Leg day doesn't have to last a long time — just ask ACE-certified personal trainer and Under Armour trainer Ariel Belgrave [1], who created this 20-minute lower-body HIIT workout. The session is part of the Under Armour 21 Days to a Stronger Self challenge, and it's meant to get your heart pumping with explosive movements, as well as strengthen your quads, glutes, hamstrings, and calves. It also puts your stability to the test while burning calories.

20-Minute Lower-Body HIIT Workout

Equipment needed: comfortable shoes, mat for support, and water for hydration.

Directions: Belgrave suggests starting with a two-minute dynamic warmup: jumping jacks, knee hugs [2], hip circles [3], inchworms [4], rotational lunges, and hamstring scoops [5]. You can also do some of the exercises linked here for the warmup instead [6]. For the workout itself, do the five exercises listed ahead for 40 seconds with 10 seconds of recovery between each. You'll do three rounds total with a one-minute rest in between rounds. Cool down afterward with full-body stretches [7], making sure to properly stretch your legs.

"Going from the speed skaters to the squat jumps, which are both explosive moves, having a lesser break in between is really going to make it more effective, get the heart rate up in a shorter period of time," Belgrave told POPSUGAR. Keep reading for instructions for each move in this workout, and get ready to sweat!

Speed Skater

• Start with your legs slightly wider than shoulder-distance apart and arms at your sides.
• Lean forward, then jump to the right onto your right foot, bringing your left foot behind you and bringing your left arm in front of you.
• Jump to the left onto your left foot, bringing your right arm in front of you and your right foot behind you.
• Repeat this side-to-side movement for 40 seconds. Rest for 10 seconds.

Squat Jump

• Stand with your feet slightly wider than hip-width apart and your hands in front of your chest.
• Hinge forward at your hips, and sit your butt back into a squat like you're sitting into a chair. Bend your knees until your thighs are parallel to the ground.
• Jump up into the air as high as you can, and straighten out your legs. Swing your arms down by your sides for momentum, and keep your back straight and chest lifted.
• Land back on the floor with soft knees. Go directly into another squat.
• Continue for 40 seconds. Rest for 10 seconds.

Explosive Sprinter's Lunge

• Stand tall with your feet hip-width apart.
• Step your right foot back a few feet into a lunge position.
• Push through your left foot to explosively jump into the air, driving your right knee toward your chest.
• Land with a soft knee, and step back immediately into another lunge.
• Repeat on the same side for 20 seconds, then switch to the other leg for the final 20 seconds. Rest for 10 seconds.

Curtsy Lunge

• Stand tall with your feet hip-width apart.
• Step your right leg diagonally behind your left leg, and bend your knees to lower into a lunge.
• Push through your left heel to stand, and bring your right leg back to your starting position.
• Repeat on the other side. Continue for 40 seconds. Rest for 10 seconds.

Squat Jack

• Stand with feet together, core engaged, and hands at your chest with your elbows out wide.
• Hop in place, then hop your feet hip-width apart, dropping into a squat by sending your hips back.
• Squeeze your glutes, and if you want to make the move more advanced, tap the floor with your right fingertips.
• Stand and hop your feet back together to return to your starting position. If you want to make the move more advanced, tap your left fingertips to the ground during the next squat.
• Continue for 40 seconds. Rest for 10 seconds.