The semitendinosus, or ST, the semimembranosus, or SM, and the biceps femoris long and short heads (BFLH and BFSH) are part of the hamstring muscle group. They primarily function with the extension of the hip and flexion of the knee as well as providing multi-directional stability of the tibia and pelvis. These three muscles which make up the hamstring muscle group, cross the posterior aspect of both the hip and the knee joints, making them bi-articular. As a result, they are consistently responding to large mechanical forces created by upper limb, trunk and lower limb locomotion as a means of concentric and eccentric mobilization. During sporting activities, these forces will tend to increase, augmenting the frequency of injury.
In a study conducted at the University of Melbourne, biomechanical analysts measured the musculotendinous strain, velocity, force, power, work and other biomechanical loads experienced by the hamstrings throughout the course of over-ground sprinting and compared the biomechanical load across each individual hamstring muscle.
Basically, the hamstrings are subjected to a stretch-shortening cycle when sprinting, with the lengthening phase occurring during the terminal swing and the shortening phase commencing just before each foot strike, continuing throughout the stance. Then, the biomechanical load on the bi-articular hamstring muscles were determined to be stronger during the terminal swing.
BFLH had the greatest musculotendinous strain, ST displayed considerable musculotendinous lengthening velocity, and SM produced the highest musculotendinous force and both absorbed and generated the most musculotendinous power. Similar research also distinguished peak musculotendinous strain as a large contributor to eccentric muscle damage or injury, most commonly acute hamstring injuries, instead of peak muscle strength. This is why eccentric strengthening is often a rehabilitation recommendation for acute hamstring injuries.
Several sports and physical activities which involve a high demand of excessive stretching or sprinting, including kicking, sliding and split positions, have been determined to increase the risk of acute hamstring injuries among athletes. Acute hamstring injuries vary greatly from one another and because of this, offering the proper recommendations regarding rehabilitation can be challenging. For more information, please feel free to ask Dr. Jimenez or contact us at (915) 850-0900.