Effects of Dynamic Apnea Conditions on Performance, Kinematic Parameters, and Physiological Markers in 50 m Monofin Sprinting

Finswimming is a high-intensity aquatic sport in which performance is influenced by the interaction between biomechanical and physiological factors, particularly during underwater apnea sprint events. This study compared performance, kinematic characteristics, cardiovascular responses, metabolic responses, and perceived exertion during a maximal 50 m monofin sprint performed under three conditions: underwater apnea swimming (UW), surface swimming without a snorkel (SN), and surface swimming with a closed snorkel (SC). Ten highly trained young male national-level finswimmers completed a randomized repeated-measures protocol. Performance time, dolphin kick number and frequency, heart rate (HR), blood lactate concentration, blood glucose concentration, and rating of perceived exertion (RPE) were assessed. Sprint performance was significantly faster during UW (17.38 ± 1.32 s) than during both SN (19.20 ± 1.64 s) and SC (19.39 ± 1.53 s; p < 0.001), with a very large condition effect (ηp2 = 0.882). This was accompanied by fewer dolphin kicks during UW (40 ± 5) than during SN (44 ± 6) and SC (44 ± 5), with a large condition effect (ηp2 = 0.651), whereas kick frequency did not differ significantly among conditions (~137–140 kicks·min−1; ηp2 = 0.038). HR exhibited a biphasic recovery pattern across all conditions, declining rapidly from peak exercise values (HRpeak: ~169–171 bpm) to HRlow (~141–147 bpm) before increasing to HRhigh (~160–162 bpm) during early recovery, with a very large main effect of time (p < 0.001; ηp2 = 0.823). Post-exercise blood lactate concentration increased significantly in all conditions from ~1.3–1.5 to ~10.7–11.9 mmol·L−1 (p < 0.001), with a very large time effect (ηp2 = 0.954) and no significant between-condition differences. Blood glucose concentration (~5.4–5.9 mmol·L−1) and RPE (7–8 a.u.) showed no statistically significant condition-specific differences. In conclusion, underwater apnea swimming was associated with faster 50 m sprint performance and fewer dolphin kicks than the surface swimming conditions in highly trained young male national-level finswimmers. These performance and kick characteristics are consistent with potential biomechanical and hydrodynamic explanations described in previous research, although propulsive efficiency and hydrodynamic resistance were not directly measured in the present study. A biphasic HR recovery pattern was observed across conditions; however, the autonomic mechanisms underlying this response cannot be determined from the present measurements.