If you're a guy who lifts weights and gets close to failure—like stopping just 1 or 2 reps short—you'll get just as strong as if you pushed yourself to the absolute max. Over 10 weeks, both ways boost leg strength by 20–35%.

If you're lifting heavy weights and stop just before your muscles give out, you'll still gain about as much muscle as if you pushed to the very last rep you can possibly do.

If you're a guy who lifts weights and stops just before your muscles give out, you'll do fewer reps and lift less total weight than if you go all the way to failure — but you'll still gain just as much muscle and strength. That means pushing close to failure might be a smarter, more efficient way to train.

If you lift heavy weights (80–85% of your max) instead of doing lots of lighter reps (60% of your max), your legs get stronger faster — after 6 weeks, you’ll likely gain 5–6 kg more in leg strength.

If young guys who already lift weights do intense leg workouts every day for two weeks, they get about 6% stronger in their leg press, showing their muscles and nerves adapt quickly.

If you're a young guy who already lifts weights, doing workouts until you can't do another rep for 12 weeks will make your legs and shoulders just as strong whether you use light or heavy weights—but for the bench press, heavy weights make you stronger than light ones.