Doing leg exercises with both legs at the same time for 12 weeks makes you stronger at lifting with both legs together, while doing them one leg at a time makes you stronger at lifting with each leg separately.
Scientific Claim
Twelve weeks of progressive heavy resistance training is associated with a 19% increase in bilateral one-repetition maximum (1 RM) strength and a 13% increase in unilateral 1 RM strength in middle-aged and elderly adults, with bilateral training showing greater gains in bilateral strength tasks.
Original Statement
“the average relative increase of 19±12% (P<0.001) in bilateral 1 RM in all BIL trained subjects was greater (P<0.05) than that of 13±8% (P<0.001) recorded for all UNIL trained subjects.”
Evidence Quality Assessment
Claim Status
overstated
Study Design Support
Design cannot support claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The study lacks confirmed randomization, so causal language like 'leads to' or 'produces' is inappropriate. Only associations between training type and strength gains can be claimed.
More Accurate Statement
“Twelve weeks of progressive heavy resistance training is associated with a 19% increase in bilateral one-repetition maximum (1 RM) strength and a 13% increase in unilateral 1 RM strength in middle-aged and elderly adults, with bilateral training associated with greater gains in bilateral strength tasks.”
Evidence from Studies
Supporting (1)
Neuromuscular adaptations during bilateral versus unilateral strength training in middle-aged and elderly men and women.
People who trained both legs at once got stronger at doing that, and people who trained one leg at a time got stronger at that — and each group improved more in the way they trained, just like the claim says.