Health Claims

When you start lifting heavy weights, your brain and nerves get better at telling your muscles to work harder faster — and that’s why you get stronger so quickly at first.

Correlational

When you lift heavy weights, tiny cells in your muscles wake up and stick to muscle fibers, and this seems to help your muscles grow bigger faster.

Correlational

When you lift heavy weights regularly, your muscles get bigger because the individual muscle fibers inside them grow thicker and more numerous.

Mechanistic

Lifting heavy weights makes your muscles stronger, and that happens because your brain gets better at telling your muscles how to work together, and your muscle fibers themselves grow bigger with help from special repair cells.

Mechanistic

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.

Causal

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.

Causal

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.

Causal

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.

Causal

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.

Causal

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.

Causal

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.

Causal

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.

Causal

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.

Causal

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).

Causal

After doing 12 weeks of static strength exercises, whether your quadriceps muscle fibers change their angle doesn’t seem to affect how much stronger you get.

Correlational

When guys get stronger from doing isometric leg exercises, their hamstring muscles don’t start working differently alongside their quads—so the way their hamstrings fire doesn’t predict whether they’ll get stronger or not.

Correlational

If you're already strong before starting isometric training, you won't get as much stronger compared to someone who started weaker — and this pattern explains about 1 in 10 of the differences in how much people improve.

Correlational

When young men do isometric leg exercises for 12 weeks, their thigh muscles get bigger—and that bigger muscle size helps explain about 1 in 5 of their strength gains, even if their nerves aren’t getting better at telling muscles to work harder.

Correlational

When your thigh muscles fire more strongly during a max effort leg push, you tend to get stronger faster after doing 12 weeks of holding a knee extension position — and this muscle firing explains about 30% of why some people get stronger than others.

Correlational

How fast or slow you lift and lower weights probably doesn’t make much difference in building muscle—unless you’re doing something very specific, but we’re not sure what that is yet.

Descriptive

When people lift weights, whether they do the lifting part slowly or the lowering part slowly, or train until they can't do another rep, it doesn’t make much difference in how much their muscles grow — and sometimes the difference is so small it might not even matter.

Descriptive

Whether you lift weights slowly or quickly, you’re probably not going to build more muscle with one over the other — the difference is so tiny it doesn’t really matter.

Quantitative

Whether you lift weights slowly or quickly, you’ll likely gain about the same amount of muscle—so don’t stress over the speed, just keep lifting.

Correlational

If you're a young adult who doesn't lift weights or do strength training for 8 weeks, your muscles won't get noticeably bigger or stronger on their own — you need to actually train to see changes.

Descriptive