Doing short bursts of intense exercise can help your muscles make more proteins, especially the ones in energy factories inside cells, but it doesn’t always make your muscles bigger if you only do it for less than six weeks.

After 10 weeks of working out, men who are already somewhat active don't build muscle as efficiently as before, and their bodies don't respond as strongly to exercise—this happens whether they're doing cardio or weight training.

For men who exercise regularly, doing both weight training and intense cardio together doesn't slow down muscle building compared to just weight training alone, even after 10 weeks of working out.

Taking a lot of creatine for 5 days doesn’t seem to boost muscle repair or growth right after a workout in young, healthy guys—even though it does increase creatine levels in their muscles. So, creatine might help muscles grow in other ways, not by speeding up protein building right after exercise.

When rats do strength exercises for two weeks, their muscles don't get bigger or heavier, even though their muscle-building processes speed up. This might mean the muscles are just reorganizing themselves instead of growing in the short term.

Even though the muscles grew bigger, the body didn’t make more muscle or connective tissue proteins at a faster rate — meaning the growth happened without the usual increase in protein building.