You breathe the hardest not when you’re lifting, but right after you finish a set and are resting—your body is catching up on oxygen debt built up during the effort.

You can make your workout feel harder and your muscles burn more by resting less between sets—but you can still lift the same total weight without getting weaker.

Right after leg presses with only 1-minute breaks, your body gasps for air more intensely in the first minute than if you took 3-minute breaks—but this doesn’t happen with chest flys.

Both men and women burn more fat after heavy weights before cardio, even though women tend to breathe harder during the cardio than men do.

To know how many calories you burn during a weightlifting session, you have to measure your breathing for at least 90 minutes after you finish—most of the burn happens after you’re done lifting.

After a tough weight session, women tend to breathe harder during their cardio workout than after an easy weight session or no weights, but men don’t show this difference as clearly.