Whether people lift heavy weights with few reps or lighter weights with more reps—while doing the same total amount of work—both ways make their muscles grow about the same size in the chest and thighs after 8 weeks.

After 8 weeks of either heavy or light lifting, the middle part of the outer thigh didn’t get any thicker—no matter which way they trained.

When people who already lift weights do either mostly heavy lifts or mostly lighter lifts—but keep the total amount of work the same—both ways make them just as strong after 8 weeks.

Neither heavy nor light lifting made people better at doing more reps in a row—except maybe a small, not certain improvement with lighter lifts in squats.

Even doing a huge number of leg sets—over 50 a week—didn’t make anyone’s muscles shrink, which means there might be a very high limit to how much training your muscles can handle without losing size.

If you do the same workout three times a week instead of once, and you end up doing more total weight lifted, you’ll get stronger and build more muscle—because you’re doing more work overall.