Stretching your chest muscles regularly might make them stronger—almost as much as lifting weights does—if you do it for 15 minutes, 4 times a week for two months.

Stretching your chest muscles for 15 minutes, 4 times a week for 8 weeks, might build muscle just as much as lifting weights — studies say it could increase muscle thickness by around 6%.

If you stretch your chest muscles regularly for about 15 minutes, 4 times a week, for 8 weeks, you’ll likely get more shoulder flexibility—more than if you just did strength training.

If you stretch or lift weights for 8 weeks, your chest muscle might grow a little, but that growth doesn’t explain much of why you get stronger—other factors are probably doing more of the work.

If you're someone who exercises regularly, doing chest workouts 3 times a week for 8 weeks might make your chest muscles about 10% stronger, but it won’t change how far you can move your shoulders.

Doing static stretching for five weeks, twice a week for half an hour, can slightly but noticeably make your calf and ankle muscles stronger. This happens because stretching helps your nerves and muscles work together better, rather than actually making the muscle tissue itself bigger.