Use heavy eccentric contractions to prevent injury when sprinting and improve speed. Research shows that based on sprinting movement analysis, the best way to prepare the hamstring for high speed and extreme ground reaction forces is heavy eccentric training.
Hamstrings are one of the most commonly strained muscles in high speed sports such as soccer, rugby, football, and sprinting. The majority of hamstring injuries occur while running at maximal speeds, partly because the hamstring is a biarticular muscle that crosses two joints—the hip and knee and joints. A contributing factor is that the musculotendon unit of the hamstring is at its longest during terminal swing just prior to foot strike when sprinting. Peak length is about 10 percent longer than when in an upright stance.
It is well known that the hamstrings utilize the stretch-shortening cycle when sprinting, with the muscles lengthening during the terminal swing before touchdown, switching to a shortening phase just prior to foot-strike. During the terminal swing the hamstring muscles have the greatest biomechanical load because each of the individual muscles that make up the hamstring reach peak strain and perform large amounts of negative or eccentric work.
Interestingly, the movement analysis found that the three hamstring muscles experience the terminal phase differently: the biceps femoris had the largest peak strain (12 percent increase in length from upright stance), the semitendinosus had the greatest lengthening speed, and the semimembranosus produced the highest force and performed the largest amount of positive and negative work. These mechanical differences do not explain why the biceps femoris is the most commonly injured hamstring muscle. Rather, researchers suggest that the fact that the biceps femoris experiences the largest peak strain is a more effective predictor of injury or vulnerability. Essentially, the muscle damage suffered by the biceps femoris during an eccentric contraction is not just a function of peak muscle force, but rather a result of the magnitude of strain experienced by the musculotendon unit during contraction.
Apply this movement analysis to your training by using high load eccentric exercises that include negative contractions at longer musculotendon lengths. The Nordic Eccentric Hamstring exercise along with lying hamstring curls with feet inward, outward, and neutral are a great place to start to keep you healthy. Good Mornings, Romanian Deadlifts, and Reverse Hyperextensions can be added as you get stronger. For a complete hamstring workout to promote structural balance, read Fast Track to Bulging Hamstrings
Schache, A., Dorn, T., et al. Mechanics of the Human Hamstring Muscles During Sprinting. Medicine and Science in Sports and Exercise. September 2011. Published Ahead of Print.