ABSTRACTThe present study aimed to investigate whether nocturnal melatonin (MEL) ingestion has beneficial effects against exercise-induced oxidative stress and muscle damage in young athletes. Fourteen healthy-trained teenagers performed two-test sessions separated by at least, 1 week. During each session, participants completed the Running-Based Anaerobic Sprint Test (RAST) at 20:00 h. Then, they ingested a single 10-mg tablet of MEL or Placebo (PLA) in a double-blind randomized order at 22:00 h. The following morning (i.e., 07:30 h), participants performed the same test as the previous night. Blood samples were taken before and after exercise. MEL intake increased the peak power (P
peak) (
p < .01), mean power (P
mean) (
p < .001) and decreased the total time (TT) (
p < .001) and the fatigue index (FI) (
p < .05). Furthermore, MEL ingestion attenuated the hematologic parameters before and after exercise (White Blood Cells (WBC:
p < .001 and
p < .001, respectively); Neutrophiles (NE:
p < .001 and
p < .001, respectively); Lymphocytes (LY:
p < .001 and
p < .001, respectively)) and the ultra-sensitive C-reactive protein (us-CRP:
p < .001 and
p < .001; respectively) compared to PLA. Also, MEL reduced muscle and hepatic damage enzymes before and after exercise (creatine kinase (CK:
p < .001 and
p < .001; respectively), lactate dehydrogenase (LDH:
p < .05 and
p < .01; respectively), aspartate aminotransferase (ASAT:
p < .01 and
p < .001; respectively)),
Malondialdehyde (MDA:
p < .001 and
p < .001; respectively) and Homocysteine (Hcy:
p < .001 and
p < .001; respectively)) from placebo. Plasma lactate [La] and glucose (GL) remained unchangeable during the two conditions. In summary, acute MEL ingestion after strenuous late-evening exercise attenuated transient leucocytosis and protected against lipid peroxidation and muscle damage induced by strenuous exercise the following morning in healthy male teenage athletes.
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