Browse evidence-based analysis of health-related claims and assertions
Watches and fitness trackers that measure training intensity and duration are better at linking exercise to heart plaque than asking athletes to remember how much they trained.
Correlational
Men who train a lot for years—especially long hours at high intensity—tend to have more plaque in their heart arteries, even if they’re otherwise healthy.
After a hard workout, your muscles keep making the big energy store only if you eat a lot of carbs — if you eat few carbs, that big store doesn’t grow at all over two days.
Descriptive
Right after a super-hard workout, only about 1 in 8 of your muscle’s energy stores is in the big storage form — but if you eat lots of carbs afterward, that big store grows to nearly half of all your muscle energy.
Between 4 and 24 hours after a hard workout, your muscles keep rebuilding their first energy store no matter how many carbs you eat, but the bigger energy store only grows if you eat lots of carbs.
Right after a super-hard workout, eating lots of carbs makes your muscles start rebuilding their first energy store (proglycogen) three times faster than if you eat fewer carbs.
After a really hard workout, eating a lot of carbs helps your muscles rebuild a special type of stored energy (macroglycogen) much better than eating fewer carbs.
Lowering weights slowly makes the connective tissue around your muscles rebuild and strengthen more than lifting does, helping your muscle adapt structurally.
Mechanistic
Lowering weights slowly wakes up muscle stem cells right after exercise, but lifting weights regularly over time builds up more of these cells permanently.
Lowering weights slowly turns on different cellular signals and makes your muscle’s scaffolding change more than lifting does—even if both make your muscle bigger.
Your muscles don’t make more protein faster when you lower weights slowly vs. lifting them up—so growth must come from rearranging what’s already there, not just making more.
Lowering weights slowly makes muscle fibers longer, while lifting them quickly makes them thicker and more angled—both make muscles bigger, but in different ways.
Whether you push weights up or lower them slowly, if you do the same amount of total work, your muscles grow about the same size.
Protein plus alanine keeps your muscles in 'build mode' a little longer than protein alone, but the total amount built is the same.
Quantitative
The protein signal that tells your muscles to grow (mTOR) turns on just as well with plain protein as it does with protein plus sugar or alanine.
Even though sugar and alanine make insulin go up, that doesn’t stop your muscles from breaking down any more than protein alone does.
A small protein shake makes your muscles start growing, but adding sugar or alanine doesn’t make it grow any faster or stronger.
Adding sugar or alanine to a protein drink doesn't make your muscles grow more than the protein drink alone in healthy young people.
Lifting weights refills muscle energy slower than sprinting or HIIT, maybe because you don’t build up as much lactic acid and your muscles get more sore from stretching under load.
Hard, explosive workouts use muscle fibers that are naturally better at refilling energy stores, which helps you recover faster.
When you work out really hard and your muscles burn, the buildup of lactic acid might help your muscles refill energy faster—but after lifting weights, less lactic acid means slower recovery.
After a hard, short workout, your body releases more sugar and insulin into the blood, which helps your muscles refill their energy faster.
After a short, super-hard workout, your muscles refill their energy stores way faster than after a long, slow one—even if you eat the same amount of carbs.
If you lift light or heavy weights but do the same total amount of work, your muscles grow about the same amount—so lifting light weights can be just as good for building muscle as lifting heavy ones.