One of my all-time least favorite things that a trainer asks me to do in a workout—besides a round of burpees—is to pause. It happened in a HIIT class recently, and instead of doing regular squats, I was instructed to pause and hold between each rep before standing up. So yeah, my butt was on fire.

Pausing at the hardest part of a strength training move, AKA an “isometric hold,” is one of the best things you can do in a workout. You know that burn you feel in your muscles when you’re sitting a second too long at the bottom of a squat? That’s exactly why. “Pausing at the hardest part of each movement requires full activation of the muscle that you’re working,” says Julia Stern, a trainer at Rumble Training in New York City. “Sometimes when we don’t pause, we’re relying too much on momentum to finish the movement. So when you pause at the bottom of a squat, for example, you’re building muscle endurance.” This means that you’re only relying on those activated muscles to stand or move back up… which is no easy feat.

You’re also recruiting more muscles to do these holds, says Mitchell Fischer, a fitness expert with Gold’s Gym. “The muscle recruitment is much greater with increased time under tension with the isometric hold,” he says. When you pause right before the contraction, or ‘up’ part of the move, you then “explode out into the finishing position,” he says. “As your fast twitch muscle fibers fatigue in the pause, slow twitch fibers are recruited to help with the stability, which results in your muscles and neurons recruiting all available muscle for a maximal effort lift.” Anthony Crouchelli,  fitness instructor at Grit Bxng, echoes this, noting that this act of holding before an explosive movement means “you’re working in a controlled tempo under heavy volume,” he says, so you’re getting more bang for your exercise buck.

Thankfully, isometric holds are there for you whenever you want to sneak them in (yay!)—you can incorporate them in practically any of your staple strength training moves. Stern’s fave exercises to pause in? “Holding at the bottom of a push-up, and keeping your arms at their most extended point before doing that next bicep curl,” she says. Fischer recommends starting by adding two to three seconds at the hardest part of your strength training exercises, then work your way up from there. Who knew pausing in a workout had so much power?

Before you start trying the pause technique, make sure you work through some dynamic stretching exercises. And here’s your guide on the best stretching methods to do afterwards, according to the pros.