This is a typical hip flexor test that I do to look for muscular imbalances, especially for sprinters. This is something you can eliminate automatically, and it will let you know if you are not getting full extension on your stride, in your sprint. Its really simple. All you need a bench and 30 seconds. If they cannot maintain this position for 30 seconds then they have tight hip flexors and it needs to be addressed. Addressing this issue will ensure that you are getting full extension in your sprint stride.