A hamstring strain can occur during an isolated athletic activity (acute) or result from persistent repetitive stress (chronic). Often an acute strain occurs as a result of a chronic condition which has rendered the muscle weak and vulnerable .
As in the case of the football player, hamstring strains often occur while sprinting. They also can occur during jumping and other activities where quick starts and stops are required. High risk sports for hamstring strains are: triathlon, rugby, tennis, basketball, and many track and field events. Runners are especially susceptible to chronic hamstring strains due to the repetitive nature of the sport.
The major factors in hamstring strains are low levels of fitness and poor flexibility. Children very seldom suffer hamstring strains, probably because they are so flexible. Muscle fatigue and not warming up properly can contribute to hamstring injuries.
Imbalances in the strength of different leg muscles can lead to hamstring strain. The hamstring muscles of one leg may be much stronger than the other leg, or the quadriceps muscles on the front of the thigh may overpower the hamstrings.
Hamstring strains usually occur during heavy exercise. In especially bad cases, an athlete may suddenly hear a pop and fall to the ground. The athlete may be able to walk with only mild pain even in a severe injury. But taking part in strenuous exercise will be impossible, and the pain will continue.
In less severe cases, athletes notice a tight feeling or a pulling in their hamstring that slows them down. This type of hamstring strain often turns into a long-lasting problem.