The possible cause of hamstring strains was investigated in football players and track athletes, The subjects were divided into those who did (experimental) and those who did not (control) sustain hamstring strains. Five members of the San Diego Chargers football team and 12 track athletes made up the experimental group while 50 athletes were used as controls. Three tests, cable-tension knee flexion, cable-tension knee extension, and the sit-and-reach were administered to each subject. Two strength relationships were found significant at the .05 level. These relationships were concerned with the strength between the hamstrings, and unequal flexion-extension strength ratio.