Keep in mind that it's been the rookies - who are adjusting to the NFL and have worked with Woicik the least - who are having these hamstring issues.
And I firmly believe that the Cowboys are being overly cautious in bringing them back when the games don't count.
That said, on a related note, I think the entire NFL can do a better job of physical training. A huge focus on the weight room, but little to none on yoga, Pilates, or a dedicated stretching program. The first team to take that seriously will have a distinct advantage in my opinion.