RESUMO

Nitrate (NO3 -) is an ergogenic nutritional supplement that is widely used to improve physical performance. However, the effectiveness of NO3 - supplementation has not been systematically investigated in individuals with different physical fitness levels. The present study analysed whether different fitness levels (non-athletes v. athletes or classification of performance levels), duration of the test used to measure performance (short v. long duration) and the test protocol (time trials v. open-ended tests v. graded-exercise tests) influence the effects of NO3 - supplementation on performance. This systematic review and meta-analysis was conducted and reported according to the guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement. A systematic search of electronic databases, including PubMed, Web of Science, SPORTDiscus and ProQuest, was performed in August 2017. On the basis of the search and inclusion criteria, fifty-four and fifty-three placebo-controlled studies evaluating the effects of NO3 - supplementation on performance in humans were included in the systematic review and meta-analysis, respectively. NO3 - supplementation was ergogenic in non-athletes (mean effect size (ES) 0·25; 95 % CI 0·11, 0·38), particularly in evaluations of performance using long-duration open-ended tests (ES 0·47; 95 % CI 0·23, 0·71). In contrast, NO3 - supplementation did not enhance the performance of athletes (ES 0·04; 95 % CI -0·05, 0·15). After objectively classifying the participants into different performance levels, the frequency of trials showing ergogenic effects in individuals classified at lower levels was higher than that in individuals classified at higher levels. Thus, the present study indicates that dietary NO3 - supplementation improves physical performance in non-athletes, particularly during long-duration open-ended tests.

Assuntos

RESUMO

In the present study, we investigated whether the daily fluctuations of internal body temperature (Tb) and spontaneous locomotor activity (SLA) interact with the thermal and neuronal adjustments induced by high-intensity aerobic exercise until fatigue. The body temperature and SLA of adult Wistar rats (n = 23) were continuously recorded by telemetry for 48 h. Then, the rats were subjected to a protocol of graded exercise until fatigue or rest on the treadmill during light and dark-phases. Tb, tail skin temperature and ambient temperature during each experimental session were recorded. At the end of the last experimental session, the animals were anaesthetized; the brains were perfused and removed for immunohistochemical analysis of c-fos neuronal activation. The daily rhythms of SLA and Tb were strongly correlated (r = 0.88 and p < 0.001), and this was followed by a daily oscillation in both the ratio and the correlation index between these variables (p < 0.001). Exercise capacity was associated with a lower resting Tb (p < 0.01) and was higher in the light-phase (p < 0.001), resulting in an increased capacity to accumulate heat during exercise (p < 0.01). Independent of time-of-day, high intensity exercise strongly activated the hypothalamic paraventricular nucleus (PVN), the supra-optic nucleus (SON) and the locus coeruleus (LC) (p < 0.001) but not the suprachiasmatic nucleus (SCN). Taken together, our results points toward a role of the circadian system in a basal activity control of the thermoregulatory system as an important component for the onset of physical activities. In fact, rather than directly limiting the adjustments induced by exercise the present study brings new evidence that the effect of time-of-day on exercise performance occurs at the threshold level for each thermoregulatory system effector activity. This assumption is based on the observed resilience of the central clock to high-intensity exercise and the similarities in exercise-induced neuronal activation in the PVN, SON, and LC.

RESUMO

The endocannabinoid system plays an important role in thermal control and modulates several behaviors, such as locomotion and food intake (FI) that may affect the body temperature (Tb). To test whether the changes in Tb induced by anandamide (AEA) are related to behavioral changes, adult Wistar rats received an intracerebroventricular injection of AEA (0.1, 1.0 and 10.0 µg) and vehicle. Total FI was weighted daily, and Tb and spontaneous locomotor activity (SLA) were simultaneously and continuously recorded. AEA induced an increase in Tb without changing SLA and FI. For all doses tested, the Tb average in the post-injection period was higher than in the pre-injection period. The higher thermal effect was verified using a dose of 10.0 µg AEA, starting within the first hour post-injection, and was maintained for 8h after treatment. A dose-dependent thermal effect was observed (r=0.953; p<0.05) at 1h post-injection. Hypoactivity was verified only at a dose of 1.0 µg AEA. As expected, both the Tb and SLA values during the dark phase were always higher than during the light phase and were positively correlated (r=0.834, p<0.001); however, this correlation was inverted (r=-0.852, p<0.01) after the rats received 10.0 µg AEA. In summary, our results suggest that brain AEA induces an increase in Tb, and that this effect may occur independently of changes in both locomotion and FI. Moreover, it is possible that the hypolocomotion induced by AEA could be an adaptive response to the increased Tb.

Assuntos