Muscle Mechanical Properties Research Articles

Acute effects of muscle mechanical properties after 2000-m rowing in young male rowers.

The mechanical properties of muscles, such as changes in muscle tone and stiffness, are related to sports performance and injuries. Rowers are at increased risk of muscle fatigue and injury during high-repetition and heavy-load cyclic muscle actions. In view of this, the aim of the present study was to investigate the acute effect on muscle tone and stiffness, as well as bilateral muscle asymmetry, in high school rowers after a 2000-meter rowing ergometer test. Twelve young male rowers (age = 17.1 ± 0.9 years, body weight = 73.5 ± 9.7 kg) were included in the study. The data of muscle tone (frequency) and stiffness of the posterior deltoids (PD), latissimus dorsi (LD), and rectus femoris (RF) (dominant and non-dominant side) before and after a 2000-m rowing ergometer test were collected using a handheld MyotonPRO device. After the rowing ergometer test, the muscle tone of dominant side PD, LD, and RF were significantly increased (p < 0.05). On the other hand, the muscle stiffness of the non-dominant side LD and RF, as well as the dominant side PD, LD, and RF were significantly increased after the rowing ergometer test (p < 0.05). The muscle tone and stiffness results showed that the dominant side PD, LD, and RF were all significantly higher than the non-dominant side after the rowing ergometer test (p < 0.05), where bilateral PD and RF exhibits moderate asymmetry (5% < symmetry index < 10%). After a high-intensity and high-load 2000-m rowing ergometer test, PD, LD, and RF showed increases in muscle tone and stiffness, as well as changes in the symmetry of bilateral muscle mechanical properties.

Akıllı Telefon Bağımlılığına Bağlı Boyun Ağrısında Kı̇nesyolojik Bandın Ağrı ve Trapez Kasının Mekanı̇k Özellı̇klerı̇ Üzerı̇ne Akut Etkı̇sı̇

This study aimed to assess the short-term effects of inhibitory kinesiologic tape (KT) and sham tape on neck pain and muscle tone in individuals with smartphone addiction. Forty-two healthy participants were randomized to receive either KT or sham tape application to their upper trapezius muscle (UTM). Smartphone addiction was assessed using the Smartphone Addiction Scale (SAS), and pain severity was measured using the Visual Analogue Scale (VAS). Muscle tone and stiffness were evaluated using a myotonometer. No significant differences were found in pain or muscle mechanical properties between the groups after treatment. However, KT recipients had significantly higher tone and stiffness in their left trapezius muscle compared to their right trapezius muscle (p &lt; 0.05). Additionally, right trapezius stiffness was significantly higher in participants with SAS scores of 100 points or more compared to those with SAS scores below 100 points (p &lt; 0.05). Finally, left trapezius elasticity increased significantly in participants with SAS scores of 100 points or more (p &lt; 0.05). Overall, the study findings suggest that short-term application of KT to the UTM may reduce neck pain in individuals with smartphone addiction.

Evaluation of the Reproducibility of MR Elastography Measurements of the Lumbar Back Muscles.

MR elastography (MRE) may provide quantitative imaging biomarkers of lumbar back muscles (LBMs), complementing MRI in spinal diseases by assessing muscle mechanical properties. However, reproducibility analyses for MRE of LBM are lacking. To assess technical failure, within-day and inter-day reproducibility, robustness with the excitation source positioning, and inter-observer agreement of MRE of muscles. Prospective. Seventeen healthy subjects (mean age 28 ± 4 years; 11 females). 1.5 T, gradient-echo MRE, T1-weighted turbo spin echo. The pneumatic driver was centered at L3 level. Four MRE were performed during two visits, 2-4 weeks apart, each consisting of two MRE with less than 10 minutes inter-scan interval. At Visit 1, after the first MRE, the coil and driver were removed, then reinstalled. The MRE was repeated. At Visit 2, following the first MRE, only the driver was moved down 5 cm. The MRE was repeated. Two radiologists segmented the multifidus and erector spinae muscles. Paired t-test, analysis of variance, intraclass correlation coefficients (ICCs). P-values <0.05 were considered statistically significant. Mean stiffness of LBM ranged from 1.44 to 1.60 kPa. Mean technical failure rate was 2.5%. Inter-observer agreement was excellent (ICC ranging from 0.82 [0.64-0.96] to 0.99 [0.98-0.99] in the multifidus, and from 0.85 [0.69-0.92] to 0.99 [0.97-0.99] in the erector spinae muscles). Within-day reproducibility was fair in the multifidus (ICC: 0.53 [0.47-0.77]) and good in the erector spinae muscles (ICC: 0.74 [0.48-0.88]). Reproducibility after moving the driver was excellent in both multifidus (ICC: 0.85 [0.69-0.93]) and erector spinae muscles (ICC: 0.84 [0.67-0.92]). Inter-day reproducibility was excellent in the multifidus (ICC: 0.76 [0.48-0.89]) and poor in the erector spinae muscles (ICC: 0.23 [-0.61 to 0.63]). MRE of LBM provides measurements of stiffness with fair to excellent reproducibility and excellent inter-observer agreement. However, inter-day reproducibility in the multifidus muscles indicated that the herein used MRE protocol may not be optimal for this muscle. 2 TECHNICAL EFFICACY: Stage 1.

Between-sexes differences in lumbopelvic muscle mechanical properties of non-climacteric adults: a cross-sectional design

The lumbopelvic muscle mechanical properties (MMPs) are clinically relevant, but their dependence on sex remains unknown. Therefore, this study aimed to identify if lumbopelvic MMPs depend on the sex in a young adult population. Thirty-five healthy nulliparous women and 35 healthy men were analyzed (age range: 18–50). Lumbopelvic MMPs, that is, tone, stiffness, elasticity, relaxation and creep, assessed with MyotonPRO®, and pelvic floor (PF) health questionnaires were compared between-sexes. Intra-group correlations between sociodemographic and clinical data, and MMPs were also determined. The MMPs of PF were different between healthy non-climacteric adults of both sexes, with women showing higher values of tone and stiffness and lower values of elasticity and viscoelastic properties than men (in all cases, p < 0.03). At lumbar level, tone and stiffness were higher for men at both sides (in all cases, p < 0.04), and relaxation was lower at left side (p = 0.02). The MMPs showed few correlations with sociodemographic data within women. However, within males, there were positive correlations for PF stiffness and viscoelastic parameters with age, BMI and function (0.334 < r < 0.591) and, at lumbar level, negative correlations for tone and stiffness ( − 0.385 < r < −0.590) and positive correlations for viscoelastic properties (0.564 < r < 0.719), with BMI. This indicated that between-sexes differences of lumbopelvic MMPs depend on the specific location of assessment in healthy non-obese young individuals. Women show higher tone and stiffness and lower elasticity and viscoelasticity than men, at PF level.

Acute and Chronic Effects of Static Stretching on Neuromuscular Properties: A Meta-Analytical Review

The aim of this review was to provide an overview of the recent findings on the acute and chronic effects of static stretching on joint behaviors and neuromuscular responses and to discuss the overall effects of acute and chronic static stretching on selected outcomes via meta-analyses, using a total of 50 recent studies. The results of our meta-analyses demonstrated that acute static stretching results in increased range of motion (ROM), decreased passive resistive torque (PRT), increased maximum tolerable PRT (PRTmax), decreased maximum voluntary isometric torque, decreased muscle–tendon unit stiffness, decreased muscle stiffness, decreased tendon stiffness, and decreased shear elastic modulus. Moreover, the chronic effects of static stretching included increased ROM, increased PRTmax, decreased muscle stiffness, and decreased shear elastic modulus (or shear wave speed). These results suggest that static stretching interventions have the potential to increase ROM and reduce the mechanical properties of muscle–tendon tissue, but they may not change corticospinal excitability and spinal reflex excitability or muscle architecture parameters.

Effects of Online Pilates and Face-to-Face Pilates Intervention on Body Composition, Muscle Mechanical Properties, Cardiometabolic Parameters, Mental Health, and Physical Fitness in Middle-Aged Women with Obesity.

With the emergence of coronavirus disease 2019, individuals have been participating in online exercises to maintain their health while avoiding infection. Among these online exercises, Pilates intervention is a popular modality. This study aimed to examine the differences between online and face-to-face Pilates interventions in terms of various physiological parameters and included 30 middle-aged individuals (age 43.3 ± 5.5 years) with obesity. These individuals were randomly divided into a face-to-face Pilates group (FPG), an online Pilates group (OPG), and a control group (CG). The FPG and OPG performed a 60-min mat Pilates program with a Borg scale of 11-17, three times a week for 12 weeks. The participants in the CG maintained their daily routines. Body composition, mechanical muscle properties, cardiometabolic parameters, mental health, and physical fitness were assessed before and after 12 weeks of intervention. No significant differences in body composition or cardiometabolic parameters were observed between groups. However, the FPG and OPG showed greater improvements than the CG in terms of muscle mechanical properties, cardiometabolic parameters, mental health, and physical fitness. In addition, the FPG showed greater improvement than the OPG. In conclusion, face-to-face Pilates is a more effective modality than online Pilates, although both modalities improve health-related parameters.

Skeletal Muscle Compliance and Echogenicity in Resistance-Trained and Nontrained Women.

Mongold, SJ, Ricci, AW, Hahn, ME, and Callahan, DM. Skeletal muscle compliance and echogenicity in resistance-trained and nontrained women. J Strength Cond Res 38(4): 671-680, 2024-Noninvasive assessment of muscle mechanical properties in clinical and performance settings tends to rely on manual palpation and emphasizes examination of musculotendinous stiffness. However, measurement standards are highly subjective. The purpose of the study was to compare musculotendinous stiffness in adult women with varying resistance training history while exploring the use of multiple tissue compliance measures. We identified relationships between tissue stiffness and morphology, and tested the hypothesis that combining objective measures of morphology and stiffness would better predict indices of contractile performance. Resistance-trained (RT) women (n = 11) and nontrained (NT) women (n = 10) participated in the study. Muscle echogenicity and morphology were measured using B-mode ultrasonography (US). Vastus lateralis (VL) and patellar tendon (PT) stiffness were measured using digital palpation and US across submaximal isometric contractions. Muscle function was evaluated during maximal voluntary isometric contraction (MVIC) of the knee extensors (KEs). Resistance trained had significantly greater PT stiffness and reduced echogenicity (p < 0.01). Resistance trained also had greater strength per body mass (p < 0.05). Muscle echogenicity was strongly associated with strength and rate of torque development (RTD). Patellar tendon passive stiffness was associated with RTD normalized to MVIC (RTDrel; r = 0.44, p < 0.05). Patellar tendon stiffness was greater in RT young women. No predictive models of muscle function incorporated both stiffness and echogenicity. Because RTDrel is a clinically relevant measure of rehabilitation in athletes and can be predicted by digital palpation, this might represent a practical and objective measure in settings where RTD may not be easy to measure directly.

Hamstring stiffness and injury risk factors during the handball season in female players.

Monitoring the muscle mechanical properties and functions of female athletes throughout their training season is relevant to understand the relationships between these factors and to predict noncontact injuries, which are prevalent among female athletes. The first aim of this study was to determine whether female handball players' passive stiffness of the hamstring muscles is associated with hamstring extensibility, strength of knee flexors and extensors, and lower limb stiffness. Additionally, the study monitored fluctuations in these factors over 25 weeks. The study utilized an isokinetic dynamometer to record hamstring passive stiffness, extensibility, and hamstring and quadriceps strength of 18 young handball players. Lower limb stiffness was determined from a countermovement vertical jump conducted on a force plate. The countermovement jump involved the calculation of the peak force during the eccentric phase and the mean force during the concentric phase. The results showed a positive correlation between hamstring passive stiffness and lower limb stiffness (r=0.660, p<0.01), knee flexion and extension strength (r=0.592, p<0.01 and r=0.497, p<0.05, respectively), and eccentric peak force (r=0.587, p<0.01) during jumping. The strength of knee extensors increased significantly after 6 weeks, and hamstring stiffness after 12 weeks of training. In conclusion, the increased hamstring stiffness following training did not match other factors associated with injury risk. Therefore, preventing multifactorial injury risk requires a comprehensive approach, and monitoring one factor alone is insufficient to predict noncontact injuries in female handball players.

In vivo vastus lateralis fascicle excursion during speed skating imitation

Mechanical power is a key performance indicator in long track speed skating. Maximal power output in athletic performance can be achieved when mechanical properties of muscles, such as the force-length relationship, are optimized. The purpose of this study was to determine the in vivo operating range of vastus lateralis (VL) fascicle lengths during speed skating imitation and compare the fascicle lengths to those that define the VL force-length relationship. Sixteen sub-elite long track speed skaters (7 females and 9 males; body mass: 72.5 [11.5] kg; age: 22.1 [2.7] years) performed maximal voluntary isometric knee extensions at nine different knee joint positions (20–120°) on the left leg to obtain the maximal vastus lateralis (VL) force-length relationship. Participants then performed a speed skating imitation exercise, the turn-cable, at three progressive perceived efforts (50%, 75%, 100%) to identify the VL fascicle excursion during a complete imitation skating stroke. Fascicle lengths and knee joint angles were examined at initial-contact, peak EMG, and take-off. Fascicles between initial contact and peak EMG covered the descending limb of both the maximal and submaximal force-length relationships while operating over the plateau region from peak EMG to take-off. We conclude that the VL works at sub-optimal length during the gliding phase of skating, but at optimal length for maximal force production during the crucial push-off phase where propulsion is provided.

Fascicle shortening upon activation in voluntary human muscle contractions

BACKGROUND: The dependence of fascicle length on complex interactions with joint angle and force challenges the interpretation of in vivo joint mechanics, muscle mechanical properties, contractile behavior, and muscle function. AIM: The purpose of this study was to determine the complex interaction between muscle activation, joint angle, and fascicle length for isometric contractions of the human vastus lateralis muscle (VL). METHOD: Knee extensor torques, joint angles, EMG activation, and fascicle lengths were determined in nine healthy subjects during maximal and submaximal isometric contractions. RESULTS: Fascicle shortening during isometric contractions depended on muscle-tendon unit length/joint angle and activation, reaching a maximum between angles where VL had its maximum force potential and minimum resistance to fascicle shortening. Maximal fascicle shortening shifted to shorter muscle-tendon unit lengths with decreasing activation. CONCLUSION: Fascicle shortening upon activation depends crucially on the force generating potential and stiffness of the muscle and can reach 30% of the resting fascicle length. Not accounting for the complex interactions between muscle length, force potential, muscle structure, and muscle stiffness has led to erroneous interpretations of the function and properties of healthy and diseased muscles.

Novel Assessment of Viscoelastic Skeletal Muscle Properties in Chronic Kidney Disease: Association with Physical Functioning

Chronic kidney disease (CKD) is characterised by poor physical function. Mechanical muscle properties such as tone, elasticity, and stiffness influence the functional state of the muscle. Measuring these muscle mechanical properties is difficult and data on CKD are sparse. Using a novel myotonometer device, the aims of this study were to compare the viscoelastic muscle properties in CKD patients with previously reported data and to explore the association with muscle function. Non-dialysis-dependent CKD participants were recruited into a cross-sectional study conducted between 2018 and 2020. Muscle properties (tone, stiffness, elasticity) were assessed using a myotonometer (MyotonPRO). Muscle function was assessed using physical performance tests (sit-to-stand 5 and 60, timed up and go, short physical performance battery, gait speed, incremental shuttle walk, postural sway). General linear regression models were used to explore the association between muscle properties and physical function. Thirty-nine participants were included (age 64.2 (SD: 10.4) years; 51% male; eGFR 40.9 (SD: 20.0) mL/min/1.73 m2). Participants with CKD had reduced muscle tone, stiffness, and elasticity compared to previously reported studies. Muscle tone (B = −0.567, p = 0.003) and muscle stiffness (B = −0.368, p = 0.071) were greater in males than females. Increased BMI was associated with lower muscle tone (B = −0.528, p = 0.002) and muscle stiffness (B = −0.577, p = 0.002). No meaningful nor consistent associations were found between these properties and measures of muscle function and physical performance. In conclusion, using a novel handheld myotonometer, this study found that CKD patients exhibit a reduction in muscle tone, stiffness, and elasticity. In a passive state, these viscoelastic muscle properties showed no consistent associations with physical performance.

Reliability of lower leg muscle elasticity using shear wave elastography in non-weight-bearing and weight-bearing

PurposeMuscle elasticity can be quantified with shear wave elastography (SWE) and has been used as an estimate of muscle force but reliability has not been established for lower leg muscles. The purpose of this study was to examine the intra-rater and inter-rater reliability of elasticity measures in non-weight-bearing (NWB) and weight-bearing (WB) for the tibialis anterior (TA), tibialis posterior (TP), peroneal longus (PL), and peroneal brevis (PB) muscles using SWE. MethodsA total of 109 recreationally active healthy adults participated. The study employed a single-cohort, same-day repeated-measures test–retest design. Elasticity, measured in kilopascals as the Young’s modulus, was converted to the shear modulus. All four muscles were measured in NWB and at 90% WB. ResultsIntra-rater reliability estimates were good to excellent for NWB (ICC = 0.930–0.988) and WB (ICC = 0.877–0.978) measures. Inter-rater reliability estimates were moderate to good (ICC = 0.500–0.795) for NWB measures and poor to good (ICC = 0.346–0.910) for WB measures. ConclusionDespite the studies poor to good inter-rater variability, the intra-rater reproducibility represents the potential benefit of SWE in NWB and WB. Establishing the reliability of SWE with clinical and biomechanical approaches may aid in improved understanding of the mechanical properties of muscle.

Effects of blood flow restriction on mechanical properties of the rectus femoris muscle at rest.

Introduction: This study examined the effects of blood flow restriction (BFR) and reperfusion on the mechanical properties of the rectus femoris muscle at rest (frequency and stiffness). Methods: Fourteen trained men (body weight = 81.0 ± 10.3kg; BMI = 25 ± 3.0m/kg2; height = 181 ± 4cm; training experience = 6.0 ± 2.2years) participated in an experimental session involving their dominant (BFR) and non-dominant leg (control). Muscle mechanical properties were measured using Myoton's accelerometer at the midpoint of the rectus femoris muscle at five time points. In the BFR leg, an 80% arterial occlusion pressure was applied by a cuff for 5min. No cuff was applied in the control leg. Femoral Myoton measurements were taken from both legs 2 and 4min after the start of BRF as well as 30s and 2min after the end of the occlusion period. Results: The two-way ANOVA revealed a statistically significant interaction effect for stiffness and frequency (p < 0.001; η2 > 0.67). The post hoc analysis showed that both stiffness and frequency increased during BFR compared with rest and then dropped to the resting levels post BFR period. Also, stiffness and frequency were higher than control only during the BFR period, and similar during rest and post BFR. Conclusion: These results indicate that the application of BFR at rest leads to significant changes in mechanical properties of the rectus femoris muscle.

Acute Effects of Supra- and High-Loaded Front Squats on Mechanical Properties of Lower-Limb Muscles.

Knowledge about the acute effects of supramaximal-loaded resistance exercises on muscle mechanical properties is scarce. Therefore, this study aimed to examine changes in dominant limb biceps femoris and vastus lateralis oscillation frequency and stiffness before and after high- and supramaximal-loaded front squats. Nineteen male handball players participated in the experimental session with a barbell front squat 1RM. The first set was performed at 70% of the 1RM for four repetitions, and the second and third sets were performed at 90%1RM in an eccentric-concentric or an eccentric-only manner at 120% of the 1RM for three repetitions. The handheld myometer was used for the measurement of the biceps femoris and vastus lateralis stiffness and the oscillation frequency of the dominant limb 5 min before and at the 5th and 10th min after front squats. A two-way ANOVA neither indicated a statistically significant interaction (p = 0.335; η2 = 0.059 and p = 0.103; η2 = 0.118), the main effect of a condition (p = 0.124; η2 = 0.126 and p = 0.197; η2 = 0.091), nor the main effect of the time point (p = 0.314; η2 = 0.06 and p = 0.196; η2 = 0.089) for vastus lateralis and biceps femoris stiffness. However, there was a statistically significant interaction (F = 3.516; p = 0.04; η2 = 0.163) for vastus lateralis oscillation frequency. The post hoc analysis showed a significantly higher vastus lateralis oscillation frequency at POST (p = 0.037; d = 0.29) and POST_10 (p = 0.02; d = 0.29) compared to PRE during the SUPRA condition. Moreover, Friedman's test indicated statistically significant differences in biceps femoris oscillation frequency (test = 15.482; p = 0.008; Kendall's W = 0.163). Pairwise comparison showed a significantly lower biceps femoris oscillation frequency in POST (p = 0.042; d = 0.31) and POST_10 (p = 0.015; d = 0.2) during the HIGH condition compared to that in the corresponding time points during the SUPRA condition. The results of this study indicate that the SUPRA front squats, compared to the high-loaded ones, cause a significant increase in biceps femoris and vastus lateralis oscillation frequency.

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

BackgroundArthritis-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. MethodsKnee 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. FindingsAfter 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. InterpretationOur 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.

Exploring the relationship of static and dynamic balance with muscle mechanical properties of the lower limbs in healthy young adults.

There is emerging evidence that mechanical properties of in vivo muscle tissues are associated with postural sway during quiet standing. However, it is unknown if the observed relationship between mechanical properties with static balance parameters generalise to dynamic balance. Thus, we determined the relationship between static and dynamic balance parameters with muscle mechanical properties of the ankle plantar flexors [lateral gastrocnemius (GL)] and knee extensors [vastus lateralis (VL)] in vivo. Twenty-six participants (men = 16, women = 10; age = 23.3 ± 4.4years) were assessed for static balance [centre of pressure (COP) movements during quiet standing], dynamic balance (reach distances for the Y-balance test) and mechanical properties (stiffness and tone) of the GL and VL measured in the standing and lying position. Significant (p < .05) small to moderate inverse correlations were observed between the mean COP velocity during quiet standing with stiffness (r = -.40 to -.58, p = .002 to .042) and tone (r = -0.42 to -0.56, p = 0.003 to 0.036) of the GL and VL (lying and standing). Tone and stiffness explained 16%-33% of the variance in the mean COP velocity. Stiffness and tone of the VL measured in the lying (supine) condition were also inversely significantly correlated with Y balance test performance (r = -0.39 to -0.46, p = 0.018 to 0.049). These findings highlight that individuals with low muscle stiffness and tone exhibit faster COP movements during quiet standing, indicative of reduced postural control but also reveal that low VL stiffness and tone are associated with greater reach distances in a lower extremity reaching task, indicative of greater neuromuscular performance.

Shear wave ultrasound elastography of the biceps brachii can be used as a precise proxy for passive elbow torque in individuals with hemiparetic stroke.

Muscle tissue is prone to changes in composition and architecture following stroke. Changes in muscle tissue of the extremities are thought to increase resistance to muscle elongation or joint torque under passive conditions. These effects likely compound neuromuscular impairments, exacerbating movement function. Unfortunately, conventional rehabilitation is devoid of precise measures and relies on subjective assessments of passive joint torques. Shear wave ultrasound elastography, a tool to measure muscle mechanical properties, may be readily available for use in the rehabilitation setting as a precise measure, albeit at the muscle-tissue level. To support this postulation, we evaluated the criterion validity of shear wave ultrasound elastography of the biceps brachii; we investigated its relationship with a laboratory-based criterion measure for quantifying elbow joint torque in individuals with moderate to severe chronic stroke. Additionally, we evaluated construct validity, with the specific sub-type of hypothesis testing of known groups, by testing the difference between arms. Measurements were performed under passive conditions at seven positions spanning the arc of elbow joint flexion-extension in both arms of nine individuals with hemiparetic stroke. Surface electromyography was utilized for threshold-based confirmation of muscle quiescence. A moderate relationship between the shear wave velocity and elbow joint torque was identified, and both metrics were greater in the paretic arm. Data supports the progression toward a clinical application of shear wave ultrasound elastography in evaluating altered muscle mechanical properties in stroke, while acknowledging that undetectable muscle activation or hypertonicity may contribute to the measurement. Shear wave ultrasound elastography may augment the conventional method of manually testing joint mobility by providing a high-resolution precise value. Tissue-level measurement may also assist in identifying new therapeutic targets for patient-specific impairment-based interventions.

Cervical and axioscapular muscle stiffness measured with shear wave elastography: A comparison between different levels of work-related neck disability.

Assessing muscle mechanical properties in terms of stiffness may provide important insights into mechanisms underlying work-related neck pain. This study compared stiffness of cervical and axioscapular muscles between 92 participants (sonographers) with no (n=31), mild (n=43) or moderate/severe (n=18) neck disability. It was hypothesized that participants with more severe neck pain and disability would present with altered distribution of stiffness in cervical and axioscapular muscles than those with no disability. Using shear wave elastography, the shear modulus (kPa) of five cervical and six axioscapular muscles or muscle segments were measured in a relaxed seated upright or side-lying position. Muscle activity was measured simultaneously using surface electromyography during the elastography measurements and scapular depression was measured using a measurement tape and inclinometer before the elastography measurements to evaluate their potential confounding influences on shear modulus. Increased shear modulus was found in deeper than superficial cervical muscles and more cranial than caudal axioscapular muscles. However, no differences in shear modulus of the cervical or axioscapular muscles were found between sonographers with varying levels of disability. This study suggests no alterations in stiffness of cervical and axioscapular muscles were associated with work-related neck pain and disability.

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.

Effect of focused ultrasound peripheral nerve stimulation on muscle mechanical properties: An in vivo murine model

Electrical muscle stimulation is limited to surface muscle activation; however, focused ultrasound (fUS) has the potential to stimulate deep skeletal muscles. This study aims to evaluate the effects of fUS peripheral nerve stimulation on muscle mechanical properties in an in vivo murine model. The sciatic nerve of 19 Sprague-Dawley rats was insonified with 3.68-MHz fUS (p+ = 6.4 MPa, p− = 5 MPa) using 10-ms pulses (0.9-ms on/0.1-ms off, 10 times) repeated at 0.5-Hz for 30, 90, or 180 severy second day for two weeks. Stimulation was monitored using electromyography (EMG) with indwelling electrodes inserted in the gastrocnemius muscle belly. Bilateral muscles were harvested for tensile mechanical testing (n = 15) and histology (n = 4). Muscle contraction was confirmed via EMG in 16/19 rats. Elastic moduli of stimulated muscles (133.2 ± 42.1 kPa) and controls (101.4 ± 39.2 kPa) were not different (ANOVA, p = 0.053). A trend toward increased elastic modulus with number of muscle stimulations was observed until 450 stimulations (not significant: ANOVA, p = 0.437), after which elastic modulus began to decrease. No tissue damage was observed histologically. The results of this pilot study demonstrate that fUS can induce repeatable muscle contraction that may improve muscle strength and mechanical properties over time. [Work supported by PSU College of Engineering Seed Grant 2021.]