Anatomy of the hamstrings: The hamstrings are a collection of 3 individual muscles 1.Biceps femoris 2.Semitendinosus 3.Semimembranosus They all work together but have slightly different roles. During sprinting the biceps femoris takes the biggest load, the semitendinosus is lengthened the most and semimebranosus acts as a force producer. During rehab you want to target the hamstrings collectively as they work together to achieve both hip extension and knee flexion, however, it is important to note the different functions so you can target the specific activity of the desired muscle. Injuries and Rehab During sprinting most injuries occur in the terminal swing phase whereby the hamstrings are in their lengthened position and are working eccentrically. If you have a reduced capacity to develop high eccentric force you are more predisposed to hamstring injuries. Another factor which increases risk is fascicle (muscle fibers) shortening. To reduce the risk of injury you want to aim to keep your hamstrings lengthened and strong. Research shows the eccentric strengthening programmes can help increase strength as well as lengthen the fascicles. The load and volume of these exercises are not definitive in the research but incorporating programmes like the Nordic hamstring exercises may decrease your risk of injury. Hamstring injuries are typically seen in the final 3rd of training/competition where fatigue is involved. Incorporating isometric exercises (exercises where the length of the muscle does not change) can help develop fatigue resistance
Isometric exercises are also beneficial following an injury as they work to overcome muscle inhibition as a result of the bodies protective reaction to injury. Isometric exercises are also chosen over eccentric exercises when pain is a limiting factor in your rehab. There are lots of rehab exercises and options that are available, but there is not one plan that fits all. It is a good idea to get assessed and receive advice on where to start and how to progress your rehabilitation.