As I understand it, volume overtraining aerobically is counterproductive to hypertrophy. Is this true? If so, how/why does this occur? Also, how does one gauge (in order to prevent) volume aerobic overtraining?
I think your question has a couple of parts that kind of fit together, so I will answer to the best of my understanding. You asked about aerobic (over) training and its effect on hypertrophy.
First, let's tackle overtraining: ANY form of activity/exercise can cause overtraining. Overtraining is simply a state in which the body is unable to restore or recuperate its energy supply. It should be quite clear that when the body is in a state of overtraining, it will not have the proper energy supply to dedicate to increasing tissue in the body (hypertrophy). This is one of the main reasons why so many people try so hard to gain muscle mass and never seem to change.
Secondly, aerobic training (I'm assuming is meant to be "cardio") can cause interference with hypertrophy by simply expending excess calories. To gain weight the body must have a caloric surplus (more calories/energy than it needs to maintain balance). By performing "aerobic" exercise, the body burns more calories and if it is enough can keep the body at a balanced or negative state. If it is balanced, no weight will be lost or gained. If it is negative weight will be lost. A lot of people feel that aerobic training or endurance training emphasizes slow twitch type I muscle fibers and thus detours development of type II fast twitch fibers that are more predominant in hypertrophy. However, there is very little research on endurance training and hypertrophy. There is research on endurance training and strength, but it is mixed. Lastly, the simplest way to gauge overtraining is:
- Through communication with the client about their daily physical and mental states (trouble sleeping)
- Observing their workouts for decreased motivation, decreased strength,increased soreness and for longer periods of time