Fatigue shifts and scatters heart rate variability in elite endurance athletes.
OBJECTIVE
This longitudinal study aimed at comparing heart rate variability (HRV) in elite athletes identified either in 'fatigue' or in 'no-fatigue' state in 'real life' conditions.


METHODS
57 elite Nordic-skiers were surveyed over 4 years. R-R intervals were recorded supine (SU) and standing (ST). A fatigue state was quoted with a validated questionnaire. A multilevel linear regression model was used to analyze relationships between heart rate (HR) and HRV descriptors [total spectral power (TP), power in low (LF) and high frequency (HF) ranges expressed in ms(2) and normalized units (nu)] and the status without and with fatigue. The variables not distributed normally were transformed by taking their common logarithm (log10).


RESULTS
172 trials were identified as in a 'fatigue' and 891 as in 'no-fatigue' state. All supine HR and HRV parameters (Beta±SE) were significantly different (P<0.0001) between 'fatigue' and 'no-fatigue': HRSU (+6.27±0.61 bpm), logTPSU (-0.36±0.04), logLFSU (-0.27±0.04), logHFSU (-0.46±0.05), logLF/HFSU (+0.19±0.03), HFSU(nu) (-9.55±1.33). Differences were also significant (P<0.0001) in standing: HRST (+8.83±0.89), logTPST (-0.28±0.03), logLFST (-0.29±0.03), logHFST (-0.32±0.04). Also, intra-individual variance of HRV parameters was larger (P<0.05) in the 'fatigue' state (logTPSU: 0.26 vs. 0.07, logLFSU: 0.28 vs. 0.11, logHFSU: 0.32 vs. 0.08, logTPST: 0.13 vs. 0.07, logLFST: 0.16 vs. 0.07, logHFST: 0.25 vs. 0.14).


CONCLUSIONS
HRV was significantly lower in 'fatigue' vs. 'no-fatigue' but accompanied with larger intra-individual variance of HRV parameters in 'fatigue'. The broader intra-individual variance of HRV parameters might encompass different changes from no-fatigue state, possibly reflecting different fatigue-induced alterations of HRV pattern.
National School of Mountain Sports/National Ski-Nordic Centre, Premanon, Les Rousses, France. laurent.schmitt@ensm.sports.gouv.fr
Laurent
L
Schmitt
Jacques
J
Regnard
Maxime
M
Desmarets
Fréderic
F
Mauny
Laurent
L
Mourot
Jean-Pierre
JP
Fouillot
Nicolas
N
Coulmy
Grégoire
G
Millet
D056352:Athletes; D005221:Fatigue; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate; D006801:Humans; D008297:Male; D010807:Physical Endurance / Q000502:physiology*; D011187:Posture; D056152:Respiratory Rate