Aquatic exercise may be better tolerated by sedentary, overweight individuals than land-based exercise. The purpose of the present study was to determine the effects of five weeks of aquatic high-intensity interval training (AHIIT) using standard calisthenic pool exercises, on cardiorespiratory fitness and body composition in sedentary young adults. Eleven college-age participants (9 women, 2 men) completed 15 exercise sessions that included three sessions per week for five weeks. Each session consisted of a five-minute warm-up period, 25 minutes of exercise, and a five-minute cool down. A training progression based upon standard progression principals from a pilot study was implemented. The exercises consisted of 25 exercise intervals lasting 10-30 seconds in duration, utilizing combinations of 8-12 different exercises. Twenty-two standard aquatic upper body, lower body, and full body aerobic exercises, most of which utilized aquatic dumbbells or hand paddles, were performed in an AHIIT protocol during each exercise session. Reductions in body composition (32.6 to 30.6% fat), submaximal (169 to 165 b·min^-1) and peak heart rate (199 to 192 b·min^-1), submaximal VO₂ (21.7 to 19.3 ml·kg^-1·min^-1 and peak VO₂ (30.5 to 31.95 ml·kg^-1·min^-1) occurred from pre- to post-program. This is the first study to determine the effectiveness of standard aquatic calisthenic exercises used in an AHIIT protocol. Improvements in cardiorespiratory fitness and exercise economy as well as body composition were observed in these sedentary individuals.

• Aquatic calisthenic high intensity exercise, when used in a progressive fashion, is tolerated by sedentary, overweight individuals.

• Aquatic calisthenic high intensity exercise, when used in a progressive fashion, is effective in improving cardiorespiratory fitness and body composition.

• Effective aquatic calisthenic high intensity exercise can be conducted without aquatic treadmills or cycles.