What makes an exercise good for building muscle?
Here are six criteria to consider:
It targets one/several of the functions of the muscle. An easy-to-use resource is ExRx, if you’re unsure of a muscle’s functions and anatomy.
It takes the target muscle close to failure. This one is a bit subjective. As a rule of thumb, an isolation exercise will be better in this regard, since there are fewer other muscles that could give out first. Another rule of thumb - if you don’t feel anything in the target muscle during a set, between sets, or even the days after, it may not be trained close to failure with this exercise! Similarly, a chest supported machine row would likely be better for the upper back than a bent over row, since it doesn’t involve the lower back, which both adds fatigue and adds another potential bottleneck.
It focuses on the stretch. Ideally, this means that you can get into a deep stretch for the target muscle, and there is plenty of resistance in that position. If you can move through that part of the lift effortlessly (e.g. a dumbbell kickback or rear delt dumbbell fly), it probably isn’t an ideal exercise. Ideally, since lengthened partials might cause more muscle growth than a full range of motion, the exercise should also be safe to perform lengthened partials on. A dumbbell press would be better than a barbell bench press in this regard.
Loadability (minor). The reason this isn’t a primary criterion of an effective exercise is because muscle growth can be maximised within a wide rep range of 5 to 50 reps per set, provided you actually go close to failure. However, if you can’t get 5 or more reps, or the exercise cannot be loaded, and is so light you need to do 50+ reps to reach failure, it becomes less effective.
Stability. While the research isn’t clear on this yet, we probably want to be reasonably stable (i.e. squatting on a bosu ball isn’t helping our quads grow).
Time efficiency. Certain exercises are just much more time efficient. Since most people have time constraints, picking the right exercises can allow them to perform more volume, and likely grow more muscle. Pin-loaded machines, dumbbell exercises, and bodyweight exercises all work great in this regard.
