Semitendinosus

The semitendinosus is part of the collective hamstring muscles, along with the biceps femoris (long and short heads) and semimembranosus, which are located at the rear of the thigh. The semitendinosus has a long tendon insertion.

The semitendinosus is recruited during flexion of the knee and also extension of the hip.

As the semitendinosus is responsible for both flexion of the knee, and extension of the hip, the muscle can be recruited by exercises that involve both actions. Exercises such as leg curls will recruit the hamstrings via flexion of the knee. Exercises such as good mornings or SLDL (stiff leg deadlift) will recruit the hamstrings via extension of the hip.

The mindset of some people seems to be that SLDL is the superior choice for stimulation of the hamstrings. The reason behind this is likely as compounds are usually seen as a better alternative to isolation exercises as they recruit more muscles, and therefore more stimulus.

SLDL is an effective exercise to stimulate the hamstrings via extension of the hip, however isolation exercises that require flexion of the knee can play an integral role in development of the hamstrings. Exercises that isolate the flexion of the knee can also prove advantageous as an outlet for trainers who have issues with not being able to perform SLDL, such as concerns with a back injury.

The hamstrings have been shown to have an abundance of type ii fibres.

6-12 reps will likely provide optimal time under tension for the semitendinosus muscle, providing adequate stimulation for sarcoplasmic hypertrophy for its type ii fibre majority make up. Furthermore, acute response to anabolic hormone concentrations, compared to that of lower rep ranges.
1-5 reps may prove more advantageous if the goal is power and strength. This will ideal for recruitment of the large motor units and type iiB fibres, and neural adaptations of the nervous system.