I’m not an advocate of treadmill running either, but if Surin (who I would consider a “top sprinter”) can run 9.84 after having done at least one treadmill session a week throughout all of his GPP and half of his SPP it can’t be too harmful for your speed development. The best three male sprinters of all time don’t seem to be doing heavy squats as part of their training, does that mean Charlie was wrong in having his athletes do them?