Including one isolated arm exercise in a workout routine that already includes compound movements leads to only a small increase in muscle size, even if the total amount of exercise is not kept the...
Mechanism
Synthesis from 1 study
When you do big exercises like bench presses, your arm muscles are already pushed as hard as they need to be to grow. Adding a separate arm exercise doesn’t help much more because your muscles are already getting the full growth signal — the study 10.1139/apnm-2012-0176 shows that extra work...
Most probable mechanism
When you do compound exercises like bench presses, your arm muscles are already working hard and getting the signal to grow. Adding a separate arm exercise doesn’t help much more because the muscles are already fully stimulated — the same muscle fibers are being used again, and the body doesn’t make more growth signals just because you added another set. This is shown in the study where adding an arm isolation exercise didn’t increase arm growth beyond what compound exercises alone achieved (10.1139/apnm-2012-0176).
Compound exercises recruit a high proportion of motor units in the target muscle group, activating a large fraction of available muscle fibers during contraction (10.1139/apnm-2012-0176)
The mechanical tension and metabolic stress from compound movements trigger intracellular signaling pathways (e.g., mTOR) that initiate muscle protein synthesis at near-maximal levels for the given training stimulus (10.1139/apnm-2012-0176)
Adding an isolation exercise to the same muscle group does not significantly increase the number of recruited muscle fibers beyond what was already activated by compound movements, nor does it further elevate protein synthesis signaling beyond the saturation point established by the compound exercise volume (10.1139/apnm-2012-0176)
Evidence from Studies
Supporting (1)
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Effect of adding single-joint exercises to a multi-joint exercise resistance-training program on strength and hypertrophy in untrained subjects.
Contradicting (0)
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