seems like there are several questions:
1) at what point (if ever) is LBM (essential) burned for energy during a workout and is there a non-invasive way to know if LBM is converting to glucose compared to native glucose being burned
2) assuming #1 occurs, at what point is this detrimental to overall LBM as compared to a temporary loss replaced at the next meal
3) at what point does long term endurance training result in the dropping of weight and loss of LBM that is associated with elite athletes in endurance sports
ETA: or what Alan said
