Physiological and Perceptual Internal Load During Kitesurfing Under Real-World Sea Conditions

<b><i>Background:</i></b> Kitesurfing is a wind-propelled water sport performed in highly variable environmental conditions. Scientific evidence describing internal load under standardized ecological sea constraints remains limited. <b><i>Aim:</i></b> This study aimed to characterize cardiovascular and perceptual responses during a standardized kitesurfing session and to examine associations among heart rate-based internal load indices, session rating of perceived exertion, and global navigation satellite system-derived external output variables. <b><i>Methods:</i></b> A total of 112 male recreational kitesurfers (32.1 ± 6.8 years) completed a 40-50 min standardized session under monitored wind conditions (17-22 knots) along a predefined approximately 800 m course. Heart rate was continuously recorded, and session rating of perceived exertion (Borg Category-Ratio 10 scale) was collected 30 ± 5 min post-session. Training impulse, mean percentage of maximal heart rate, and session rating of perceived exertion load were calculated. Pearson correlation analyses with bootstrapping (1000 resamples) and five percent trimming were performed, with statistical significance set at 0.05. <b><i>Results:</i></b> Sessions were performed at 78.4 ± 9.1 percent of maximal heart rate. Training impulse and mean percentage of maximal heart rate were strongly associated (correlation coefficient = 0.90, probability value < 0.001), reflecting the shared heart rate-based structure of these metrics. Training impulse showed a moderate association with session rating of perceived exertion load (correlation coefficient = 0.46, probability value < 0.001). No significant associations were observed between internal load indices and global navigation satellite system-derived mean speed (correlation coefficient = -0.14, probability value = 0.149) or distance (correlation coefficient = 0.06, probability value = 0.555). Sensitivity analyses confirmed the stability of the observed associations. <b><i>Conclusions:</i></b> Under standardized ecological sea conditions, kitesurfing sessions were characterized by sustained high submaximal cardiovascular intensity. Heart rate-based and perceptual measures showed consistent associations within this protocol, whereas global navigation satellite system-derived external outputs were not significantly related to internal load indices. Within the limits of this cross-sectional ecological design, the combined use of one heart rate-based indicator and session rating of perceived exertion offers a coherent and practically interpretable description of session internal load in open-water kitesurfing.