40-Minute Do-Anywhere Bodyweight Circuit

Reps: 20, alternating sides

• Start in a traditional plank — shoulders over hands and weight on your toes.
• With your core engaged, twist to bring your right knee forward under to your left elbow. Return to your basic plank to complete a rep. Switch legs, bringing the left knee forward to the right knee for your second rep.
• Do 20 reps, alternating sides.

Mountain climbers are such an effective exercise, and adding a twist really works the abs from all angles.