This remarkable study demonstrated an improvement in sprinting ability in a group of elite male soccer players, after training using (open chain) lying leg curls with eccentric overload. (strengthandconditioningresearch.com)
Alternate between seated and lying leg curls on each workout to achieve best results. (fitnessandpower.com)
You probably do your hamstring exercises after doing an hour of quads, which exhausts them, and at the very end you just do a few lying leg curls that are rarely performed with the adequate intensity. (fitnessandpower.com)