Stress-strain relationship of individual hamstring muscles: A human cadaver study.

The incidence of hamstring muscle strain varies among muscles, suggesting that the mechanical stresses associated with elongation may differ among muscles. However, the passive mechanical properties of whole human muscles have rarely been directly measured and clarified. This study aimed to clarify the stress-strain relationship of the hamstring muscles using a soft-embalmed Thiel cadaver. The long heads of the biceps femoris (BFlh), semimembranosus (SM), and semitendinosus (ST) muscles were dissected from eight cadavers. The proximal and distal hamstring tendons were affixed to the mechanical testing machine. Slack length was defined as the muscle length at the initial loading point detected upon the application of a tensile load. Muscle length was measured using a tape measure, and the anatomical cross-sectional area (ACSA) of the muscle was measured at the proximal and distal sites using B-mode ultrasonography. In the loading protocol, the muscle was elongated from its slack length to a maximum of 8% strain at an average rate of 0.83 L0/s, and the amount of displacement and tensile load were measured for each muscle. Further, the strain (%, displacement/slack muscle length) and stress (kPa, tensile load/ACSA) were calculated to evaluate the mechanical properties. Two-way repeated-measures analysis of variance (ANOVA) was used to compare stress changes with increasing muscle strain. A significant interaction between the muscle and strain factors was observed with respect to stress. Post-hoc tests revealed higher stresses in the BFlh and SM than in ST after 3% strain (P < 0.01). However, no significant differences were observed between the BFlh and SM groups. At 8% strain, the BFlh, SM, and ST exhibited stresses of 63.7 ± 12.1, 53.7 ± 23.2, and 21.0 ± 11.9 kPa, respectively. The results indicate that the stress changes associated with muscle strain differed among muscles. In particular, the stress applied to the three muscles at the same strain was found to be higher in the BFlh and SM. Thus, these findings suggest that increased mechanical stress during elongation may contribute to the frequent occurrence of muscle strain in BFlh and SM.

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.

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.

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.

Relationship between shear elastic modulus and passive muscle force in human hamstring muscles using a Thiel soft-embalmed cadaver.

PURPOSE: Assessing muscle flexibility and architecture is important for hamstring strain injury (HSI) prevention. We investigated the relationship between shear modulus and passive force in hamstring muscles at different sites and the effect of muscle architecture on the slope of the shear modulus-passive force using shear wave elastography (SWE). METHODS: The biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM) muscles were dissected from nine Thiel-embalmed cadavers and fixed to a custom-made mechanical testing machine. Calibrated weights (0-1800 g) were applied gradually in 150-g increments. The shear modulus and anatomical cross-sectional area (ACSA) were measured at proximal, central, and distal points using SWE. The muscle mass and length were measured before the loading test. The shear modulus-passive load relationship of each tested muscle region was analyzed by fitting a least-squares regression line. The increase in shear modulus slope per unit load was calculated and compared between the muscles before and after normalization by the muscle mass, length, and ACSA. RESULTS: The shear modulus and passive force for all hamstring muscles in each region showed a statistically significant linear correlation. Furthermore, the increase in shear modulus slope was greater for BFlh and ST than for SM (P < 0.05), but after normalization by the muscle length and ACSA, there were no significant differences among the muscles. CONCLUSION: The local mechanical properties of individual hamstring muscles can be indirectly estimated using SWE, and the slope of increase in shear modulus reflects characteristics of the muscle architecture.

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

INTRODUCTION: Intramuscular heterogeneity exists in the shear modulus of the rectus femoris (RF) muscle. However, the underlying heterogeneity mechanisms are not entirely understood. Previous research has reported that detachment of superficial tissues reduces the shear modulus by 50%. The aim of this study was to examine the effects of the skin, deep fascia, and intermuscular connections on the shear modulus of the RF at multiple sites. MATERIALS AND METHODS: Eleven donors were fixed using the Thiel method. Measurements were performed at 0°, 60°, and 120° knee flexion in a neutral hip position. Tissue processing was performed under four conditions: superficial tissue (CONT), skin off (SKIN), deep fascia detachment (FASC), and intermuscular connections detachment (ALL). The shear modulus at the proximal, central, and distal regions were measured using ultrasound shear wave elastography. The study was approved by the Sapporo Medical University Ethical Committee. RESULTS: Three-way ANOVA revealed no significant interaction between treatment, site, and angle (P = 0.156), treatment and angle (P = 0.067), or site and angle (P = 0.441). There was a significant effect of treatment (P < 0.001), site (P = 0.010), and angle (P < 0.001) and interaction between treatment and site (P < 0.001). The proximal shear modulus was greater than the central for CONT. There were no significant differences between the measurement sites for SKIN. The distal shear modulus was greater than the proximal for FASC. The distal shear modulus was also greater than the proximal and central for ALL. CONCLUSIONS: Intramuscular regional differences that influence superficial tissue and intermuscular connections of RF elasticity heterogeneity were observed.

Effect of chest mobilization on intercostal muscle stiffness.

This study examined the effect of chest mobilization on intercostal (IC) muscle stiffness using the IC muscle shear modulus. Sixteen healthy young men participated on two days with a minimum of 24 h between the stretching and control conditions (SC and CC). The tasks were resting breathing and deep breathing. The IC muscle shear modulus and muscle activity and rib cage circumference were measured before and after each condition. In the SC, IC stretching was performed for 1 min x 5 sets. In the CC, resting breathing, in a sitting position, was performed for 5 min. In the SC, the IC muscle shear modulus decreased significantly (p < 0.05) at maximum inspiration in the deep breathing task, but there was no significant difference in the CC pre- and post-intervention. The results suggest that IC muscle stretching decreases IC muscle stiffness and improves muscle flexibility and that the IC muscle shear modulus may measure the effectiveness of chest mobilization.

Adductor longus: An anatomical study to better understand groin pain.

We investigated the shear modulus-passive force relationship in the hip adductor longus (AL) muscles of human cadavers and explored the effect of muscle architecture on the elastic properties of the AL muscle using shear wave elastography (SWE). Nine AL muscles were harvested from a soft, embalmed cadaver. The AL muscles were affixed to a custom-built device comprising two clamps, a pulley, and a cable to provide passive loads, which were increased from 0 to 600 g in 60-g increments. The shear modulus of the AL muscle was measured in the proximal (Pro), middle (Mid), and distal (Dis) regions. The masses and anatomical cross-sectional areas (ACSAs) of the AL muscles were measured. The shear modulus-passive load relationship of each tested muscle region was analyzed by fitting a least-squares regression line. Moreover, the rate of increase in the shear modulus per unit load (s) was calculated. The shear modulus and passive force were linearly correlated for all AL muscles in each region (p < 0.01). The mean coefficients of determination (R2 ) for Pro, Mid, and Dis were 0.989, 0.986, and 0.982, respectively. The rate of increase in the shear modulus per unit load significantly correlated with the reciprocal of the muscle mass (r = 0.77, p = 0.02) and ACSA (r = 0.43, p = 0.03). Shear wave elastography can be used as an indirect measure of passive force in any region of the AL muscle. Additionally, the rate of increase in the shear modulus per unit load could be associated with muscle architectural parameters.

Intramuscular differences in shear modulus of the rectus femoris muscle during passive knee flexion.

PURPOSE: This study aimed to determine (1) intramuscular regional differences in the changes in the shear modulus of the rectus femoris (RF) muscle during passive knee flexion and (2) the relationship between shear modulus and passive knee extension torque. METHOD: The shear modulus maps as an index of muscle stiffness and the passive torque were obtained at seven regions during passive knee flexion at 2°/s within a knee joint range of motion of 0°-130° in 16 healthy males. RESULTS: The shear modulus of RF increased with the knee angle of flexion. The shear modulus of each longitudinal region was greater in the order of proximal, central, and distal region (p < 0.05). The relationship between the shear modulus and passive torque was highly fitted for all 16 subjects (p < 0.05). The mean coefficient of determination (R2) at second-order polynomial model per subject was 0.96 (± 0.03; range 0.61-0.99), and whole group was 0.58 (± 0.03; range 0.54-0.64) in all regions. CONCLUSIONS: The passive stiffness of RF was higher in the proximal region than in the other regions during passive knee flexion. Furthermore, the shear modulus-passive torque was related regardless of the measurement region within a muscle, and the results suggest that the passive knee extension torque reflects passive muscle stiffness of the RF.

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

PURPOSE: Estimation of muscle passive force from elasticity using shear wave elastography (SWE) has been reported. However, the relationship between the elasticity and passive force of human muscles has not been elucidated. This study investigated the elastic modulus-passive force relationship in human skeletal muscles at multiple sites. METHODS: Four rectus femoris (RF) muscles were dissected from a human Thiel-embalmed cadaver. Calibration weights (0-600 g in 60-g increments) were applied to the distal tendon via a pulley system, and the shear elastic modulus as an index of elasticity was measured using SWE. The shear elastic modulus of the RF was measured at the proximal, central, and distal portions. RESULTS: The results demonstrated that the relationships between the elasticity in the longitudinal direction of the muscle and the passive force were nearly linear for all tested sites, with coefficients of determination ranging from 0.813 to 0.993. CONCLUSION: Shear wave elastography may be used as an indirect method to measure the changing passive force at any site within human muscles.

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.