[Clinical biochemical evaluation of central fatigue with 24-hour continuous exercise]

The present study was conducted to clarify the effects of ultra-marathon (ultra long-term aerobic exercise in which people run long distances) on the brain; examine the issue of central fatigue; verify the serotonin hypothesis of exercise-induced brain fatigue, and ascertain relationships between central fatigue and oxidative stress.

Subjects consisted of 15 individuals (12 men, 3 women) who ran continuously for 24 h. Mean age was 44 +/- 9 years (range, 31 approximately 64 years). Blood tests were conducted: (1) before starting to run (around 09:00); (2) 16h after starting (02:00 the next day); and (3) just after the finish (around 10:00 the next day) to measure the serum levels of serotonin, melatonin, free tryptophan (f-Tp) and free fatty acid. At the same time, urine samples were collected to measure levels of urinary biopyrrins (BPn). Subjective symptoms were investigated using the Japanese version of the Profile of Mood States (POMS) instrument.

(1) Participants ran a mean (+/- SD) distance of 162.6 +/- 18.3 km. (2) There were not marked changes in serum serotonin levels. Serum melatonin levels at 3 time points were 3.4 +/- 0.6 pg/ml, 57.2 +/- 15.2pg/ml and 7.8 +/- 8.9pg/ml, respectively(p < 0.01 before start vs. 16h after start). Serum f-Trp levels at the 3 time points were 5.4 +/- 0.9 nmol/ml, 9.7 +/- 2.1 nmol/ml and 11.5 +/- 4.9 nmol/ml, respectively (p< 0.05 before start vs. just before finish). Free fatty acid levels were 0.42 +/- 0.10 nmol/ml, 1.26 +/- 0.11 nmol/ml and 1.39 +/- 0.23 nmol/ml, respectively (p < 0.01 before start vs. 16 hours after start) (p < 0.05 before start vs. just after finish). (3) Urinary BPn levels increased with time, from 1.2 +/- 0.7 nmol/ml to 2.6 +/- 1.0 nmol/ml to 4.0 +/- 1.5 nmol/ml, respectively (p < 0.01 before the start vs. 16 hours after the start). (4) In terms of POMS scores, fatigue score (Factor F) increased, but vitality score (Factor V) was high at all time points and did not demonstrate any marked changes. Scores for anger and hostility were low (Iceberg profile-type: convex type). Urinary BPn levels were correlated significantly with both serum f-Trp level and Factor F:(y = 8.41x + 2.5, r = 0.708, n = 42) and (y = 2.82x + 5.9, r = 0.568, n = 42), respectively. Urinary BPn thus reflected the degree of subjective fatigue with a high level of sensitivity.

The present results suggest that running continuously for 24h induces brain fatigue and that oxidative stress may be involved.