Author(s): YE, Y., GAO, B., Institution: SHANGHAI UNIVERSITY OF SPORT, Country: CHINA, Abstract-ID: 508

INTRODUCTION:
External training load refers to the imposed training stimulus, while internal training load (ITL) reflects athletes’ physiological responses. Olympic sailing, often held in summer coastal areas, exposes athletes to hot and humid conditions, making ITL monitoring crucial. Heart rate variability (HRV) is a non-invasive, convenient tool for ITL assessment, with RMSSD (root mean square of successive R-R interval differences) and its derivatives (LnRMSSD, RMSSD-Slope) being reliable indicators of parasympathetic activity. This study aimed to evaluate hot and humid environments’ impact on HRV and verify HRV’s utility for ITL control, hypothesizing that HRV could assess ITL in such environments, which would increase training intensity and delay RMSSD recovery.
METHODS:
A randomized cross-over study was conducted on 9 male Laser sailors (age: 20.8±2.2 years; training years: 8.2±2.3 years). They completed a 6 km rowing test in two environments: cool (Ta=23±1.4°C, RH=60.5±0.7%) and hot (Ta=31.2±1.3°C, RH=64.3±3.8%), separated by 7-14 days. HRV indices (RMSSD, LnRMSSD, RMSSD-Slope, TLHRV) and blood lactate (BLa) were measured pre-exercise, post-exercise (0/3/7/15 min), and during 30-min seated recovery. Data were analyzed via repeated measures ANOVA, correlation analysis, and t-tests (P<0.05).
RESULTS:
Significant HOT*Time interactions were observed for BLa, RMSSD, and LnRMSSD (P<0.05). BLa was higher in the HOT group at post-0/3/15 min (P<0.05). RMSSD was lower in the HOT group at post-20/25/30 min (P<0.05), and LnRMSSD was lower after post-15 min recovery (P<0.05). RMSSD-Slope was significantly lower in the HOT group during 30-min recovery (P=0.004). RMSSD and LnRMSSD were negatively correlated with BLa (r=-0.436, P<0.001; r=-0.471, P<0.001), while TLHRV showed no significant correlations with BLa or RMSSD (P>0.05).
CONCLUSION:
RMSSD and its derivatives (LnRMSSD, RMSSD-Slope) are valid for monitoring ITL in hot and humid environments, primarily influenced by training intensity. Hot and humid conditions increase relative ITL and prolong parasympathetic recovery (RMSSD recovery rate 50% slower than cool environment). TLHRV is impractical for sailors due to field condition limitations. This study broadens non-invasive ITL monitoring systems, though future research should use thermal environment meters and verify applicability across populations. In conclusion, training intensity induces graded effects on parasympathetic reactivation, and RMSSD-based indices effectively assess ITL in hot and humid environments.