[The effects of an extreme endurance exercise event on autonomic nervous system activity]

Initial response of human body to exercise consists of a decrease in vagal tone, followed by an increase in sympathetic activity. After exercise cessation, the parasympathetic component quickly regains its pre-exercise level, whereas signs of sympathetic activation have been reported to persist as long as 24 hours after intense exercise.

To verify in a group of young marathon runners whether extreme endurance exercise may induce an increase of sympathetic activity for up to 48 hours during recovery.

Twelve athletes aged 32+/-12 years, taking part in a marathon (42 km) were studied. We measured baroreflex sensitivity using the transfer function method (BRS-WBA), as well as standard spectral indexes of short-term heart rate variability (LF and HF power, LFnu, LF/HF). These parameters were measured before the marathon and on the second day (about 48 hours) following the event. Comparisons were made between the two measurements (after vs. before).

We found a statistically significant decrease in BRS-WBA (15.1+/-4.5 vs. 10.5+/-3.5 ms/mmHg, p=0.013), as well as a trend towards higher values of LF/HF (1.0+/-1.0 vs. 1.4+/-1.4, p=0.09). An increase in LF (from 1048+/-874 to 1427+/-1678 ms2) was observed, but it did not reach statistical significance.

These results suggest that increased sympathetic activity can persist for up to 24 hours after an extreme endurance exercise such as a marathon. It is thus likely that in less trained and less physically active people exposed to excessive amounts of strenuous exercise, the autonomic nervous system response can be similar. Further studies are needed, however, to verify this inference.