Sitting too much: Being in positions where your hamstrings are shortened, like sitting for long periods of time, can also lead to tight hamstrings, Matheny said.Not stretching your hamstring muscles: Failure to use your hamstrings in their full range of motion can lead to tightness, said Albert Matheny, R.D., C.S.C.S.There are a few potential reasons why you might have tight hamstrings.