Popsugar Fitness Workouts Abs and Legs HIIT Workout Sculpt Your Abs and Legs With This Trainer's 25-Minute Equipment-Free HIIT Workout June 28, 2019 by Tamara Pridgett View On One Page Photo 4 of 8 ADVERTISEMENT () Start Slideshow Share This Link Copy ← Use Arrow Keys → 4 High Knees Run in place while lifting your knees high to the level of your waist. Engage your abs as your knee comes up. Repeat for 40 seconds followed by 20 seconds of rest. Previous Next Start Slideshow WorkoutsStrength TrainingHIITAb WorkoutsTrainer TipsIntermediate Workouts30-Minute WorkoutsLeg WorkoutsAb ExercisesLeg Exercises