Aquatic reduced exertion high-intensity interval training (REHIT) increases cardiorespiratory fitness in untrained young adults compared with a land-based protocol

Purpose: This randomized control trial compared cardiometabolic, performance, and subjective outcomes following an 8-week reduced exertion high intensity interval training (REHIT) program in land (LAND) vs. aquatic (AQUA) exercise matched for relative intensity. Methods: Young, untrained adults were randomized to LAND or AQUA groups and followed a REHIT exercise protocol (3 min warm up, 20 second maximal effort, 3 min active recovery, 20 second maximal effort, 3 min cool down) matched for exercise intensity 3x/wk for 8 consecutive weeks on a cycle ergometer (LAND) or with maximal jump squats in the pool (AQUA). Pre and post measures included height, body mass, BMI, resting blood pressure and heart rate, fasting glucose, estimated VO2max test, Wingate Test, vertical jump, and the Physical Activity Enjoyment Questionnaire. Results: Neither the AQUA or LAND training influenced weight, BMI, or cardiometabolic variables (p>0.05). The AQUA group (Pre: 36.9 ± 7.7 vs Post: 43.9 ± 8.8 mL/kg/min), but not LAND group (Pre: 33.1 ± 6.9 vs Post: 34.9 ± 6.1 mL/kg/min), increased estimated VO2max (p<0.05). The LAND group increased both absolute (Pre: 644.6 ± 210.7 vs Post: 794.1 ± 208.1 Watts) and relative maximal power (Pre: 8.6 ± 3.0 vs 10.7 ± 3.1 W/kg) (p<0.05) as assessed by the Wingate test; however, there was no difference in the AQUA group in absolute (Pre: 633.8 ± 172.5 vs Post: 683.8 ± 158.8 Watts) or relative maximal power (Pre: 9.2 ± 2.3 vs Post: 9.9 ± 1.9 W/kg) (p>0.05). There was no difference in vertical jump height or average change in response on the questionnaire in either group (p>0.05). Conclusion: Compared with a land-based protocol matched for relative intensity, an 8-week aquatic REHIT program increased estimated cardiorespiratory fitness, but not maximal power production, in young, untrained adults. Aquatic REHIT can be recommended as a time-efficient exercise program for those just starting exercise that need or prefer an alternate to land-based exercise. This study was registered on clinicaltrials.gov (NCT05573087) on Oct. 10, 2022.