During your overspeed training please consider the below factors:
1. Complete warm-up and flexability exercises prior to overspeed training(especially the hamstrings toprevent injury)
2. Caliber of sprinter ( i've seen slower sprinters fall due to very tense bands over great distances or steep hills). Each coach should monitor the distance being covered during band pulls in relation to the sprinter. It can get really ugly!!
3. Time of season. Make sure your muscles are ready to fire at that rate or you hamstring will give you problems.