The belt movement and structure of both machines enables each leg to help the other a bit too much—the hip flexors of your right leg take the pressure off your left glute and vice versa. That leads to “glute laziness.” You don’t need to put a moratorium on treadmills and elliptical, but if you use them exclusively, you’ll miss out on toning those buns! Instead, or in between, train on firm ground, hills, or stairs, and when you run on the treadmill, incline it five to seven percent to engage your booty.

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