CC, can you please explain why sprints post workout will burn muscle?[/quote]
Sprints, or any high intensity cardio, done right after weights will be more prone to burning muscle/protein for fuel since you’ll be somewhat more glycogen depleted from lifting. If cardio is going to be done right after weights, lower intensity is more appropriate in order to preserve muscle. The right peri-workout nutrition might help this to some degree, but I still wouldn’t push it.
Simple energy management is another factor. The “high intensity” of a HIIT session will be higher as a session by itself compared to how “high intensity” you can be after you’ve already been lifting for an hour and a half.
I think I know what you mean, but I wouldn’t say they’re “catabolic” in the sense that they’re only going to destroy muscle. HIIT and weight training can both be anabolic/stimulate hypertrophy to some extent. It’s just a matter of nutrition (daily and peri-workout) and managing the intensity, volume, and frequency of training.
Depending on what the HIIT session looks like, it wouldn’t be like doing just one more weight training exercise. It would be like doing a big compound lift for 5 or 6 very heavy sets of 2. By itself… good workout. Done right after you’ve already trashed the target muscle group… no real benefit.