Even though the players got stronger, their ability to jump higher or more powerfully didn’t improve after five weeks of leg press training — meaning strength on the machine doesn’t automatically make you jump better.

Scientific Claim

Five weeks of unilateral or bilateral leg press training does not improve vertical jump height or peak power in adolescent male rugby players, as no significant changes were observed in countermovement jump performance despite increases in lower body strength, indicating a lack of transfer from machine-based strength training to explosive power in this context.

Original Statement

“There was no significant effect of time for the CMJ height (F2, 13 = 4.606, p = 0.051, = 0.262) or CMJ PP (F1,13 = 0.959, p = 0.345, = 0.069), nor was there a significant interaction effect of time and group for the CMJ height (F2, 13 = 0.336, p = 0.717, = 0.049) or CMJ PP (F2, 13 = 0.385, p = 0.687, = 0.136).”

From study:The Effect of Unilateral and Bilateral Leg Press Training on Lower Body Strength and Power and Athletic Performance in Adolescent Rugby Players

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 with objective, reliable measurements (force plate) and non-significant p-values (p>0.05) supports definitive language. The authors correctly avoid inferring mechanisms beyond the data.

Evidence from Studies

Supporting (1)

The Effect of Unilateral and Bilateral Leg Press Training on Lower Body Strength and Power and Athletic Performance in Adolescent Rugby Players

Randomized Controlled Trial

Human

2023 Mar

Even though the players got stronger from doing leg presses, they didn’t jump any higher—showing that getting stronger on machines doesn’t always make you more explosive in sports.

Contradicting (0)

No contradicting evidence found

Source Study

The Effect of Unilateral and Bilateral Leg Press Training on Lower Body Strength and Power and Athletic Performance in Adolescent Rugby Players

Score: 54

DOI: 10.5114/jhk/159626

Similar Assertions

Doing leg press exercises twice a week for five weeks makes teenage rugby players much stronger when pushing with both legs at once, whether they use one leg or both legs at a time.

88%

Even though the players got stronger from doing leg presses, they didn’t run any faster after five weeks — meaning just getting stronger on a machine doesn’t automatically make you sprint better.

87%

When teenage rugby players train one leg at a time on the leg press machine, they get much stronger in that single leg than when they train both legs together at the same time.

85%

Training one leg at a time makes that leg much stronger than training both legs together — even though both methods make you equally strong when using both legs at once.

84%

Both training methods made athletes jump higher and turn faster, but didn’t make them run straight-line sprints any faster.

74%