Tight hamstrings is spastic contracture of hamstring muscles, but its mechanism has not been well known. We studied about growth factors including age, sex and height when we measured SLR, FFD, Looseness test in 3219 healthy young people (age range, 5-18years). The hamstrings in male were tighter than those in female in each age, which was same in cases with Tight hamstrings. The time of peak of SLR in healthy male and female is seen at the same period as the time of growth spurt. Tight hamstrings tend to appear in this time, and SLR, FFD are severely restricted if some factors of lumbosacral regions are mixed.
