In order to understand what good exercises for injury free hamstrings are, a basic understanding of the hamstring muscles and their anatomy is required. The hamstrings are composed of 3 muscles on the back of the thigh: the semimembranosus and semitendinosus on the inner side, and the biceps femoris on the outer side. Collectively the hamstrings contract to produce bending of the knee and extension of the hip. The inside muscles (semimembranosus and semitendinosus) tend to act more in bending the knee, whereas the outside muscle (biceps femoris) tends to act more in extending the hip.
The vast majority of hamstring injuries involve the biceps femoris muscle. The reason this happens is because of the role this muscle performs when running. When running at high speeds the biceps femoris muscle contracts to decelerate the leg after you take a stride forwards (being stretched in the process), and then as soon as your foot hits the ground it contracts forcefully to drive your hip into extension and propel your body forwards. As a result, this muscle has to contract strongly and quickly at the same time it is being stretched. This makes it more prone to being injured. Add in demands of sports such as bending forward to pick up a ball or running off a mark that add further stretch to the hamstrings, and you can see why this injury is so common.
In light of the predominant involvement of the biceps femoris muscle in hamstrings injuries, exercises that help to strengthen this muscle are believed to be the best choice for protecting against strains and tears. This is particularly important if the muscle has previously been strained – even if pain free and healed, the muscle will tend to remain weaker and inhibited for a number of months after injury. Particular focus is placed on exercises that train the ability to contract the biceps femoris effectively and strongly when it is in a lengthened state - so as to protect against the injury mechanism. These exercises are commonly referred to as ‘hamstring eccentric exercises’. Supplementary exercises should also be included to help to build muscle size (hypertrophy) and maintain symmetry between the inside and outside hamstrings muscles.
The following videos demonstrate two eccentric exercises for targeting biceps femoris (arabesques, Nordics) and one supplementary exercise that focuses on eccentric open chain control with resisted concentric contraction.
Try some of these exercises in your training program to decrease the risk of a hamstring injury and spending time on the sidelines.
The Gap Physio