Browse evidence-based analysis of health-related claims and assertions
We know muscles stretch less the second time you do a tough workout, but we don’t yet know why that happens.
Descriptive
Even though guys lifted less weight per rep with dumbbells, they did more reps to make up for it, so the total weight lifted ended up being about the same for everyone.
Quantitative
After the second tough arm workout, blood markers of muscle damage tend to be lower, but the difference isn't strong enough to be sure it's real.
After a tough leg workout, a blood marker of muscle damage (CK) spikes by more than 1.5 times and stays high for two days, showing the muscles are still healing.
After a tough chest workout, your ability to push your arm across your chest comes back fully within three days, no matter if you used a machine, barbell, or dumbbells.
Causal
The first time you stretch your biceps in each workout, it stretches the same amount—even if the second workout causes less damage overall.
After a heavy leg workout, the thigh muscles get noticeably thicker due to swelling, and this lasts for at least two days.
Even after a super hard chest workout, the size of the triceps muscles goes back to normal within a day—meaning the workout didn’t actually tear them up much.
During a tough leg workout, testosterone levels spike temporarily, but they go back to normal by the next day and don’t stay high.
People push just as hard during the second workout as the first, even though they feel less sore and recover faster.
No matter which type of chest press you do—machine, barbell, or dumbbells—you’ll feel about the same level of soreness in your chest muscles after a hard workout, and it’ll go away at the same rate.
How much your biceps stretch during your first hard workout tells you how sore and weak you’ll feel the next day—but not how much enzyme leaks into your blood.
Correlational
After a heavy leg workout, men can't push as hard with their legs for at least two days — even though they're trained, their strength is still a little weaker.
After doing a barbell chest workout, guys felt way more tired and less recovered than after using dumbbells or a machine—even two days later—suggesting barbells leave you feeling more drained.
The more the biceps stretched during the first workout, the more 'swelling' showed up on the ultrasound scan afterward.
After a really tough leg workout, trained men feel weak and tired for about 3 days, but by day 6, they start feeling better than they did before the workout.
Even though guys lifted the same total weight, those using barbells felt way more sore in their triceps for longer than those using dumbbells—suggesting barbells might be harder on the back of the arm.
After doing heavy leg workouts, the muscles of trained men show a big spike in two specific proteins (IGF-IEa and MGF) that help repair muscle damage, and this spike happens about two days later.
The more the biceps stretched during the first tough workout, the more strength the person lost the next day.
After a tough chest workout, guys using barbells or machines feel sore in their triceps for a few days, but those using dumbbells don’t feel any soreness at all—even though they lifted the same total weight.
People feel less sore after doing the same tough arm workout a second time, four weeks later.
When trained men do different types of chest presses—using a machine, barbell, or dumbbells—their chest muscles and shoulder strength bounce back at about the same rate after a tough workout, no matter how stable the equipment is.
The second time people do a tough arm workout, their muscles show less 'swelling' on ultrasound scans, meaning there's probably less damage or inflammation.
After doing a hard arm workout twice, four weeks apart, people feel stronger sooner the second time—even though they did the same amount of work.