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.

Scientific Claim

In untrained young adults performing single-joint upper-body resistance exercises (biceps curls and triceps pushdowns) for eight weeks, using external momentum ('cheating') during repetitions produces similar increases in muscle thickness and arm circumference as strict form, despite performing approximately double the volume load.

Original Statement

“Results showed similar between-conditions increases for all muscle thickness sites as well as circumference measures, generating consistent support for the null hypothesis (BF = 0.06 to 0.61). Volume load was markedly greater for CHEAT compared to STRICT across each week of the intervention.”

From study:Do Cheaters Prosper? Effect of Externally Supplied Momentum During Resistance Training on Measures of Upper Body Muscle Hypertrophy

Evidence Quality Assessment

Claim Status

appropriately stated

Study Design Support

Design supports claim

Appropriate Language Strength

probability

Can suggest probability/likelihood

Assessment Explanation

The study design (RCT) supports causal inference, but the authors correctly used probabilistic language ('similar', 'no discernible effect') due to Bayesian evidence supporting the null hypothesis, not definitive proof of equivalence.

More Accurate Statement

“In untrained young adults performing single-joint upper-body resistance exercises (biceps curls and triceps pushdowns) for eight weeks, using external momentum ('cheating') during repetitions is likely to produce similar increases in muscle thickness and arm circumference as strict form, despite performing approximately double the volume load.”

Evidence from Studies

Supporting (1)

Do Cheaters Prosper? Effect of Externally Supplied Momentum During Resistance Training on Measures of Upper Body Muscle Hypertrophy

Randomized Controlled Trial

Human

2025

Even when people cheated by swinging the weights, their arms grew just as much as when they did the exercises slowly and carefully—despite doing almost twice as much work.

Contradicting (0)

No contradicting evidence found

Source Study

Do Cheaters Prosper? Effect of Externally Supplied Momentum During Resistance Training on Measures of Upper Body Muscle Hypertrophy

Score: 54

DOI: 10.70252/GDBL2230

Similar Assertions

Whether you lift your arm weights slowly or with a little swing, your biceps and triceps both get noticeably bigger after eight weeks of training—your triceps grow even more than your biceps.

79%

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.

76%

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.

75%

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.

75%

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%.

75%