence

Level 3.

Assessment of forearm muscles with ultrasound shear wave elastography in patients with acromegaly

PURPOSE

The effects of acromegaly on soft tissues, bones and joints are well-documented, but information on its effects on muscle mass and quality remains limited. The primary goal of this study is to assess the sonoelastographic features of forearm muscles in patients with acromegaly.

METHOD

Forty-five patients with acromegaly and 45 healthy controls similar in terms of gender, age, and body mass index (BMI) were included in a single-center, multidisciplinary, cross-sectional study. The body composition was analyzed using bioelectrical impedance analysis (BIA), and height-adjusted appendicular skeletal muscle index (hSMI) was calculated. The dominant hand's grip strength was also measured. Two radiologists specialized in the musculoskeletal system employed ultrasound shear wave elastography (SWE) to assess the thickness and stiffness of brachioradialis and biceps brachii muscles.

RESULTS

The acromegaly group had significantly higher thickness of both the biceps brachii (p = 0.034) and brachioradialis muscle (p = 0.046) than the control group. However, the stiffness of the biceps brachii (p = 0.001) and brachioradialis muscle (p = 0.001) was lower in the acromegaly group than in the control group. Disease activity has not caused a significant difference in muscle thickness and stiffness in the acromegaly group (p > 0.05). The acromegaly group had a higher hSMI (p = 0.004) than the control group. The hand grip strength was similar between the acromegaly and control group (p = 0.594).

CONCLUSION

The patients with acromegaly have an increased muscle thickness but decreased muscle stiffness in the forearm muscles responsible for elbow flexion. Acromegaly can lead to a permanent deterioration of the muscular structure regardless of the disease activity.

Impact of lower muscle stiffness on ankle dorsiflexion restriction in children with cerebral palsy evaluated using ultrasound elastography

BACKGROUND

Plantar flexor muscles always contribute to limiting the range of motion of ankle dorsiflexion in children with spastic cerebral palsy, but the individual contributions of these muscles are not well defined. This study aimed to identify which muscles' stiffness impacts the dorsiflexion range of motion in children with cerebral palsy.

METHODS

Twenty-five children with cerebral palsy were included. The maximum passive dorsiflexion range of motion was measured in two positions: hip and knee joints in flexion, and both joints in full extension. Strain ratios indicating muscle stiffness were measured using strain elastography of the lateral and medial gastrocnemius, soleus, flexor hallucis longus, peroneus longus, peroneus brevis, and tibialis posterior muscles. To analyze which muscles impact the limitation of the dorsiflexion range, multiple regression analyses were conducted. The values of muscle stiffness were included as independent valuables, and the values of the dorsiflexion range were included as dependent valuables. A p-value <0.05 was considered statistically significant.

FINDINGS

In the analyses, the soleus and flexor hallucis longus muscle stiffness were significant independent factors for the dorsiflexion range of motion of hip and knee flexion (adjusted R2: 0.50). The lateral gastrocnemius muscle stiffness was a significant independent factor for the dorsiflexion range of motion with both joints in full extension (adjusted R2: 0.61).

INTERPRETATION

Flexor hallucis longus muscle stiffness, in addition to triceps surae muscle stiffness, was shown to impact dorsiflexion range; attention should be paid to muscle stiffness in children with cerebral palsy.

The relationship between elastography-based muscle properties and vertical jump performance, countermovement utilization ratio, and rate of force development

This study explored the relationships between passive muscle stiffness (shear modulus) and vertical jumping performance, countermovement utilization ratio (CUR) and rate of force development (RFD) in an attempt to unravel the mechanism that may explain the association between shear modulus and performance. 32 recreationally active participants (16 males, 16 females; age: 22.4 ± 5.1 years) participated. Shear modulus was assessed for the lateral and medial gastrocnemius (GL and GM), and vastus medialis (VM) and lateralis (VL) muscles using shear wave elastography. Squat jump (SJ) and countermovement (CMJ) jump were determined, with CUR being expressed as the ratio between the two. RFD in ankle and knee extension tasks was measured using isometric dynamometers. Our results suggest that within a heterogeneous group of recreational athletes, passive muscle stiffness is not related to RFD and jump performance, but positively related to CUR. In males, shear modulus of the GL was positively related to SJ height (r = 0.55). We also found inverse moderate correlations between VL and VM shear modulus and RFD in females only (r = -0.50 to -0.51), but this relationship was possibly affected by age and body fat content. Different mechanisms may underpin the association between shear modulus and performance depending on the muscle, task and population investigated.

Effect of age on postural performance and control strategies during changes in visual input and dual-tasking stances

Background

With age, people begin to experience deterioration in standing balance, especially when sensory input is suddenly removed or added. Here, we sought to explore the effects of age on postural performance and postural control strategies.

Methods

The convenience sample consisted of 15 young, 10 middle-aged, and 14 elderly healthy adults. They were instructed to stand with their feet together in four randomly administered conditions involving visual input removal/addition and single-/dual-tasking. Dual-tasking involved continuous subtraction by 3s.

Results

Postural sway displacement in the two older groups seemed larger than that in the younger group; however, neither the main effect of group (F_{2, 36} = 1.152, p = .327) nor the group × time interaction effect (F_{4, 27} = 0.229, p = .922) was significant. Greater stiffness of the lower leg muscles was observed in the vision-addition condition than in the vision-removal condition in only the elderly group (t₁₃ = -2.755, p = .016). The dual-tasking condition resulted in smaller sway displacement (F_{1, 36} = 7.690, p = .009) and greater muscle stiffness (F_{1, 36} = 5.495, p = .025). In the vision-removal condition, the increase in muscle stiffness due to dual-tasking was significantly larger in the middle-aged (t₉ = -3.736, p = .005) and elderly groups (t₁₃ = -2.512, p = .026).

Conclusions

In healthy older individuals, age-related changes were observed in control strategies used to maintain standing balance upon changes in visual input. The dual-task paradigm induced the use of an ankle-stiffening strategy in middle-aged and elderly adults.

Functional and morphological changes in shoulder girdle muscles after repeated climbing exercise

This study aimed to investigate the acute effect of repeated climbing actions on functional and morphological measures of the shoulder girdle. Fifteen male indoor climbers participated in this study. All the climbers declared route level 6a+, as the best climbing grade (French climbing grade scale). Functional (range of motion - ROM and muscle strength), and morphological measurements (muscle/tendon stiffness and thickness) after a repeated climbing exercise protocol were analysed. The ROM and muscle strength showed significant decreases from baseline to Immediate-Post (IA) as well as significant increases from IA to 1 h-Post for all movements (p ≤ .001 for all). Muscle stiffness showed significant increases from baseline to IA after as well as significant decreases from IA to 1 h-Post for all muscles (p ≤ .001 for all). However, the thickness showed significant increases from baseline to IA for supraspinatus tendon and muscle thickness and occupation ratio (p ≤ .001 for all), while a significant decrease was observed in acromiohumeral distance (p ≤ .001). Significant decreases from IA to 1 h-Post were found for muscles/tendons and occupation ratio (p ≤ .001 for all), while a significant increase for AHD (p ≤ .001). Our data demonstrated acute alterations in tendon thickness due to acute signs of implement symptom in climbers.

Changes in passive stiffness and length of the semitendinosus muscles in rats with arthritis-induced knee flexion contracture

BACKGROUND

Arthritis-induced joint contracture is caused by arthrogenic and myogenic factors. The arthrogenic factor, localized within the joint, is naturally accepted as the cause of contracture. However, the detailed mechanisms underlying arthritis-induced myogenic contracture are largely unknown. We aimed to elucidate the mechanisms of arthritis-induced myogenic contracture by examining the muscle mechanical properties.

METHODS

Knee arthritis was induced in rats by injecting complete Freund's adjuvant into the right knees, while the untreated contralateral knees were used as controls. After one or four weeks of injection, passive stiffness, length, and collagen content of the semitendinosus muscles were assessed, along with passive knee extension range of motion.

FINDINGS

After one week of injection, flexion contracture formation was confirmed by a decreased range of motion. Range of motion restriction was partially relieved by myotomy, but still remained even after myotomy, indicating the contribution of both myogenic and arthrogenic factors to contracture formation. After one week of injection, the stiffness of the semitendinosus muscle was significantly higher in the injected side than in the contralateral side. After four weeks of injection, the stiffness of the semitendinosus muscle in the injected side returned to levels comparable to the contralateral side, parallel to partial improvement of flexion contracture. Muscle length and collagen content did not change due to arthritis at both time points.

INTERPRETATION

Our results suggest that increased muscle stiffness, rather than muscle shortening, contributes to myogenic contracture detected during the early stage of arthritis. The increased muscle stiffness cannot be explained by excess collagen.

Measuring resistance to externally induced movement of the wrist joint in chronic stroke patients using an objective hand-held dynamometer

Objective

We evaluated the resistance to externally induced wrist extension in chronic stroke patients. We aimed to objectively measure and distinguish passive (muscle and soft tissue stiffness) and active (spasticity and spastic dystonia) components of the resistance.

Methods

We used a hand-held dynamometer, which measures torque, joint movement and electromyography (EMG) simultaneously, to assess the resistance to externally induced wrist extension. Slow and fast stretches were applied to the affected and unaffected wrists in 57 chronic stroke patients (57 ± 11 years). We extracted from the data parameters that represent passive and muscle activity components and assessed the validity, test-retest reliability and the clinical utility of the measurement.

Results

The analysis showed (1) a significant difference in the passive and muscle activity components between the affected and unaffected sides; (2) a significant correlation between passive and muscle activity components and the modified Ashworth scale (MAS); (3) a significant difference between the subgroups of patients stratified by the MAS; (4) an excellent intra-rater reliability on each of the passive and muscle activity components with intra-class coefficients between 0.92 and 0.99; (5) and small measurement error.

Conclusions

Using a hand-held dynamometer, we were able to objectively measure the resistance to muscle stretch in the wrist joint in chronic stroke patients and discriminate muscle overactivity components from muscle and soft tissue stiffness. We demonstrated validity, test-retest reliability and the clinical utility of the measurement.

Significance

Quantification of the different components of resistance to externally induced movement enables the objective evaluation of neurorehabilitation effects in chronic stroke patients.

Fatigue-induced changes in hamstrings' active muscle stiffness: effect of contraction type and implications for strain injuries

PURPOSE

Hamstring strain injuries may occur due to differential fatigue and compromised mechanical properties among the hamstring muscles. We examined (1) the effect of fatigue on hamstrings active muscle stiffness, and (2) whether contraction type affects active muscle stiffness changes during a submaximal fatiguing task.

METHODS

Nine healthy males completed 99 submaximal knee flexions in isometric (ISO), concentric (CON), and eccentric (ECC) conditions. We measured the knee flexor maximal voluntary torque (MVT) (pre/post), shear wave velocity (SWV) during contraction and transverse relaxation times (T2) (pre/post) in biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM) muscles.

RESULTS

MVT decreased substantially after all conditions (- 18.4 to - 33.6%). The average relative torque sustained during the task was lower in CON than ISO and ECC, but absolute torque was similar. SWV interindividual responses were highly variable across muscles and contraction types. On average, BFlh SWV tended to increase in ISO (0.4 m/s, 4.5%, p = 0.064) but decreased in ECC condition (- 0.8 m/s, - 7.7%, p < 0.01). ST SWV decreased in CON (- 1.1 m/s, - 9.0%, p < 0.01), while it remained unchanged in ISO and ECC. SM SWV decreased in CON (- 0.8 m/s, - 8.1%, p < 0.01), but it was unaffected in ISO and variable in ECC.

CONCLUSION

Fatigue has a differential effect on the mechanical properties of the constituent hamstring muscles, as measured with shear wave elastography, depending upon contraction type. We found preliminary evidence that BFlh is more fatigued than ST or SM during eccentric contractions, which may explain its susceptibility to strain injuries.

Effects of superficial tissue and intermuscular connections on rectus femoris muscle shear modulus heterogeneity

INTRODUCTION

Intramuscular heterogeneity exists in the shear modulus of the rectus femoris (RF) muscle. However, the underlying heterogeneity mechanisms are not entirely understood. Previous research has reported that detachment of superficial tissues reduces the shear modulus by 50%. The aim of this study was to examine the effects of the skin, deep fascia, and intermuscular connections on the shear modulus of the RF at multiple sites.

MATERIALS AND METHODS

Eleven donors were fixed using the Thiel method. Measurements were performed at 0°, 60°, and 120° knee flexion in a neutral hip position. Tissue processing was performed under four conditions: superficial tissue (CONT), skin off (SKIN), deep fascia detachment (FASC), and intermuscular connections detachment (ALL). The shear modulus at the proximal, central, and distal regions were measured using ultrasound shear wave elastography. The study was approved by the Sapporo Medical University Ethical Committee.

RESULTS

Three-way ANOVA revealed no significant interaction between treatment, site, and angle (P = 0.156), treatment and angle (P = 0.067), or site and angle (P = 0.441). There was a significant effect of treatment (P < 0.001), site (P = 0.010), and angle (P < 0.001) and interaction between treatment and site (P < 0.001). The proximal shear modulus was greater than the central for CONT. There were no significant differences between the measurement sites for SKIN. The distal shear modulus was greater than the proximal for FASC. The distal shear modulus was also greater than the proximal and central for ALL.

CONCLUSIONS

Intramuscular regional differences that influence superficial tissue and intermuscular connections of RF elasticity heterogeneity were observed.

Shear wave elastography characterizes passive and active mechanical properties of biceps brachii muscle in vivo

Mechanical characterization of individual muscles in their in vivo environment is not well studied. Shear wave elastography (SWE) as a non-invasive technique was shown to be promising in quantifying the local mechanical properties of skeletal muscles. This study aimed to investigate the mechanics of the biceps brachii muscle (BB) derived from SWE in relation to elbow joint position and contraction intensity during isometric contraction. 14 healthy, young subjects participated in the study and five different joint positions (60°-180° elbow angle) were investigated. Shear elastic modulus and surface electromyography (sEMG) of the BB and elbow torque were measured simultaneously, both in passive (i.e., resting) and active states during slow, sub-maximal isometric ramp contractions up to 25%, 50%, and 75% of the maximum voluntary contraction. At passive state, the shear elastic modulus of the BB increased with increasing elbow angle (p < 0.001). Maximum elbow flexion torque was produced at 60° and it decreased with increasing elbow angle (p = 0.001). During sub-maximal contractions, both elbow angle (p < 0.001) and contraction intensity (p < 0.001) had significant effects on the shear elastic modulus but only contraction intensity (p < 0.001) affected sEMG amplitude of the BB. Although torque was decreased at extended elbow positions (150°, 180°), higher active shear elastic modulus of BB muscle was found compared to flexed positions (60°, 90°). Linear regression of the BB sEMG amplitude over elbow torque showed good agreement for all joint positions (R² between 0.69 and 0.89) while the linear agreement between shear elastic modulus of BB and elbow torque differed between flexed (R² = 0.70 at 60° and R² = 0.79 at 90°) and extended positions (with the lowest R² = 0.57 at 150°). We conclude that using SWE, we can detect length-dependent mechanical changes of BB both in passive and active states. More importantly, SWE can be used to characterize active muscle properties in vivo. The present findings have critical importance for developing muscle stiffness as a measure of individual muscle force to validate muscle models and using SWE in clinical diagnostics.

Variability of Biceps Muscle Stiffness Measured Using Shear Wave Elastography at Different Anatomical Locations With Different Ultrasound Machines

Shear wave elastography is an emerging diagnostic tool used to assess for changes in the stiffness of muscle. Each region of the muscle may have a different stiffness; therefore, the anatomical region should be carefully selected. Machine vendors each have unique methods for calculating the returned stiffness values and, consequently, a high level of agreement in measurement between machines (quantified using the intraclass correlation coefficient [ICC] and Bland-Altman analysis) will allow research findings to be translated to the clinic. This study assessed three locations within the biceps muscle (50% and 75% of the distance between the acromioclavicular joint and antecubital fossa, and superior to distal myotendinous junction [MTJ]) of 32 healthy volunteers with two different machines, the Canon Aplio i600 and SuperSonic Imagine Aixplorer (SSI), to compare the reported shear wave velocities and the variability by coefficient of variation (CV) and ICC. There was no difference in the CV between machines, but a significant difference in the CV at muscle regions, with the 75% location having a 40.2% reduction in CV. The 75% location had the highest ICC values with good posterior mean ICCs of 0.84 on the Canon and 0.83 on the SSI. The 50% and MTJ locations had poor ICC values. The 75% location provided the lowest CV and highest ICC and should be used for future stiffness assessments.

Short-time recovery skeletal muscle from dexamethasone-induced atrophy and weakness in old female rats

BACKGROUND

Several pathological conditions (atrophy, dystrophy, spasticity, inflammation) can change muscle biomechanical parameters. Our previous works have shown that dexamethasone treatment changes skeletal muscle tone, stiffness, elasticity. Exercise training may oppose the side effects observed during dexamethasone treatment. The purpose of this study was to examine the changes in biomechanical parameters (tone, stiffness, elasticity) of skeletal muscle occurring during dexamethasone treatment and subsequent short-time recovery from glucocorticoid-induced muscle atrophy and weakness, as well as the effect of mild therapeutic exercise.

METHODS

17 old female rats, aged 22 months were used in this study. The hand-held and non-invasive device (MyotonPRO, Myoton Ltd., Tallinn, Estonia) was used to study changes in biomechanical properties of muscle. Additionally, body and muscle mass, hind limb grip strength were assessed.

FINDINGS

Results showed that dexamethasone treatment alters muscle tone, stiffness and elasticity. During 20-day recovery period all measured parameters gradually improved towards the average baseline, however, remaining significantly lower than these values. The body and muscle mass, hind limb grip strength of the rats decreased considerably in the groups that received glucocorticoids. After 20 days of recovery, hind limb grip strength of the animals was slightly lower than the baseline value and mild therapeutic exercise had a slight but not significant effect on hind limb grip strength. Biomechanical parameters improved during the recovery period, but only dynamic stiffness and decrement retuned to baseline value.

INTERPRETATION

The study results show that monitoring muscle biomechanical parameters allows to assess the recovery of atrophied muscle from steroid myopathy.

Evaluation of muscle stiffness in adhesive capsulitis with Myoton PRO

Background

Adhesive capsulitis (AC) is characterized by pain and limited range of motion, caused by stiffness of the joint capsule and coracohumeral ligament. On the other hand, there have been few reports on muscle stiffness in AC. The purpose of this study was to assess muscle stiffness in patients of AC with a portable and noninvasive device, Myoton PRO. We hypothesized that muscle stiffness around shoulder joint increases in AC.

Methods

At first, we surveyed correlation between Myoton PRO and shear wave elastography with phantoms. Second, reproducibility and repeatability of healthy volunteers with Myoton PRO were evaluated. Finally, muscle stiffness was measured in 40 patients who were diagnosed with AC. Muscle stiffness was quantitatively measured with Myoton PRO. We compared the stiffness of the anterior deltoid (AD), pectoralis major, and latissimus dorsi (LD) in AC patients on both the affected and nonaffected sides.

Results

Correlation coefficient in shear wave elastography and Myoton PRO was 0.99(P = .001). Reliability of intraoperator and interoperator with Myoton PRO was 0.9 or higher. Muscle stiffness values (N/m) of the AD, pectoralis major, and LD were 355 ± 61, 252 ± 54, 207 ± 51 in the affected sides and 328 ± 50, 252 ± 41, 186 ± 37 in the nonaffected sides, and the differences were significant in the AD and LD (P = .005, P = .002, respectively).

Conclusions

We used Myoton PRO to evaluate muscle stiffness in AC. The AD and LD muscles of AC patients were significantly stiffer on the affected side compared to the nonaffected side.

Comparison between 6-week foam rolling intervention program with and without vibration on rolling and non-rolling sides

PURPOSE

The chronic effects of unilateral foam rolling (FR) or FR with vibration (VFR) intervention on the rolling and non-rolling sides (cross-education effects) are still unclear. Thus, this study aimed to investigate the effects of unilateral 6-week FR or VFR intervention on ankle dorsiflexion range of motion (DF ROM), muscle stiffness, and muscle strength in both rolling and non-rolling sides.

METHODS

Thirty healthy young men were randomly allocated into the FR (n = 15) or the VFR intervention group (n = 15). Participants performed three sets of unilateral FR or VFR interventions for 60 s of the calf muscles twice/week, for 6 weeks. DF ROM, gastrocnemius muscle stiffness, and maximal voluntary isometric contraction (MVIC) torque were assessed in the rolling and non-rolling sides before and after the intervention.

RESULTS

The DF ROM increased significantly (p < 0.05) to the same extent in the FR and VFR intervention groups on both rolling (FR: d = 0.58, VFR: d = 0.63) and non-rolling (FR: d = 0.39, VFR: d = 0.50) sides. Similarly, the passive torque at DF ROM increased significantly (p < 0.05) to the same extent in the FR and VFR intervention groups on both rolling (FR: d = 0.85, VFR: d = 0.77) and non-rolling (FR: d = 0.76, VFR: d = 0.68) sides. However, there were no significant changes in muscle stiffness and MVIC after FR and VFR interventions on both the rolling and non-rolling sides. FR and VFR interventions could increase the ROM in both the rolling and non-rolling sides but could not change muscle stiffness and strength.

CONCLUSIONS

The results showed that it is not necessarily needed to perform VFR to increase ROM in the long term.

Relationship Between Muscle Quality or Stiffness Measured by Ultrasonography and Range of Motion in Hospitalized Older Adults

Older adults who require nursing care have joint contractures characterized by limited range of motion (ROM). The present study investigated age-related muscle changes using ultrasonography and the relationship between ROM and muscle changes in older adults. Twenty-two healthy young adults (mean age: 23.3 y) and 60 hospitalized older adults (mean age: 86.1 y) participated. ROM of hip abduction was measured using a goniometer. Echo intensity (EI), reflecting interstitial fibrous tissue or fat within adductor longus (ADDl) was measured using B-mode ultrasonography, and strain ratio (SR), reflecting ADDl stiffness, was measured by strain elastography. The Mann-Whitney U-test and Spearman's correlation test were used for analysis. The ROM and SR of older adults were significantly lower than those of young adults (both p values <0.001). The EI was significantly higher in older adults than in young adults (p < 0.001). In older adults, the SR was moderately correlated with ROM (ρ = 0.49, p < 0.001). In conclusion, limited ROM and increase in interstitial fibrous tissue or fat and stiffness occur with aging, and the SR measured by strain elastography is useful for investigating the effect of muscle stiffness on the ROM of hospitalized older adults.

Feasibility and reliability of measuring muscle stiffness in Parkinson's Disease using MyotonPRO device in a clinical setting in Ghana

OBJECTIVES

To examine the feasibility and within-session reliability of Myoton technology to measure muscle stiffness objectively in people with Parkinson's disease in an outpatient setting.

DESIGN

An exploratory quantitative study design was used.

SETTING

The study was conducted in the outpatient physiotherapy department of a Teaching Hospital in Ghana. Participants were recruited from three sites.

PARTICIPANTS

Thirty adults with Parkinson's disease over 18 years with increased tone (muscle stiffness) and at Hoehn and Yahr Stages I-III were studied. Persons with severe comorbidities were excluded.

INTERVENTION

There was no intervention before testing. The MyotonPRO device measured the mechanical properties of the biceps brachii, flexor carpi radialis and tibialis anterior muscles in a relaxed supine position. The probe applied mechanical impulses to the skin, eliciting tissue oscillations. The muscles' three parameters (stiffness, non-neural tone and elasticity) were recorded bilaterally. The reliability of two sets (of 5 impulses) of Myoton data on all three muscles was examined.

RESULTS

All 30 participants (66.3±8.9 years) were recruited and tested within eight weeks. Intraclass correlation coefficients (ICC 3,2) were above 0.92 for biceps brachii and tibialis anterior and above 0.86 for flexor carpi radialis.

CONCLUSION

The MyotonPRO was reliable for measuring two sets of data within the same session, indicating that only one set of measurements is needed. The technique is feasible and easy to use in a clinical setting in Ghana, with the potential to assess the effect of medical and physiotherapy interventions on muscles in people with Parkinson's disease.

FUNDING

M.S discloses a grant from the Science and Technology Facilities Council Impact Acceleration Account at the University of Southampton to support this collaborative research (no personal finance received). All other authors, M.W.A, P.E.M, C.O.Y, B.E.A.S, S.A.-B, and A.A have no financial disclosure.

Structural and passive mechanical properties of the medial gastrocnemius muscle in ambulatory individuals with chronic stroke

BACKGROUND

This study aimed to investigate the structural, morphological and passive mechanical properties of the medial gastrocnemius muscle among ambulating chronic stroke survivors using a computational model previously established in healthy individuals without stroke.

METHODS

Individuals with chronic stroke (n = 14, age = 63.4 ± 6.0 years) and healthy controls (n = 15, age = 59.6 ± 8.4 years) participated in the study. The mechanical properties of the medial gastrocnemius were measured during continuous passive ankle motion using ultrasound elastography and a corresponding muscle mechanical property-angle curve was estimated where slack angle and elasticity were determined. Muscle thickness, fascicle length, pennation angle, and echo intensity were also assessed using B-mode ultrasound.

FINDINGS

No significant differences in slack angle (paretic: -16.2° ± 6.13°, non-paretic: -16.93° ± 6.80°, p = 0.82), or slack elasticity (paretic: 4.36 ± 1.94 kPa, non-paretic: 4.54 ± 1.24 kPa, p = 0.64) were found between sides or groups. Lower muscle pennation angle (paretic: 13.6 ± 2.9°, non-paretic: 15.9 ± 2.0°, p = 0.019) and higher echo intensity (paretic: 80.5 ± 13.6, non-paretic: 63.4 ± 17.1, p = 0.003) were observed for paretic muscles. No significant between-sides differences were found for muscle thickness (paretic: 1.5 ± 0.3 cm, non-paretic: 1.6 ± 0.2 cm, p = 0.255) or fascicle length (paretic: 6.6 ± 1.9 cm, non-paretic: 7.1 ± 2.2 cm, p = 0.216). Significant between-groups difference was also observed for fascicle length [non-dominant side (control): 6.2 ± 0.8 cm, paretic side (stroke): 6.6 ± 1.9 cm, p = 0.017].

INTERPRETATION

Although muscle mechanical properties increased exponentially over the slack ankle, measures between paretic and non-paretic sides were similar in ambulating participants with chronic stroke. Side-to-side differences in structural and morphological measures suggest the impact of stroke was relatively more pronounced for these muscle parameters than for passive mechanical properties.

Ultrasound elastography in the assessment of post-stroke muscle stiffness: a systematic review

Background

Post-stroke muscle stiffness is a major challenge in the rehabilitation of stroke survivors, with no gold standard in clinical assessment. Muscle stiffness is typically evaluated by the Modified Ashworth Scale or the Tardieu Scale; however, these can have low reliability and sensitivity. Ultrasound elastography is an advanced imaging technology that can quantitatively measure the stiffness of a tissue and has been shown to have good construct validity when compared to clinically assessed muscle stiffness and functional motor recovery.

Objective

The purpose of this article is to systematically review the literature regarding the change in muscle stiffness as measured by ultrasound elastography in stroke survivors.

Methods

Scopus, PubMed, Embase, CINAHL, MEDLINE and Cochrane Library were searched for relevant studies that assessed the change in stiffness of post-stroke muscle stiffness measured by ultrasound elastography following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines.

Results

In total, 29 articles were identified, using either strain elastography and shear wave elastography to measure the stiffness of muscles in stroke survivors, most frequently in the biceps and medial gastrocnemius muscles. The stiffness was typically higher in the paretic compared to the non-paretic or healthy control. Other variations that increased the stiffness include increasing the joint angle and introducing a passive stretch or muscle activation. The paretic muscle has also been assessed pre- and post-treatment demonstrating a decrease in stiffness.

Conclusion

Ultrasound elastography is a promising imaging technology for determining the muscle stiffness in stroke survivors with need for a standardized imaging protocol.

Muscle Contractures in Adults With Cerebral Palsy Characterized by Combined Ultrasound-Derived Echo Intensity and Handheld Dynamometry Measures

We used ultrasound-derived echo intensity and hand-held dynamometry to characterize plantar flexor muscle contractures in adults with cerebral palsy (CP). Eleven adults with CP (aged 41 ± 12 y, Gross Motor Function Classification System I-II) and 11 neurologically intact adults (aged 35 ± 10 y) participated in the study. Echo intensity was measured from the medial gastrocnemius muscle using brightness mode ultrasound. Hand-held dynamometry was used to quantify plantar flexor passive muscle stiffness and ankle joint passive range of motion (pROM). Echo intensity correlated with both passive muscle stiffness (r = 0.57, p = 0.006) and pROM (r = -0.56, p = 0.006). Ultrasound echo intensity (p = 0.02, standardized mean difference [SMD] = 1.13) and passive muscle stiffness (p < 0.001, SMD = 1.99) were higher and ankle joint pROM (p < 0.001, SMD = 2.69) was lower in adults with CP than in neurologically intact adults. We conclude that combined ultrasound-derived echo intensity and hand-held dynamometry may be used to provide an objective characterization of muscle contractures.

Cross-education effect of 4-week high- or low-intensity static stretching intervention programs on passive properties of plantar flexors

This study aimed to compare the cross-education effect of unilateral stretching intervention programs with two different intensities (high- vs. low-intensity) on dorsiflexion range of motion (DF ROM), muscle stiffness, and muscle architecture following a 4-week stretching intervention. Twenty-eight healthy males were randomly allocated into two groups: a high-intensity static stretching (HI-SS) intervention group (n = 14; stretch intensity 6-7 out of 10) and a low-intensity static stretching (LI-SS) intervention group (n = 14; stretch intensity 0-1 out of 10). The participants were asked to stretch their dominant leg (prefer to kick a ball) for 4 weeks (3 × week for 3 × 60 s). Before and after the intervention, the non-trained leg passive properties (DF ROM, passive torque, and muscle stiffness) of the plantar flexors and the muscle architecture of the gastrocnemius medialis (muscle thickness, pennation angle, and fascicle length) were measured. Non-trained DF ROM and passive torque at DF ROM were significantly increased in the HI-SS group (p < 0.01, d = 0.64, 50.6%, and p = 0.044, d = 0.36, 18.2%, respectively), but not in the LI-SS group. Moreover, there were no significant changes in muscle stiffness and muscle architecture in both groups. For rehabilitation settings, a high-intensity SS intervention is required to increase the DF ROM of the non-trained limb. However, the increases in DF ROM seem to be related to changes in stretch tolerance and not to changes in muscle architecture or muscle stiffness.

Stiff-person syndrome with paraneoplastic neurological syndrome: a case report and literature review

BACKGROUND

Stiff-person syndrome (SPS) manifests by progressive rigidity along with muscle spasms that affect the axial and limb muscles. First discovered in 1956, significant progress has been made in its clinical characterization, comprehension of pathogenesis, as well as effective treatment therapy.

CASE PRESENTATION

A 67-year old female patient presented with a 2-year history of progressive stiffness along with painful spasms in both legs, with her condition worsening over the previous year making it considerably difficult for her to stand and walk. Here, we report a Stiff-person syndrome patient (SPS) with lung adenocarcinoma who was positive for anti-glutamate decarboxylase (anti-GAD) antibodies. Treatment with hormones and gamma-globulin improved her symptoms. In addition, we present a literature review of SPS patients with tumors.

CONCLUSIONS

The diagnosis of autoimmune SPS was on the basis of clinical, electrophysiological, as well as immunological findings. Early SPS detection is critical to preventing long-term disability.

Muscle stiffening is associated with muscle mechanoreflex-mediated cardioacceleration

PURPOSE

Although the muscle mechanoreflex is an important mediator to cardiovascular regulation during exercise, its modulation factors remain relatively unknown. Therefore, the purpose of this study was to investigate the effect of muscle stiffness on the muscle mechanoreflex.

METHODS

Participants were divided based on their median muscle stiffness (2.00 Nm/mm) into a low group (n = 15) and a high group (n = 15), and the muscle mechanoreflex was compared between the groups. After a 15-min rest in the supine position, heart rate (HR), blood pressure (BP), stroke volume (SV), and cardiac output (CO) were measured at rest for 3 min and during static passive dorsiflexion (SPD) at 20° for 1 min. Following a 15-min re-rest, muscle stiffness and passive resistive torque were evaluated in the distal end of the muscle belly of the medial gastrocnemius.

RESULTS

Peak relative changes in HR (low group: 6 ± 4% and high group: 12 ± 4%) and CO (low group: 8 ± 10% and high group: 13 ± 9%) were greater in the high group than in the low group (both, P < 0.05). A significant positive correlation was found between resistive torque during SPD and muscle stiffness and peak relative changes in HR (r = 0.51 and 0.61, both P < 0.05). However, there was no correlation between muscle elongation during SPD and peak relative changes in HR (r = - 0.23, P = 0.20).

CONCLUSION

These findings suggest that muscle stiffness may be modulatory factor of muscle mechanoreflex.

Effects of resistance training on hypertrophy, strength and tensiomyography parameters of elbow flexors: role of eccentric phase duration

The aim of the study was to compare the effects of two different training protocols, which differ in the duration of the eccentric phase, on the one-repetition maximum (1RM), thickness and contractile properties of elbow flexors. Twenty untrained college students were randomly divided into two experimental groups, based on the training tempo: FEG (Faster Eccentric Group: 1/0/1/0) and SEG (Slower Eccentric Group: 4/0/1/0). Training intervention was a biceps bending exercise, conducted twice a week for 7 weeks. The intensity (60–70% RM), sets (3–4) and rest intervals (120 s) were held constant, while repetitions were performed until it was not possible to maintain a set duration. In the initial and final measurements, 1RM, muscle thickness and tensiomyography parameters – contraction time (Tc) and radial deformation (Dm) – were evaluated. An ANCOVA model (using baseline outcomes as covariates) was applied to determine between-group differences at post-test, while Pearson’s product-moment correlation coefficient was used to investigate the relationship between absolute changes in muscle thickness and Dm. Muscle strength increase was greater for SEG than for FEG (6.0 ± 1.76 vs. 3.30 ± 2.26 kg, p < 0.01). In both groups muscle thickness increased equally (FEG: 3.24 ± 2.01 vs. SEG: 3.57 ± 1.17 mm, p < 0.01), while an overall reduction in Dm was observed (FEG: 1.99 ± 1.20 vs. SEG: 2.26 ± 1.03 mm, p < 0.01). Values of Tc remained unchanged. A significant negative relationship was observed between changes in muscle thickness and Dm (r = -0.763, Adj.R² = 0.560, p < 0.01). These results indicate that the duration of the eccentric phase has no effect on muscle hypertrophy in untrained subjects, but that slower eccentric movement significantly increases 1RM.

Reliability and discriminative validity of real-time ultrasound elastography in the assessment of tissue stiffness after calf muscle injury

OBJECTIVE

To investigate the reliability and discriminative validity of real-time ultrasound elastography (RTE) measures of soft-tissue elasticity after calf muscle tear.

DESIGN

Cross-sectional, intra/inter-examiner reliability and comparative validity study.

SETTING

Department of Physical Therapy.

PARTICIPANTS

Twenty-one recreational athletes were included and examined 6 weeks after sustaining a grade I-II calf musculature tear.

MAIN OUTCOME MEASURES

Soft-tissue elasticity was measured by two experienced assessors using RTE assessments in both the longitudinal and transverse planes of the athletes' injured and uninjured calf muscles. Elasticity was estimated by using the strain ratio (SR), which was calculated by dividing the strain (displacement) value taken at the medial gastrocnemius-soleus myotendinous junction (reference) by the strain value taken at the centre of the injury (index) as visualized on B-mode sonogram. Intra- and inter-observer reliability was estimated calculating intra-class correlation coefficients (ICCs) and standard error of measurement (SEM). Differences in elasticity between injured and healthy legs were assessed using t-tests or Wilcoxon tests for repeated measures.

RESULTS

All RTE assessments in both planes showed ICC values ranging from 0.77 to 0.95 and SEM values ranging from 0.72 to 0.99. Additionally, RTE enabled both assessors to determine differences in elastic properties between injured and control legs (p < 0.001).

CONCLUSION

RTE measures of calf muscles demonstrated good reliability and were able to differentiate injured from non-injured muscle tissue. RTE may provide a fast and objective measure in sports medicine to improve the detection of risk factors for muscle injury related to alterations of the mechanical behaviour of soft tissues during healing process.

Beyond muscles: role of intramuscular connective tissue elasticity and passive stiffness in octopus arm muscle function

The octopus arm is a 'one of a kind' muscular hydrostat, as demonstrated by its high maneuverability and complexity of motions. It is composed of a complex array of muscles and intramuscular connective tissue, allowing force and shape production. In this study, we investigated the organization of the intramuscular elastic fibers in two main muscles composing the arm bulk: the longitudinal (L) and the transverse (T) muscles. We assessed their contribution to the muscles' passive elasticity and stiffness and inferred their possible roles in limb deformation. First, we performed confocal imaging of whole-arm samples and provided evidence of a muscle-specific organization of elastic fibers (more chaotic and less coiled in T than in L). We next showed that in an arm at rest, L muscles are maintained under 20% compression and T muscles under 30% stretching. Hence, tensional stresses are inherently present in the arm and affect the strain of elastic fibers. Because connective tissue in muscles is used to transmit stress and store elastic energy, we investigated the contribution of elastic fibers to passive forces using step-stretch and sinusoidal length-change protocols. We observed a higher viscoelasticity of L and a higher stiffness of T muscles, in line with their elastic fiber configurations. This suggests that L might be involved in energy storage and damping, whereas T is involved in posture maintenance and resistance to deformation. The elastic fiber configuration thus supports the specific role of muscles during movement and may contribute to the mechanics, energetics and control of arm motion.

Quantity versus quality: Age-related differences in muscle volume, intramuscular fat, and mechanical properties in the triceps surae

With aging comes reductions in the quality and size of skeletal muscle. These changes influence the force-generating capacity of skeletal muscle and contribute to movement deficits that accompany aging. Although declines in strength remain a significant barrier to mobility in older adults, the association between age-related changes in muscle structure and function remain unresolved. In this study, we compared age-related differences in (i) muscle volume and architecture, (ii) the quantity and distribution of intramuscular fat, and (iii) muscle shear modulus (an index of stiffness) in the triceps surae in 21 younger (24.6 ± 4.3 years) and 15 older (70.4 ± 2.4 years) healthy adults. Additionally, we explored the relationship between muscle volume, architecture, intramuscular fat and ankle plantar flexion strength in young and older adults. Magnetic resonance imaging was used to determine muscle volume and intramuscular fat content. B-mode ultrasound was used to quantify muscle architecture, shear-wave elastography was used to measure shear modulus, and ankle strength was measured during maximal isometric plantar flexion contractions. We found that older adults displayed higher levels of intramuscular fat yet similar muscle volumes in the medial (MG) and lateral gastrocnemius (LG) and soleus, compared to younger adults. These age-related higher levels of intramuscular fat were associated with lower muscle shear modulus in the LG and MG. We also found that muscle physiological cross-sectional area (PCSA) that accounted for age-associated differences in intramuscular fat showed a modest increase in its association with ankle strength compared to PCSA that did not account for fat content. This highlights that skeletal muscle fat infiltration plays a role in age-related strength deficits, but does not fully explain the age-related loss in muscle strength, suggesting that other factors play a more significant role.

Quantitative Evaluation of Gastrocnemius Medialis Stiffness During Passive Stretching Using Shear Wave Elastography in Patients with Parkinson's Disease: A Prospective Preliminary Study

Objective

To prospectively investigate the feasibility of shear wave elastography (SWE) as a new quantitative and objective method for evaluating the stiffness of the gastrocnemius medialis (GM) muscle during passive stretching in patients with Parkinson's disease (PD).

Materials and Methods

SWE of the GM muscle was performed in 28 patients with PD [13 female and 15 male; mean age ± standard deviation (SD): 63.0 ± 8.5 years] and 12 healthy controls (5 female and 7 male; mean age ± SD: 59.3 ± 6.4 years) during passive ankle rotation. A Young's modulus-ankle angle curve was constructed. The GM slack angle and baseline Young's modulus (E₀) were compared between the markedly symptomatic and mildly symptomatic sides of patients with PD, and healthy controls. Additionally, the correlation between the GM slack angle and the severity of rigidity, and the observer reproducibility of SWE in determining the GM slack angle were evaluated.

Results

The GM slack angle was smaller on both the markedly and mildly symptomatic sides in patients with PD than in healthy controls (mean ± SD of −29.13° ± 3.79° and −25.65° ± 3.39°, respectively, vs. −21.22° ± 3.52°; p < 0.001 and p = 0.006, respectively). Additionally, in patients with PD, the GM slack angle on the markedly symptomatic side was smaller than that on the mildly symptomatic side (p = 0.003). The E₀ value was lower on both the markedly and mildly symptomatic sides in patients with PD than in healthy controls (mean ± SD of 10.11 ± 2.85 kPa and 10.08 ± 1.88 kPa, respectively, vs. 12.23 ± 1.02 kPa; p = 0.012 and p < 0.001, respectively). However, no significant difference was found between the markedly and mildly symptomatic sides in patients with PD (p = 0.634). A negative linear relationship was observed between the GM slack angle and lower limb rigidity score on the markedly symptomatic side in patients with PD (r = −0.719; p < 0.001). The intraclass correlation coefficients for observer reproducibility of SWE ranged from 0.880 to 0.951.

Conclusion

The slack angle determined by SWE may be a useful quantitative and reproducible method for evaluating muscle stiffness in patients with PD.

How muscle stiffness affects human body model behavior

BACKGROUND

Active human body models (AHBM) consider musculoskeletal movement and joint stiffness via active muscle truss elements in the finite element (FE) codes in dynamic application. In the latest models, such as THUMS™ Version 5, nearly all human muscle groups are modeled in form of one-dimensional truss elements connecting each joint. While a lot of work has been done to improve the active and passive behavior of this 1D muscle system in the past, the volumetric muscle system of THUMS was modeled in a much more simplified way based on Post Mortem Human Subject (PMHS) test data. The stiffness changing effect of isometric contraction was hardly considered for the volumetric muscle system of whole human body models so far. While previous works considered this aspect for single muscles, the effect of a change in stiffness due to isometric contraction of volumetric muscles on the AHBM behavior and computation time is yet unknown.

METHODS

In this study, a simplified frontal impact using the THUMS Version 5 AM50 occupant model was simulated. Key parameters to regulate muscle tissue stiffness of solid elements in THUMS were identified for the material model MAT_SIMPLIFIED_FOAM and different stiffness states were predefined for the buttock and thigh.

RESULTS

During frontal crash, changes in muscle stiffness had an effect on the overall AHBM behavior including expected injury outcome. Changes in muscle stiffness for the thigh and pelvis, as well as for the entire human body model and for strain-rate-dependent stiffness definitions based on literature data had no significant effect on the computation time.

DISCUSSION

Kinematics, peak impact force and stiffness changes were in general compliance with the literature data. However, different experimental setups had to be considered for comparison, as this topic has not been fully investigated experimentally in automotive applications in the past. Therefore, this study has limitations regarding validation of the frontal impact results.

CONCLUSION

Variations of default THUMS material model parameters allow an efficient change in stiffness of volumetric muscles for whole AHBM applications. The computation time is unaffected by altering muscle stiffness using the method suggested in this work. Due to a lack of validation data, the results of this work can only be validated with certain limitations. In future works, the default material models of THUMS could be replaced with recently published models to achieve a possibly more biofidelic muscle behavior, which would even allow a functional dependency of the 1D and 3D muscle systems. However, the effect on calculation time and model stability of these models is yet unknown and should be considered in future studies for efficient AHBM applications.

Ultrasound Elastography in the Assessment of the Stiffness of Spastic Muscles: A Systematic Review

The incidence of muscle spasticity is high in patients with diseases of the central nervous system. This condition leads to significant limitations in movement and impaired functional capacities. Muscle spasticity manifests as changes in the mechanical properties of the muscles. This muscle disorder is generally assessed using qualitative methods, whose validity, reliability and sensitivity are questionable. In recent years, ultrasound elastography (USE) has been used as a non-invasive technique for characterizing the stress response and mechanical properties of individual muscles in the evaluation of spasticity. This article presents a systematic review of the USE techniques, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) declaration guidelines, used for the evaluation of muscle stiffness caused by spasticity. The articles selected in this study were evaluated using the Quality Appraisal of Diagnostic Reliability (QAREL) tool. Mainly, studies on the assessment of spasticity involving the evaluation of muscle stiffness with USE techniques (i.e., shear-wave elastography [SWE] or compression elastography [CE]) were selected. Then, common topics related to the assessment of spastic muscles and the statistical results of these studies were classified. Of 21 articles, nine used only CE, 10 used only SWE and two used both techniques. In the studies, statistically significant differences were observed in the measurements of muscle stiffness between the paretic and non-paretic sides as well as between patients and healthy patients. The clinical measurements obtained, devices used and assessment and probe positions for both techniques were discussed. The most frequently studied muscles were the biceps (n = 7) and gastrocnemius (n = 11). On applying the QAREL tool, we found that only two studies showed compliance at 80%-90%, seven studies at 50%-70% and the remaining 12 at 10%-40%. The results showed that USE techniques have limitations in spasticity assessment, such as subjectivity because of the lack of standardized protocols. A deficit of studies on intra-operator and inter-operator measurements indicates that this technique is not yet mature for spasticity diagnosis, although it is a promising diagnostic tool for designing treatment plans and monitoring the effectiveness of therapeutic modalities.

Immediate decrease of muscle biomechanical stiffness following dry needling in asymptomatic participants

BACKGROUND

Biomechanical muscle stiffness has been linked to musculoskeletal disorders. Assessing changes in muscle stiffness following DN may help elucidate a physiologic mechanism of DN. This study characterizes the effects of dry needling (DN) to the infraspinatus, erector spinae, and gastrocnemius muscles on biomechanical muscle stiffness.

METHOD

60 healthy participants were randomized into infraspinatus, erector spinae, or gastrocnemius groups. One session of DN was applied to the muscle in standardized location. Stiffness was assessed using a MyotonPRO at baseline, immediately post DN, and 24 h later. The presence of a localized twitch response (LTR) during DN was used to subgroup participants.

RESULTS

A statistically significant decrease in stiffness was observed in the gastrocnemius, the LTR gastrocnemius, and the LTR erector spinae group immediately following DN treatment. However, stiffness increased after 24 h. No significant change was found in the infraspinatus group.

CONCLUSIONS

DN may cause an immediate, yet transitory change in local muscle stiffness. It is unknown whether these effects are present in a symptomatic population or related to improvements in clinical outcomes. Future studies are necessary to determine if a decrease in biomechanical stiffness is related to improvement in symptomatic individuals.

Age-Related Changes in Shear Wave Elastography Parameters of the Gastrocnemius Muscle in Association with Physical Performance in Healthy Adults

BACKGROUND/AIMS

to investigate new indicators for early recognition of physical performance decline. Shear wave elastrography, a new ultrasound technique, was discussed in this study.

METHODS

Gastrocnemius muscle thickness and muscle stiffness were detected by traditional ultrasound and shear wave elastrography in 108 Chinese aged 20-85 years, and then analyzed with physical performance together.

RESULTS

After 70 years old, the decline rate of muscle stiffness under contractive state was significantly faster than that of muscle thickness, muscle relaxed stiffness, and physical performance indicators. The correlation analysis showed that gastrocnemius contractive stiffness was positively related with handgrip strength, step length, and fast gait speed after adjusted by age and gender. Among physical performance variants, step length had closer relationship with muscle strength than repeated chair stands.

CONCLUSIONS

The detection of gastrocnemius muscle by shear wave elastography reflected the change of lower-limb muscle stiffness with aging. Muscle contractive stiffness and step length measurement supplied novel ways for muscle performance and motor function assessment.

A profile of reference data for shear modulus for lower limb muscles in typically developing children

BACKGROUND

Shear wave elastography can measure shear wave speed in muscles, which is used to estimate shear modulus. Normative values and standardized methodology are needed for children. Study aims were to: estimate shear modulus behavior of lower limb muscles of typically developing children; and establish a profile of reference data and recommendations for clinical assessment.

METHODS

Forty-one typically developing children (mean 9.7 y, SD 1.9 y) completed assessment of resting shear modulus of rectus femoris, biceps femoris, gastrocnemius lateralis and tibialis anterior at short and long lengths using shear wave elastography. Effects of muscle length, age, sex and BMI were examined. Then, our data and data from a scoping review for typical individuals were collated according to Net-Longitudinal Tension Angle (net proximal and distal joint angles).

FINDINGS

Shear modulus was: higher at long versus short muscle lengths for all four muscles (P < 0.001); correlated with increasing age for tibialis anterior at short (r = 0.39) and long lengths (r = 0.42) (both P = 0.01); but not related to sex or BMI. Shear modulus: tended to increase with increasing Net-Longitudinal Tension Angle for 18 lower limb muscles; and was higher for children than adults for some muscles (e.g. tibialis anterior and gastrocnemius lateralis, both P < 0.001).

INTERPRETATION

In typically developing children, shear modulus of lower limb muscles increases with increasing Net-Longitudinal Tension Angle. Recommendations enable comparison of values across different test positions and populations. Some relation between shear modulus and age was identified, but more research is needed.

A comparison of foam rolling and vibration foam rolling on the quadriceps muscle function and mechanical properties

Purpose

The purpose of the study was to investigate the effects of using a vibration foam roll (VFR) or a non-vibration foam roll (NVFR) on maximum voluntary isometric contraction peak torque (MVIC), range of motion (ROM), passive resistive torque (PRT), and shear modulus.

Methods

Twenty-one male volunteers visited the laboratory on two separate days and were randomly assigned to either a VFR group or a NVFR group. Both interventions were performed for 3 × 1 min each. Before and after each intervention, passive resistive torque and maximum voluntary isometric contraction peak torque of the leg extensors were assessed with a dynamometer. Hip extension ROM was assessed using a modified Thomas test with 3D-motion caption. Muscle shear modulus of the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) was assessed with shear wave elastography (SWE).

Results

In both groups (VFR, NVFR) we observed an increase in MVIC peak torque (+ 14.2 Nm, + 8.6 Nm) and a decrease in shear modulus of the RF (− 7.2 kPa, − 4.7 kPa). However, an increase in hip extension ROM (3.3°) was only observed in the VFR group. There was no change in PRT and shear modulus of the VL and VM, in both the VFR group and the NVFR group. Our findings demonstrate a muscle-specific acute decrease in passive RF stiffness after VFR and NVFR, with an effect on joint flexibility found only after VFR.

Conclusion

The findings of this study suggest that VFR might be a more efficient approach to maximize performance in sports with flexibility demands.

Relationship between shear elastic modulus and passive force of the human rectus femoris at multiple sites: a Thiel soft-embalmed cadaver study

PURPOSE

Estimation of muscle passive force from elasticity using shear wave elastography (SWE) has been reported. However, the relationship between the elasticity and passive force of human muscles has not been elucidated. This study investigated the elastic modulus-passive force relationship in human skeletal muscles at multiple sites.

METHODS

Four rectus femoris (RF) muscles were dissected from a human Thiel-embalmed cadaver. Calibration weights (0-600 g in 60-g increments) were applied to the distal tendon via a pulley system, and the shear elastic modulus as an index of elasticity was measured using SWE. The shear elastic modulus of the RF was measured at the proximal, central, and distal portions.

RESULTS

The results demonstrated that the relationships between the elasticity in the longitudinal direction of the muscle and the passive force were nearly linear for all tested sites, with coefficients of determination ranging from 0.813 to 0.993.

CONCLUSION

Shear wave elastography may be used as an indirect method to measure the changing passive force at any site within human muscles.

Decreased passive muscle stiffness of vastus medialis is associated with poorer quadriceps strength and knee function after anterior cruciate ligament reconstruction

BACKGROUND

Muscle deficits of the quadriceps and hamstrings are common after anterior cruciate ligament reconstruction, and increase the risk of knee reinjury. Muscle stiffness is an important factor for dynamic joint stability. However, the changes in quadriceps and hamstring muscle stiffness and its influence after anterior cruciate ligament reconstruction remain unclear.

METHOD

Twenty-five male subjects with anterior cruciate ligament reconstruction and twenty-one matched healthy subjects participated in this study. The passive muscle stiffness of the quadriceps and hamstrings was assessed by shear modulus using ultrasound shear wave elastography. The isokinetic muscle strengths of the quadriceps and hamstrings were tested. Knee function was evaluated by the International Knee Documentation Committee and Lysholm score. Muscle stiffness was compared between limbs via non-parametric tests. Correlation analysis was used to detect the relationship between muscle stiffness, isokinetic muscle strength and knee functional scores.

FINDINGS

The involved limb exhibited significantly decreased shear modulus in the vastus medialis compared to the dominant limbs(z = -3.585;P = 0.001;ES = 1.13) and non-dominant limbs(z = -3.551;P = 0.002;ES = 1.24) of healthy controls. The shear modulus of ST was also significantly lower in the involved limb when compared with the contralateral limbs(z = -3.996;P < 0.001;ES = 1.33), dominant limbs(z = -4.477;P < 0.001;ES = 1.65) and non-dominant limbs(z = -4.234;P = 0.001;ES = 1.43) of healthy controls. The shear modulus of the vastus medialis was associated with quadriceps peak torque at 60°/s(r = 0.470; p < 0.001) and knee functional score(r = 0.459; p = 0.021).

INTERPRETATION

The passive muscle stiffness of the vastus medialis decreased after anterior cruciate ligament reconstruction, which is associated with poorer quadriceps strength and knee function. The effect of modulation of muscle stiffness on improving knee function warrants future investigation.

The relationship between muscle activation and shear elastic modulus of the sternocleidomastoid muscle during 3-D torque production

The sternocleidomastoid (SCM) is a primary neck torque generator, but the relationship between its muscle activation and shear elastic modulus during 3-D torque production is unknown. This study examined variations in neural control and shear elastic modulus of the SCM across various 3-D isometric torques. Our primary hypothesis was that the SCM would display similar preferred directions where muscle activity and shear elastic modulus were maximal during voluntary 3-D isometric torque production. Surface electromyography (EMG) and ultrasound shear wave elastography (SWE) data were collected from the SCM in 20 participants performing 3-D isometric target-matching at two different torque amplitudes. We used spherical statistics to compare the preferred directions calculated from the SWE and EMG data at 40% and 80% torque level during 3-D isometric torque production. We demonstrated a small but significant difference between EMG and SWE preferred directions, with the SWE preferred direction oriented more towards ipsilateral bending and less towards contralateral axial rotation than the preferred direction for the EMG data. We conclude that, although small differences exist, SCM shear elastic modulus is largely driven by activation during 3-D neck torques for healthy individuals.

Usability and Pitfalls of Shear-Wave Elastography for Evaluation of Muscle Quality and Its Potential in Assessing Sarcopenia: A Review

Sarcopenia is age-related progressive and generalized loss of skeletal muscle mass and strength. Its prevalence is rising, which poses a burden for society because it increases disability and dependency and therefore raises health care costs. Muscle mass quality, however-an essential part of sarcopenia-is not easily diagnosable yet. Recent interest has risen for ultrasonographic evaluation of muscle. This review introduces muscle elastography as a possible, easy and cheap tool to evaluate qualitative muscle parameters. Basic principles of muscle elastography are described, as well as different elastography techniques and some technical considerations. Furthermore, a proposal for practical guidelines is offered and factors influencing muscle stiffness are highlighted.

Effects of trunk lean and foot lift exercises in sitting position on abdominal muscle activity and the contribution rate of transversus abdominis

PURPOSE

Abdominal hollowing exercise has been recommended to improve trunk stability. Trunk lean and foot lift exercises while sitting may easily promote abdominal muscle activity even in people who cannot perform abdominal hollowing consciously. The purpose of the present study was to examine the changes in abdominal muscle activity and contribution rate of the transversus abdominis muscle (TrA) when leaning the trunk and lifting the foot during sitting.

METHODS

The muscle stiffnesses (indicators of muscle activity) of the right rectus abdominis, external oblique, internal oblique, and TrA of 14 healthy men were measured during abdominal hollowing and the following nine sitting tasks: reference posture, 15° and maximal posterior trunk lean, 20° and maximal ipsilateral and contralateral trunk lean, and ipsilateral and contralateral foot lift. The TrA contribution rate was calculated by dividing the TrA stiffness by the sum of the abdominal muscles' stiffnesses.

RESULTS

The TrA stiffness was significantly higher in abdominal hollowing than in reference posture, posterior and ipsilateral trunk lean, and ipsilateral foot lift, but not higher than in contralateral trunk lean and contralateral foot lift. There was no significant difference in the TrA contribution rates between abdominal hollowing and ipsilateral or contralateral foot lift.

CONCLUSION

The contralateral trunk lean or contralateral foot lift could enhance TrA activity for people who cannot perform abdominal hollowing consciously. The contralateral foot lift could particularly be beneficial to obtain selective activity of TrA.

Change in levator ani muscle stiffness and active force during pregnancy and post-partum

INTRODUCTION AND HYPOTHESIS

It is assumed changes occur to the biomechanics and viscoelastic response of the levator ani muscle during pregnancy; however, there is limited evidence of this. This study used instrumentation and clinical measures to determine the stiffness and active force capacity of levator ani muscle during pregnancy and post-partum, investigated any associations with delivery outcomes, and explored the biomechanical properties associated with symptoms of pelvic floor dysfunction.

METHODS

This was a prospective observational study, with nulliparous women with a singleton low-risk pregnancy. Data were collected at two stages during pregnancy and post-partum. Measurements included the Australian Pelvic Floor Questionnaire, palpation of active force, and elastometry measurements. Post-partum, 3D/4D ultrasound measurements were included. Repeated measures ANOVAs, pairwise comparisons, Pearson correlation coefficients, and Student's t-tests were used as appropriate.

RESULTS

Fifty-nine women took part in the study. Active force was significantly different over the pregnancy and post-partum, measured with instrumentation (p = 0.002) and palpation (p = 0.006 right, p = 0.029 left). There was no significant change in muscle stiffness during pregnancy. Post-partum muscle stiffness was significantly different between women who gave birth vaginally vs. caesarean section (p = 0.002). Post-partum there were differences in levator hiatal area, symptoms of bladder dysfunction, prolapse symptoms, and sexual dysfunction symptoms.

CONCLUSIONS

Active force of the levator ani muscle was significantly reduced during pregnancy and in the post-partum period, while muscle stiffness reduced only in those who had vaginal deliveries.

Hip position influences shear wave elastography measurements of the hamstring muscles in healthy subjects

Ultrasound shear wave elastography (SWE) has recently emerged as a non-invasive tool for assessing muscle stiffness. The majority of studies utilizing SWE have focused primarily on upper-extremity muscles, with little attention attributed to lower-extremity muscles. In addition, of the studies that have been published, various joint and muscle positions have been examined, rendering it difficult to compare results across studies. Thus, the purpose of this investigation was to examine lower extremity medial hamstring muscles (semitendinosus and semimembranosus) and to determine how hip position (0° versus 90°) and muscle position (knee flexed versus extended) impacted resulting shear modulus values. Ten subjects varying widely in age participated in this study, and their hamstring stiffness was assessed in four separate positions: seated with the knee flexed and extended, and lying prone with the knee flexed and extended. Higher shear modulus values were found at the group-level when participants were seated compared to prone (hip placed at 90° compared to 0°). In addition, higher values were also found when the knee was extended compared to flexed, but only when the hip was placed at 90° (not 0°). These results demonstrate that joint and muscle position, particularly when assessing the hamstrings, largely impact resulting shear modulus values. Therefore, joint and muscle position need to be systematically controlled for and reported when establishing normative ranges for shear modulus values across specific age groups. This will enable physicians to more precisely determine whether patients' shear modulus values indicate clinically meaningful differences in comparison to normative data.

Identifying predictors of upper extremity muscle elasticity with healthy aging

Ultrasound shear wave elastography (SWE) can provide accurate in vivo measurements of the effect of advanced age on muscle elasticity. Our objective was to determine whether passive muscle elasticity was influenced by posture, chronological age, sex, body mass index, and clinical measures of upper extremity function for healthy adults. The dominant arm of 33 male and 33 female participants (ranging from 20 to 89 years old) was examined using a Supersonic Imagine Aixplorer ultrasound SWE system. The mean and standard deviation of shear wave velocity (SWV) was measured from elastography maps for five upper extremity muscles examined at rest: anterior deltoid (AD), biceps brachii (BB), clavicular (CL) and sternocostal (SC) region of the pectoralis major and middle trapezius (MT). Linear mixed models for each muscle were used to assess how SWV was influenced by humeral elevation, chronological age, sex, BMI and three functional measures. All significances are reported at α = 0.05. Humeral elevation influenced shear wave velocity at a statistically significant level for AD, BB, SC and MT (all p < 0.047). Chronological age was a significant predictor of mean SWV for the sternocostal region of the pectoralis major and the middle trapezius (both p < 0.03). These same muscles were also less homogenous (based on their standard deviations) with increased age, particularly for female participants. Performance-based functional assessments of the upper extremity were predictors of mean SWV for the clavicular region of the pectoralis major (all p < 0.04). These results suggest ultrasound SWE has potential utility for assessing age-related changes to muscle elasticity, but these associations were muscle-dependent.

Effects of static stretching programs performed at different volume-equated weekly frequencies on passive properties of muscle-tendon unit

Whether static stretching (SS) frequency has an effect on increasing the range of motion (ROM) and decreasing muscle stiffness remains unclear. Therefore, this study aimed to investigate the effects of two 6-week SS programs performed with different frequencies but generally the same duration of stretching on the passive properties of the medial gastrocnemius muscle-tendon unit. The study participants comprised 24 male volunteers randomly assigned to either the one-time/week group or the three-times/week group, performing 6 min of SS once per week and 2 min of SS thrice per week, respectively. The dorsiflexion ROM (DF ROM) and muscle stiffness of the medial gastrocnemius during passive ankle dorsiflexion were assessed using a dynamometer and ultrasonography before and after 6 weeks of SS programs. The results show that the DF ROM was increased and muscle stiffness was decreased significantly in the three-times/week group (P < 0.01 and P < 0.01, respectively), whereas no significant changes were observed in DF ROM and muscle stiffness in the one-time per week group (P = 0.25 and P = 0.32, respectively). These results suggest that a high-frequency SS program is more effective than a low-frequency SS program in increasing ROM and decreasing muscle stiffness.

Sedentary behaviour at work increases muscle stiffness of the back: Why roller massage has potential as an active break intervention

There is increasing evidence that subjects who are exposed to long sitting periods suffer from musculoskeletal discomfort and back pain. The underlying mechanism and effective prevention strategies are still largely unknown. In this study, muscle stiffness of the back was measured in 59 office workers who followed their usual desk work regime for 4.5 h in a sitting posture. The sitting period was either followed by an 8-min roller massage intervention or a controlled standing task. Results showed that muscle stiffness increased significantly after the 4.5 h sitting period. When the sitting period was followed by roller massage, the stiffness values dropped slightly below baseline stiffness. In contrast, the stiffness values remained increased when the sitting period was followed by controlled standing. This study indicates that short-duration tissue manipulation can be an effective active break between prolonged sitting periods to prevent musculoskeletal issues, such as musculoskeletal discomfort and back pain.

The problem with skeletal muscle series elasticity

Muscles contain contractile and (visco-) elastic passive components. At the latest since Hill’s classic works in the 1930s, it has been known that these elastic components affect the length and rate of change in length of the contractile component, and thus the active force capability of dynamically working muscles. In an attempt to elucidate functional properties of these muscle elastic components, scientists have introduced the notion of “series” and “parallel” elasticity. Unfortunately, this has led to much confusion and erroneous interpretations of results when the mechanical definitions of parallel and series elasticity were violated.

In this review, I will focus on muscle series elasticity, by first providing the mechanical definition for series elasticity, and then provide theoretical and experimental examples of the concept of series elasticity. Of particular importance is the treatment of aponeuroses. Aponeuroses are not in series with the tendon of a muscle nor the muscle’s contractile elements. The implicit and explicit treatment of aponeuroses as series elastic elements in muscle has led to incorrect conclusions about aponeuroses stiffness and Young’s modulus, and has contributed to vast overestimations of the storage and release of mechanical energy in cyclic muscle contractions.

Series elasticity is a defined mechanical concept that needs to be treated carefully when applied to skeletal muscle mechanics. Measuring aponeuroses mechanical properties in a muscle, and its possible contribution to the storage and release of mechanical energy is not trivial, and to my best knowledge, has not been (correctly) done yet.