Race Segment Variability In Physiological Responses During Half Ironman Triathlon

Ultra-endurance triathlon is a physiologically challenging and potentially hazardous sport, with limited research on the acute cardiac and pulmonary responses throughout competition. PURPOSE: To compare specific physiologic responses—heart rate (HR), breathing rate (BR), relative time in heart rate zones (HRZ), and cardiac strain (CS)—across Half IM swim, bike, and run race segments. METHODS: Participants (n = 9) from the TriCities, WA Half IM were equipped with a two-lead electrocardiogram (ECG) and instructed to wear the device throughout competition. Freidman's test was performed to determine mean rank of each physiologic response for race segments, including occurrences of CS (ST segment deviation ±0.2 Mv), as well as min, max, mean HR, BR, and relative time in HRZs. Post hoc Hedges G was calculated to determine effect size by segment when insignificant results were found with Friedman’s test. RESULTS: Mean BR during the swim (35.7 ± 4.1), bike (39.3 ± 6.5), and run (43.0 ± 4.0) varied significantly, x2(2, N = 9) 12.667, p = .002. Additionally, max BR during the swim (43.0 ± 5.8), bike (51.9 ± 3.8), and run (51.7 ± 4.6), x2(2, N = 9) 8.400, p = .015, and min BR during the swim (26.6 ± 4.6), bike (27.7 ± 6.0), and run (32.7 ± 4.0), x2(2, N = 9) 8.971, p = .011, also varied. When comparing max HR during the bike segment (171.1 ± 6.7) to the swim (164.7 ± 7.0), a large effect size was seen (d = 0.81 95% CI [-1.77 - .15]). Likewise, a large effect size for min HR was found between the bike segment (114.6 ± 16.5) and the run (134.3 ± 14.4) (d = 1.17 95% CI [-2.17 - -.17]). No significant differences for CS and relative time in HRZs by race segments were observed. CONCLUSION: Findings indicate that BRs (min, max, mean) all differ significantly by race segment, suggesting variable pulmonary workloads throughout triathlon competition. Race segment comparisons also show max HR differences between the swim and bike, and min HR differences between the bike and run, indicating exertion levels to be highest during the run.