Yamagata Prefectural University of Health Sciences

Supraspinatus (SSP), infraspinatus (ISP), and subscapularis (SSC) muscles from the rotator cuff (RC) are comprised of anatomical subregions based on muscle fiber alignment and tendon attachments. Previous studies have shown mechanical interactions between the SSP and ISP tendons, with abduction angle influencing these interactions. However, changes in strain distribution originating from the RC muscle subregions, including the SSC, due to differences in abduction angle have not been investigated. Therefore, this study aimed to determine the strain distribution in intact RC cadaveric shoulders with loading from the SSP, ISP, and SSC muscles and their subregions at different abduction angles. Surface strains in the bursal side of the SSP, ISP and SSC tendons of eight fresh frozen cadaveric intact shoulders were obtained by applying tension on these muscles and on their subregions at 25° and 45° glenohumeral abduction using an MTS system. When the SSP muscle or anterior region was loaded, no significant strain differences were observed within the footprint regions at 45° abduction. However, when the posterior region was loaded, strains concentrated on the middle facet as the abduction angle increased. Significantly higher strains were also observed in the inferior portion of the footprint with increasing abduction angle when the ISP or SSC muscles, or their subregions, were loaded. The differences in strain distribution patterns observed between the anterior and posterior regions of the SSP muscle highlight the importance of addressing each region and tendon separately when managing RC tears and repairs.

Introduction Deep squats are important functional movements in many Asian cultures, and the ability to perform this movement is a key indicator of lower-limb function. Ankle joint range of motion, particularly dorsiflexion, plays an important role in deep squats. This study aimed to investigate the relationship between muscle stiffness in the triceps surae (medial and lateral heads of the gastrocnemius and the soleus) and the ability to perform deep squatting motions, as measured by the shear modulus. Methods A total of 45 healthy participants were recruited for this study, including 24 males (53.3%) and 21 females (46.7%). We measured the stiffness (shear modulus) of the gastrocnemius and soleus muscles at various ankle dorsiflexion angles (0-40°) in the flexed knee position. The participants were divided into a "possible group" (those able to perform a deep squat with heels on the floor) and an "impossible group" (those unable to perform the deep squat with heels on the floor). The shear modulus values of the medial and lateral heads of the gastrocnemius and the soleus muscle were compared between the two groups. Results The shear modulus of the soleus muscle at 40° of ankle dorsiflexion was significantly lower in the impossible group (14.09 ± 6.79 kPa) than in the possible group (9.37 ± 5.55 kPa, p < 0.05). The intraclass correlation coefficient (ICC) values for the muscle measurements ranged from 0.75 to 0.89, indicating good reproducibility. Conclusion This study showed that soleus muscle stiffness at 40° ankle dorsiflexion differed between individuals who can and cannot perform deep squats. This suggests that insufficient elongation of the soleus muscle may hinder the achievement of the dorsiflexion angle necessary for deep squats.