With statistics and trends over the last 20 years pointing towards an increase in overuse injuries among kids who are playing sports, the obvious next step is to determine the causes and then do everything possible to reverse the trend. Pinpointing the exact cause will be difficult, while the answer is simple.
I will start by dissecting a year-round training program. Generally, sports programs have two areas of coaching influence. The first comes from the discipline coach. Using rowing as an example, the discipline coach teaches a kid how to row, which includes the proper use of technique and tactics. Technique involves the skills necessary to get in a boat and row. Tactics are how the game is played - or, in the case of rowing, how the race is managed.
The second area of influence comes from the conditioning coach. This individual might be hired privately by the parent to help a child get into shape for sport. Or, he or she is a paid coach hired by a high school to prepare athletes for all sports during a school year.
There is a potential third coaching influence: a specialty skills coach. For example, some baseball teams have a batting coach. Or a parent might hire a batting coach for some "extra" swing work. Whatever the case, it is possible that a child will have one or more coaches from the sports side and then a conditioning coach who either comes with the program or is hired privately.
Given all of these coaching possibilities and influences, the first question to ask is straightforward: "Who is in charge?" With a potential of two or more coaches - each talented and with an agenda - telling a kid what to do, the possibility is very high for a problem developing. This is generally not a concern if the coaching staff all works together under the direction of a head coach. However, problems start to arise when there are outside coaches. It doesn't even matter if all of the coaches are the "best".
Too many workouts, along with too many directions, can cause problems, even with the best of intentions. It can lead to over training, confusion, extra pressure and potentially end a kid's sports life forever.
The simple answer to the question in the first paragraph is to drop one of the teams and one of the extra coaches. Let your young aspiring athlete get more rest, perhaps some unstructured play, and then with the "right" type and volume of exercise and sports participation, you will see fewer injuries and more success.