Doing leg extensions one leg at a time for 12 weeks makes each leg stronger and more active when tested alone, better than doing both legs together — even though both methods improve overall leg strength similarly.

Whether you train one leg or both legs at once for 12 weeks, your legs get just as big and strong overall — the way you do the exercise doesn’t change how much muscle you build or how strong you become in general.

Training one leg at a time makes it harder for both legs to work together at full power, while training both legs together makes them work better together — the way you train changes how your legs coordinate.

Even though people who trained one leg at a time ended up lifting heavier weights than those who trained both legs together, both groups ended up with the same muscle size and overall strength — so lifting heavier with one leg doesn’t automatically make you stronger overall.

If you train one leg at a time, that leg gets much stronger than the other when tested alone — but if you train both legs together, both legs get stronger at the same rate, with no one leg getting ahead.

When untrained men get stronger in a static leg press, the main reason is that their thigh muscle near the hip gets bigger and its fibers angle more, which helps push harder.