For beginners, lifting heavy weights a few times or lighter weights many times both make your calf muscles about 15-18% stronger after 8 weeks.

If young, healthy guys lift weights for 12 weeks, their muscles get stronger at moderate speeds — like kicking or swinging — and they can generate 13% to 32% more force, no matter how they did the lifting.

When you train one muscle at a time (like leg extensions), you get a bit better at holding still with that muscle—more than if you train big compound moves like squats. But either way, you get way stronger at moving than holding.

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.

Lifting light weights for nine weeks didn't make people stronger on a machine that tests muscle power at different speeds, and in fact, their performance slightly dropped — while heavy lifting kept their strength steady.

Lifting heavier weights for nine weeks made young men stronger in a max lift test than lifting lighter weights, even when both groups worked until they couldn't do another rep.