Associations of passive muscle stiffness, muscle stretch tolerance, and muscle slack angle with range of motion: individual and sex differences

The effects of static and dynamic stretching on deep fascia stiffness: a randomized, controlled cross-over study

AIM

Previous stretching studies mostly investigated effects on the skeletal muscle but comprehensive explorations regarding the role of the connective tissue are scarce. Since the deep fascia has been demonstrated to be sensitive to mechanical tension, it was hypothesized that the fascia would also respond to stretching, contributing to enhanced range of motion (ROM).

METHODS

Forty (40) recreationally active participants (male: n = 25, female: n = 15) were included in the randomized controlled cross-over trial and allocated to different groups performing 5 min static (STAT) or dynamic (DYN) plantar flexor stretching or control condition (CC) in a random order. Pre- and immediately post-intervention, muscle and fascia stiffness, as well as muscle and fascia thickness were measured using high-resolution ultrasound and strain elastography. ROM was assessed in the ankle joint via the knee to wall test (KtW) and goniometer.

RESULTS

STAT reduced both, muscle and fascia stiffness (d = 0.78 and 0.42, p < 0.001, respectively), while DYN did not reduce stiffness compared to the control condition (p = 0.11-0.41). While both conditions showed significant increases in the KtW (d = 0.43-0.46, p = 0.02-0.04), no significant differences to the CC were observed for the isolated ROM testing (p = 0.09 and 0.77). There was a small correlation between fascia stiffness decreases and ROM increases (r = - 0.25, p = 0.006) but no association was found between muscle stiffness decreases and ROM increases (p = 0.13-0.40).

CONCLUSION

Our study is the first to reveal stretch-induced changes in fascia stiffness. Changes of fascia`s but not muscle`s mechanical properties may contribute to increased ROM following stretching.

Regional and widespread pain sensitivity decreases following stretching in both men and women - Indications of stretch-induced hypoalgesia

INTRODUCTION

This study aimed to investigate the effect of sex on regional and widespread pain sensitivity following acute bouts of stretching and to investigate the acute effect of stretching on regional and widespread pain sensitivity following stretching.

METHODS

73 healthy adults (36 females; mean age 25.6 ± 6.7 years) with an age range from 19 to 62 years were recruited for this experimental study. Regional and distant pain pressure pain thresholds, passive knee extension range of motion and passive resistive torque were measured before and 30 s after four bouts of 30-s static muscle stretching of the knee flexors with 20-s rest between bouts.

RESULTS

No significant sex differences were found for pressure pain thresholds (p > 0.132), range of motion (p = 0.446) or passive resistive torque (p = 0.559) between pre-stretch and post-stretch measures. There were significant increases in pressure pain thresholds (p = 0.010), range of motion (p = 0.001) and passive resistive torque (p = 0.007) between pre-stretch and post-stretch measures.

CONCLUSION

Muscle stretching significantly decreased regional and widespread pain sensitivity, indicating that central pain-modulating mechanisms are engaged during muscle stretching, resulting in stretch-induced hypoalgesia. Moreover, the results showed that the effect of stretching on regional and widespread pain sensitivity is not sex-specific.

Biceps femoris long head stiffens after 2 weeks of training cessation in highly trained sprinters

PURPOSE

Most athletes experience short-term training cessation because of illness, injury, post-season vacation, or other reasons. Passive muscle stiffness is a potential risk factor for a sprint-type hamstring strain injury, but limited information is available about the effect of short-term training cessation on passive muscle stiffness. The present study aimed to identify whether and how passive muscle stiffness of the biceps femoris long head (BFlh) would vary due to 2 weeks of training cessation in sprinters.

METHODS

Passive BFlh shear-wave speed (a proxy for stiffness) was measured using ultrasound shear-wave elastography in 28 male sprinters, before and after 2 weeks of intervention. During the 2 weeks, the participants in the training-cessation group (n = 14) were allowed to maintain their normal daily activities but not to perform any physical training, including stretching and resistance exercises. The participants in the training continuation group (n = 14) performed the training (including maximum speed sprint, plyometric, and weight training) prescribed by their coaches 5 days per week.

RESULTS

In the training-cessation group, passive BFlh shear-wave speed increased after the 2 weeks of training cessation (4.75 ± 0.77 to 5.00 ± 0.88 m/s, P < 0.001). In contrast, there was no significant difference before and after the 2 weeks of training continuation (4.90 ± 0.85 to 4.93 ± 0.85 m/s, P = 0.521).

CONCLUSIONS

The present findings indicate that muscles stiffen by training cessation in sprinting athletes.

Referential values for lower limb flexibility in healthy children and adolescents in Japan: A five-year cross-sectional study

BACKGROUND

Lower limb flexibility (LLF) is an essential motor function. However, assessing LLF during adolescence is difficult because of the influence of marked physical changes. We, therefore, assessed LLF and investigated the relationship between LLF and sex and age in healthy children and adolescents.

METHODS

We conducted a five-year cross-sectional study with students aged 8-14 years at a single school in Japan. We evaluated the heel-buttock distance (HBD), straight leg raising angle (SLRA), and dorsiflexion angle of the ankle joint (DFA) at the beginning of each year. We conducted a comparative analysis on the performance of the HBD, SLRA, and DFA techniques, stratified by both sex and age. The statistical significance of observed differences was assessed through the application of Mann-Whitney U and Kruskal-Wallis tests. Furthermore, we analyzed the effects of sex, age, height, and weight on LLF using a multivariable linear regression model.

RESULTS

Of the 4221 initial study participants, 3370 were analyzed. Mean HBD, SLRA, and DFA values were 1.6 cm, 77.0°, and 15.7°, respectively. Girls showed significantly higher HBD and lower SLRA and DFA values than boys and 14-year-olds (p < 0.01). Median HBD value for girls was 0 cm, whereas for boys, it exceeded 0 cm after age 13. The median SLRA value for girls was 80-85°, while for boys, it was 70-75°. The median DFA value for girls was 15-19°, and for boys, it was 12-15°. A multivariable linear regression model indicated that boys had significantly greater tightness than girls (p < 0.01).

CONCLUSIONS

The reference values of HBD, SLRA, and DFA differed according to age and sex. Furthermore, we showed that sex differences were significantly associated with LLF. Data in this study provide the reference value for assessing LLF in children and adolescents.

Explorative study using ultrasound time-harmonic elastography for stiffness-based quantification of skeletal muscle function

Time-harmonic elastography (THE) is an emerging ultrasound imaging technique that allows full-field mapping of the stiffness of deep biological tissues. THE's unique ability to rapidly capture stiffness in multiple tissues has never been applied for imaging skeletal muscle. Therefore, we addressed the lack of data on temporal changes in skeletal muscle stiffness while simultaneously covering stiffness of different muscles. Acquiring repeated THE scans every five seconds we quantified shear-wave speed (SWS) as a marker of stiffness of the long head (LHB) and short head (SHB) of biceps brachii and of the brachialis muscle (B) in ten healthy volunteers. SWS was continuously acquired during a 3-min isometric preloading phase, a 3-min loading phase with different weights (4, 8, and 12 kg), and a 9-min postloading phase. In addition, we analyzed temporal SWS standard deviation (SD) as a marker of muscle contraction regulation. Our results (median [min, max]) showed both SWS at preloading (LHB: 1.04 [0.94, 1.12] m/s, SHB: 0.86 [0.78, 0.94] m/s, B: 0.96 [0.87, 1.09] m/s, p < 0.001) and the increase in SWS with loading weight to be muscle-specific (LHB: 0.010 [0.002, 0.019] m/s/kg, SHB: 0.022 [0.017, 0.042] m/s/kg, B: 0.039 [0.019, 0.062] m/s/kg, p < 0.001). Additionally, SWS during loading increased continuously over time by 0.022 [0.004, 0.051] m/s/min (p < 0.01). Using an exponential decay model, we found an average relaxation time of 27 seconds during postloading. Analogously, SWS SD at preloading was also muscle-specific (LHB: 0.018 [0.011, 0.029] m/s, SHB: 0.021 [0.015, 0.027] m/s, B: 0.024 [0.018, 0.037] m/s, p < 0.05) and increased by 0.005 [0.003, 0.008] m/s/kg (p < 0.01) with loading. SWS SD did not change over loading time and decreased immediately in the postloading phase. Taken together, THE of skeletal muscle is a promising imaging technique for in vivo quantification of stiffness and stiffness changes in multiple muscle groups within seconds. Both the magnitude of stiffness changes and their temporal variation during isometric exercise may reflect the functional status of skeletal muscle and provide additional information to the morphological measures obtained by conventional imaging modalities.

Relationship between pectoralis major stiffness and shoulder extension range of motion

This study aimed to investigate the correlation between the passive muscle stiffness of the pectoralis major muscle pars clavicularis (PMc) and shoulder extension range of motion (ROM) in both male and female participants. Thirty-nine (23 male/16 female) physically active and healthy participants volunteered in this study. After a standardized warm-up, the PMc stiffness was tested via shear wave elastography at a slightly stretched position (long muscle length) and in a non-stretched position (short muscle length). Additionally, a custom-made device and 3D motion capture assessed the active shoulder extension ROM. We found a significant moderate and negative relationship between shoulder extension ROM and PMc stiffness at long muscle length (rs = -0.33; p = 0.04) but not at short muscle length (r = -0.23; p = 0.17). Additionally, there was no significant difference between male and female participants in the correlation analyses at both elbow angles. The moderate correlation between PMc stiffness at a slightly stretched position and shoulder extension ROM suggests that additionally, other structures such as nerves/fascia stiffness or even stretch tolerance might be factors that can be related to shoulder extension ROM.

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.

Acute effect of static stretching on non-muscular tissue stiffness and joint flexibility: a comparative study between older and young men

PURPOSE

Non-muscular tissue stiffness is assumed to have a negative impact on joint flexibility, and a reduction in non-muscular tissue stiffness may be important, especially in older adults. The present study aimed to compare the acute effects of static stretching on non-muscular tissue stiffness between older and young adults and to investigate whether a decrease in tissue stiffness improves joint flexibility.

METHODS

Twenty older (62-83 years) and 20 young (21-24 years) males participated. Ankle dorsiflexion static stretching (five sets of 90 s each) was performed, and before and after stretching, the ankle dorsiflexion range of motion (RoM), passive ankle joint stiffness, and shear wave speed (SWS) (an index of stiffness) of the sciatic nerve, tibial nerve, and posterior thigh fascia were measured.

RESULTS

Stretching led to an increase in RoM and a decrease in passive joint stiffness in both groups (P < 0.001) with no significant between-group differences (P ≥ 0.055). The between-group difference in the effect of stretching on SWS was evident only for the sciatic nerve, and a decline in sciatic nerve SWS was only observed in the older adult group (pre-stretching: 2.5 ± 0.3 m/s; post-stretching: 2.3 ± 0.4 m/s; P = 0.027). A significant positive repeated-measures correlation was observed between the sciatic nerve SWS and passive joint stiffness (P = 0.014, rrm = 0.540).

CONCLUSION

The reduction in sciatic nerve stiffness by stretching was noticeable in older men and led to improved joint flexibility. These findings may provide insight into tissue adaptation by stretching and may be used to explore effective exercises for improving joint flexibility in older adults.

Acute effects of static and proprioceptive neuromuscular facilitation stretching on hamstrings muscle stiffness and range of motion: a randomized cross-over study

This study aimed to compare the acute effects of static stretching (SS) and proprioceptive neuromuscular facilitation (PNF) stretching on hamstrings flexibility and shear modulus. Sixteen recreationally active young volunteers participated in a randomized cross-over study. Participants underwent an aerobic warm-up (WU), followed by either SS or PNF stretching. Range of motion (RoM) during passive straight leg raise and active knee extension, as well as shear modulus of the biceps femoris (BF) and semitendinosus (ST) muscles, were measured at baseline, post-WU, and post-stretching. Both stretching techniques significantly increased RoM, with no differences observed between SS and PNF (p < 0.001; η2 = 0.59-0.68). However, only PNF stretching resulted in a significant decrease in BF shear modulus (time×stretching type interaction: p = 0.045; η2 = 0.19), indicating reduced muscle stiffness. No changes in ST shear modulus were observed after either stretching technique. There was no significant correlation between changes in RoM and shear modulus, suggesting that the increase in RoM was predominantly due to changes in stretch tolerance rather than mechanical properties of the muscles. These findings suggest that both SS and PNF stretching can effectively improve hamstring flexibility, but PNF stretching may additionally reduce BF muscle stiffness. The study highlights the importance of considering individual muscle-specific responses to stretching techniques and provides insights into the mechanisms underpinning acute increases in RoM.

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.

Chinese Ultrasound Doctors Association Guideline on Operational Standards for 2-D Shear Wave Elastography Examination of Musculoskeletal Tissues

The Ultrasound Physician Branch of the Chinese Medical Doctor Association sought to develop evidence-based recommendations on the operational standards for 2-D shear wave elastography examination of musculoskeletal tissues. A consensus panel of 22 Chinese musculoskeletal ultrasound experts reviewed current scientific evidence and proposed a set of 12 recommendations for 13 key issues, including instruments, operating methods, influencing factors and image interpretation. A final consensus was reached through discussion and voting. On the basis of research evidence and expert opinions, the strength of recommendation for each proposition was assessed using a visual analog scale, while further emphasizing the best available evidence during the question-and-answer session. These expert consensus guidelines encourage facilitation of the standardization of clinical practices for collecting and reporting shear wave elastography data.

Age-related changes and sex differences in ankle plantarflexion velocity

Ankle plantar flexors play a vital role in the mobility of older adults. The strength and velocity of plantarflexion are critical factors in determining walking speed. Despite reports on how age and sex affect plantarflexion strength, basic information regarding plantarflexion velocity is still lacking. This cross-sectional observational study investigated age-related changes and sex differences in plantarflexion velocity by comparing them with plantarflexion strength. A total of 550 healthy adults were classified into four age groups for each sex: Young (< 40 years old), Middle-aged (40-64 years old), Young-old (65-74 years old), and Older-old (≧ 75 years old). We measured plantarflexion velocity and strength in the long-sitting position using a gyroscope and a hand-held dynamometer, respectively. Two-way analysis of variance revealed no interaction between age and sex for either plantarflexion velocity or strength. Plantarflexion velocity exhibited a significant decline with aging, as did the plantarflexion strength. We found no significant sex differences in plantarflexion velocity in contrast to plantarflexion strength. The results indicated a significant decrease with age and no difference in plantarflexion velocity between males and females characteristic plantarflexion velocity. Understanding the characteristics of plantarflexion velocity could contribute to preventing a decline in mobility in older adults.

Three-dimensional mapping of ultrasound-derived skeletal muscle shear wave velocity

Introduction: The mechanical properties of skeletal muscle are indicative of its capacity to perform physical work, state of disease, or risk of injury. Ultrasound shear wave elastography conducts a quantitative analysis of a tissue's shear stiffness, but current implementations only provide two-dimensional measurements with limited spatial extent. We propose and assess a framework to overcome this inherent limitation by acquiring numerous and contiguous measurements while tracking the probe position to create a volumetric scan of the muscle. This volume reconstruction is then mapped into a parameterized representation in reference to geometric and anatomical properties of the muscle. Such an approach allows to quantify regional differences in muscle stiffness to be identified across the entire muscle volume assessed, which could be linked to functional implications. Methods: We performed shear wave elastography measurements on the vastus lateralis (VL) and the biceps femoris long head (BFlh) muscle of 16 healthy volunteers. We assessed test-retest reliability, explored the potential of the proposed framework in aggregating measurements of multiple subjects, and studied the acute effects of muscular contraction on the regional shear wave velocity post-measured at rest. Results: The proposed approach yielded moderate to good reliability (ICC between 0.578 and 0.801). Aggregation of multiple subject measurements revealed considerable but consistent regional variations in shear wave velocity. As a result of muscle contraction, the shear wave velocity was elevated in various regions of the muscle; showing pre-to-post regional differences for the radial assessement of VL and longitudinally for BFlh. Post-contraction shear wave velocity was associated with maximum eccentric hamstring strength produced during six Nordic hamstring exercise repetitions. Discussion and Conclusion: The presented approach provides reliable, spatially resolved representations of skeletal muscle shear wave velocity and is capable of detecting changes in three-dimensional shear wave velocity patterns, such as those induced by muscle contraction. The observed systematic inter-subject variations in shear wave velocity throughout skeletal muscle additionally underline the necessity of accurate spatial referencing of measurements. Short high-effort exercise bouts increase muscle shear wave velocity. Further studies should investigate the potential of shear wave elastography in predicting the muscle's capacity to perform work.

Acute and Prolonged Effects of 300 sec of Static, Dynamic, and Combined Stretching on Flexibility and Muscle Force

Static stretching (SS), dynamic stretching (DS), and combined stretching (CS; i.e., DS+SS) are commonly performed as warm-up exercises. However, the stretching method with the greatest effect on flexibility and performance remains unclear. This randomized crossover trial examined acute and prolonged effects of SS, DS, and CS on range of motion (ROM), peak passive torque (PPT), passive stiffness, and isometric and concentric muscle forces. Twenty healthy young men performed 300 sec of active SS, DS, or CS (150-sec SS followed by 150-sec DS and 150-sec DS followed by 150-sec SS) of the right knee flexors on four separate days, in random order. Subsequently, we measured ROM, PPT, and passive stiffness during passive knee extension. We also measured maximum voluntary isometric and concentric knee flexion forces and surface electromyographic activities during force measurements immediately before, immediately after, and 20 and 60 min after stretching. All stretching methods significantly increased ROM and PPT, while significantly decreasing isometric knee flexion force (all p < 0.05). These changes lasted 60 min after all stretching methods; the increases in ROM and PPT and the decreases in isometric muscle force were similar. All stretching methods also significantly decreased passive stiffness immediately after stretching (all p < 0.05). Decreases in passive stiffness tended to be longer after CS than after SS or DS. Concentric muscle force was decreased after SS and CS (all p < 0.05). On the other hand, concentric muscle force was unchanged after DS, while the decreases in surface electromyographic activities during concentric force measurements after all stretching methods were similar. Our results suggest that 300 sec of SS, DS, and CS have different acute and prolonged effects on flexibility and muscle force.

Characteristics of the static muscle stiffness of ankle plantar flexors in individuals with chronic ankle instability

PURPOSE

Individuals with chronic ankle instability (CAI) have deficits in closed kinetic chain dorsiflexion that may perpetuate injury. Determining the characteristics of muscle stiffness in the plantar flexors of individuals with CAI may help in developing appropriate treatments. We aimed to highlight the characteristics of static muscle stiffness in ankle plantar flexor muscles during the passive dorsiflexion of the ankle joint in individuals with CAI.

METHODS

A total of 30 patients were included in the study based on the International Ankle Consortium criteria. The patients were categorized evenly into healthy, coper, and CAI groups (i.e., 10 patients in each group). After measuring the dorsiflexion range of motion (non-weight-bearing/weight-bearing) of the ankle joint, the static muscle stiffness measurements of the medial gastrocnemius, lateral gastrocnemius, soleus, and peroneus longus were obtained. The measurements were performed during the knee joint's extension and 50° flexion and passive dorsiflexion between the range of 40° plantar flexion and 20° dorsiflexion.

RESULTS

The dorsiflexion range of motion of the CAI group was significantly smaller than that of the healthy and coper groups in the weight-bearing position. No interaction was observed for muscle stiffness in both the knee flexion and extension positions, and no significant differences were identified among the three groups. The shear modulus of the soleus at 20° ankle dorsiflexion with knee flexion had a significant negative correlation with the weight-bearing range of motion of the ankle.

CONCLUSION

The limitation in the weight-bearing dorsiflexion range of motion in CAI was largely due to factors other than the increased elasticity of the ankle plantar flexor muscles.

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.

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

BACKGROUND

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

METHODS

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

DISCUSSION

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

TRIAL REGISTRATION

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

Quantifying the shear modulus of the adductor longus muscle during hip joint motion using shear wave elastography

The present study aims to assess the effect of the hip flexion angle on the shear modulus of the adductor longus (AL) muscle associated with passive hip abduction and rotation. Sixteen men participated in the study. For the hip abduction task, the hip flexion angles used were - 20, 0, 20, 40, 60, and 80°, and the hip abduction angles were 0, 10, 20, 30, and 40°. For the hip rotation task, the hip flexion angles used were - 20, 0, 20, 40, 60, and 80°, hip abduction angles were 0 and 40°, and hip rotation angles were 20° internal rotation, 0° rotation, and 20° external rotation. The shear modulus at 20° extension was significantly higher than that at 80° flexion for the 10, 20, 30 and 40° hip abduction (i.e., P < 0.05). The shear modulus at 20° internal rotation and 20° extension was significantly higher than that at 0° rotation and 20° external rotation, regardless of the hip abduction angle (i.e., P < 0.05). The mechanical stress of the AL muscle associated with hip abduction was higher in the extended position. Furthermore, the mechanical stress could increase with internal rotation only at the hip-extended position.

Shear Wave Elastography for Detecting Calf Muscle Stiffness: An Effective Tool for Assessing Sarcopenia

OBJECTIVES

To explore the feasibility of shear wave elastography for evaluating sarcopenia.

METHODS

The shear wave velocities (SWV) of the tibialis anterior, medial gastrocnemius, and soleus were measured in 130 subjects in the Second Affiliated Hospital of Fujian Medical University from January 2021 to June 2022. Consistency was evaluated in 20 cases using the intraclass correlation coefficient. According to the 2019 Asian Working Group for Sarcopenia（AWGS） diagnostic criteria, the patients were divided into a healthy and a sarcopenia group. The differences in SWV between the two groups were compared, and their correlation between calf muscles and muscle mass, grip strength, and pace were analyzed. The diagnostic cutoff value of calf muscle SWV for sarcopenia was obtained using receiver operating characteristic (ROC) curves, and the diagnostic efficacy of different ROC curves was compared.

RESULTS

The SWV inter-group and intra-group correlation coefficients of the three lower limbs muscles were all greater than 0.85. Moreover, the corresponding SWV in the sarcopenia group were significantly smaller than those in the healthy control group (P < .05). Further, SWV were positively correlated with the appendicular skeletal muscle mass index (ASMI), grip strength, and gait speed. Finally, the SWV of the anterior tibialis and medial gastrocnemius muscles were 3.02 and 2.26 m/s, respectively, and their diagnostic efficacy for sarcopenia did not differ significantly (Z = 0.190, P = .8497).

CONCLUSION

SWE can be used to detect the hardness of the anterior tibialis and medial gastrocnemius, calculate their muscle mass as an effective tool to evaluate sarcopenia.

Effects of gentle mechanical skin stimulation on subjective symptoms and joint range of motions in people with chronic neck and shoulder discomfort

This study aimed to examine the efficacy of a 2-week self-administered gentle mechanical skin stimulation on chronic neck and shoulder discomfort. In participants (n = 12) with chronic neck and shoulder discomfort, subjective measures of pain sensation, discomfort, and difficulty in moving using a visual analog scale (VAS, 0-10) and objective measures of 12 different joint range of motions (ROMs) for the cervical and shoulder regions, using a digital goniometer, were collected before and after self-care with contact acupuncture, called microcones. The self-care for 2 weeks significantly (p < 0.001) decreased all VAS scores to 2.2-2.3 from baseline values of 6.0-7.4. Of the 12 ROMs tested, 8 were significantly increased (p < 0.013). This open-label study suggests the use of self-care with microcones in improving subjective symptoms and joint ROMs in people suffering from chronic neck and shoulder discomfort. However, a randomized, double-blind, controlled clinical trial is needed to further investigate the efficacy and safety of microcones.

Quantitative assessment of biceps brachii muscle stiffness by using Young’s modulus–Angle curve during passive stretching in stroke patients

Purpose: This study aims to use shear wave elastography (SWE) to dynamically describe the characteristics of biceps brachii muscle stiffness during passive stretching in healthy participants, investigate changes in the Young’s modulus–angle curve under various states of muscle tone in stroke patients, and develop a new method for measuring muscle tone quantitatively.

Methods: In total, 30 healthy volunteers and 54 stroke patients were evaluated for elbow flexor muscle tone on both sides using passive motion examination and were divided into groups based on their muscle tone status. The real-time SWE video of the biceps brachii and the Young’s modulus data were recorded during the passive straightening of the elbow. The Young’s modulus–elbow angle curves were created and fitted using an exponential model. The parameters yielded from the model were subjected to further intergroup analysis.

Results: The repeatability of the Young’s modulus measurement was generally good. During passive elbow extension, the Young’s modulus of the biceps brachii steadily increased as muscle tone increased, and it increased faster when the modified Ashworth scale (MAS) score got higher. The exponential model’s fitness was generally good. The curvature coefficient was significantly different between the MAS 0 group and the hypertonia groups (MAS 1, 1+, and 2 groups).

Conclusion: The passive elastic characteristics of the biceps brachii are consistent with the exponential model. The Young’s modulus–elbow angle curve of the biceps brachii changes in distinct ways depending on the muscle tone status. SWE can be used to quantify muscular stiffness during passive stretching as a new way of muscle tone evaluation, allowing for quantitative muscle tone evaluation and mathematical assessment of muscle mechanical properties in stroke patients.

Mechanical Linkage between Achilles Tendon and Plantar Fascia Accounts for Range of Motion of Human Ankle-Foot Complex

PURPOSE

The human ankle-foot complex possesses a passive range of motion (ROM) through changes in tibiocalcaneal ( θcal ) and foot arch ( θarch ) angles. Based on the anatomical linkage between the Achilles tendon (AT) and plantar fascia (PF), we hypothesized that AT and PF with different mechanical properties conjointly modulate the passive ROM of the human ankle-foot complex. We examined the association of AT and PF stiffness with passive ankle-foot ROM and further addressed differences between sexes.

METHODS

A series of sagittal magnetic resonance images of the foot and passive ankle plantar flexion torque were obtained for 20 men and 20 women with their ankle-foot passively rotated from 30° of plantar flexion to 20° of dorsiflexion. Based on the measured changes in AT and PF lengths, θcal , θarch , and passive torque, AT and PF stiffness were determined.

RESULTS

Upon passive ankle dorsiflexion, AT and PF were lengthened; their length changes were inversely correlated. Men showed a stiffer AT, more compliant PF, less calcaneal rotation, and greater foot arch deformation compared with women. Furthermore, we found inverse correlations between AT stiffness and ROM of θcal , and between PF stiffness and ROM of θarch in men and women.

CONCLUSIONS

Passive AT and PF extensibility counter each other. AT and PF stiffness and passive ROM of ankle-foot components were countered between sexes; however, associations between stiffness and passive ROM of the ankle-foot complex were consistent between sexes. Our findings support the notion that the balanced mechanical interaction between the AT and PF can account for the passive ROM of the human ankle-foot complex in vivo , and the differences between sexes.

Contribution of muscle stiffness of the triceps surae to passive ankle joint stiffness in young and older adults

This study aimed to investigate whether triceps surae muscle stiffness is associated with passive ankle joint stiffness in 40 young (21-24 years) and older (62-83 years) males. Using ultrasound shear wave elastography, the shear modulus of each muscle of the triceps surae (the medial [MG], lateral gastrocnemius [LG], and soleus [Sol]) was assessed as muscle stiffness at the ankle neutral position (NP) and 15-degree dorsiflexed position (DF15) with the knee fully extended. Passive ankle joint stiffness at the NP and DF15 was calculated as the gradient of the angle-torque relationship at each joint angle during passive ankle dorsiflexion at 1°∙s^-1 controlled by using an isokinetic dynamometer. Passive ankle joint stiffness was normalized by the body mass. There was no correlation between the absolute ankle joint stiffness and muscle shear modulus of triceps surae in the young and older groups at the NP (r ≤ 0.349, p ≥ 0.138). Significant positive correlations between absolute ankle joint stiffness and muscle shear modulus at DF15 were observed for MG and Sol in the young group (r ≥ 0.451, p ≤ 0.044) but not in the older group. The normalized ankle joint stiffness at the NP was significantly positively correlated with the LG shear modulus in young participants and with the MG and LG shear modulus in older participants (r ≥ 0.466 and p ≤ 0.039). There were significant positive correlations between the normalized ankle joint stiffness and the muscle shear modulus of the triceps surae at DF15 in young and older participants (r ≥ 0.464 and p ≤ 0.040), except for the MG shear modulus in older participants (r = 0.419 and p = 0.066). These results suggest that the material properties of the entire triceps surae, even Sol, which is the most compliant muscle among the triceps surae, affect passive ankle joint stiffness, especially when the triceps surae is lengthened and body size is considered.

Effects of Quercetin Glycoside Supplementation Combined With Low-Intensity Resistance Training on Muscle Quantity and Stiffness: A Randomized, Controlled Trial

Objective

Aging of skeletal muscle is characterized not only by a decrease of muscle quantity but also by changes in muscle quality, such as an increase in muscle stiffness. The present study aimed to investigate the effects of supplementation with quercetin glycosides (QGs), well-known polyphenolic flavonoids, combined with resistance exercise on muscle quantity and stiffness.

Materials and Methods

A randomized, controlled trial was conducted in community-dwelling, Japanese people aged 50-74 years who were randomly allocated to exercise with placebo or 200 or 500 mg of QG supplementation. All participants performed low-intensity resistance training mainly targeting thigh muscles with 40% of 1-repetition maximum, 3 days per week for 24 weeks. Muscle cross-sectional area (CSA), lean mass, and vastus lateralis (VL) muscle stiffness were measured before and after the 24-week intervention.

Results

Forty-eight subjects completed the 24-week intervention. There were no significant group × time interactions in thigh CSA for primary outcome, as well as lean mass. VL muscle stiffness in the stretched position was significantly lower in both the 200 mg and 500 mg QG groups than in the placebo group after the 24-week intervention (p < 0.05). No significant correlation was observed between changes of VL muscle CSA and stiffness during the 24-week intervention.

Conclusion

Quercetin glycoside supplementation combined with low-intensity resistance exercise improved passive muscle stiffness independently of muscle quantity.

Clinical Trial Registration

[www.umin.ac.jp/ctr/], identifier [UMIN000037633].

Sex-related differences and effects of short and long trail running races on resting muscle-tendon mechanical properties

The purpose of the study was to assess sex-related differences in resting mechanical properties and adaptations of skeletal muscles and tendons in response to trail running races of different distances using multi-site shear wave elastography assessments of the lower limb, force capacity and blood analyses. Sex differences in resting mechanical properties of knee extensor and plantar flexor muscles and tendons were characterized by shear wave velocity measurements in healthy males (N=42) and females (N=25) trained in long distance running. Effects of running distance on muscle and tendon properties were assessed in short (<60km, N=23) vs. long (>100km, N=26) distance races. Changes in isometric maximal voluntary contraction torque, serum C-reactive protein and creatine kinase activity were also quantified after running races. Higher shear wave velocity of relaxed triceps surae muscle was detected in females as compared to males before running races (+4.8%, p=0.006), but the significant increases in triceps surae muscle group (+7.0%, p=0.001) and patellar tendon shear wave velocity (+15.4%, p=0.001) after short-distance races were independent of sex. A significant decrease in triceps surae muscle shear wave velocity was found after long-distance races in the whole experimental population (-3.1%, p=0.049). Post-races increase in C-reactive protein and creatine kinase activity were significantly correlated to the relative decreases in triceps surae and quadriceps femoris skeletal muscle shear wave velocity (ρ=-0.56, p=0.001 and ρ=-0.51, p=0.001, respectively). Resting mechanical properties of muscles and tendons are affected by sex, and that adaptations to trail races are related to running distance. Exercise-induced changes in resting skeletal muscle mechanical properties are associated with enhanced indirect markers of inflammation and muscle damage.

Acute changes in passive stiffness of the individual hamstring muscles induced by resistance exercise: effects of contraction mode and range of motion

PURPOSE

Recent studies raise an interesting possibility that resistance exercise also decreases passive muscle stiffness, as does stretching exercise. However, little is known about how program variables of resistance exercise acutely influence muscle stiffness. We aimed to examine the acute changes in passive stiffness of the individual hamstring muscles after resistance exercises using different combinations of contraction modes and ranges of motion (ROMs).

METHODS

Thirteen healthy young male participants performed three sessions of resistance exercises that comprised stiff-leg deadlift with different contraction modes and exercise ROMs on separate days as follows: (1) eccentric contractions with a wide exercise ROM (EW); (2) eccentric contractions with a narrow exercise ROM (EN); and (3) concentric contractions with a wide exercise ROM (CW). Maximal joint ROM, passive torque, shear modulus of the individual hamstring muscles, and maximal isometric torque of knee flexion were measured before and 3 min, 30 min, and 60 min after completing each session.

RESULTS

The shear modulus of the semimembranosus was significantly lower at 3 min post-exercise (121.8 ± 16.0 kPa) than at pre-exercise (129.0 ± 18.9 kPa, p = 0.021, r = 0.45) in EW, but not in EN or CW. There were no significant changes in the shear moduli of the biceps femoris long head or the semitendinosus at any timepoint in any exercise protocols.

CONCLUSIONS

The present results suggest that the combination of eccentric contraction and wide ROM during resistance exercise has the potential to acutely decrease passive stiffness (shear modulus) of a specific muscle.

Reliability of Gradient-Echo Magnetic Resonance Elastography of Lumbar Muscles: Phantom and Clinical Studies

Magnetic resonance elastography (MRE) has been used to successfully characterize the mechanical behavior of healthy and diseased muscles, but no study has been performed to investigate the reliability of MRE on lumbar muscles. The objective of this work was to determine the reliability of MRE techniques on lumbar muscles in both ex vivo phantom and in vivo human studies. In this study, fresh porcine leg muscles were used in the phantom study, and 80 healthy adults (38.6 ± 11.2 years, 40 women) were recruited in the human study. Five repeated stiffness maps were obtained from both the phantom and human muscles by using a gradient-echo MRE sequence with a pneumatic vibration on a 1.5 T MR scanner. The technical failure rate, coefficient of variation (CV), and quality score were assessed to evaluate the reliability of MRE, respectively. Analysis of variance was performed to compare the stiffness between different lumbar muscles, and the difference was significant if p < 0.05 after Bonferroni correction. The results showed that the MRE achieved a zero technical failure rate and a low CV of stiffness (6.24 ± 1.41%) in the phantom muscles. However, in the human study, the MRE exhibited high CVs of stiffness (21.57%−25.24%) in the lumbar muscles, and the technical failure rate was higher in psoas muscles (60.0−66.3% in) than in paraspinal muscles (0.0−2.5%). Further, higher quality scores were noticed in paraspinal muscles (7.31−7.71) than those in psoas muscles (1.83−2.06). In conclusion, the MRE was a reliable technique to investigate the mechanical property of lumbar muscles, but it was less reliable to assess stiffness in psoas muscles than paraspinal muscles.

Relationship between Eccentric-Exercise-Induced Loss in Muscle Function to Muscle Soreness and Tissue Hardness

It is well-known that unusual exercise, especially eccentric contraction (ECC), could cause delayed-onset muscle soreness. However, the factors related to the loss of muscle strength and range of motion (ROM) caused by eccentrically damaged muscle, such as increases in muscle soreness, tissue hardness, and pain threshold, have not been investigated in detail. Thus, this study was conducted to investigate the factors related to the loss of muscle strength and ROM caused by eccentrically damaged muscle in a large sample. Fifty-six sedentary healthy young male volunteers were instructed to perform 60 repetitions of ECC exercise. The outcome variables were measured before and 48 h after the ECC exercise. The results showed that a decrease in ROM was correlated to an increase in tissue hardness, whereas a decrease in muscle strength was correlated to an increase in muscle soreness. Our results suggested that tissue hardness must be controlled for ROM loss, and muscle soreness must be controlled for muscle-strength loss.

Evaluation of Muscle Mass and Stiffness with Limb Ultrasound in COVID-19 Survivors

BACKGROUND

acute illnesses, like COVID-19, can act as a catabolic stimulus on muscles. So far, no study has evaluated muscle mass and quality through limb ultrasound in post-COVID-19 patients.

METHODS

cross sectional observational study, including patients seen one month after hospital discharge for SARS-CoV-2 pneumonia. The patients underwent a multidimensional evaluation. Moreover, we performed dominant medial gastrocnemius ultrasound (US) to characterize their muscle mass and quality.

RESULTS

two hundred fifty-nine individuals (median age 67, 59.8% males) were included in the study. COVID-19 survivors with reduced muscle strength had a lower muscle US thickness (1.6 versus 1.73 cm, p =0.02) and a higher muscle stiffness (87 versus 76.3, p = 0.004) compared to patients with normal muscle strength. Also, patients with reduced Short Physical Performance Battery (SPPB) scores had a lower muscle US thickness (1.3 versus 1.71 cm, p = 0.01) and a higher muscle stiffness (104.9 versus 81.07, p = 0.04) compared to individuals with normal SPPB scores. The finding of increased muscle stiffness was also confirmed in patients with a pathological value (≥ 4) at the sarcopenia screening tool SARC-F (103.0 versus 79.55, p < 0.001). Muscle stiffness emerged as a significant predictor of probable sarcopenia (adjusted OR 1.02, 95% C.I. 1.002 - 1.04, p = 0.03). The optimal ultrasound cut-offs for probable sarcopenia were 1.51 cm for muscle thickness (p= 0.017) and 73.95 for muscle stiffness (p = 0.004).

DISCUSSION

we described muscle ultrasound characteristics in post COVID-19 patients. Muscle ultrasound could be an innovative tool to assess muscle mass and quality in this population. Our preliminary findings need to be confirmed by future studies comparing muscle ultrasound with already validated techniques for measuring muscle mass and quality.

In vivo assessment of the passive stretching response of the bi-compartmental human semitendinosus muscle using shear wave elastography

The semitendinosus muscle contains distinct proximal and distal compartments arranged anatomically in-series but separated by a tendinous inscription, with each compartment innervated by separate nerve branches. Although extensively investigated in other mammals, compartment-specific mechanical properties within the human semitendinosus have scarcely been assessed in vivo. Experimental data obtained during muscle-tendon unit stretching (e.g., slack angle) can also be used to validate and/or improve musculoskeletal model estimates of semitendinosus muscle force. The purpose of this study was to investigate the passive stretching response of proximal and distal humans semitendinosus compartments to distal joint extension. Using two-dimensional shear wave elastography, we bilaterally obtained shear moduli of both semitendinosus compartments from 14 prone-positioned individuals at ten knee flexion angles (from 90° to 0° [full extension] at 10° intervals). Passive muscle mechanical characteristics (slack angle, slack shear modulus, and the slope of the increase in shear modulus) were determined for each semitendinosus compartment by fitting a piecewise exponential model to the shear modulus-joint angle curves. We found no differences between compartments or legs for slack angle, slack shear modulus, or the slope of the increase in shear modulus. We also found the experimentally determined slack angle occurred at ~15-80° higher knee flexion angles compared to estimates from two commonly used musculoskeletal models, depending on participant and model used. Overall, these findings demonstrate that passive shear modulus-joint angle curves do not differ between proximal and distal human semitendinosus compartments, and provide experimental data to improve semitendinosus force estimates derived from musculoskeletal models.

Sarcopenia Diagnosis: Reliability of the Ultrasound Assessment of the Tibialis Anterior Muscle as an Alternative Evaluation Tool

Sarcopenia is a skeletal muscle disorder characterized by reduced muscle mass, strength, and performance. Muscle ultrasound can be helpful in assessing muscle mass, quality, and architecture, and thus possibly useful for diagnosing or screening sarcopenia. The objective of this study was to evaluate the reliability of ultrasound assessment of tibialis anterior muscle in sarcopenia diagnosis. We included subjects undergoing total or partial hip replacement, comparing measures with a healthy control group. We measured the following parameters: tibialis anterior muscle thickness, echogenicity, architecture, stiffness, skeletal muscle index (SMI), hand grip strength, and sarcopenia related quality of life evaluated through the SarQoL questionnaire. We included 33 participants with a mean age of 54.97 ± 23.91 years. In the study group we found reduced tibialis anterior muscle thickness compared to the healthy control group (19.49 ± 4.92 vs. 28.94 ± 3.63 mm, p < 0.05) with significant correlation with SarQoL values (r = 0.80, p < 0.05), dynamometer hand strength (r = 0.72, p < 0.05) and SMI (r = 0.76, p < 0.05). Moreover, we found reduced stiffness (32.21 ± 12.31 vs. 27.07 ± 8.04 Kpa, p < 0.05). AUC measures of ROC curves were 0.89 predicting reduced muscle strength, and 0.97 predicting reduced SMI for tibialis anterior muscle thickness, while they were 0.73 and 0.85, respectively, for muscle stiffness. Our findings showed that ultrasound assessment of tibialis anterior muscle might be considered a reliable measurement tool to evaluate sarcopenia.

Effects of Intermittent and Continuous Static Stretching on Range of Motion and Musculotendinous Viscoelastic Properties Based on a Duration-Matched Protocol

The different effects of intermittent and continuous stretching on the mechanical properties of the musculotendinous complex have been unclear. This study aimed to compare the effects of intermittent and continuous stretching for the same duration on the range of motion (ROM), passive resistive torque (PRT), and musculotendinous stiffness (MTS) of ankle plantar flexors. Eighteen healthy young men participated in the study. Intermittent (four sets × 30 s) and continuous stretching (one set × 120 s) were performed in random orders on two separate days. Both stretching protocols were conducted using a dynamometer with a constant torque applied. ROM and PRT were determined using a dynamometer, and MTS was calculated using the torque-angle relationship measured before and after stretching. Two-way repeated measures analysis of variance was performed for all parameters. Both intermittent and continuous stretching significantly increased ROM and decreased PRT and MTS (p < 0.05). Intermittent stretching led to greater changes in ROM and PRT than continuous stretching. However, the reduction in MTS did not differ between the two conditions. These results suggest that intermittent stretching is more effective in increasing ROM and changing the mechanical properties of the musculotendinous complex.

Effects of Self-Myofascial Release Using a Foam Roller on the Stiffness of the Gastrocnemius-Achilles Tendon Complex and Ankle Dorsiflexion Range of Motion

Increased muscle stiffness can contribute to reduced range of motion (ROM) and impaired function. Reduced ankle dorsiflexion ROM has been associated with increased injury risk in the ankle. Self-myofascial release (SMR) has been widely used in clinical and sports settings, but the effects of SMR on gastrocnemius and Achilles tendon (AT) stiffness are unclear. Therefore, we investigated the effects of self-myofascial release using a foam roller (FR) on the stiffness of the gastrocnemius–AT complex and ankle dorsiflexion ROM. Fifty healthy, untrained, and non-sedentary participants (age=22.5±2.6years) were randomly divided into an intervention group (FR group) and a control group. The subjects in the intervention group received a single foam roller intervention (three sets of 1min), while the subjects in the control group performed a 5-min sedentary rest. Stiffness of the gastrocnemius–AT complex was evaluated using MyotonPRO and the ankle dorsiflexion ROM was assessed using the weight-bearing lunge test. For the foam roller and control groups, the between-group analysis revealed a statistically significant difference in gastrocnemius stiffness and ankle dorsiflexion ROM after intervention (p<0.05). Within-group analysis revealed a significant increase in ROM and a significant decrease in medial and lateral gastrocnemius (LG) stiffness for the foam roller group after the intervention (p<0.05). In addition, further analysis of the preintervention data revealed a significant negative correlation between ankle dorsiflexion ROM and AT stiffness (r=−0.378 and p=0.007). These results suggest that self-myofascial release using a foam roller on the calf is an effective method for decreasing the stiffness of the gastrocnemius and increasing ankle dorsiflexion ROM.

Female Athletes Genetically Susceptible to Fatigue Fracture Are Resistant to Muscle Injury: Potential Role of COL1A1 Variant

PURPOSE

We aimed to investigate the hypothesis that type I collagen plays a role in increasing bone mineral density (BMD) and muscle stiffness, leading to low and high risks of fatigue fracture and muscle injury, respectively, in athletes. As a potential mechanism, we focused on the effect of the type I collagen alpha 1 chain gene (COL1A1) variant associated with transcriptional activity on bone and skeletal muscle properties.

METHODS

The association between COL1A1 rs1107946 and fatigue fracture/muscle injury was evaluated in Japanese athletes. Effects of the polymorphism on tissue properties (BMD and muscle stiffness) and type I collagen α1/α2 chain ratios in muscles were examined in Japanese nonathletes.

RESULTS

The C-allele carrier frequency was greater in female athletes with fatigue fracture than in those without (odds ratio = 2.44, 95% confidence interval [CI] = 1.17-5.77) and lower in female athletes with muscle injury than in those without (odds ratio = 0.46, 95% CI = 0.24-0.91). Prospective validation analysis confirmed that in female athletes, muscle injury was less frequent in C-allele carriers than in AA genotype carriers (multivariable-adjusted hazard ratio = 0.27, 95% CI = 0.08-0.96). Among female nonathletes, the C-allele of rs1107946 was associated with lower BMD and lower muscle stiffness. Muscle biopsy revealed that C-allele carriers tended to have a larger type I collagen α1/α2 chain ratio than AA genotype carriers (2.24 vs 2.05, P = 0.056), suggesting a higher proportion of type I collagen α1 homotrimers.

CONCLUSION

The COL1A1 rs1107946 polymorphism exerts antagonistic effects on fatigue fracture and muscle injury among female athletes by altering the properties of these tissues, potentially owing to increased levels of type I collagen α1 chain homotrimers.

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.

Characteristics of the Passive Muscle Stiffness of the Vastus Lateralis: A Feasibility Study to Assess Muscle Fibrosis

Skeletal muscle fibrosis occurs with aging and has been suggested to impair muscle performance, thereby decreasing quality of life. Recently, muscle stiffness, a surrogate measure of muscle fibrosis, was noninvasively quantified as the shear modulus using ultrasound shear wave elastography (SWE) in humans. We aimed to investigate thigh muscle stiffness in females and males, respectively, across a broad range of ages by using SWE. Eighty-six community-dwelling Japanese people who were aged 30 to 79 years and did not regularly exercise participated in this study. The vastus lateralis (VL) shear modulus was measured at three different knee joint angles: full extension, 90° of flexion, and full flexion. There were no significant main effects of sex or age on the VL shear modulus in full extension or 90° of flexion of the knee. However, the VL shear modulus in knee full flexion was significantly smaller in females than in males and increased with age from 47.9 years. The results suggest that the accelerated increase in VL stiffness that occurs after an individual passes their late 40s may be an important therapeutic target for developing effective treatments and programs that preserve and improve quality of life.

Relationship between resting medial gastrocnemius stiffness and drop jump performance

Although the influence of the series elastic element of the muscle-tendon unit on jump performance has been investigated, the corresponding effect of the parallel elastic element remains unclear. This study examined the relationship between the resting calf muscle stiffness and drop jump performance. Twenty-four healthy men participated in this study. The shear moduli of the medial gastrocnemius and the soleus were measured at rest as an index of muscle stiffness using ultrasound shear wave elastography. The participants performed drop jumps from a 15 cm high box. The Spearman rank correlation coefficient was used to examine the relationships between shear moduli of the muscles and drop jump performance. The medial gastrocnemius shear modulus showed a significant correlation with the drop jump index (jump height/contact time) (r = 0.414, P = 0.044) and jump height (r = 0.411, P = 0.046), but not with contact time (P > 0.05). The soleus shear modulus did not correlate with these jump parameters (P > 0.05). These results suggest that the resting medial gastrocnemius stiffness can be considered as one of the factors that influence drop jump performance. Therefore, increase in resting muscle stiffness should enhance explosive athletic performance in training regimens.

Association between the Range of Motion and Passive Property of the Gastrocnemius Muscle-Tendon Unit in Older Population

Range of motion has been widely known to decrease with age; however, factors associated with its decrease in the elderly population and especially its gender difference have been unclear. Therefore, this study aimed to investigate the factors associated with ankle dorsiflexion range of motion in the older population. Both male (n = 17, mean ± SD; 70.5 ± 4.2 years; 165.4 ± 5.3 cm; 63.8 ± 7.7 kg) and female (n = 25, 74.0 ± 4.0 years; 151.2 ± 4.9 cm; 50.1 ± 5.6 kg) community-dwelling older adults participated in this study. The ankle dorsiflexion and passive torque of both legs were measured using a dynamometer, and shear elastic modulus of the medial gastrocnemius muscle at 0° ankle angle was measured using ultrasonic shear wave elastography. In this study, we defined the passive torque at dorsiflexion range of motion (DF ROM) as the index of stretch tolerance, and shear elastic modulus as the index of passive muscle stiffness. The partial correlation coefficient adjusted by age, height, weight, and side (dominant or nondominant side) was used to analyze the relationship between DF ROM and passive torque at DF ROM or shear elastic modulus of MG in each male and female participant, respectively. Our results revealed that dorsiflexion range of motion was significantly associated with passive torque at dorsiflexion range of motion in both male (r = 0.455, p = 0.012) and female (r = 0.486, p < 0.01), but not with shear elastic modulus in both male (r = -0.123, p = 0.519) and female (r = 0.019, p = 0.898). Our results suggested that the ankle dorsiflexion range of motion could be related to the stretch tolerance, but not to passive muscle stiffness in community-dwelling elderly population regardless of gender.

Associations between Range of Motion and Tissue Stiffness in Young and Older People

Supplemental digital content is available in the text.

Purpose

The purpose of this study was to investigate differences in the associations between passive ankle dorsiflexion range of motion (ROM) and stiffness of the triceps surae, sciatic nerve, and deep fascia located in the posterior leg between young and older people.

Methods

Twenty young and twenty older males were recruited and were placed in a prone position with their hip and knee fully extended. Passive ankle dorsiflexion ROM was determined based on the onset of pain during passive dorsiflexion at 1°·s⁻¹ using an isokinetic dynamometer. Shear wave speeds (as a stiffness index) of the triceps surae, the sciatic nerve, and the deep fascia in the posterior leg were evaluated by ultrasound shear wave elastography.

Results

The shear wave speeds of the medial and lateral gastrocnemius measured at 15° dorsiflexion correlated negatively with passive ROM in young but not in older participants. The shear wave speed of the sciatic nerve measured at 15° dorsiflexion correlated negatively with passive ROM only in older participants. No association was observed between passive ROM and shear wave speed of the deep fascia in the posterior leg. For data measured at maximal dorsiflexion angle (as an index of stretch tolerance), shear wave speeds of the triceps surae and passive joint torque correlated positively with passive ROM in both groups.

Conclusion

These results suggest that the tissues limiting passive ankle dorsiflexion ROM are muscle and nerve for young and older people, respectively, whereas stretch tolerance influences passive ROM for both groups. This implies that the relative contribution of nonmuscular tissues to joint flexibility become stronger than that of muscles with age.

Association between medial gastrocnemius muscle-tendon unit architecture and ankle dorsiflexion range of motion with and without consideration of slack angle

Joint flexibility is theoretically considered to associate with muscle-tendon unit (MTU) architecture. However, this potential association has not been experimentally demonstrated in humans in vivo. We aimed to identify whether and how MTU architectural parameters are associated with joint range of motion (RoM), with a special emphasis on slack angle. The fascicle length, pennation angle, tendinous tissue length, MTU length, and shear modulus of the medial gastrocnemius (MG) were assessed during passive ankle dorsiflexion using ultrasound shear wave elastography in 17 healthy males. During passive dorsiflexion task, the ankle joint was rotated from 40° plantar flexion to the maximal dorsiflexion joint angle at which each subject started experiencing pain. From the ankle joint angle-shear modulus relationship, the angle at which shear modulus began to rise (slack angle) was calculated. Two dorsiflexion RoMs were determined as follows; 1) range from the anatomical position to maximal angle (RoM_anat-max) and 2) range from the MG slack angle to maximal angle (RoM_slack-max). The MTU architectural parameters were analyzed at the anatomical position and MG slack angle. The resolved fascicle length (fascicle length × cosine of pennation angle) and ratios of resolved fascicle or tendinous tissue length to MTU length measured at the MG slack angle significantly correlated with the RoM_slack-max (r = 0.491, 0.506, and -0.506, respectively). Any MTU architectural parameters assessed at the anatomical position did not correlate with RoM_anat-max or RoM_slack-max. These results indicate that MTUs with long fascicle and short tendinous tissue are advantageous for joint flexibility. However, this association cannot be found unless MTU architecture and joint RoM are assessed with consideration of muscle slack.

HAMSTRING MUSCLE ARCHITECTURE AND VISCOELASTIC PROPERTIES: RELIABILITY AND RETROSPECTIVE COMPARISON BETWEEN PREVIOUSLY INJURED AND UNINJURED ATHLETES

The architecture of the biceps femoris (BF) and stiffness of the hamstrings have been found to be associated with injury risk. However, less is known about the architecture of the equally voluminous semitendinosus (ST) and viscoelastic properties of both muscles in individuals with a prior injury. Methods: BF and ST of 15 athletes (previously injured, [Formula: see text]; control, [Formula: see text]) were assessed using ultrasonography and myotonometry. Mean architecture (muscle thickness (MT), pennation angle (PA) and fascicle length (FL)) and viscoelastic measures (stiffness, oscillation frequency and decrement) were compared between the previously injured and contralateral uninjured limb, and between the previously injured and control limbs (mean of both limbs of the control group). Control group participants returned for a duplicate measurement. Findings: Both muscles exhibited high reliability between sessions (intraclass correlation coefficient [Formula: see text]) for architecture. BF PA was larger in the previously injured than both uninjured [Formula: see text] and control [Formula: see text]. BF fascicles were shorter in the previously injured limb compared to the uninjured [Formula: see text] and control [Formula: see text]. BF was stiffer in the previously injured compared to uninjured [Formula: see text]. ST architecture and viscoelasticity were similar across limbs. Conclusion: A prior hamstring strain injury is associated with a stiffer BF characterized by larger PAs and shorter fascicles.

Greater Muscle Stiffness during Contraction at Menstruation as Measured by Shear-Wave Elastography

It is important to measure mechanical properties of muscle, since muscle stiffness is an important component of stabilizing or controlling joint stability. The levels of sex hormones especially estrogen vary over the phase of the menstrual cycle and impact the mechanical properties of soft tissue such as muscle, tendon, and ligaments due to the presence of 17-β estradiol receptor in human connective tissues. Recently, shear-wave elastography (SWE), based on ultrasound imaging, has been used as an accurate technique for visualizing and assessing tissue stiffness. The purpose of this study was to compare the muscle stiffness at rest and during contraction condition between the early follicular phase (menstruation) and ovulation in young women, measured using SWE. Thirty-seven young women with regular menstrual cycles completed this study throughout one full menstrual cycle. Stiffness of lower limb muscles such as the rectus femoris, biceps femoris, tibialis anterior, and medial gastrocnemius was measured at resting and during contraction conditions using SWE during menstruation and ovulation. All muscles showed significantly greater stiffness during the menstruation than ovulation when muscles were actively contracted (P < 0.05), whereas no significant differences in muscle stiffness at rest were noted across phase of the menstrual cycle. These significant findings suggest that muscular factors are changed with estradiol fluctuations; muscles are less stiff during ovulation where the levels of estradiol peak when muscles in a contraction condition. As muscle stiffness is an important part of joint stability, these differences should be recognized to prevent the risk of musculoskeletal injuries.

Normative Parameters of Gastrocnemius Muscle Stiffness and Associations with Patient Characteristics and Function

BACKGROUND

Quantifying muscle stiffness may aid in the diagnosis and management of individuals with muscle pathology. Therefore, the primary purpose of this study was to establish normative parameters and variance estimates of muscle stiffness in the gastrocnemius muscle in a resting and contracted state. A secondary aim was to identify demographic, anthropometric, medical history factors, and biomechanical factors related to muscle stiffness.

METHODS

Stiffness of the gastrocnemius muscle was measured in both a resting and contracted state in 102 asymptomatic individuals in this cross-sectional study. Differences based on muscle state (resting vs contracted) and sex (female vs male) were assessed using a 2 X 2 analysis of variance (ANOVA). Associations between muscle stiffness and sex, age, BMI, race, exercise frequency, exercise duration, force production, and step length were assessed using correlation analysis.

RESULTS

Gastrocnemius muscle stiffness significantly increased from a resting to a contracted state [mean difference: 217.5 (95% CI: 191.3, 243.8), p < 0.001]. In addition, muscles stiffness was 35% greater for males than females in a resting state and 76% greater in a contracted state. Greater muscle stiffness in a relaxed and contracted state was associated with larger plantarflexion force production (r = .26, p < 0.01 and r = .23, p < 0.01 respectively).

CONCLUSION

Identifying normative parameters and variance estimates of muscle stiffness in asymptomatic individuals may help guide diagnosing and managing individuals with aberrant muscle function.

LEVEL OF EVIDENCE

2b Individual Cohort Study.

CLINICAL RELEVANCE

What is known about the subject: Muscle stiffness has been shown to be related to individuals with pathology such as Achilles tendinopathy; however, research is sparse regarding normative values of muscle stiffness. Measuring muscle stiffness may also be a way to potentially predict individuals prone to injury or to monitor the effectiveness of management strategies.What this study adds to existing knowledge: This study establishes defined estimates of muscle stiffness of the gastrocnemius in both a relaxed and contracted state in healthy individuals. Myotonometry measures of muscle stiffness demonstrated an increase in stiffness during contraction that varies by sex. Greater gastrocnemius muscle stiffness was associated with increased plantarflexion force production.

Passive stiffness of fibrotic skeletal muscle in mdx mice relates to collagen architecture

KEY POINTS

The amount of fibrotic material in dystrophic mouse muscles relates to contractile function, but not passive function. Collagen fibres in skeletal muscle are associated with increased passive muscle stiffness in fibrotic muscles. The alignment of collagen is independently associated with passive stiffness in dystrophic skeletal muscles. These outcomes demonstrate that collagen architecture rather than collagen content should be a target of anti-fibrotic therapies to treat muscle stiffness.

ABSTRACT

Fibrosis is prominent in many skeletal muscle pathologies including dystrophies, neurological disorders, cachexia, chronic kidney disease, sarcopenia and metabolic disorders. Fibrosis in muscle is associated with decreased contractile forces and increased passive stiffness that limits joint mobility leading to contractures. However, the assumption that more fibrotic material is directly related to decreased function has not held true. Here we utilize novel measurement of extracellular matrix (ECM) and collagen architecture to relate ECM form to muscle function. We used mdx mice, a model for Duchenne muscular dystrophy that becomes fibrotic, and wildtype mice. In this model, extensor digitorum longus (EDL) muscle was significantly stiffer, but with similar total collagen, while the soleus muscle did not change stiffness, but increased collagen. The stiffness of the EDL was associated with increased collagen crosslinking as determined by collagen solubility. Measurement of ECM alignment using polarized light microscopy showed a robust relationship between stiffness and alignment for wildtype muscle that broke down in mdx muscles. Direct visualization of large collagen fibres with second harmonic generation imaging revealed their relative abundance in stiff muscles. Collagen fibre alignment was linked to stiffness across all muscles investigated and the most significant factor in a multiple linear regression-based model of muscle stiffness from ECM parameters. This work establishes novel characteristics of skeletal muscle ECM architecture and provides evidence for a mechanical function of collagen fibres in muscle. This finding suggests that anti-fibrotic strategies to enhance muscle function and excessive stiffness should target large collagen fibres and their alignment rather than total collagen.

Association between plantar flexor muscle volume and dorsiflexion flexibility in healthy young males: ultrasonography and magnetic resonance imaging studies

Background

Although joint flexibility is important for human locomotion, the determinants of joint flexibility are not fully understood. In this study, we examined the relationship between dorsiflexion flexibility and plantar flexor muscle size in healthy young males.

Methods and results

The dorsiflexion flexibility was assessed using range of motion (ROM) and stiffness during active and passive dorsiflexion. Active ROM was defined as the maximal angle during voluntary dorsiflexion. Passive ROM was defined as the angle at the onset of pain during passive dorsiflexion. Passive stiffness was calculated as the slope of the linear portion of the torque-angle curve between 10º and 20º dorsiflexion of the ankle during passive dorsiflexion. In the first study, the plantar flexor muscle volume (MV) in 92 subjects was estimated on the basis of the lower leg length and plantar flexor muscle thickness, as measured using ultrasonography. The estimated plantar flexor MV correlated significantly with active ROM (r = -0.433), passive ROM (r = -0.299), and passive stiffness (r = 0.541) during dorsiflexion (P = 0.01 for all). In the second study, the plantar flexor MV in 38 subjects was measured using magnetic resonance imaging. The plantar flexor MV correlated significantly with plantar flexor active ROM (r = -0.484), passive ROM (r = -0.383), and passive stiffness (r = 0.592) during dorsiflexion (P = 0.05 for all).

Conclusions

These findings suggest that a larger plantar flexor MV is related to less dorsiflexion flexibility in healthy young males.

Acute effects of dynamic stretching on neuromechanical properties: an interaction between stretching, contraction, and movement

PURPOSE

The present study aimed to investigate the acute effects of dynamic stretching on neurophysiological and mechanical properties of plantar flexor muscles and to test the hypothesis that dynamic stretching resulted from an interaction between stretching, movement, and contraction.

METHODS

The dynamic stretching conditioning activity (DS) was compared to static stretching (SS), passive cyclic stretching (PCS), isometric contractions (IC), static stretching followed by isometric contractions (SSIC), and control (CO) conditions. Stretching amplitude (DS, SS, PCS and SSIC), contraction intensity (DS, IC and SSIC) and duration (all 6 conditions) were matched. Thirteen volunteers were included. Passive torque, fascicle length, and stiffness were evaluated from a dynamometer and ultrasonography during passive dorsiflexion. Neuromuscular electrical stimulation was used to investigate contractile properties [peak twitch torque (PTT), and rate of torque development (RTD)] and muscle voluntary activation (%VA). Gastrocnemius lateralis electromyographic activity (GL EMG/Mwave) was obtained during maximal voluntary contraction. All of these parameters were measured immediately before and 10 s after each experimental condition.

RESULTS

Peak twitch torque, RTD, %VA, GL EMG/Mwave remained unaltered, while passive torque was significantly reduced after DS (- 8.14 ± 2.21%). SS decreased GL EMG/Mwave (- 7.83 ± 12.01%) and passive torque (- 2.16 ± 7.25%). PCS decreased PTT (- 3.40 ± 6.03%), RTD (- 2.96 ± 5.16%), and passive torque (- 2.16 ± 2.05%). IC decreased passive torque (- 7.72 ± 1.97%) and enhanced PTT (+ 5.77 ± 5.19%) and RTD (+ 7.36 ± 8.35%). However, SSIC attenuated PTT and RTD improvements as compared to IC.

CONCLUSION

These results suggested that dynamic stretching is multi-component and would result from an interaction between stretching, contraction, and movement.

Interrater and Intrarater Reliability of a Handheld Myotonometer in Measuring Mechanical Properties of the Neck and Orofacial Muscles

OBJECTIVE

The purpose this study was to investigate the reliability of a handheld myotonometer in measuring the mechanical properties of the neck and orofacial muscles in asymptomatic individuals.

METHODS

The study included 16 healthy participants. The mechanical properties (frequency, decrement, stiffness, relaxation time, and creep) of the selected muscles were measured with a MyotonPRO myotonometer (Mumeetria Ltd, Tallinn, Estonia). The sternocleidomastoid, upper trapezius, cervical extensor, and masseter muscles were selected to determine the reliability of the device. Measurements were performed by 2 examiners to determine interrater reliability; for intrarater reliability, an examiner repeated the measurements 1 week after the first measurements.

RESULTS

The results revealed moderate to excellent intrarater and interrater reliability (intraclass correlation coefficients: 0.50-0.95) in measuring muscle mechanic properties. The standard error of measurement in the tested muscles ranged from 0.3 to 0.8 Hz for frequency, from 7.4 to 20.9 N/m for stiffness, from 0.1 to 0.2 for decrement, and from 0.8 to 1.4 ms for relaxation time. The minimum detectable change ranged from 0.8 to 2.2 Hz for frequency, from 20.5 to 57.9 N/m for stiffness, from 0.2 to 0.6 for decrement, from 2.2 to 3.9 ms for relaxation time, and from 0.2 to 0.3 for creep. In addition, the coefficients of variation were below 9.1% for all the assessed parameters.

CONCLUSION

The obtained results demonstrate that the MyotonPRO device is a reliable and repeatable tool to quantify the frequency, stiffness, decrement, relation time, and creep of the neck and orofacial muscles in asymptomatic individuals.

Effect of hip flexion angle on stiffness of the adductor longus muscle during isometric hip flexion

This study examined the effect of hip flexion angle on the stiffness of the adductor longus (AL) muscle during isometric hip flexion. Seventeen men were recruited. Ten participants performed submaximal voluntary contraction at 0%, 25%, 50%, and 75% of maximal voluntary contraction (MVC) during isometric hip flexion after performing MVC at 0°, 40°, and 80° of hip flexion. Seven participants performed submaximal voluntary tasks during isometric hip extension in addition to hip flexion task. The shear modulus of the AL muscle was used as the index of muscle stiffness, and was measured using ultrasound shear-wave elastography during the tasks at each contraction intensity for each hip flexion angle. During hip flexion, the shear modulus of the AL muscle was higher at 0° than at 40° and 80° of hip flexion at each contraction intensity (p < 0.016). Conversely, a significant effect was not found among hip flexion angle during hip extension at 75% of MVC (p = 0.867). These results suggest that mechanical stress of the AL muscle may be higher at 0° of hip flexion during isometric hip flexion.

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.