When women who lift weights do squats with a really heavy weight (close to their max), their leg and butt muscles have to work a lot harder than when they use lighter weights.

For women who lift weights regularly, squatting with 80% or 90% of your max weight activates your muscles about the same — going heavier doesn’t seem to turn on more muscle once you hit that range.

When doing a hip thrust with a barbell instead of a squat, the butt and back of the thighs light up more on muscle sensors during the same level of effort.

When strong guys do fast squats with heavy weights, their leg muscles don't work harder the heavier the weight gets—until they go all the way up to their max. At max weight, two of the three main quad muscles actually fire way more.

When women who lift weights do squats with 80% of their max weight, their butt muscles work way harder compared to their hamstrings — more than with lighter or heavier weights.

When women who lift weights do squats with a light weight (about 40% of their max), their butt and hamstring muscles work together in perfect balance as they lower down.