Fatigue is mediated by cholinoceptors within the ventromedial hypothalamus independent of changes in core temperature.

We investigated brain mechanisms modulating fatigue during prolonged physical exercise in cold environments. In a first set of studies, each rat was subjected to three running trials in different ambient temperatures (T(a)). At 8 °C and 15 °C, core body temperature (T(core)) decreased and increased, respectively, whereas at 12 °C, the T(core) did not change throughout the exercise. In another set of experiments, rats were randomly assigned to receive bilateral 0.2 µL injections of 2.5 × 10(-2) M methylatropine or 0.15 M NaCl solution into the ventromedial hypothalamic nuclei (VMH). Immediately after the injections, treadmill exercise was started. Each animal was subjected to two experimental trials at one of the following T(a) : 5 °C, 12 °C or 15 °C. Muscarinic blockade of the VMH reduced the time to fatigue (TF) in cold environments by 35-37%. In all T(a) studied, methylatropine-treated rats did not present alterations in T(core) and tail skin temperature compared with controls. These results indicate that, below the zone of thermoneutrality, muscarinic blockade of the VMH decreases the TF, independent of changes in T(core). In conclusion, our data suggest that VMH muscarinic transmission modulates physical performance, even when the effects of thermoregulatory adjustments on fatigue are minimal.

Maximal lactate steady state is altered in the heat.

The aim of this study was to compare the maximal lactate steady state (MLSS) and ventilatory threshold (VT) under different environments (TEMP: 22°C; and HOT: 40°C; 50% RH). 8 male subjects (age 23.9±2.4 years, body mass 75.9±7.3 kg and VO2(max) 47.8±4.9 mL·kg(-1)·min(-1)) performed a series of tests to determine the peak workload (W(peak)), VT and MLSS on a cycle ergometer. W(peak) was higher in the TEMP as compared to the HOT condition (225±9 W vs. 195±8 W, respectively; p<0.05). The workload at MLSS was higher at 22°C (180±11 W) than 40°C (148±11 W; p<0.05), as well as VT at 22°C (156±9 W) was higher than 40°C (128±6 W). Likewise, the blood lactate concentration at MLSS was higher at 22°C (5.60±0.26 mM) than 40°C (4.22±0.48 mM; p<0.05). The mean of heart rate (HR) was not statistically different between TEMP (168±3 bpm) and HOT (173±3 bpm) at MLSS, despite being different at trials between the 25(th) and the 30(th) min of exercise. The HR at VT was significantly higher in HOT (153±4 bpm) as compared to the TEMP (145±2 bpm). Our results suggest that environmental conditions may influence the determination of MLSS and VT. Moreover, VT was appropriate for estimation of the workload at MLSS in the HOT.

Competition, estimated, and test maximum heart rate.

AIM: The aim of the present study was to compare the highest heart rate (HR) of soccer players recorded during competition matches with the maximum HR (HR(max)) estimated from age and the highest HR recorded in effort tests within a single category (intracategory) and between categories (intercategories). METHODS: The sample was made up of 19 under-17 athletes, 12 under-20 athletes and 14 professional athletes of a Brazilian first division soccer team. Players' HR was monitored during official competition matches and maximum effort test with a set of HR monitors. The highest HR recorded during competitive matches (MHR1) was considered as the highest HR value attained by each player during matches. HR(max) estimated from age (MHR2) was estimated by using the equation HR(max)= (220-age). The highest HR recorded in effort tests (MHR3) was determined as being the highest HR value recorded during a maximum effort test (1 000-m run). The Wilcoxon test was used in intracategory statistical analysis. The Kruskal Wallis test was used in intercategory statistical analysis. The significance level adopted was P<0.05. RESULTS: In all categories, MHR3 was lower than MHR1. Concerning intercategory analysis, the three categories did not exhibit a difference in MHR1 RESULTS: Relative to MHR3, the under-17 and under-20 categories were not different from each other. These two categories exhibited larger MHR3 values than the professional one did. CONCLUSION: HR(max) measured during field tests can be underestimated in relation to that measured during competition activities, maybe because the tests represent an artificial situation for athletes, who do not feel as motivated as during competitions.

Luteal phase of the menstrual cycle increases sweating rate during exercise.

The present study evaluated whether the luteal phase elevation of body temperature would be offset during exercise by increased sweating, when women are normally hydrated. Eleven women performed 60 min of cycling exercise at 60% of their maximal work load at 32 degrees C and 80% relative air humidity. Each subject participated in two identical experimental sessions: one during the follicular phase (between days 5 and 8) and the other during the luteal phase (between days 22 and 25). Women with serum progesterone >3 ng/mL, in the luteal phase were classified as group 1 (N = 4), whereas the others were classified as group 2 (N = 7). Post-exercise urine volume (213 +/- 80 vs 309 +/- 113 mL) and specific urine gravity (1.008 +/- 0.003 vs 1.006 +/- 0.002) changed (P < 0.05) during the luteal phase compared to the follicular phase in group 1. No menstrual cycle dependence was observed for these parameters in group 2. Sweat rate was higher (P < 0.05) in the luteal (3.10 +/- 0.81 g m-2 min-1) than in the follicular phase (2.80 +/- 0.64 g m(-2) min(-1)) only in group 1. During exercise, no differences related to menstrual cycle phases were seen in rectal temperature, heart rate, rate of perceived exertion, mean skin temperature, and pre- and post-exercise body weight. Women exercising in a warm and humid environment with water intake seem to be able to adapt to the luteal phase increase of basal body temperature through reduced urinary volume and increased sweating rate.

Luteal phase of the menstrual cycle increases sweating rate during exercise

The present study evaluated whether the luteal phase elevation of body temperature would be offset during exercise by increased sweating, when women are normally hydrated. Eleven women performed 60 min of cycling exercise at 60 percent of their maximal work load at 32°C and 80 percent relative air humidity. Each subject participated in two identical experimental sessions: one during the follicular phase (between days 5 and 8) and the other during the luteal phase (between days 22 and 25). Women with serum progesterone >3 ng/mL, in the luteal phase were classified as group 1 (N = 4), whereas the others were classified as group 2 (N = 7). Post-exercise urine volume (213 ± 80 vs 309 ± 113 mL) and specific urine gravity (1.008 ± 0.003 vs 1.006 ± 0.002) changed (P < 0.05) during the luteal phase compared to the follicular phase in group 1. No menstrual cycle dependence was observed for these parameters in group 2. Sweat rate was higher (P < 0.05) in the luteal (3.10 ± 0.81 g m-2 min-1) than in the follicular phase (2.80 ± 0.64 g m-2 min-1) only in group 1. During exercise, no differences related to menstrual cycle phases were seen in rectal temperature, heart rate, rate of perceived exertion, mean skin temperature, and pre- and post-exercise body weight. Women exercising in a warm and humid environment with water intake seem to be able to adapt to the luteal phase increase of basal body temperature through reduced urinary volume and increased sweating rate.

Thermoregulation in hypertensive men exercising in the heat with water ingestion.

Hydration is recommended in order to decrease the overload on the cardiovascular system when healthy individuals exercise, mainly in the heat. To date, no criteria have been established for hydration for hypertensive (HY) individuals during exercise in a hot environment. Eight male HY volunteers without another medical problem and 8 normal (NO) subjects (46 +/- 3 and 48 +/- 1 years; 78.8 +/- 2.5 and 79.5 +/- 2.8 kg; 171 +/- 2 and 167 +/- 1 cm; body mass index=26.8 +/- 0.7 and 28.5 +/- 0.6 kg/m2; resting systolic (SBP)=142.5 and 112.5 mmHg and diastolic blood pressure (DBP)=97.5 and 78.1 mmHg, respectively) exercised for 60 min on a cycle ergometer (40% of VO2peak) with (500 ml 2 h before and 115 ml every 15 min throughout exercise) or without water ingestion, in a hot humid environment (30 masculine C and 85% humidity). Rectal (Tre) and skin (Tsk) temperatures, heart rate (HR), SBP, DBP, double product (DP), urinary volume (Vu), urine specific gravity (Gu), plasma osmolality (Posm), sweat rate (S R), and hydration level were measured. Data were analyzed using ANOVA in a split plot design, followed by the Newman-Keuls test. There were no differences in Vu, Posm, Gu and S R responses between HY and NO during heat exercise with or without water ingestion but there was a gradual increase in HR (59 and 51%), SBP (18 and 28%), DP (80 and 95%), Tre (1.4 and 1.3%), and Tsk (6 and 3%) in HY and NO, respectively. HY had higher HR (10%), SBP (21%), DBP (20%), DP (34%), and Tsk (1%) than NO during both experimental situations. The exercise-related differences in SBP, DP and Tsk between HY and NO were increased by water ingestion (P<0.05). The results showed that cardiac work and Tsk during exercise were higher in HY than in NO and the difference between the two groups increased even further with water ingestion. It was concluded that hydration protocol recommended for NO during exercise could induce an abnormal cardiac and thermoregulatory responses for HY individuals without drug therapy.

Thermoregulation in hypertensive men exercising in the heat with water ingestion

Hydration is recommended in order to decrease the overload on the cardiovascular system when healthy individuals exercise, mainly in the heat. To date, no criteria have been established for hydration for hypertensive (HY) individuals during exercise in a hot environment. Eight male HY volunteers without another medical problem and 8 normal (NO) subjects (46 ± 3 and 48 ± 1 years; 78.8 ± 2.5 and 79.5 ± 2.8 kg; 171 ± 2 and 167 ± 1 cm; body mass index = 26.8 ± 0.7 and 28.5 ± 0.6 kg/m²; resting systolic (SBP) = 142.5 and 112.5 mmHg and diastolic blood pressure (DBP) = 97.5 and 78.1 mmHg, respectively) exercised for 60 min on a cycle ergometer (40 percent of VO2peak) with (500 ml 2 h before and 115 ml every 15 min throughout exercise) or without water ingestion, in a hot humid environment (30ºC and 85 percent humidity). Rectal (Tre) and skin (Tsk) temperatures, heart rate (HR), SBP, DBP, double product (DP), urinary volume (Vu), urine specific gravity (Gu), plasma osmolality (Posm), sweat rate (S R), and hydration level were measured. Data were analyzed using ANOVA in a split plot design, followed by the Newman-Keuls test. There were no differences in Vu, Posm, Gu and S R responses between HY and NO during heat exercise with or without water ingestion but there was a gradual increase in HR (59 and 51 percent), SBP (18 and 28 percent), DP (80 and 95 percent), Tre (1.4 and 1.3 percent), and Tsk (6 and 3 percent) in HY and NO, respectively. HY had higher HR (10 percent), SBP (21 percent), DBP (20 percent), DP (34 percent), and Tsk (1 percent) than NO during both experimental situations. The exercise-related differences in SBP, DP and Tsk between HY and NO were increased by water ingestion (P < 0.05). The results showed that cardiac work and Tsk during exercise were higher in HY than in NO and the difference between the two groups increased even further with water ingestion. It was concluded that hydration protocol recommended for NO during exercise could induce an abnormal cardiac and thermoregulatory responses for HY individuals without drug therapy.

Effects of submaximal exercise with water ingestion on intraocular pressure in healthy human males

The effects of exercise and water replacement on intraocular pressure (IOP) have not been well established. Furthermore, it is not known whether the temperature of the fluid ingested influences the IOP response. In the present study we determined the effect of water ingestion at three temperatures (10, 24 and 38ºC; 600 ml 15 min before and 240 ml 15, 30 and 45 min after the beginning of each experimental session) on the IOP of six healthy male volunteers (age = 24.0 ± 3.5 years, weight = 67.0 ± 4.8 kg, peak oxygen uptake (VO2peak) = 47.8 ± 9.1 ml kg-1 min-1). The subjects exercised until exhaustion on a cycle ergometer at a 60 percent VO2peak in a thermoneutral environment. IOP was measured before and after exercise and during recovery (15, 30 and 45 min) using the applanation tonometry method. Skin and rectal temperatures, heart rate and oxygen uptake were measured continuously. IOP was similar for the right eye and the left eye and increased post-water ingestion under both exercising and resting conditions (P<0.05) but did not differ between resting and exercising situations, or between the three water temperatures. Time to exhaustion was not affected by the different water temperatures. Rectal temperature, hydration status, heart rate, oxygen uptake, carbon dioxide extraction and lactate concentration were increased by exercise but were not affected by water temperature. We conclude that IOP was not affected by exercise and that water ingestion increased IOP as expected, regardless of water temperature

Effects of submaximal exercise with water ingestion on intraocular pressure in healthy human males.

The effects of exercise and water replacement on intraocular pressure (IOP) have not been well established. Furthermore, it is not known whether the temperature of the fluid ingested influences the IOP response. In the present study we determined the effect of water ingestion at three temperatures (10, 24 and 38 degrees C; 600 ml 15 min before and 240 ml 15, 30 and 45 min after the beginning of each experimental session) on the IOP of six healthy male volunteers (age = 24.0 +/- 3.5 years, weight = 67.0 +/- 4.8 kg, peak oxygen uptake (VO2peak) = 47.8 +/- 9.1 ml kg-1 min-1). The subjects exercised until exhaustion on a cycle ergometer at a 60% VO2peak in a thermoneutral environment. IOP was measured before and after exercise and during recovery (15, 30 and 45 min) using the applanation tonometry method. Skin and rectal temperatures, heart rate and oxygen uptake were measured continuously. IOP was similar for the right eye and the left eye and increased post-water ingestion under both exercising and resting conditions (P<0.05) but did not differ between resting and exercising situations, or between the three water temperatures. Time to exhaustion was not affected by the different water temperatures. Rectal temperature, hydration status, heart rate, oxygen uptake, carbon dioxide extraction and lactate concentration were increased by exercise but were not affected by water temperature. We conclude that IOP was not affected by exercise and that water ingestion increased IOP as expected, regardless of water temperature.

Assessment of functional capacity through oxygen consumption in patients with asymptomatic probable heart disease.

PURPOSE: To compare peak exercise oxygen consumption (VO2peak) of healthy individuals with asymptomatic individuals with probable heart disease. METHODS: Ninety-eight men were evaluated. They were divided into two groups: 1) 39 healthy individuals (group N) with an age range of 50 +/- 4.6 years; and 2) 59 asymptomatic individuals with signs of atherosclerotic and/or hypertensive heart disease (group C) with an age range of 51.9 +/- 10.4 years. In regard to age, height, body surface area, percentage of fat, lean body mass, and daily physical activity, both groups were statistically similar. Environmental conditions during the ergometric test were also controlled. RESULTS: Maximal aerobic power (watts), VO2peak, maximal heart rate, and maximal pulmonary ventilation were lower in group C (p < 0.01) than in group N; weight, however, was lower in group N (p = 0.031) than in group C. Differences in the respiratory gas exchange index, heart rate at rest, and the maximal double product of the two groups were not statistically significant. CONCLUSION: Signs of probable heart disease, even though asymptomatic, may reduce the functional capacity, perhaps due to the lower maximal cardiac output and/or muscle metabolic changes.

Water replacement and thermoregulatory responses during prolonged exercise.

The present study was designed to compare the thermoregulatory responses of 12 young adult males who were required to exercise wearing heavy clothing under three different conditions: 1) without water replacement (WW), 2) with water replacement (600 ml prior to exercise and 240 ml at the 15th, 30th and 45th minute of exercise) (W15), and 3) with water replacement (600 ml prior to exercise, 36 ml during the first minute of exercise and 36 ml at 3-min intervals throughout exercise) (W3). The mean heart rate (HR) (147 +/- 14.6 beats/min), mean rectal temperature (Mtre) (37.39 +/- 0.24 degrees C) and mean body temperature (MBT) (36.73 +/- 0.24 degrees C) under WW conditions were significantly higher than the values observed under W15 conditions (137 +/- 6.18 beats/min, 37.18 +/- 0.17 degrees C and 36.57 +/- 0.18 degrees C, respectively) and W3 conditions (138 +/- 10.1 beats/min, 37.18 +/- 0.21 degrees C and 36.51 +/- 0.24 degrees C, respectively). The temperature differences could be partially attributed to a direct effect of the cold water ingested. No significant differences were detected between conditions W15 and W3 for any of the variables studied.

Water replacement and thermoregulatory responses during prolonged exercise

The present study was designed to compare the thermoregulatory responses of 12 young adult males who were required to exercise wearing heavy clothing under three different conditions: 1) without water replacement (WW), 2) with water replacement (600 ml prior to exercise and 240 ml at the 15th, 30th and 45th minute of exercise) (W15), and 3) with water replacement (600 ml prior to exercise, 36 ml during the first minute of exercise and 36 ml at 3-min intervals throughout exercise) (W3). The mean heart rate (HR) (147 +/- 14.6 beats/min), mean rectal temperature (Mtre) (37.39 +/- 0.24 degrees C) and mean body temperature (MBT) (36.73 +/- 0.24 degrees C) under WW conditions were significantly higher than the values observed under W15 conditions (137 +/- 6.18 beats/min, 37.18 +/- 0.17 degrees C and 36.57 +/- 0.18 degrees C, respectively) and W3 conditions (138 +/- 10.1 beats/min, 37.18 +/- 0.21 degrees C and 36.51 +/- 0.24 degrees C, respectively). The temperature differences could be partially attributed to a direct effect of the cold water ingested. No significant differences were detected between conditions W15 and W3 for any of the variables studied