Using momentum to help lift weights builds arm muscles just as well as lifting slowly and carefully for beginners doing bicep curls and triceps pushdowns over 8 weeks.

When beginners do arm curls and triceps exercises with a little swing to lift heavier weights, their arms grow just as much as when they do the movements slowly and strictly—even though they lift way more total weight with the swing.

Even though people who swing weights use their whole body more, their upper arms don’t get any thicker than those who lift strictly—so the extra movement doesn’t help build more arm muscle.

People who swing the weights while doing arm exercises can lift a lot more total weight over time than those who do it slowly and strictly—even though both groups end up with the same size arms.

Training one arm with heavy eccentric curls makes the other arm stronger too—even though it didn’t lift any weights—by about 10%, while the trained arm gets even stronger, by nearly 20%.

When untrained adults want bigger biceps, doing simple curl exercises works better than doing rows that use multiple muscles at once.