When young men lift weights, if a specific protein in their muscles gets activated strongly exactly 5 hours after working out, they tend to build more muscle over the next 4 months—so this protein spike might tell us who’s going to grow the most from training.

In guys who are new to weightlifting, how strongly their muscles signal growth right after a workout (at the 5-hour mark) seems to predict how much muscle they’ll gain over the next 4 months.

A quick chemical change in muscles after exercise doesn't tell us if those muscles will grow bigger over time, which means we can't use this early signal to predict long-term muscle growth.

When guys who don’t normally lift weights do a tough leg workout on an empty stomach, their muscles show a big spike in two specific signals that tell the body to build more muscle, and this might mean doing more sets makes those signals even stronger.

If you slow down the lowering part of weightlifting, your muscles might get more damaged and your body might release more of the hormones that help build muscle—this is what the claim says about guys who lift weights.

When you lift weights, your muscles temporarily stop building protein, but right after you finish, they kick into high gear to repair and grow—this happens because key signaling molecules in your muscles get activated during recovery.