Autonomic adaptations to intensive and overload training periods: a laboratory study.
OBJECTIVE
Looking for practical and reliable markers of fatigue is of particular interest in elite sports. One possible marker might be the autonomic nervous system activity, known to be well affected by physical exercise and that can be easily assessed by heart rate variability.


METHODS
We designed a laboratory study to follow six sedentary subjects (32.7 +/- 5.0 yr) going successively through 2 months of intensive physical training and 1 month of overload training on cycloergometer followed by 2 wk of recovery. Maximal power output over 5 min (Plim5'), VO(2) and standard indices of heart rate variability were monitored all along the protocol.


RESULTS
During the intensive training period, physical performance increased significantly VO(2peak) : +20.2%, < 0.01; Plim5': +26.4%, < 0.0001) as well as most of the indices of heart rate variability (mean RR, Ptot, HF, rMSSD, pNN50, SDNNIDX, SDNN, all < 0.05) with a significant shift in the autonomic nervous system toward a predominance of its parasympathetic arm (LF/HF, LFnu, HFnu, < 0.01). During the overload training period, there was a stagnation of the parasympathetic indices associated to a progressive increase in sympathetic activity (LF/HF, < 0.05). During the week of recovery, there was a sudden significant rebound of the parasympathetic activity (mean RR, HF, pNN50, rMSSD, all < 0.05). After 7 wk of recovery, all heart rate variability indices tended to return to the prestudy values.


CONCLUSIONS
Autonomic nervous system status depends on cumulated physical fatigue due to increased training loads. Therefore, heart rate variability analysis appears to be an appropriate tool to monitor the effects of physical training loads on performance and fitness, and could eventually be used to prevent overtraining states.
Pichot
Vincent
V
Laboratorie de Physiologie, GIP E2S, Université de Saint-Etienne, France. Vincent.Pichot@univ-st-etienne.fr
Busso
Thierry
T
Roche
Frédéric
F
Garet
Martin
M
Costes
Frédéric
F
Duverney
David
D
Lacour
Jean-René
JR
Barthélémy
Jean-Claude
JC
D000222:Adaptation, Physiological; D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D002940:Circadian Rhythm; D005080:Exercise Test; D006339:Heart Rate; D006801:Humans; D008297:Male; D010806:Physical Education and Training; D005082:Physical Exertion / Q000502:physiology*; D012146:Rest; D013997:Time Factors