“There’s a difference between hyperextending your back and creating a natural arc,” says Men’s Health Fitness Director BJ Gaddour.
Letting your lower back gently arc allows you to wrap your shoulders around the bench. This improves your stability and lets your chest muscles stretch more for greater muscle activation and strength gains, Gaddour says.
On the other hand, lying flat rounds your shoulders – increasing your risk for shoulder injury – and puts you in a less-than-ideal position to engage your chest muscles, he says.
