Mountain Climber

Start in a high plank with your hands directly under your shoulders. Brace your core and glutes and first create a straight line without swaying.

Drive one knee toward your chest. Keeping your torso from sagging and continuing to push the floor away matters more than leg speed.

Send that leg back and switch sides. Even as you speed up, use your core to prevent your pelvis from rocking up and down.

Although it looks like cardio, core engagement changes greatly with how well you stabilize your torso. Slow down and reset your plank if your core starts to give out.

Raised hips or a sagging back greatly reduce core engagement. Keep your plank alignment even if you have to slow down.

Exhale as you drive a knee in and inhale as you switch. Keep breathing instead of holding your breath as the pace rises.

Start by switching one foot at a time slowly. Increase speed only after your plank alignment is stable.