People’s muscles before they start lifting weights already have different gene activity patterns, and those patterns seem to predict how much their muscles will grow after training.

Lifting light weights and lifting heavy weights both temporarily turn up the activity of muscle-building genes right after you work out, but after 12 weeks of training, your body’s baseline gene activity returns to normal no matter which weight you use.

Even if your muscles don’t get much bigger from lifting weights, your body still improves how it uses energy, like making your muscles better at burning fuel efficiently.

Very few gene patterns actually changed in sync with muscle growth — most of the important signals were already there before training even started.

If older people who didn’t get stronger from doing just one set of weight exercises start doing four sets instead, they’ll likely grow bigger muscles in their thighs after 10 weeks of working out twice a week.

Doing your workouts more often per week doesn’t seem to help you build more muscle, as long as the total amount of lifting stays the same.