Browse evidence-based analysis of health-related claims and assertions
Not all thigh muscles respond the same way — one part might grow a bit better with stopping short, while another grows a bit better with pushing to failure.
Descriptive
Stopping a few reps short lets you do about the same total amount of work over weeks as going all the way to failure — because you can recover faster and do more sets without burning out.
Lifting weights until you can't do another rep leaves you much more tired during and after the workout than stopping a few reps short — even if both methods build muscle equally.
If you lift weights until you can't do another rep, or stop just before failure, your thigh muscles grow about the same amount after eight weeks — but stopping short feels less exhausting each time.
Working out with weights three times a week for 10 weeks makes you better at doing more reps — but how much better depends on whether you used heavy or light weights.
Lifting heavy weights makes your legs much stronger than lifting light weights, but for your arms, both heavy and light weights make you about equally stronger.
Causal
Using light weights for arm exercises can make your arms slightly more muscular, but using light or heavy weights for leg exercises doesn’t change leg muscle size in young women who haven’t trained before.
When lifting weights with your arms, whether you use heavy or light weights, you get about the same improvement in how many reps you can do with both heavy and light weights.
If you lift heavy weights, you get better at doing more reps with heavy weights; if you lift light weights, you get better at doing more reps with light weights — your muscles adapt specifically to the weight you use.
When you train hard enough to fail on every set, how heavy the weights are matters less than your body’s natural ability to grow muscle.
Getting stronger from lifting weights doesn’t always mean your muscles are getting bigger—and vice versa. Strength and size don’t go hand in hand.
Correlational
Your muscles make more protein at first when you start lifting weights, but after a few weeks, that boost fades—even if you keep lifting harder.
Some people’s muscles grow a lot with training, others don’t—but if one person’s arms grow, their legs usually grow similarly, meaning your body’s natural response is more important than which muscles you train.
Whether you lift heavy weights with fewer reps or light weights with more reps—as long as you push until you can’t do another rep—your muscles grow about the same amount.
If you train hard enough to fail on every set, how heavy the weights are matters less than your body’s natural ability to grow muscle.
Some people’s muscles grow a lot with training, others don’t—but if one person’s arms grow, their legs usually grow similarly, meaning your body’s natural response is more important than which muscle you train.
Whether you lift heavy weights for fewer reps or light weights for more reps—as long as you push until you can’t do another rep—your muscles grow about the same amount.
After 12 weeks of lifting weights, both strong and weak older women gained about the same amount of muscle—starting strength didn’t affect how much muscle they built.
After doing strength training for 12 weeks, older women—whether they started strong or weak—gained about the same amount of strength in their arms and the same amount of muscle, no matter how strong they were at the start.
Older women who started out weaker in their legs got stronger in their legs more than the stronger ones after doing leg exercises for 12 weeks, but everyone gained about the same amount of muscle and upper-body strength.
When you lift light weights until you're exhausted, your muscles might still grow because they get really tired and activate the same powerful muscle fibers as heavy lifting.
Mechanistic
The total amount of work done (weight × reps × sets) seems to matter for muscle growth — more work generally leads to more muscle, even if the weights are light.