Actor’s secret weapon for building muscle

Dwayne Johnson, a.k.a. The Rock, is known for his Herculean dedication to the gym and for sharing his brutal workouts with his 70+ million Instagram followers. Recently he posted a picture of his expansive back, but the curious thing was what hung from his right hand.

The Rock is holding a chain. No, he’s not about to tow something. Lifting with chains is an old-school way to boost your strength and see new gains.

Chains can weigh up to 60 pounds. They can make strength exercises more effective by making key parts of a move harder and other parts easier, says JC Deen, a personal trainer from Nashville, Tennessee.

But here’s where it gets interesting: As you lower the bar to your chest, the chains pile on the ground, essentially “removing” some of the weight—the bar is now lighter. As you press the bar back up, you “pick up” the chains with it, so the bar becomes successively heavier the higher it travels.

Most people are weakest at the bottom of the bench and get stronger the higher the bar is off their chests, especially during the final lockout phase of the lift, says Deen.

So the chains allow you to use just the right load throughout the lift: more resistance in your strongest areas and less in your weakest, helping you gain more strength and muscle.

The bench press is just one example.

Chains can be used in any exercise where the weight feels lighter as you get closer to the lockout phase of the exercise, such as squats, deadlifts, or military presses, Deen says. You can also use them to add extra weight to pullups.

Training with lifting chains can also help improve your core stability. Oftentimes the chains sway as you lift, so you have to engage your stabilizing muscles to control the weight.

Want to try it? You can buy chains that are designed specifically for training—like this one—which usually have a clasp or a mechanism to secure them to the barbell. They come in various thicknesses, lengths, and materials, all of which modify their weight.