Browse evidence-based analysis of health-related claims and assertions
Even if a rat's muscles aren't actually torn or damaged, it can still feel sore after exercise — this soreness seems to come from nerve sensitivity, not from physical damage, especially when the exercise isn't too intense.
When rats do certain muscle exercises, they get sore deep in their muscles—not on the skin—starting a day later, peaking after 2–3 days, and going away by day 4. This soreness is due to increased sensitivity in the muscles themselves.
After a tough workout, a certain protein in your pee doesn’t really match up with how sore you feel — it might be more about actual muscle damage than just feeling pain.
After a tough workout, a protein found in your pee might show how much your muscles are struggling to recover — the more of it there is, the more your muscle power seems to drop.
After a tough workout, a protein fragment in your pee might show muscle damage just like a well-known blood test does — and they seem to go up together.
After a tough workout, men and women who regularly lift weights show similar levels of a muscle damage marker in their urine, suggesting it works just as well for tracking muscle soreness in both sexes.
After a tough leg workout, a certain protein in pee goes up two days later — this might show how much muscle damage happened during exercise.
Lifting weights for three months increases the number of tiny blood vessels in arm muscles of young men, and the growth keeps up with how much the muscle fibers get bigger.
Lifting weights for three months didn’t increase the number of muscle fibers in young guys’ biceps, so their muscles got bigger without adding new fibers.
Lifting weights for three months makes the muscle fibers in young men's biceps get bigger — both the endurance-type and power-type fibers.
Lifting weights for three months can make the upper arm muscle about 13% bigger in young college guys.
If college guys who've lifted weights before do a specific 12-week workout plan—3 times a week, 8 exercises, 3 sets each—they'll get 25% stronger in their arms, based on how much they can lift in one go on a curl machine.
After just one leg workout, the muscles in young men's thighs get temporarily thicker by about 8%, which is likely due to fluid buildup from the workout. This finding is from the abstract summary - full study details were not available.
Lifting weights (3 sets of 8 reps at 80% of your max) three times a week for six weeks can increase the thickness of thigh muscles in young men who haven't trained before by about 2.9%.
If a guy new to lifting weights gets a bigger muscle swell right after his first workout, he’s likely to gain more muscle over the next 6 weeks.
Even though muscle fibers get 23% bigger with high-rep training, the amount of actin protein inside doesn’t go up, and the usual tight link between fiber size and actin breaks down.
After young guys stop intense weight training, their muscle proteins stay low for over a week, suggesting it's not just temporary swelling or soreness.
Lifting heavy weights for six weeks changes specific proteins in the muscles of fit young men. This suggests their muscles are switching to a way of making energy that doesn't require oxygen.
When young guys who already work out do a lot of high-rep weight training for a short time, their muscles get bigger but their energy-producing parts actually become less dense, meaning bigger muscles don’t always mean more energy factories inside them.
When young guys who already work out do a lot of high-volume weight training for 6 weeks, their muscles grow mostly because of fluid and non-contracting parts inside the muscle cells, not because they’re building more of the actual muscle-building proteins — and this change sticks around for over a week after they stop training.
You can get muscle benefits from blood flow restriction even if your muscles aren’t burning or working super hard—so something else, like cell swelling, might be doing the work. (This finding is from the abstract summary - full study details were not available)
When you do blood flow restriction training, your muscle cells might swell up, and that swelling could be what makes your muscles grow — even if there’s not much buildup of fatigue-related chemicals.
Squeezing blood flow while doing light weight training might still help your muscles grow and get stronger — you don’t have to lift heavy to see results.
The total amount of work your muscles do when lifting weights — how hard and how long you push — decides how strong the muscle-building signals get turned on.