Try a Trainer's 5-Move Bodyweight HIIT Workout If You've Never Done HIIT Before

Mountain climbers target the abdominals and you'll feel the burn in your triceps and deltoids, too, Melissa told POPSUGAR.

• Start in a high plank — shoulders over your hands and weight on your toes.
• With your core engaged, bring your right knee forward under your chest, with the toes just off the ground. Return to your basic plank. Switch legs, bringing the left knee forward.
• Keep switching legs and pick up the pace until it feels a little like running in place in a plank position.
• Continue for 30 seconds.