Effective Stretching Positions of the Piriformis Muscle Evaluated Using Shear Wave Elastography.

CONTEXT: Piriformis syndrome is often associated with muscle spasms and shortening of the piriformis muscle (PM). Physical therapy, including static stretching of the PM, is one of the treatments for this syndrome. However, the effective stretching position of the PM is unclear in vivo. This study aimed to determine the effective stretching positions of the PM using ultrasonic shear wave elastography. DESIGN: Observational study. METHODS: Twenty-one healthy young men (22.7 [2.4] y) participated in this study. The shear elastic modulus of the PM was measured at 12 stretching positions using shear wave elastography. Three of the 12 positions were tested with maximum internal rotation at 0°, 20°, or 40° hip adduction in 90° hip flexion. Nine of the 12 positions were tested with maximum external rotation at positions combined with 3 hip-flexion angles (70°, 90°, and 110°) and 3 hip-adduction angles (0°, 20°, and 40°). RESULTS: The shear elastic modulus of the PM was significantly higher in the order of 40°, 20°, and 0° of adduction and higher in external rotation than in internal rotation. The shear elastic modulus of the PM was significantly greater in combined 110° hip flexion and 40° adduction with maximum external rotation than in all other positions. CONCLUSION: This study revealed that the position in which the PM was most stretched was maximum external rotation with 110° hip flexion and 40° hip adduction.

Effect of age on shear modulus, muscle thickness, echo intensity of the upper limb, lower limb, and trunk muscles in healthy women.

PURPOSE: This study aimed to examine the effect of age on the mechanical properties, muscle size, and muscle quality in the upper and lower limb and trunk muscles. METHODS: We evaluated the shear modulus (G), muscle thickness (MT), and echo intensity (EI) of the upper and lower limb and trunk muscles of 83 healthy women (21-83-year-old). The G values of some limb muscles were measured in relaxed and stretched positions. RESULTS: Regarding the effect of age on G at the distinct positions, the G of the upper limb muscles were not significantly correlated with age in the relaxed and stretched positions. In contrast, the G of the iliacus showed a significant negative correlation in both positions. Additionally, the G of the rectus femoris had a significant negative correlation only in the relaxed position. Regarding differences among body parts, the G of the lower limb and oblique abdominal muscles showed a significant negative correlation, but no correlation in the upper limb, rectus abdominis, and back muscles. Moreover, MT showed a significant negative correlation with age in the lower limb, abdominal, and erector spinae muscles, but no correlation was detected in the upper limb and lumbar multifidus muscles. EI had a significant positive correlation in all the muscles. CONCLUSION: The effect of age on G depended on body parts, and the G of the lower limb and oblique abdominal muscles negatively associated with age. Additionally, G in the relaxed position may be more susceptible to aging than G in the stretched position.

Rhythmic auditory stimulation during gait adaptation enhances learning aftereffects and savings by reducing common neural drives to lower limb muscles.

Rhythmic auditory stimulation (RAS) improves gait symmetry in neurological patients with asymmetric gait patterns. However, whether RAS can accelerate gait adaptation remains unclear. This study aimed to investigate whether RAS during gait adaptation can enhance learning aftereffects and savings of gait symmetries. Furthermore, we investigated the differences in the coherence of paired surface electromyographic (EMG) recordings during gait adaptation between with and without RAS. Nineteen healthy young adults were subjected to continuous treadmill gait with swing phase perturbation (adaptation period) with or without RAS (RAS or no-RAS condition) for 5 or 10 min (short- or long-time condition), without the perturbation for 5 min (de-adaptation period), and with the perturbation for another 5 min (re-adaptation period). Swing phase and step length symmetries were significantly greater in the RAS conditions than in the no-RAS conditions during the adaptation period. Learning aftereffects and savings of gait symmetries were significantly greater in the RAS conditions than in the no-RAS conditions in the early de-adaptation and re-adaptation periods, respectively. There were no significant differences in savings in the early re-adaptation period between the short- and long-time conditions in the RAS condition. EMG-EMG coherence in the rectus femoris muscle in the ß band (15-35 Hz) on the perturbed side was significantly lower during the early adaptation period in the RAS than in the no-RAS conditions. Therefore, RAS may enhance learning efficiency by reducing common neural drives from a cortical structure during gait adaptation, which could induce high savings of a learned gait pattern, even within short-time periods.NEW & NOTEWORTHY RAS during gait adaptation against swing phase perturbation enhances learning aftereffects and savings of gait symmetries. EMG-EMG coherence in the rectus femoris muscle in the ß band on the perturbed side during the swing phase was significantly lower in the RAS than in the no-RAS conditions during the early adaptation period. These results support the application of RAS as external feedback to improve gait symmetry during gait adaptation in the rehabilitation of neurological patients.

Different modulation of oscillatory common neural drives to ankle muscles during abrupt and gradual gait adaptations.

Different neural contributions to motor learning might be involved when different error sizes of perturbation are introduced. Although the corticospinal drive contributes to abrupt gait adaptation processes, no studies have investigated whether cortical involvement during gait differs between perturbations applied abruptly and gradually. This study aimed to investigate the differences in oscillatory common neural drives to ankle muscles during gait between abrupt and gradual adaptations, using coherence analyses of paired surface electromyographic (EMG) recordings. Sixteen healthy young adults performed the treadmill gait with perturbation resisting forward movement of the swing leg for 10 min under two conditions: abrupt (a large perturbation from the beginning of the adaptation period) and gradual (a series of small perturbations that gradually increased). Swing phase duration and step length showed significantly greater asymmetry in the abrupt condition than in the gradual condition in the early adaptation period (p < 0.01), despite no significant differences in gait symmetries between the two conditions in the early post-adaptation period. EMG-EMG coherence calculated from the tibialis anterior muscle in the beta band (15-35 Hz) on the perturbed side was significantly higher in the early adaptation period in the abrupt condition (p < 0.05), but not in the gradual condition. There were significant relationships between changes in temporal gait symmetry and EMG-EMG coherence during the different adaptation periods between the two conditions (p < 0.05). The abrupt large perturbation seems to require a cortical involvement, whereas a gradual adaptation with small gait asymmetry requires no modulation of cortical involvement.

Effective stretching position for the posterior deltoid muscle evaluated by shear wave elastography.

BACKGROUND: Deteriorated extensibility of the posterior deltoid muscle is one of the factors of posterior shoulder tightness, and improvement in its extensibility is needed. However, no study has investigated which shoulder positions effectively stretch the posterior deltoid muscle in vivo. The aim of this study was to verify the effective stretching position of the posterior deltoid muscle in vivo by shear wave elastography. METHODS: Fifteen healthy men participated in this study. The shear modulus of the posterior deltoid was measured at resting and 13 stretching positions: 60°, 90°, and 120° shoulder flexion; maximum shoulder flexion, horizontal adductions at 60°, 90°, and 120° shoulder flexion; internal rotations at 60°, 90°, and 120° shoulder flexion; and combinations of horizontal adduction with internal rotation at 60°, 90°, and 120° shoulder flexion. The shear moduli of each stretching position were compared to those of the rest. Then, among the stretching positions for which the shear modulus was significantly different from the rest, the shear moduli were compared using a three-way analysis of variance with repeated measures of the 3 factors-flexion, horizontal adduction, and internal rotation. RESULTS: The shear moduli in all stretching positions were significantly higher than those of the rest, except for maximum shoulder flexion. The three-way analysis of variance with repeated measures revealed significant main effects in flexion and horizontal adduction. Comparing the flexion angles, the shear modulus was significantly higher at 90° than that at 60° and 120°. The shear modulus with horizontal adduction was significantly higher than that without horizontal adduction. Moreover, a significant two-way interaction was found only at flexion and horizontal adduction. The shear modulus with horizontal adduction was significantly higher at all angles than that without horizontal adduction at each flexion angle. Comparing the flexion angles with horizontal adduction, the shear modulus was significantly higher at 90° than that at 60° and 120°. No significant three-way interactions were found. CONCLUSION: Shoulder flexion and horizontal adduction affected the extensibility of the posterior deltoid muscle, whereas the effect of shoulder internal rotation was limited. More precisely, maximal horizontal adduction at 90° shoulder flexion was the most effective stretching position for the posterior deltoid muscle.

Relationship Between Muscle Swelling and Hypertrophy Induced by Resistance Training.

ABSTRACT: Hirono, T, Ikezoe, T, Taniguchi, M, Tanaka, H, Saeki, J, Yagi, M, Umehara, J, and Ichihashi, N. Relationship between muscle swelling and hypertrophy induced by resistance training. J Strength Cond Res 36(2): 359-364, 2022-Muscle swelling immediately after resistance exercise may be induced by metabolic stress. The accumulation of metabolic stress is considered to promote muscle hypertrophy after several weeks of resistance training (RT). The purpose of this study was to determine the relationship between muscle swelling immediately after the first session of RT and muscle hypertrophy after a 6-week RT using ultrasonography. Twenty-two untrained young men performed knee extension resistance exercise consisting of 3 sets with 8 repetitions at a load of 80% of one repetition maximum for 6 weeks (3 d·wk-1). Muscle thickness of the quadriceps femoris was measured using ultrasonography device at 3 anatomical sites (proximal, medial, and distal sites) of the middle, lateral, and medial part of the anterior thigh. The sum of the muscle thickness at 9 measurement sites was used for analysis. Acute change in muscle thickness immediately after the first session of RT was used as an indicator of muscle swelling. Chronic change in muscle thickness after the 6-week RT was used as an indicator of muscle hypertrophy. A significant increase in muscle thickness was observed immediately after the first session of RT (8.3 ± 3.2%, p < 0.001). After the 6-week RT, muscle thickness increased significantly (2.9 ± 2.6%, p < 0.001). A significant positive correlation was found between muscle swelling and muscle hypertrophy (ρ = 0.443, p = 0.039). This study suggests that the greater the muscle swelling immediately after the first session of RT, the greater the muscle hypertrophy after RT.

Chronic Effects of a Static Stretching Program on Hamstring Strength.

ABSTRACT: Nakao, S, Ikezoe, T, Nakamura, M, Umegaki, H, Fujita, K, Umehara, J, Kobayashi, T, Ibuki, S, and Ichihashi, N. Chronic effects of a static stretching program on hamstring strength. J Strength Cond Res 35(7): 1924-1929, 2021-This study investigated the effects of a 4-week static stretching (SS) program on isokinetic and isometric knee flexor peak torque and angle of peak torque. Thirty healthy men (age, 22.7 ± 2.2 years) were randomized to receive either of the following: (a) a 4-week stretch intervention for the hamstrings (SS intervention group; n = 15) or (b) no intervention (control group; n = 15). The maximum pain-free knee angle, passive stiffness, which was determined by a slope of torque-angle curve, isometric and isokinetic (at 60°·s-1 and 180°·s-1) peak torque, and angle of peak torque for knee flexors were measured before and after 4 weeks. After 4 weeks, passive stiffness decreased significantly in the intervention group. There were no significant changes in isometric and isokinetic (neither at 60°·s-1 nor at 180°·s-1) peak torque, or angle of peak torque at 180°·s-1. A significantly increased peak extension angle at 60°·s-1 was observed in the intervention group. These results suggest that SS intervention is effective for decreasing musculotendinous unit stiffness of the hamstrings and that an SS program influences the angle of peak torque, whereas no significant changes occur in peak torque. Because a previous study suggests that angle of peak torque is associated with hamstring strain injuries, the results of this study would be helpful when considering the training program for preventing or treating hamstring strain injuries.

Acute and Prolonged Effects of Stretching on Shear Modulus of the Pectoralis Minor Muscle.

Increased muscle stiffness of the pectoralis minor (PMi) could deteriorate shoulder function. Stretching is useful for maintaining and improving muscle stiffness in rehabilitation and sport practice. However, the acute and prolonged effect of stretching on the PMi muscle stiffness is unclear due to limited methodology for assessing individual muscle stiffness. Using shear wave elastography, we explored the responses of shear modulus to stretching in the PMi over time. The first experiment (n = 20) aimed to clarify the acute change in the shear modulus during stretching. The shear modulus was measured at intervals of 30 s × 10 sets. The second experiment (n = 16) aimed to observe and compare the prolonged effect of different durations of stretching on the shear modulus. Short and long stretching duration groups underwent 30s × 1 set and 30s × 10 sets, respectively. The assessments of shear modulus were conducted before, immediately after, and at 5, 10, and 15 min post-stretching. In experiment I, the shear modulus decreased immediately after a bout (30 s) of stretching (p < 0.001, change: -2.3 kPa, effect size: r = 0.72) and further decreased after 3 repetitions (i.e., 90 s) of stretching (p = 0.03, change: -1.0 kPa, effect size: r = 0.53). In experiment II, the change in the shear modulus after stretching was greater in the long duration group than in the short duration group (p = 0.013, group mean difference: -2.5 kPa, partial η2 = 0.36). The shear modulus of PMi decreased immediately after stretching, and stretching for a long duration was promising to maintain the decreased shear modulus. The acute and prolonged effects on the PMi shear modulus provide information relevant to minimum and persistent stretching time in rehabilitation and sport practice.

Relationship between ankle plantar flexor force steadiness and postural stability on stable and unstable platforms.

PURPOSE: This study was aimed at determining the relationship between ankle plantar flexor force steadiness and postural control during single leg standing on stable and unstable platforms. METHODS: For the thirty-three healthy participants, force steadiness, at target torques of 5%, 20%, and 50% of the maximum voluntary torque (MVT) of the ankle plantar flexors, was measured. Force steadiness was calculated as the coefficient of variation of force. Single leg standing on stable and unstable platforms was performed using the BIODEX Balance System SD. The standard deviation of the anteroposterior center of pressure (COP) displacements was measured as the index for postural control. During both measurements, muscle activities of the soleus were collected using surface electromyography. RESULTS: On the stable platform, the COP fluctuation significantly correlated with force steadiness at 5% of MVT (r = 0.512, p = 0.002). On the unstable platform, the COP fluctuation significantly correlated with force steadiness at 20% of MVT (r = 0.458, p = 0.007). However, the extent of muscle activity observed for a single leg standing on both stable and unstable platforms was significantly greater than the muscle activity observed while performing force steadiness tasks at 5% and 20% of MVT, respectively. CONCLUSION: Postural stability during single leg standing on stable and unstable platforms may be related to one's ability to maintain constant torque at 5% and 20% of MVT regardless of the muscle activity. These results suggest that the required abilities to control muscle force differ depending on the postural control tasks.

Comparison of shoulder muscle strength, cross-sectional area, acromiohumeral distance, and thickness of the supraspinatus tendon between symptomatic and asymptomatic patients with rotator cuff tears.

BACKGROUND: The purpose of this study was to demonstrate the differences in shoulder muscle strength, cross-sectional area of the rotator cuff muscles, acromiohumeral distance, and supraspinatus tendon thickness between symptomatic and asymptomatic patients with rotator cuff tears. METHODS: Thirty-two symptomatic patients and 23 asymptomatic patients with rotator cuff tears participated in this study. Data of the patients with any type of tear and supraspinatus tear were analyzed. We evaluated the isometric torque, cross-sectional area of the rotator cuff muscles, supraspinatus tendon thickness, acromiohumeral distance, range of motion, and Western Ontario Rotator Cuff Index. RESULTS: Asymptomatic patients showed greater isometric torque of shoulder abduction and internal rotation than symptomatic patients with any type of tear (P ≤ .01). Asymptomatic patients also demonstrated greater cross-sectional area of the supraspinatus (P < .01); however, there was no significant difference in the cross-sectional area of the other cuff muscles. There was also no significant difference in the supraspinatus tendon thickness (P = .10). The acromiohumeral distance at 90° of shoulder abduction was larger (P = .04) in asymptomatic patients. Additionally, similar tendencies were observed in the results of patients with supraspinatus tears, except for the isometric torque of shoulder external rotation. This torque was greater (P < .01) in asymptomatic patients. CONCLUSION: Asymptomatic patients showed greater shoulder range of motion, muscle strength of shoulder abduction and internal rotation, small occupation ratio of supraspinatus tendon thickness as a percentage of acromiohumeral distance, and large cross-sectional area of supraspinatus.

Effect of different trunk postures on scapular muscle activities and kinematics during shoulder external rotation.

BACKGROUND: Shoulder external rotation at abduction (ER) is a notable motion in overhead sports because it could cause strong stress to the elbow and shoulder joint. However, no study has comprehensively investigated the effect of different trunk postures during ER. This study aimed to investigate the effect of different trunk postures on scapular kinematics and muscle activities during ER. METHODS: Fourteen healthy men performed active shoulder external rotation at 90° of abduction with the dominant arm in 15 trunk postures. At maximum shoulder external rotation in 15 trunk postures, including 4 flexion-extension, 6 trunk rotation, and 4 trunk side-bending postures, as well as upright posture as a control, scapular muscle activities and kinematics were recorded using surface electromyography and an electromagnetic tracking device, respectively. The data obtained in the flexion-extension, trunk rotation, and trunk side-bending postures were compared with those obtained in the upright posture. RESULTS: In the flexion-extension condition, scapular posterior tilt and external rotation significantly decreased, but the muscle activities of the lower trapezius and infraspinatus significantly increased in maximum trunk flexion. Moreover, scapular upward rotation and the activity of the serratus anterior significantly increased in maximum trunk extension. In the rotation condition, scapular posterior tilt and external rotation significantly decreased, but the activity of the serratus anterior significantly increased in the maximum contralateral trunk rotation posture. In the trunk side-bending condition, scapular posterior tilt and the external rotation angle significantly decreased. CONCLUSION: Trunk postures affected scapular kinematics and muscle activities during ER. Our results suggest that different trunk postures activate the lower trapezius and serratus anterior, which induce scapular posterior tilt.

Improvement in muscle strength with low-load isotonic training depends on fascicle length but not joint angle.

INTRODUCTION: In this study we investigate whether low-load isotonic training will elicit greater improvement in muscle strength at the same fascicle length, rather than at the same joint angle. METHODS: Sixteen healthy men (24.1 ± 2.5 years of age) were randomly divided into intervention and control groups. Pre- and posttraining maximum isometric and isokinetic strengths and fascicle lengths of the medial gastrocnemius muscle were measured. Isotonic resistance training at 15 ° to 30 ° ankle plantarflexion at low intensity was conducted for 4 weeks. RESULTS: The maximum isometric and isokinetic strength of the intervention group increased significantly only at 15 ° dorsiflexion and 8 ° to 12 ° dorsiflexion. Fascicle length during maximum voluntary contraction at 15 ° dorsiflexion to 0 ° was similar to fascicle length under training conditions. DISCUSSION: It is possible that the improvement in muscle strength with low-load training depends on fascicle length rather than joint angle. Muscle Nerve 57: 83-89, 2018.

Electrical Stimulation to the Infraspinatus on Hypertrophy and Strength of the Shoulder.

The purpose of this study was to determine the effects of six weeks of electrical muscle stimulation (EMS) on the strength and muscle mass of the infraspinatus muscle. Twenty non-athletes (age: 24±3.4 years, height: 171.5±5.6 cm, mass: 65.2±8.1 kg) were randomly classified into two groups, an electrical muscle stimulation group (EMS group) and a control group (CON group). The EMS group completed a total of 18 20- min EMS sessions, three times per week over a period of six weeks, while the CON group received no intervention. The muscle thicknesses of both the infraspinatus and the deltoid muscles, the cross-sectional area (CSA) of the whole infraspinatus muscle, and the isometric and isokinetic peak torques of shoulder external rotations were measured before and after intervention. It was found that the muscle thickness of the superior infraspinatus (Pre 0.92±0.19 cm2, Post 0.99±0.16 cm2, p=0.02) and the CSA (Pre 10.99±1.32 cm2, Post 11.99±1.02 cm2, p=0.03) significantly increased in the EMS group. This study demonstrated that EMS of the infraspinatus muscle over a period of six weeks resulted in hypertrophy of the infraspinatus muscle.

Scapular kinematic alterations during arm elevation with decrease in pectoralis minor stiffness after stretching in healthy individuals.

BACKGROUND: Pectoralis minor tightness may be seen in individuals with scapular dyskinesis, and stretching is used for the treatment of altered scapular motion in sports and clinical fields. However, few researchers have reported on the effects of pectoralis minor stiffness on scapular motion during arm elevation. This study investigated whether an acute decrease of pectoralis minor stiffness after stretching changes the scapular motion during arm elevation. METHODS: The study allocated 15 dominant and 15 nondominant upper limbs in healthy men as control and interventional limbs, respectively. In the intervention limb group, the shoulder was passively and horizontally abducted at 150° of elevation for 5 minutes to stretch the pectoralis minor muscle. Before and after stretching, an electromagnetic sensor was used to examine 3-dimensional scapular motion during abduction and scaption. Ultrasonic shear wave elastography was used to measure pectoralis minor stiffness before and immediately after stretching and after arm elevation. RESULTS: In the interventional limb, pectoralis minor stiffness decreased by 3.2 kPa immediately after stretching and by 2.5 kPa after arm elevation. The maximal changes in scapular kinematics after stretching were 4.8° of external rotation and 3.3° of posterior tilt in abduction, and 4.5° of external rotation and 3.7° of posterior tilt in scaption. Upward rotation in abduction or scaption did not change. CONCLUSIONS: Stretching for the pectoralis minor muscle increases external rotation and posterior tilt of the scapula during arm elevation.

Scapular kinematic and shoulder muscle activity alterations after serratus anterior muscle fatigue.

BACKGROUND: Although the serratus anterior muscle has an important role in scapular movement, no study to date has investigated the effect of serratus anterior fatigue on scapular kinematics and shoulder muscle activity. The purpose of this study was to clarify the effect of serratus anterior fatigue on scapular movement and shoulder muscle activity. METHODS: The study participants were 16 healthy men. Electrical muscle stimulation was used to fatigue the serratus anterior muscle. Shoulder muscle strength and endurance, scapular movement, and muscle activity were measured before and after the fatigue task. The muscle activity of the serratus anterior, upper and lower trapezius, anterior and middle deltoid, and infraspinatus muscles was recorded, and the median power frequency of these muscles was calculated to examine the degree of muscle fatigue. RESULTS: The muscle endurance and median power frequency of the serratus anterior muscle decreased after the fatigue tasks, whereas the muscle activities of the serratus anterior, upper trapezius, and infraspinatus muscles increased. External rotation of the scapula at the shoulder elevated position increased after the fatigue task. CONCLUSION: Selective serratus anterior fatigue due to electric muscle stimulation decreased the serratus anterior endurance at the flexed shoulder position. Furthermore, the muscle activities of the serratus anterior, upper trapezius, and infraspinatus increased and the scapular external rotation was greater after serratus anterior fatigue. These results suggest that the rotator cuff and scapular muscle compensated to avoid the increase in internal rotation of the scapula caused by the dysfunction of the serratus anterior muscle.

Acute effect and time course of extension and internal rotation stretching of the shoulder on infraspinatus muscle hardness.

BACKGROUND: A decrease in flexibility of the infraspinatus muscle causes limitations in the range of shoulder motion. Static stretching (SS) is a useful method to improve muscle flexibility and joint mobility. Previous researchers investigated effective stretching methods for the infraspinatus. However, few researchers investigated the acute effect of SS on the infraspinatus muscle's flexibility. In addition, the minimum SS time required to increase the infraspinatus muscle's flexibility remains unclear. The aims of this study included investigating the acute effect of SS on the infraspinatus muscle's hardness (an index of muscle flexibility) by measuring shear elastic modulus and determining minimum SS time to decrease the infraspinatus muscle's hardness. METHODS: This included measuring the effect of SS with extension and internal rotation of the shoulder on the infraspinatus muscle's hardness in 20 healthy men. Hence, shear elastic modulus of the infraspinatus was measured by ultrasonic shear wave elastography before and after every 10 seconds up to 120 seconds of SS. RESULTS: Two-way analysis of variance indicated a significant main effect of SS duration on shear elastic modulus. The post hoc test indicated no significant difference between shear elastic modulus after 10 seconds of SS and that before SS. However, shear elastic modulus immediately after a period ranging from 20 seconds to 120 seconds of SS was significantly lower than that before SS. CONCLUSION: The results suggested that shoulder extension and internal rotation SS effectively decreased the infraspinatus muscle's hardness. In addition, the results indicated that a period exceeding 20 seconds of SS decreased the infraspinatus muscle's hardness.

Shoulder horizontal abduction stretching effectively increases shear elastic modulus of pectoralis minor muscle.

BACKGROUND: Stretching maneuvers for the pectoralis minor muscle, which involve shoulder horizontal abduction or scapular retraction, are performed in clinical and sports settings because the tightness of this muscle may contribute to scapular dyskinesis. The effectiveness of stretching maneuvers for the pectoralis minor muscle is unclear in vivo. The purpose of this study was to verify the effectiveness of stretching maneuvers for the pectoralis minor muscle in vivo using ultrasonic shear wave elastography. METHODS: Eighteen healthy men participated in this study. Elongation of the pectoralis minor muscle was measured for 3 stretching maneuvers (shoulder flexion, shoulder horizontal abduction, and scapular retraction) at 3 shoulder elevation angles (30°, 90°, and 150°). The shear elastic modulus, used as the index of muscle elongation, was computed using ultrasonic shear wave elastography for the 9 aforementioned stretching maneuver-angle combinations. RESULTS: The shear elastic modulus was highest in horizontal abduction at 150°, followed by horizontal abduction at 90°, horizontal abduction at 30°, scapular retraction at 30°, scapular retraction at 90°, scapular retraction at 150°, flexion at 150°, flexion at 90°, and flexion at 30°. The shear elastic moduli of horizontal abduction at 90° and horizontal abduction at 150° were significantly higher than those of other stretching maneuvers. There was no significant difference between horizontal abduction at 90° and horizontal abduction at 150°. CONCLUSIONS: This study determined that shoulder horizontal abduction at an elevation of 90° and horizontal abduction at an elevation of 150° were the most effective stretching maneuvers for the pectoralis minor muscle in vivo.

The effects of a 4-week static stretching programme on the individual muscles comprising the hamstrings.

The aims of this study were to investigate the effects of a 4-week intervention of static stretching (SS) on muscle hardness of the semitendinosus (ST), semimembranosus (SM) and biceps femoris (BF) muscles. Shear elastic modulus was measured by using ultrasound shear wave elastography as the index of muscle hardness. Thirty healthy men (age 22.7 ± 2.2 years) volunteered for this study and were randomly assigned to the SS intervention group (n = 15) or the control group (n = 15). Participants in the SS intervention group received a 4-week stretch intervention for the hamstrings of their dominant leg. Shear elastic moduli of the hamstrings were measured at initial evaluation and after 4 weeks in both groups at a determined angle. In all muscles, the shear elastic modulus decreased significantly after SS intervention. The percentage change in the shear elastic modulus from the value at initial evaluation to after 4 weeks intervention was greatest in the SM. These results suggest that SS intervention has chronic effects on reducing hardness of the hamstring muscle components, especially the SM muscle.

Effects of two stretching methods on shoulder range of motion and muscle stiffness in baseball players with posterior shoulder tightness: a randomized controlled trial.

BACKGROUND: The cross-body stretch and sleeper stretch are widely used for improving flexibility of the posterior shoulder. These stretching methods were modified by Wilk. However, few quantitative data are available on the new, modified stretching methods. A recent study reported the immediate effects of stretching and soft tissue mobilization on the shoulder range of motion (ROM) and muscle stiffness in subjects with posterior shoulder tightness. However, the long-term effect of stretching for muscle stiffness is unknown. The objective of this study was to examine the effects of 2 stretching methods, the modified cross-body stretch (MCS) and the modified sleeper stretch (MSS), on shoulder ROM and muscle stiffness in baseball players with posterior shoulder tightness. METHODS: Twenty-four college baseball players with ROM limitations in shoulder internal rotation were randomly assigned to the MCS or MSS group. We measured shoulder internal rotation and horizontal adduction ROM and assessed posterior shoulder muscle stiffness with ultrasonic shear wave elastography before and after a 4-week intervention. Subjects were asked to perform 3 repetitions of the stretching exercises every day, for 30 seconds, with their dominant shoulder. RESULTS: In both groups, shoulder internal rotation and horizontal adduction ROM were significantly increased after the 4-week intervention. Muscle stiffness of the teres minor decreased in the MCS group, and that of the infraspinatus decreased in the MSS group. CONCLUSIONS: The MCS and MSS are effective for increasing shoulder internal rotation and horizontal adduction ROM and decreasing muscle stiffness of the infraspinatus or teres minor.

Influences of Fascicle Length During Isometric Training on Improvement of Muscle Strength.

Tanaka, H, Ikezoe, T, Umehara, J, Nakamura, M, Umegaki, H, Kobayashi, T, Nishishita, S, Fujita, K, Araki, K, and Ichihashi, N. Influences of fascicle length during isometric training on improvement of muscle strength. J Strength Cond Res 30(11): 3249-3255, 2016-This study investigated whether low-intensity isometric training would elicit a greater improvement in maximum voluntary contraction (MVC) at the same fascicle length, rather than the joint angle, adopted during training. Sixteen healthy women (21.8 ± 1.5 years) were randomly divided into an intervention group and a control group. Before (Pre) and after (Post) training, isometric plantarflexion MVCs were measured every 10° through the range of ankle joint position from 20° dorsiflexion to 30° plantarflexion (i.e., 6 ankle angles). Medial gastrocnemius fascicle length was also measured at each position, using B-mode ultrasound under 3 conditions of muscle activation: at rest, 30%MVC at respective angles, and MVC. Plantarflexion resistance training at an angle of 20° plantarflexion was performed 3 days a week for 4 weeks at 30%MVC using 3 sets of twenty 3-second isometric contractions. Maximum voluntary contraction in the intervention group increased at 0 and 10° plantarflexion (0°; Pre: 81.2 ± 26.5 N·m, Post: 105.0 ± 21.6 N·m, 10°; Pre: 63.0 ± 23.6 N·m, Post: 81.3 ± 20.3 N·m), which was not the angle used in training (20°). However, the fascicle length adopted in training at 20° plantarflexion and 30%MVC was similar to the value at 0 or 10° plantarflexion at MVC. Low-intensity isometric training at a shortened muscle length may be effective for improving MVC at a lengthened muscle length because of specificity of the fascicle length than the joint angle.