This study examined the effects of a resistance-type high-intensity interval training (RHIIT) matched with the lowest velocity that elicited (Formula presented.) O2peak (100% v (Formula presented.) O2peak) in well-trained kayak sprint athletes. Responses in cardiac structure and function, cardiorespiratory fitness, anaerobic power, exercise performance, muscular strength, and hormonal adaptations were examined. Male kayakers (n = 24, age: 27 ± 4 years) were randomly assigned to one of three 8-wk conditions (N = 8): (RHIIT) resistance training using one-armed cable row at 100% v (Formula presented.) O2peak; paddling-based HIIT (PHIIT) six sets of paddling at 100% v (Formula presented.) O2peak; or controls (CON) who performed six sessions including 1-h on-water paddling/sessions at 70–80% maximum HR per week. Significant increases (p < 0.05) in (Formula presented.) O2peak, v (Formula presented.) O2peak, maximal cardiac output, resting stroke volume, left ventricular end-systolic dimension, 500-m paddling performance were seen pre- to post-training in all groups. Change in (Formula presented.) O2peak in response to PHIIT was significantly greater (p = 0.03) compared to CON. Also, 500-m paddling performance changes in response to PHIIT and RHIIT were greater (p = 0.02, 0.05, respectively) than that of CON. Compared with pre-training, PHIIT and RHIIT resulted in significant increases in peak and average power output, maximal stroke volume, end-diastolic volume, ejection fraction, total testosterone, testosterone/cortisol ratio, and 1,000-m paddling performance. Also, the change in 1,000-m paddling performance in response to PHIIT was significantly greater (p = 0.02) compared to that of CON. Moreover, maximum strength was significantly enhanced in response to RHIIT pre- to post-training (p < 0.05). Overall, RHIIT and PHIIT similarly improve cardiac structure and hemodynamics, physiological adaptations, and performance of well-trained kayak sprint athletes. Also, RHIIT enhances cardiorespiratory fitness and muscular strength simultaneously.
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