Hamstrings Tissue Arrangement Aids Function Fact Check

The initial limb bud arises from the lateral plate mesoderm.[6] Between weeks 5 and 7 of embryogenesis, these migrating cells accumulate in the posterior compartment of the thigh, where mesodermal cells differentiate into myoblasts, which proliferate and fuse to form functional muscle tissue.[7] By week 8, individual hamstring muscles are distinguishable, and anatomic relationships to the femur and sciatic nerve are established.

During this rapid transition of functional biomechanics of these muscles, they are most vulnerable to injury.[2] Besides this, dual nerve supply of two heads of biceps femoris leading to asynchronous stimulation as well as an anatomical variance of attachment of its two heads makes it more commonly injured hamstring.[3] ... Grade 2: Identifiable partial disruption of tissue with moderate pain and swelling, leading to loss of function.

Each individual hamstring MTU is unique, differing with respect to muscle fibre arrangement, PCSA, fascicle lengths, pennation angles, volume and connective tissue characteristics among other features (Table 2) [40, 42, 166]. In addition, some of these architectural characteristics, such as fascicular arrangement, fascicle lengths and pennation angles, display high variability within individual hamstring muscles [42]. Relative to one another, some of the hamstring muscles, such as semitendinosus and BFsh, are arranged in a manner that appears most beneficial for facilitating large fascicular excursions.

The skin, subcutaneous tissue, superficial and deep fasciae, gluteus maximus, and neurovascular bundles were removed from the posterior thigh to reveal the hamstring muscles. The SM, ST, and BFlh were then released from the ischial tuberosity, and the BFsh was removed from the lateral lips ...

These findings could be due to the infiltration of non-contractile tissue in aged hamstrings (Overend et al., 1992; Yoshiko et al., 2017), altered MU facilitation, age-related remodeling (Webber et al., 2009; Hepple and Rice, 2016), muscle fiber membrane dysfunction, decreased sarcoplasmic reticulum function, altered calcium ion kinetics, and changes in connective tissue elements (Narici et al., 2008; Hepple and Rice, 2016). Hamstrings have a significantly lower MU discharge rates in the elderly, as opposite to findings in the vastus medialis portion of the quadriceps (Roos et al., 1999). In vitro and animal studies suggest that the loss of proprioceptive sensory neurons and innervation differences occur at different rates between flexors and extensors during the aging process (Vaughan et al., 2016).

While Nordic hamstring exercise (NHE) training has been shown to reduce hamstring strains, the muscle-specific adaptations to NHE across the 4 hamstrings remain unclear. This study investigates architectural and microstructural adaptations of the biceps femoris short head (BFsh), biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM) in response to an NHE intervention. Eleven subjects completed 9 weeks of supervised NHE training followed by 3 weeks of detraining. Magnetic resonance imaging was performed at pre-training, post-training, and detraining to assess architectural (volume, fiber tract length, and fiber tract angle) and microstructural (axial (AD), mean (MD), radial (RD) diffusivities, and fractional anisotropy (FA)) parameters of the 4 hamstrings.

Besides this, dual nerve supply of two heads of biceps femoris leading to asynchronous stimulation as well as an anatomical variance of attachment of its two heads makes it more commonly injured hamstring. ... Grade 2: Identifiable partial disruption of tissue with moderate pain and swelling, leading to loss of function.