Hamlin, Michael J.Lizamore, C.Olsen, P.Marshall, H.Masters, R.2021-02-1020202703-240Xhttps://hdl.handle.net/10182/13386Introduction: Repeated sprint training in hypoxia is a popular training regime, but careful monitoring is needed to avoid overtraining. This study aimed to determine whether heart rate variability (HRV) measures taken in the training period are associated with post-training running performance in rugby players. Methods: Amateur club rugby players completed 3 weeks of twice-weekly repeated sprint training (cycling) in either hypoxia (RSH, n = 9; 20.3 ± 2.1 years; 77.1 ± 10.2 kg; 173.9 ± 4.9 cm; FIO2: 14.5%) or normoxia (RSN, n = 10; 22.0 ± 4.1 years, 88.3 ± 14.1 kg; 177.9 ± 5.4 cm, FIO2: 20.9%). Resting heart rate (RHR) and HRV were monitored during normoxic rest immediately before training. Pre- and post-training aerobic endurance (Yo-Yo Intermittent Recovery Level 1 (YYIR1)) and repeated sprint ability (RSA, running) were measured. Results: Compared to RSN, RSH demonstrated possibly lower HRV (natural log of the root mean square of successive difference, RMSSD): -8.5, ± 19.1% and standard deviation of N-N intervals: -11.5, ± 25.0%; percent change, ± 90% CL), and higher RHR (3.2, ± 4.7 bpm) post-intervention. Week 3 RHR and HRV demonstrated strong, statistically significant correlations with post-intervention performances in YYIR1 (RHR: -0.82, p = 0.02; RMSSD: r = 0.58, p = 0.17; low frequency: high frequency ratio (LF/HF): r = -0.85, p = 0.01) and RSA (RHR: r = 0.73, p = 0.06; RMSSD: r = -0.53, p = 0.22; LF/HF: r = 0.77, p = 0.05) in RSH, but not RSN. Discussion: RSH likely intensified training resulting in reduced HRV, however, an absence in power reduction during training suggests overtraining was avoided. The stronger correlations between resting HRV and post-training performance in RSH may point to responders and non-responders to RSH2. Take home message: RHR and HRV may be valuable tools for monitoring added stresses associated with RSH.39-39en© Sport and Exercise Science New ZealandConference Contribution - published