Effects of melatonin on the thermoregulatory responses to intermittent exercise

Abstract

We examined the effects of a single 2.5-mg dose of melatonin on the thermoregulatory and circulatory responses to intermittent exercise at a room temperature of 27.2+/-0.4 degrees C (mean+/-S.D.), a relative humidity of 55+/-3% (mean+/-S.D.), and a light intensity of 200-300 lux. In a double-blind cross-over study, six male participants ingested either melatonin or placebo at 11:45 hr. Participants then rested in a semi-supine position for 75 min and completed an intermittent running protocol for 66 min at alternating intensities of 40, 60 and 80% of maximal oxygen uptake. Rectal and mean skin temperature, heart rate, blood pressure, skin blood flow, subjective alertness and sleepiness, ratings of perceived exertion (RPE) and thermal strain were recorded. No effects of melatonin were found on these variables measured during the resting period (P>0.10). During exercise, melatonin was found to moderate the increase in rectal temperature by approximately 0.25 degrees C (P=0.050) and magnify the increase in skin blood flow (P=0.047). Postexercise systolic blood pressure was 7.8+/-2.5 mmHg (mean+/-S.D.) lower than before the exercise in the melatonin trial; a change which differed significantly to that in the placebo trial (P=0.018). Melatonin did not influence subjective alertness and sleepiness before or after exercise and did not change the responses of mean skin temperature, RPE and thermal strain during the exercise (P>0.10). In summary it is apparent that a 2.5-mg dose of melatonin has hypothermic, but not soporific, effects during 66 min of intermittent exercise performed under moderate heat stress. Whether such effects improve endurance athletic performance in hot conditions remains to be confirmed. Our data also suggest that postexercise systolic hypotension is more marked after ingestion of melatonin.

Evaluation of anaerobic capacity and fatigue index at different times of the day on male handball players

“…Hill et al (1992) in their study they confirm the time of day effect of anaerobic capacity [8]. The results of our study were similar to the results of Atkinson and Reilly (1996) and [9,10].…”

Diurnal variation in the salivary melatonin responses to exercise: relation to exercise-mediated tachycardia

“…Therefore, it can be postulated that the rise in melatonin levels after exercise during the current study may be brought about via postganglionic b 1 adrenergic receptors (Vaughan and Reiter 1987). This rise in melatonin with exercise is similar to the elevations seen when an acute dose of exogenous melatonin is administered (Atkinson et al 2005a, b;Harris et al 2001). However, studies that have utilised an exogenous melatonin have produced equivocal findings in terms of heart rate responses.…”

“…However, studies that have utilised an exogenous melatonin have produced equivocal findings in terms of heart rate responses. Harris et al (2001) and Atkinson et al (2005a) found decreases in heart rate following administration of melatonin during the daytime. However, Atkinson et al (2005b) conversely found that heart rate was not altered by ingestion of melatonin.…”

Morning melatonin ingestion and diurnal variation of short-term maximal performances in soccer players

“…Moreover, Jones (15) showed that MEL administration (5 mg) at 11:45 h affected choice reaction time, subjective alertness, short-term memory measured both at 13:00 h and 15:00 h. These results confirm the present study findings observed at 08:00 h. It seems that daytime MEL ingestion could affect cognitive performances and exert a hypnotic effect if it is very close to the evaluation. Furthermore, Atkinson et al (5) showed that the diurnal ingestion of a lower dose of MEL (2.5 mg) at 11:45 h did not influence the subjective alertness and sleep before and after exercise done 75 min after MEL administration. Consequently, to assure that MEL does not affect the cognitive responses, it seems necessary to rise the duration between time of ingestion and the evaluation session.…”

“…MEL, often considered as a chronobiotic (12), was initially investigated in terms of its role in endocrine physiology regulating circadian and sometimes seasonal rhythms (22). Moreover, it has been shown that exogenous MEL can improve sleep quality and alleviate jet lag symptoms after transmeridian travels (5). In addition to the control of the biological rhythms, it is known that exogenous MEL administration has clear hypothermic effects (10).…”