When you squat with heavier weights, your butt muscles (glutes) have to work way harder than your thigh muscles (quads), more than you'd expect just from the added weight.

Your quads work hard during squats no matter how heavy the weight, but your glutes really kick in only when the weights are heavy or you're almost too tired to keep going.

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.

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.

For women doing Les Mills BODYPUMP, using heavier weights (about 38% of your body weight) in squats makes certain leg muscles work harder than using lighter weights (23% of your body weight).

When strong guys do fast squats with heavy weights, their butt muscles kick in later during the upward push compared to when they use lighter weights — it’s like their body adjusts how it uses those muscles depending on how heavy the weight is.