High-intensity interval training is efficient—workouts are under half an hour and often just a few minutes. And they’re effective. HIIT improves athletic endurance, strengthens the heart and cuts body fat.

Fortunately, high intensity doesn’t have to mean high impact. Lower-impact exercises are great for people with knee or ankle injuries, or anyone heading back into the gym after a hiatus. Forget the low-impact part—we got that covered. You focus on bringing the high intensity!

Choose any four of the six groups. Do the first move of the pair for 40 seconds and the second for 20 seconds. Complete four sets back-to-back, without rest, which totals four minutes. Exercises that isolate one side of the body should be alternated every set.

Rest one to two minutes, then go on to the next group. Including rest periods, the whole thing will take under 30 minutes. Do this workout once or twice a week, and vary the groups each time. As you progress, keep the 40/20 time intervals and fit in more reps.

Group 1: Reverse Mountain Climber

How to:

  • Start in a reverse plank, hands beneath shoulders, arms and legs locked out, feet flexed, forming a straight line between head and heels (shown above).
  • Keeping hips high and core tight, draw right knee back toward chin, stopping before shoulders hunch forward.
  • Return right foot to ground; one heel should be on the floor at all times.
  • Repeat on left side for 1 rep.
  • Perform for 40 sec.

Group 1: Side Plank Crunch

How to:

  • Start in a right-arm side plank, right forearm on floor, feet stacked, a straight line between head and heels, left hand reaching toward ceiling.
  • Keeping hips high and torso straight, draw left knee up and toward shoulder, and engage oblique muscles to bring left knee and left elbow together; return to start for 1 rep.
  • Perform for 20 sec.
  • Do all reps on right side, then switch sides for the next set.

Related article: The Best 20-Minute 8 Exercise Bodyweight Workout for Weight Loss

Group 2: Plyo Plank Shuffle

How to:

  • Start in a high plank, hands under shoulders, toes on a BOSU.
  • Keeping upper body still, and arms and legs straight, step left foot to the side, a foot away from the BOSU, then return foot to the ball.
  • Repeat on right side for 1 rep.
  • For a challenge, move legs in unison.
  • Start with left leg a foot away from the BOSU, then engage hips and push off with both feet, so left foot lands on the ball and right foot on floor.
  • Continue alternating sides.
  • Perform for 40 sec.

Group 2: Weighted Dead Bug

How to:

  • Lie on back, a 5-pound weight plate in each hand, arms extended above shoulders, knees bent at a 90-degree angle, to start.
  • Keeping core tight and maintaining connection between low back and the floor, extend left leg, lowering heel until it’s a couple of inches off ground, while simultaneously reaching right arm back behind head, just off floor.
  • Return to start, then alternate sides for 1 rep.
  • Perform for 20 sec.

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Group 3: Kneel to Squat

How to:

  • Start kneeling on floor, holding a 10-to 30-pound kettlebell at chest height, elbows down, torso tall.
  • Keeping core tight, draw right knee up and plant right foot (A), followed by left foot (B), to squat.
  • Reverse movement, returning to kneeling. Reverse sides for 1 rep.
  • Perform for 40 sec.

Group 3: Crab Reach + Leg Lift

How to:

  • Sit, feet flat, palms on floor next to hips.
  • Press up through hands and feet, so arms are straight and butt hovers above floor, to start.
  • Lift hips to tabletop position, chest level with pelvis, knees forming a 90-degree angle; at the same time, rotate torso slightly to the right, reach left hand over and behind head, past right hand, and lift right leg.
  • Return to start.
  • Repeat on opposite side, reaching with right hand and lifting left leg, for 1 rep.
  • Perform for 20 sec.

Related article: Compliment Your Routine With This 5 Move Warm-Up and Cool Down Workout

Group 4: Plyo Donkey Kick

How to:

  • Start in a high plank, core tight, hands under shoulders.
  • Draw left knee toward chest, as if doing a mountain climber.
  • In an explosive movement, kick left leg out and bend knee so foot points toward ceiling, and allow right foot to come off floor momentarily.
  • (Keep the air time low to make it lowest impact, as shown here, or kick higher and land lightly if it feels OK.)
  • When landing, straighten right leg, then straighten and lower left leg to return to start.
  • Perform for 40 sec.
  • Do all reps on left side, and switch to right for the next set.

Group 4: Plyo Frog Pushup

Related article:

  • Start in a high plank, hands on a BOSU, with knees bent at a 90-degree angle and hovering over floor.
  • Maintaining lower body position, slowly lower crown of head between hands, then press through palms to rise in the air, and return to start for 1 rep.
  • Perform for 20 sec.
  • Don’t let momentum lower you to the BOSU. Go slow on the descent, and explosive on the push-up.

Related article: Build Muscle And Blast Fat With This Push Pull Legs Workout Plan

Group 5: Seated Sprinter

How to:

  • Sit, legs extended, heels lightly touching floor.
  • Keeping torso tall and shoulders back, lean back until core engages, making sure lower back doesn’t slump.
  • Bend elbows at 90 degrees, and lift left knee toward ceiling, allowing left hand to come up and right hand to go back, like a runner, to start.
  • Switch arm and leg positions back and forth continuously and fast, as if sprinting.
  • Perform 40 sec.

Group 5: Sit-up to Stand

How to:

  • Lie on back, knees bent, feet on floor shoulder-width apart, arms extended behind head to start.
  • Swing arms forcefully forward to perform a sit-up; at the top of the movement, press fingertips to floor beside hips (A), and use mainly momentum to lift butt off floor and stand.
  • Drop into a low squat (B), allowing gravity to bring butt to ground near heels, roll onto back and extend legs to start for 1 rep (pictured).
  • The faster you begin the next rep, the more momentum you retain.
  • Perform for 20 sec.

Make it easier: As you reach the apex of the sit-up, press palms to floor and tuck legs under torso to achieve squat position. Make it tougher: Don’t use hands to propel up.

Related article: 5 Dumbbell Moves You Haven’t Tried Before To Tone Your Whole Body

Group 6: Kettlebell Lunge and Slam

How to:

  • Start in a split squat, right leg back and foot on BOSU, holding a medium (20-to-30-pound) kettlebell by the bell, thumbs hooked around horn.
  • Keeping a slight bend in elbows, rise to toes while bringing kettlebell just above head height, then squat and thrust arms down until weight is thigh-high, for 1 rep.
  • Perform for 40 sec.
  • Do all reps on left leg, and switch in next set.

Group 6: Kettlebell Figure 8

How to:

  • Stand with feet wider than shoulder-width apart, a medium (20- to 30-pound) kettlebell in left hand, to start.
  • Hip hinge back, thrust hips forward, and do a one-handed kettlebell swing (A).
  • As the kettlebell travels back between legs, half squat and reach right hand behind right thigh and through legs, switching kettlebell from left hand to right (B).
  • Bring kettlebell around right thigh to front, and repeat pattern with right arm for 1 rep.
  • Perform for 20 sec.