Sheykhlouvand, M, Khalili, E, Agha-Alinejad, H, and Gharaat, M. Hormonal and physiological adaptations to high-intensity interval training in professional male canoe polo athletes. J Strength Cond Res 30 (3): 859–866, 2016—This study compared the effects of 2 different high-intensity interval training (HIIT) programs in professional male canoe polo athletes. Responses of peak oxygen uptake (V [Combining Dot Above] O 2 peak), ventilatory threshold (VT), peak and mean anaerobic power output (PPO and MPO), blood volume, and hormonal adaptations to HIIT were examined. Male athletes (n= 21, age: 24±3 years; height: 181±4 cm; mass: 85±6 kg; and body fat: 12.9±2.7%) were randomly assigned to one of 3 groups (N= 7):(a)(G 1) interval paddling with variable volume (6, 7, 8, 9, 9, 9, 8, 7, 6 repetitions per session from first to ninth session, respectively)× 60 second at lowest velocity that elicited V [Combining Dot Above] O 2 peak (vV [Combining Dot Above] O 2 peak), 1: 3 work to recovery ratio;(b)(G 2) interval paddling with variable intensity (6× 60 second at 100, 110, 120, 130, 130, 130, 120, 110, 100% vV [Combining Dot Above] O 2 peak from first to ninth session, respectively, 1: 3 work to recovery); and (c)(G CON) the control group performed three 60 minutes paddling sessions (75% vV [Combining Dot Above] O 2 peak) per week for 3 weeks. High-intensity interval training resulted in significant (except as shown) increases compared with pretest, in V [Combining Dot Above] O 2 peak (G 1=+ 8.8% and G 2=+ 8.5%), heart rate at VT (b· min− 1)(G 1=+ 9.7% and G 2=+ 5.9%) and (% maximum)(G 1=+ 6.9%; p= 0.29 and G 2=+ 6.5%), PPO (G 1=+ 9.7% and G 2=+ 12.2%), MPO (G 1=+ 11.1%; p= 0.29 and G 2=+ 16.2%), total testosterone (G 1=+ 29.4% and G 2=+ 16.7%), total testosterone/cortisol ratio (G 1=+ 40.9% and G 2=+ 28.1%), and mean corpuscular hemoglobin (G 1=+ 1.7% and G 2=+ 1.3%). No significant changes were found in G CON. High-intensity interval paddling may improve both aerobic and anaerobic performances in professional male canoe polo athletes under the conditions of this study.