There’s only one set of muscles that is on display year-round and can create the impression you have an action-hero physique overall (even if you don’t): your forearms. Adam Ernster, a Hollywood trainer who helped Sylvester Stallone peak for 2008’s Rambo, can show you how Sly got his so you can build a pair of your own.

This vintage Rambo pic posted on Sly's Instagram page shows just how hard he worked on those action-hero muscles in an effort to keep up with Arnold Schwarzenegger's incredible physique in Commando:

 

When Rambo was trying to keep up with Commando!…#sunburn #arnoldschwarzenegger #rockybalboa.1976 #Rambo3#desert

A post shared by Sly Stallone (@officialslystallone) on

 

Use the following routine frequently—as often as every other day to build your own action-hero forearms.

1. Reverse Wrist Curl

Hold a dumbbell in each hand and sit on a bench, box, or chair. Rest your forearms on your thighs and allow your wrists to bend over your knees so your palms face down and the weights hang mid-air. Curl the dumbbells up by extending your wrists, raising the back of your hands closer to your forearms.

Sets: 2
Reps: 15–20
Rest: 0 sec.

2. Wrist Curl

Hold a dumbbell in each hand and sit on a bench, box, or chair. Rest your forearms on your thighs and allow your wrists to bend back over your knees so the weights hang down. Curl the dumbbells up by just flexing your wrists.

Sets: 2
Reps: 15–20
Rest: 0 sec.

3. Hammer Curl

Hold a dumbbell in each hand with palms facing your sides and arms extended straight down. Keeping your upper arms against your sides, curl both weights at the same time, minimizing momentum used during the curl.

Sets: 2
Reps: 10–15
Rest: 0 sec.

4. Bar Hang

Grip an overhead bar with a shoulder-width grip, making sure to pull your shoulder blades down your back and inflate your chest to really stimulate your back. Your feet should be suspended off the floor as you hang, and your arms should be fully extended. 

Sets: 2
Reps: Hang 30–60 sec.
Rest: 90 sec.