I've heard both sides: that doing reps of 20 helps build endurance and also that it's not worth doing more than 12 reps. Are there any professionals in the strength training field that have info on this? Or are there any websites out there with professional studies? I just did a high rep workout and it kicked my butt. I think sticking to this workout will help my endurance on the court but wanted to read up on it. I wonder what Nadal does.