Non‐uniform distribution of passive muscle stiffness within hamstring

Abstract

Limited information is available on whether stiffness is different within and between the constituents of the hamstring, that is, the biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM). Therefore, understanding of hamstring injuries and stretching effect on hamstring stiffness is difficult. The present study primarily aimed to identify whether passive muscle stiffness differs between the BFlh, ST, and SM and between the proximal, middle, and distal sites within each muscle. Secondly, the effect of stretching exercise on the heterogeneity in passive muscle stiffness was examined. In the lengthened hamstring positions by extending the knee joint or flexing the hip joint, passive muscle shear modulus (a measure of stiffness) at the proximal, middle, and distal sites of the BFlh, ST, and SM was measured by using ultrasound shear wave elastography. Furthermore, before and after five repetitions of 90‐seconds static stretching for the hamstring, passive muscle shear modulus at the proximal and distal sites of the SM was measured. The shear modulus was significantly higher in the SM than in the BFlh and ST and higher at the distal site than the proximal site in all muscles. After the stretching, the higher shear modulus at the distal site of the SM compared to the proximal site was still observed (pre‐stretching: +80%, post‐stretching: +81%). These findings indicate that passive muscle stiffness varies within the hamstring regardless of performing stretching exercise and that passive muscle stiffness is not highest at the proximal site of the SM where a stretching‐type hamstring strain typically occurs.

Site‐specific features of active muscle stiffness and proximal aponeurosis strain in biceps femoris long head

“…Again, the present study showed, for the first time, significant heterogeneity of BFlh muscle stiffness along its length under active condition (i.e., at 20% MVC), with the distal site being stiffer than the proximal and central sites. The difference may be explained by higher passive muscle stiffness at the distal site within the BFlh 16 . Besides, the site‐specific difference in BFlh muscle stiffness at low contraction intensity may also be explained by spatial variation in EMG activity since BFlh EMG activity at 20% MVC was greater in the distal than the proximal site.…”

“…Localized shear wave speed (a proxy for stiffness, expressed in the unit of Pascal) was quantified using the ultrasound apparatus in SWE‐mode. According to a previous study that examined the heterogeneous distribution of passive muscle stiffness within the BFlh, 16 the measurement sites of the shear wave speed and EMG activity were determined at the levels of 25% (proximal), 50% (central), and 75% (distal) of the muscle belly length (Figure 2). The optimal probe orientation was adjusted for subject by subject to identify fascicles without interruption across the B‐mode image before data acquisition.…”

“…Simulation studies reported that during running, the hamstring experiences active lengthening when decelerating the limb in the latter half of swing phase, 13,14 which is likely when the BFlh strain injury (I e , sprinting‐type hamstring strain injury) typically occurs 15 . A recent study reported higher BFlh muscle stiffness in the distal than the proximal site under passive (resting) conditions 16 . However, muscle stiffness characteristics assessed under passive conditions are unlikely to reflect the stiffness responses under active conditions 17,18 .…”

Spatial-frequency Analysis of the Anatomical Differences in Hamstring Muscles

“…In the event of a significant interaction, only comparisons between locations within the same muscle are presented in the Results as these are both clinically and anatomically meaningful. 9,17 Pennation angle for each muscle and location were summarized by means and standard deviations for comparisons with previous investigations. 9,10 Separate Pearson’s correlation coefficients were calculated between the measured pennation angles and extracted SFA parameters values.…”

“…Characterization of muscle structure and tissue properties has many important implications in research and clinical care, for example with respect to biomechanical modeling 13,14 or hamstring strain injury risk. 15,16 Recently, studies have investigated regional variation in mechanical properties 17 and activation levels 18 along the hamstrings in response to stretching and various exercises used in injury prevention programs. The role that regional variation of tissue organization of architectural arrangement, tissue properties, and muscle activation may have on factors influencing whole muscle mechanics may have important implications on regions of the hamstring muscles that may be the most susceptible to injury.…”