Research

Hormonal

High-intensity intensive training (approx. 90% VO2peak) for 8 weeks increases parasympathetic autonomic activity and aerobic performance (VO2peak), whereas subsequent overload training (5/3x workload) shifts autonomic balance toward sympathetic dominance, indicating fatigue.

To improve aerobic fitness, you need to train hard (around 90% of your max capacity). This will initially increase your body's restorative (parasympathetic) activity. If you push too hard without rest (overload), your stress (sympathetic) system takes over, signaling fatigue. Use heart rate variability to monitor this shift: a drop in parasympathetic markers suggests you need recovery to avoid overtraining.

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Globally, there was a progressive increase of both the parasympathetic and sympathetic indices with a shift of the autonomic nervous system equilibrium toward a predominance of the parasympathetic arm simultaneously to an increase of the aerobic performance during the 2-month intensive training period... During the overload training period... there was a stagnation of the parasympathetic indices associated to a progressive increase in sympathetic activity (LF/HF, P < 0.05).
Vincent Pichot et al. · Medicine & Science in Sports & Exercise · 2002

Why this rating

Controlled laboratory study with repeated measures and statistical significance, but small sample size (n=6).

Source

Autonomic adaptations to intensive and overload training periods: a laboratory study

Vincent Pichot et al. · Medicine & Science in Sports & Exercise · 2002

DOI 10.1097/00005768-200210000-00019

clinical_trial · n=6Cited 174×
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DOI resolved against Crossref · corpus check 2026-06-10

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