When untrained people lift weights using momentum instead of strict form, they can complete about 70.9% more total work over eight weeks, but muscle growth is similar between the two techniques.
Mechanism
Synthesis from 1 study
Swinging weights lets you lift more total weight because your body doesn't have to work as hard to start and stop the movement. But since the muscles aren't being stretched and squeezed as hard under control, they don't grow bigger—even though you did more work.
Most probable mechanism
When people swing weights during arm exercises, their muscles don't have to work as hard to start and stop the movement, so they can lift heavier weights more times without their nervous system shutting them down. This lets them do more total work, but because the muscles aren't being stretched and squeezed as intensely under control, they don't grow any bigger.
External momentum reduces the need for active muscle control during the initiation and deceleration phases of movement, lowering the neural demand for force production.
Reduced neural demand allows for greater total repetitions and load accumulation without triggering protective neuromuscular inhibition mechanisms that limit force output during strict contractions.
The mechanical tension experienced by muscle fibers during momentum-assisted movements is distributed over a longer time and greater range, reducing peak strain per repetition and limiting the stimulus for muscle protein synthesis.
Evidence from Studies
Supporting (1)
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Do Cheaters Prosper? Effect of Externally Supplied Momentum During Resistance Training on Measures of Upper Body Muscle Hypertrophy
Contradicting (0)
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