Active warm-up and time-of-day effects on repeated-sprint performance and post-exercise recovery.

PURPOSE: This study investigated the effects of both an active warm-up and the time-of-day variation on repeated-sprint performance. A second objective was to compare the post-exercise recovery between the experimental conditions. METHODS: Eleven male participants performed ten maximal cycling sprints (6 s each, with a 30-s interval between them) in the morning and late afternoon, either after a warm-up or control condition. The warm-up consisted of cycling for 10 min at 50% of the peak aerobic power. RESULTS: Rest measurements of rectal, muscle, and skin temperatures were higher in the afternoon compared to the morning (p < 0.05), with no significant differences in heart rate (p = 0.079) and blood lactate concentration (p = 0.300). Warm-up increased muscle temperature, heart rate, and lactate, and reduced skin temperature (all p < 0.001), though no significant differences were observed for rectal temperature (p = 0.410). The number of revolutions (p = 0.034, ηp2 = 0.375), peak (p = 0.034, ηp2 = 0.375), and mean (p = 0.037, ηp2 = 0.365) power of the first sprint (not the average of ten sprints) were higher in the afternoon compared to the morning, regardless of warm-up. However, beneficial performance effects of warming up were evident for the first (p < 0.001) and the average of ten sprints (p < 0.05), regardless of time of day. More remarkable changes during the 60-min post-exercise were observed for rectal temperature (p = 0.005) and heart rate (p = 0.010) in the afternoon than in the morning. CONCLUSION: Warming-up and time-of-day effects in enhancing muscular power are independent. Although warm-up ensured further beneficial effects on performance than the time-of-day variation, a faster post-exercise recovery was observed in the late afternoon.

Heart rate variability, thyroid hormone concentration, and neuropsychological responses in Brazilian navy divers: a case report of diving in Antarctic freezing waters.

Open-water diving in a polar environment is a psychophysiological challenge to the human organism. We evaluated the effect of short-term diving (i.e., 10 min) in Antarctic waters on autonomic cardiac control, thyroid hormone concentration, body temperatures, mood, and neuropsychological responses (working memory and sleepiness). Data collection was carried out at baseline, before, and after diving in four individuals divided into the supporting (n=2) and diving (n=2) groups. In the latter group, autonomic cardiac control (by measuring heart rate variability) was also assessed during diving. Diving decreased thyroid-stimulating hormone (effect size = 1.6) and thyroxine (effect size = 2.1) concentrations; these responses were not observed for the supporting group. Diving also reduced both the parasympathetic (effect size = 2.6) and sympathetic activities to the heart (ES > 3.0). Besides, diving reduced auricular (effect size > 3.0), skin [i.e., hand (effect size = 1.2) and face (effect size = 1.5)] temperatures compared to pre-dive and reduced sleepiness state (effect size = 1.3) compared to basal, without changing performance in the working memory test. In conclusion, short-term diving in icy waters affects the hypothalamic-pituitary-thyroid axis, modulates autonomic cardiac control, and reduces body temperature, which seems to decrease sleepiness.

A 32-day long fieldwork in Antarctica improves heat tolerance during physical exercise.

We evaluated the influence of a 32-day camping in Antarctica on physical performance and exercise-induced thermoregulatory responses. In Brazil, before and after the Antarctic camping, the volunteers performed an incremental exercise at temperate conditions and, two days later, an exercise heat stress protocol (45-min running at 60% of maximum aerobic speed, at 31°C and 60% of relative humidity). In Antarctica, core temperature was assessed on a day of fieldwork, and average values higher than 38.5°C were reported. At pre- and post-Antarctica, physiological (whole-body and local sweat rate, number of active sweat glands, sweat gland output, core and skin temperatures) and perceptual (thermal comfort and sensation) variables were measured. The Antarctic camping improved the participants' performance and induced heat-related adaptations, as evidenced by sweat redistribution (lower in the chest but higher in grouped data from the forehead, forearm, and thigh) and reduced skin temperatures in the forehead and chest during the exercise heat stress protocol. Notwithstanding the acclimatization, the participants did not report differences of the thermal sensation and comfort. In conclusion, staying in an Antarctic camp for 32 days improved physical performance and elicited physiological adaptations to heat due to the physical exertion-induced hyperthermia in the field.

Hormonal, autonomic cardiac and mood states changes during an Antarctic expedition: From ship travel to camping in Snow Island.

We evaluated the influence of an Antarctic expedition, consisting of 26-day ship travel followed by 24-day camping in the Antarctic field during the summer season, on hormonal responses, autonomic cardiac control, and mood states in individuals that live in tropical regions. Data collection was carried out in 10 individuals on the 2nd, 16th, and 26th days aboard the ship (characterized by exposure to low-luminosity and temperature-controlled environments) and on the 4th, 11th, and 23rd days of camping in the Antarctic field (prolonged exposure to natural luminosity and cold environments). Morning samples of saliva (to determine testosterone and cortisol concentrations) and blood [to determine thyroid-stimulating hormone (TSH) and thyroxine (T4) concentrations] were obtained. Next, resting heart rate variability (HRV) was recorded, and the volunteers answered a mood questionnaire. Samples of saliva for measurement of melatonin concentration were obtained at night. At the end of ship travel, blood TSH and salivary melatonin increased by 15.6% and 72.3%, respectively, whereas salivary cortisol reduced by 37.1% compared to initial values and T4 reduced by 12.2% compared to 16th day. These hormonal changes occurred alongside increased depression score and biphasic changes in HRV parameters; for example, the RMSSD, a parasympathetic-related parameter, initially decreased by 47.8% and then returned towards baseline values by the end of the ship travel. In contrast, during the camp period, blood TSH and T4 reduced by 26.5% and 34.1%, respectively, and salivary cortisol increased by 72.1%, without concomitant changes in melatonin and HRV. Also, tension score transiently reduced and then increased towards the pre-camp score by the end of the field period. Testosterone remained unaltered throughout the expedition. In conclusion, ship travel and camping in Antarctica induced distinct neuroendocrine changes, cardiac autonomic regulation, and mood states. These specific changes most likely resulted from exposure to different natural luminosity, degrees of confinement, and ambient temperature in these environments.

The changes in maximal oxygen uptake (V̊O2MAX) induced by physical exertion during an Antarctic expedition depend on the initial V̊O2MAX of the individuals: a case study of the Brazilian expedition.

Antarctic climate is challenging, since the cold, wind and sensory monotony are stressful stimuli to individuals. Moreover, camp activities and heavy clothes may contribute to increase physiological strain. Thus, we aimed to characterise the physiological demand of a 24-day period in the Antarctic field and then to evaluate the effect of this expedition on the aerobic fitness in individuals with heterogeneous initial aerobic fitness (as determined by estimating maximum oxygen consumption - V̊O2MAX). Before and after the 24-day period in Antarctica, 7 researchers and 2 mountaineers were subjected to incremental tests to estimate their V̊O2MAX. Field effort was characterised by measuring heart rate (HR). During the field trips, their HR remained 33.4% of the recording time between 50-60% HRMAX, 22.3% between 60-70% HRMAX, and only 1.4% between 80 and 90% HRMAX. The changes in estimated V̊O2MAX during the expedition depended on the pre-expedition aerobic fitness. The post-expedition V̊O2MAX increased by 5.9% and decreased by 14.3%in individuals with lower (researchers) and higher (mountaineers) initial V̊O2MAX, respectively. We concluded that physical effort in the Antarctic field is characterised as predominantly of low- to moderate-intensity. This effort represented an effective training load for individuals with lower initial V̊O2MAX, but not for those with higher V̊O2MAX.