Too much sprinting?
Before starting on PBF, my regular workout consisted mainly of cycling flat out for 15 mins commuting to work and back every day. I've since started cycling at a more leisurely pace to add to my low level cardio instead, and doing a running sprint session once a week. I kind of miss the flat out cycling first thing in the morning though, so I'm wondering if is actually a problem doing it that often? Going by Doug McGuff's explanation of cell metabolism in his Body by Science talks, I'd guess it's a great aerobic workout, but am I overtraining?
you are absolutely NOT overtraining. by all means, enjoy your flat out 15 minute cycle sesh to work. good for you, go for it.
It's play! When it starts to feel like something you have to do a certain way or it's not as good, then it becomes a workout.