A hamstring pull occurs during the switch between late leg recovery and initial leg approach in the swing phase, and the ground contact phase of running. This occurs for a number of reasons. First, a weak bicep femoris can give way during a pulling phase. Another cause can be stiffness in the hamstrings, which causes a decreased ability to absorb shock, which in return causes an abrupt pull on the muscle. Improper mechanics in running as well as a failure to warm-up the muscle can result in the pulling of a hamstring.
In order to prevent such an injury one must focus on multiple areas of performance. The hamstrings are a large muscle group that is used quite regularly and when placed under stress can provide insight into weak areas of a training regimen. As trainers we should focus on multi-joint exercises that require coordination and control under light loads in order to maintain proper mechanics. Working the hamstrings during the lengthening phase, eccentric phase, will allow the muscle to react to weight more naturally. This will train the muscle to build strength in its strongest yet most vulnerable setting. Another focus is the flexibility within the muscle. The tighter a muscle is the more likely the chance it will succumb to injury. Proper warm-up and stretching is key to maintaining a strong and healthy hamstring.