Typology of ``Fatigue'' by Heart Rate Variability Analysis in Elite Nordic-skiers

This study investigated changes in heart rate variability (HRV) in elite Nordic-skiers to characterize different types of fatigue in 27 men and 30 women surveyed from 2004 to 2008. R-R intervals were recorded at rest during 8min supine (SU) followed by 7min standing (ST). HRV parameters analysed were powers of low (LF), high (HF) frequencies, (LF+HF) (ms(2)) and heart rate (HR, bpm). In the 1063 HRV tests performed, 172 corresponded to a fatigue state and the first were considered for analysis. 4 types of fatigue (F) were identified: 1. F(HF-LF-)(SU_ST) for 42 tests: decrease in LFSU (-46%), HFSU (-70%), LFST (-43%), HFST (-53%) and increase in HRSU (+15%), HRST (+14%). 2. F(LF+ SULFST-) for 8 tests: increase in LFSU (+190%) decrease in LFST (-84%) and increase in HRST (+21%). 3. F(HFSU-HFST+) for 6 tests: decrease in HFSU (-72%) and increase in HFST (+501%). 4. F(HF+ (SU)) for only 1 test with an increase in HFSU (+2161%) and decrease in HRSU (-15%). Supine and standing HRV patterns were independently modified by fatigue. 4 fatigue-shifted HRV patterns were statistically sorted according to differently paired changes in the 2 postures. This characterization might be useful for further understanding autonomic rearrangements in different fatigue conditions.