The effects of eccentric phase tempo in squats on hypertrophy, strength, and contractile properties of the quadriceps femoris muscle

To figure out whether speeding up or slowing down the lifting vs. lowering part of a weight workout makes your muscles grow more, scientists need to test each part separately—not at the same time.

When the total amount of weight lifted is the same, changing how slowly you lower the weight during resistance training does not change how much muscle grows.

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.

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.

In untrained young adults, performing barbell squats with a 4-second lowering phase for 7 weeks results in longer muscle contraction time in the quadriceps compared to using a 1-second lowering phase.

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.