If you're a young adult who hasn't lifted weights before and you do squats for 7 weeks—whether you lower the bar slowly (4 seconds) or quickly (1 second)—your thigh muscle gets stiffer, and it doesn't matter which speed you use.

If you're a young adult who hasn't trained much before and you do squats slowly or quickly on the way down for 7 weeks, your thigh muscle gets stiffer either way — and how slow or fast you go doesn't matter.

If young people who don’t normally lift weights do squats slowly on the way down for 7 weeks, their thigh muscles might start working more like endurance muscles—slower but more tired-resistant.

If you're a young adult who hasn't trained much before and you do squats slowly on the way down for 7 weeks, your thigh muscles might start contracting more slowly, which could mean they're changing to work more like slow-twitch muscles.

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 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.