If you're a young adult who hasn't trained before and you do squats with either a slow (4-second) or fast (1-second) lowering phase for 7 weeks, your thigh muscles will grow about the same amount either way.

If you're a young adult who hasn't trained much before, doing squats slowly (4 seconds) or quickly (1 second) on the way down for 7 weeks will make your thigh muscles grow about the same amount — so how slow or fast you lower yourself doesn't really matter as long as you do the same total work.

If you're a young adult who hasn't trained much before, doing squats slowly on the way down (4 seconds) for 7 weeks will make your front thigh muscle grow more than doing it quickly (1 second).

If you're new to lifting and do squats slowly on the way down (4 seconds instead of 1), your front thigh muscle gets bigger faster after 7 weeks.

If you're new to lifting and do squats slowly on the way down (4 seconds) instead of quickly (1 second) for 7 weeks, you'll likely get stronger faster — at least according to this study.

If you're new to lifting and do squats slowly on the way down (4 seconds) for 7 weeks, you'll get stronger than if you do it quickly (1 second)—slowing down the downward part might help your muscles and nerves adapt better to lift heavier weights.