With hamstring injuries being around 16% of all athletic injuries and reports of re-injury rates as high as 34%, identifying risk factors and appropriate rehab protocols is important for helping athletes play safely. Proper recovery from an injury is extremely important as research suggests that recovery from recurrent strains takes longer than the initial insult.
Hamstring injuries in athletics usually occur in one of two ways. First, when the hamstring is stretched to the extremes of joint positions such as during a football kick. The recovery time from these tend to be slightly longer as the injured site is more frequently the proximal tendon of the semimembranosus. The second common injury mechanism occurs during running in early stance phase or late swing.
Recently, hamstring strain injury rehab protocols have begun focusing on eccentric loading in lengthened states. This is based on research showing changes in position of peak torque and length-tension relationships following injury.
Schmitt, Tyler, & McHugh proposed an updated hamstring strain rehab protocol. During the first stage of rehab, the focus should be on protecting the injuries tissue while maintaining flexibility and strength. Submax isometric hamstring strengthening at multiple angles can be started 2 days after injury. Painful stretching should be avoided but stretching is important to maintain hip and knee range of motion. The athlete can be progressed to the next rehab phase once gait is normalized and hamstring strength is 50% of the contralateral leg.
Phase 2 begins concentric and eccentric loading of the hamstrings with exercises such as straight leg deadlifts and Nordic hamstring curls (see my article on Nordic Curls here). Increased stretching may be initiated but painful ROM should continue to be avoided. This phase is completed when the hamstrings test 5/5 by manual muscle testing (MMT) and forward/backward jogging are pain-free.
The last phase of rehab focuses on increasing functional exercises and strengthening in a lengthened state. Plyometrics, high level balance activities, sport-specific drills are important in this phase. The authors also recommend perform hamstring curls while pulling the knee towards the chest (hip flexion >90 degrees) to work the muscle in an extremely lengthened state (same position as MMT testing below). The exercises is performed with the hamstrings eccentrically resisting and using the arms to bring the knee back into full flexion before beginning the eccentric contraction again. Following this stage, the athlete should have full mobility, strength, and coordination to return to full sports participation without restrictions.
For return to play decision making, the authors suggest testing hamstring strength in a lengthened state. The athlete lays supine and pulls the knee towards the chest. The examiner then passively extends the knee until soft tissue restriction. The stretch is then released 10 degrees and manual muscle testing is performed.
The authors conclude their paper by stating that lengthened state strengthening of the hamstrings will help reduce the rate of re-injury and help with deciding when athletes are ready to return to play.
(Update: See my article on the L-Protocol for hamstring rehab here)
Schmitt, Tyler, & McHugh (2012). Hamstring Injury Rehabilitation and Prevention of Reinjury Using Lengthened State Eccentric Training: A New Concept. The International Journal of Sports Physical Therapy, 7(3).