I had a similar problem. Was doing heavy squats twice a week and every time I started the squat workout my quads would burn and hurt. After a few sets it would get better but had this problem all the time. I went to doing squats once a week and replaced the other session with deadlifts and no more pain in the quads. Also weight went up quite a bit on squat and I was stuck there for a while. So my guess is he's over training. Larger muscles if worked hard need longer to recover.