This 15-Minute Workout Is Way More Effective Than What You’re Doing Right Now

Hand up if you’ve ever held a plank until your body starts shaking like a bowl full of jelly. Okay, now put your hand down and vow to never do that again.

What we just described is an extreme—and, yes, very popular—example of isometric training: contracting a muscle without changing the joint angle or muscle length. (Another classic is the wall squat. You’re sitting with burning quads, but you’re not actually moving.)

Studies do show this technique increases muscle strength and improves stability, especially in your core. But here’s the thing: For even a fit woman, after two minutes or so, your muscles are likely taxed; by the time they’re trembling intensely, your form starts to suffer, straining spots like your shoulders, neck, and lower back.

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In other words, rather than just holding a position for the sake of it, it’s better to fully engage the muscles you’re trying to work. To do that, you need to focus on your breath, not the clock. “When you squeeze your muscles as hard as you can while making forced exhalations, the magnified breath produces more powerful contractions, which increases muscle activation,” says Dean Somerset, a certified strength and conditioning specialist in Edmonton, Alberta.

Give it a shot with Somerset’s workout here: Two or three times a week, complete three rounds of this circuit, moving from one exercise to the next without resting. You won’t hold any move longer than a minute.