When people do strength exercises like knee extensions, how hard they think they're working doesn't always match how hard their body is actually working. Even trained athletes often think they can't do more reps when they actually could.

People who lift weights for over a year often guess wrong about how many more reps they can do before getting tired—they usually think they can do about 2 fewer than they actually can.

When doing intense leg exercises with 5-minute breaks between sets, people can do more total work than with only 2-minute breaks, because their muscles recover better.

Whether you lift heavy weights for a few reps or lighter weights for more reps until you can't do any more, both ways make your thigh muscles grow about the same amount in people who already work out.

When people do more reps in a row during weight training, they become worse at guessing how many more reps they could do. This means longer sets make it harder to judge your own effort accurately.