Training one arm at a time doesn’t make you stronger when lifting with both arms together — your total strength gain is the same as training both arms at once.

Scientific Claim

In untrained young women, 8 weeks of unilateral or bilateral biceps curl training produces no significant difference in bilateral 1-repetition maximum strength gains, despite unilateral training improving right-arm unilateral strength.

Original Statement

“The 1RM BIL changes were not different between groups [∆ -0.28 (-1.23, 0.66) kg].”

From study:Small muscle mass exercise enhances muscular adaptations? Effects of unilateral and bilateral biceps curl on maximum strength and muscle size changes.

Evidence Quality Assessment

Claim Status

appropriately stated

Study Design Support

Design supports claim

Appropriate Language Strength

definitive

Can make definitive causal claims

Assessment Explanation

The RCT design and direct measurement of bilateral 1RM with overlapping confidence intervals around zero support a definitive conclusion of no difference in bilateral strength adaptation.

Evidence from Studies

Supporting (1)

Small muscle mass exercise enhances muscular adaptations? Effects of unilateral and bilateral biceps curl on maximum strength and muscle size changes.

Randomized Controlled Trial

Human

2025 Dec 8

Both ways of doing bicep curls—using both arms at once or one arm at a time—led to the same increase in strength when both arms were used together, even though doing one arm at a time made that one arm stronger.

Contradicting (0)

No contradicting evidence found

Source Study

Small muscle mass exercise enhances muscular adaptations? Effects of unilateral and bilateral biceps curl on maximum strength and muscle size changes.

Score: 61

DOI: 10.1007/s00421-025-06033-4

Similar Assertions

Doing bicep curls one arm at a time makes your right arm stronger than doing them with both arms together, but doesn't make your biceps bigger than using both arms.

91%

Training your right arm alone makes your right arm stronger, but doesn’t help your left arm get stronger — the benefit stays on the side you trained.

88%

Doing bicep curls with one arm makes that arm stronger for one-arm curls, but doesn’t make you stronger for two-arm curls or the other arm.

88%

Whether you lift weights with one arm or both at the same time, your biceps grow about the same amount after 8 weeks of training.

86%

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%.

78%