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1.
Nine well-trained, unacclimatized female hockey players performed the Loughborough Intermittent Shuttle Test (LIST) interspersed with three field hockey skill tests in hot (30°C, 38% relative humidity) and moderate (19°C, 51% relative humidity) environmental conditions. Field hockey skill performance declined in both the hot and moderate conditions following 30 and 60?min of the LIST compared with pre-LIST values (P <?0.01). This decrement in performance was compounded in the hot environment with a 6% poorer performance in the heat recorded for the second skill test at 30?min (P <?0.05, hot 101.7?±?3.6 vs moderate 95.7?±?2.9?s; mean ±?s x). However, no difference was found in the decision-making element of the skill test. Fifteen-metre sprint times were slower in the hot condition (P <?0.01). In the hot environment, rectal temperature (P?<?0.01), perceived exertion (P?<?0.05), perceived thirst (P?<?0.01), blood glucose concentration (P?<?0.05) and serum aldosterone concentration (P?<?0.01) were higher. Estimated mean (?±?s x) sweat rate was higher in the hot trial (1.27?±?0.10?l?·?h?1) than in the moderate trial (1.05?±?0.12?l?·?h?1) (P?<?0.05). Body mass was well maintained in both trials. No differences in serum cortisol, blood lactate, plasma volume or plasma ammonia concentrations were found. These results demonstrate that field hockey skill performance is decreased following intermittent high-intensity shuttle running and that this decrease is greater in hot environmental conditions. The exact mechanism for this decrement in performance remains to be elucidated, but is unlikely to be due to low glycogen concentration or dehydration.  相似文献   

2.
In this study we examined the performance during, and the physiological and metabolic responses to, prolonged, intermittent, high-intensity shuttle running in hot (～30 C, dry bulb temperature) and moderate (～20 C) environmental conditions. Twelve male students, whose mean (s x ) age, body mass and maximal oxygen uptake (V O 2m ax ) were 22 ± 1 years, 69.8 ± 01.8 kg and 56.9 ± 1.1 ml . kg ?1 . min ?1 respectively, performed intermittent high- and low-speed running involving five sets of ～15 min of repeated cycles of walking and variable speed running followed by 60 s run/rest exercise until fatigue. The total distance completed in the hot and moderate trials was 8842 3790 m and 11,280 214 m respectively (P < 0.01). This decrement in performance occurred even though no differences existed in the level of dehydration, rating of perceived exertion, blood glucose and lactate, plasma free fatty acid and ammonia concentrations between the two trials. However, water consumption was almost twice as great in the hot trial (hot vs moderate: 1.18 ± 0.12 vs 0.63 ± 0.07 l . h ?1 , P < 0.01). Rectal temperature (hot vs moderate: 39.4 ± 0.1 vs 38.0 ± 0.1 C, P < 0.01) and heart rate (hot vs moderate: 186 ± 2 vs 179 ± 2 beats . min ?1 , P < 0.05) were higher at the end of the hot condition than at the same point in time in the moderate condition. The correlation between the rate of rise in rectal temperature and the distance completed during the hot condition was -0.94 (P < 0.01); for the moderate condition it was -0.65 (P <0.05). The reduced performance in the hot condition was associated with high body temperature; the precise mechanisms by which the performance decrement was brought about are, however, unclear.  相似文献   

3.
The aim of this study was to examine the effect of intermittent high-intensity shuttle running and fluid ingestion on the performance of a soccer skill. Nine semi-professional soccer players volunteered to participate in the study. Their mean (+/- s(x)) age, body mass and maximal oxygen uptake were 20.2+/-0.4 years, 73.2+/-1.8 kg and 59.1+/-1.3 ml x kg(-1) min(-1) respectively. The players were allocated to two randomly assigned trials: ingesting or abstaining from fluid intake during a 90 min intermittent exercise protocol (Loughborough Intermittent Shuttle Test: LIST). This test was designed to simulate the minimum physical demands faced by soccer players during a game. Before and immediately after performance of the test, the players completed a soccer skill test and a mental concentration test. Performance of the soccer skill test after the 'no-fluid' trial deteriorated by 5% (P<0.05), but was maintained during the fluid trial. Mean heart rate, perceived exertion, serum aldosterone, osmolality, sodium and cortisol responses during the test were higher (P<0.05) in the 'no-fluid' trial than in the fluid trial. The results of this study suggest that soccer players should consume fluid throughout a game to help prevent a deterioration in skill performance.  相似文献   

4.
Nine male student games players consumed either flavoured water (0.1 g carbohydrate, Na+ 6 mmol x l(-1)), a solution containing 6.5% carbohydrate-electrolytes (6.5 g carbohydrate, Na+ 21 mmol x l(-1)) or a taste placebo (Na+ 2 mmol x l(-1)) during an intermittent shuttle test performed on three separate occasions at an ambient temperature of 30 degrees C (dry bulb). The test involved five 15-min sets of repeated cycles of walking and variable speed running, each separated by a 4-min rest (part A of the test), followed by 60 s run/60 s rest until exhaustion (part B of the test). The participants drank 6.5 ml x kg(-1) of fluid as a bolus just before exercise and thereafter 4.5 ml x kg(-1) during every exercise set and rest period (19 min). There was a trial order effect. The total distance completed by the participants was greater in trial 3 (8441 +/- 873 m) than in trial 1 (6839 +/- 512, P < 0.05). This represented a 19% improvement in exercise capacity. However, the trials were performed in a random counterbalanced order and the participants completed 8634 +/- 653 m, 7786 +/- 741 m and 7099 +/- 647 m in the flavoured water (FW), placebo (P) and carbohydrate-electrolyte (CE) trials, respectively (P = 0.08). Sprint performance was not different between the trials but was impaired over time (FW vs P vs CE: set 1, 2.41 +/- 0.02 vs 2.39 +/- 0.03 vs 2.39 +/- 0.03 s; end set, 2.46 +/- 0.03 vs 2.47 +/- 0.03 vs 2.47 +/- 0.02 s; main effect time, P < 0.01). The rate of rise in rectal temperature was greater in the carbohydrate-electrolyte trial (rise in rectal temperature/duration of trial, degrees C x h(-1); FW vs CE, P < 0.05; P vs CE, N.S.). Blood glucose concentrations were higher in the carbohydrate-electrolyte than in the other two trials (FW vs P vs CE:rest, 4.4 +/- 0.1 vs 4.3 +/- 0.1 vs 4.2 +/- 0.1 mmol x l(-1); end of exercise, 5.4 +/- 0.3 vs 6.4 +/- 0.6 vs 7.2 +/- 0.5 mmol x l(-1); main effect trial, P < 0.05; main effect time, P < 0.01). Plasma free fatty acid concentrations at the end of exercise were lower in the carbohydrate-electrolyte trial than in the other two trials (FW vs P vs CE: 0.57 +/- 0.08 vs 0.53 +/- 0.11 vs 0.29 +/- 0.04 mmol x l(-1); interaction, P < 0.01). The correlation between the rate of rise in rectal temperature (degrees C x h(-1)) and the distance completed was -0.91, -0.92 and -0.96 in the flavoured water, placebo and carbohydrate-electrolyte conditions, respectively (P < 0.01). Heart rate, blood pressure, plasma ammonia, blood lactate, plasma volume and rate of perceived exertion were not different between the three fluid trials. Although drinking the carbohydrate-electrolyte solution induced greater metabolic changes than the flavoured water and placebo solutions, it is unlikely that in these unacclimated males carbohydrate availability was a limiting factor in the performance of intermittent running in hot environmental conditions.  相似文献   

5.
The aim of this study was to establish the effect that pre-cooling the skin without a concomitant reduction in core temperature has on subsequent self-paced cycling performance under warm humid (31 degrees C and 60% relative humidity) conditions. Seven moderately trained males performed a 30 min self-paced cycling trial on two separate occasions. The conditions were counterbalanced as control or whole-body pre-cooling by water immersion so that resting skin temperature was reduced by approximately 5-6 degrees C. After pre-cooling, mean skin temperature was lower throughout exercise and rectal temperature was lower (P < 0.05) between 15 and 25 min of exercise. Consequently, heat storage increased (P < 0.003) from 84.0+/-8.8 W x m(-2) to 153+/-13.1 W x m(-2) (mean +/- s(mean)) after pre-cooling, while total body sweat fell from 1.7+/-0.1 l x h(-1) to 1.2+/-0.1 l h(-1) (P < 0.05). The distance cycled increased from 14.9+/-0.8 to 15.8+/-0.7 km (P < 0.05) after pre-cooling. The results indicate that skin pre-cooling in the absence of a reduced rectal temperature is effective in reducing thermal strain and increasing the distance cycled in 30 min under warm humid conditions.  相似文献   

6.
The aim of this study was to determine the effects of caffeine ingestion on a 'preloaded' protocol that involved cycling for 2 min at a constant rate of 100% maximal power output immediately followed by a 1-min 'all-out' effort. Eleven male cyclists completed a ramp test to measure maximal power output. On two other occasions, the participants ingested caffeine (5 mg. kg(-1)) or placebo in a randomized, double-blind procedure. All tests were conducted on the participants' own bicycles using a Kingcycle test rig. Ratings of perceived exertion (RPE; 6-20 Borg scale) were lower in the caffeine trial by approximately 1 RPE point at 30, 60 and 120 s during the constant rate phase of the preloaded test (P <0.05). The mean power output during the all-out effort was increased following caffeine ingestion compared with placebo (794+/-164 vs 750+/-163 W; P=0.05). Blood lactate concentration 4, 5 and 6 min after exercise was also significantly higher by approximately 1 mmol. l(-1) in the caffeine trial (P <0.05). These results suggest that high-intensity cycling performance can be increased following moderate caffeine ingestion and that this improvement may be related to a reduction in RPE and an elevation in blood lactate concentration.  相似文献   

7.
The aim of this study was to examine the effect of intermittent high-intensity shuttle running and fluid ingestion on the performance of a soccer skill. Nine semi-professional soccer players volunteered to participate in the study. Their mean (± sx ) age, body mass and maximal oxygen uptake were 20.2 ± 0.4 years, 73.2 ± 1.8 kg and 59.1 ± 1.3 ml·kg-1 ·min-1 respectively. The players were allocated to two randomly assigned trials: ingesting or abstaining from fluid intake during a 90 min intermittent exercise protocol (Loughborough Intermittent Shuttle Test:LIST).This test was designed to simulate the minimum physical demands faced by soccer players during a game. Before and immediately after performance of the test,the players completed a soccer skill test and a mental concentration test. Performance of the soccer skill test after the 'no-fluid' trial deteriorated by 5% (P ? 0.05),but was maintained during the fluid trial. Mean heart rate, perceived exertion, serum aldosterone, osmolality, sodium and cortisol responses during the test were higher (P ? 0.05) in the 'no-fluid' trial than in the fluid trial. The results of this study suggest that soccer players should consume fluid throughout a game to help prevent a deterioration in skill performance.  相似文献   

8.
The aim of this study was to assess the effects of fatigue on decision making and goal shooting skill in water polo. Fourteen junior elite male players (age 17.2 +/- 0.5 years; mass 84.2 +/- 7.6 kg; height 1.85 +/- 0.05 m) completed four sets of eight repetitions of an approximately 18 s maximal water polo specific drill. Progressively declining rest ratios for each successive set of the drill were employed to induce increasing fatigue and reflect the demands of match-play. A video-based temporally occluded decision-making task (verbalized response to various tactical situations) or goal shooting skill test (qualitative and quantitative analysis of goal shooting) was performed after each set. Heart rate, rating of perceived exertion (RPE) and blood lactate concentration were recorded. Heart rate (159 +/- 12, 168 +/- 13, 176 +/- 12, 181 +/- 12 Deats min-1; P < 0.001) and RPE (13.1 +/- 2.2, 15.5 +/- 1.7, 17.3 +/- 1.6, 19.1 +/- 1.1; P < 0.001) increased with declining rest ratios. At very high fatigue, decision-making accuracy was 18.0 +/- 21.8% better than at low fatigue (P = 0.008). Shooting accuracy and velocity were unaffected by incremental fatigue; however, skill proficiency (technique) decreased by 43 +/- 24% between the pre-test and high-fatigue conditions (P < 0.001). In conclusion, incremental increases in fatigue differentially influenced decision making (improved) relative to the technical performance (declined), accuracy and speed of the ball (unchanged) of a water polo goal shot.  相似文献   

9.
To examine the influence of pre-warming on the physiological responses to prolonged intermittent exercise in ambient temperatures of 21.5 +/- 0.6 degrees C and relative humidities of 35.7 +/- 5.4% (mean +/- s), six healthy men performed intermittent treadmill running (30-s bouts at 90% of maximal oxygen uptake separated by 30-s static recovery periods) to exhaustion after active pre-warming, passive pre-warming and pre-exercise rest (control). Exercise time to exhaustion was significantly different between all conditions (active, 51.8 +/- 7.2 min; passive, 38.5 +/- 11.1 min; control, 72.0 +/- 17.2 min; P < 0.05). These changes in performance time were closely associated with a significant decline in both the rate of heat storage and heat storage capacity (P < 0.05). Rectal temperature, heart rate and ratings of perceived exertion were significantly higher during exercise in the two pre-warming conditions than in the control condition (P < 0.05). Ratings of perceived exertion were also significantly higher during exercise following passive pre-warming compared with active pre-warming (P < 0.05). During exercise there were no significant differences in serum prolactin, plasma norepinephrine and plasma free fatty acid concentrations between conditions. We conclude that both active and passive pre-warming promote a reduction in prolonged intermittent exercise capacity in environmental temperatures of 21 degrees C compared with pre-exercise rest. These performance decrements were dependent upon the mode of pre-warming and closely reflected alterations in body heat content.  相似文献   

10.
The thermoregulatory responses of upper-body trained athletes were examined at rest, during prolonged arm crank exercise and recovery in cool (21.5 +/- 0.9 degrees C, 43.9 +/- 10.1% relative humidity; mean +/- s) and warm (31.5 +/- 0.6 degrees C, 48.9 +/- 8.4% relative humidity) conditions. Aural temperature increased from rest by 0.7 +/- 0.7 degrees C (P< 0.05) during exercise in cool conditions and by 1.6 +/- 0.7 degrees C during exercise in warm conditions (P< 0.05). During exercise in cool conditions, calf skin temperature decreased (1.5 +/- 1.3 degrees C), whereas an increase was observed during exercise in warm conditions (3.0 +/- 1.7 degrees C). Lower-body skin temperatures tended to increase by greater amounts than upper-body skin temperatures during exercise in warm conditions. No differences were observed in blood lactate, heart rate or respiratory exchange ratio responses between conditions. Perceived exertion at 45 min of exercise was greater than that reported at 5 min of exercise during the cool trial (P< 0.05), whereas during exercise in the warm trial the rating of perceived exertion increased from initial values by 30 min (P < 0.05). Heat storage, body mass losses and fluid consumption were greater during exercise in warm conditions (7.06 +/- 2.25 J x g(-1) x degrees C(-1), 1.3 +/- 0.5 kg and 1,038 +/- 356 ml, respectively) than in cool conditions (1.35 +/- 0.23 J x g(-1) x degrees C(-1), 0.8 +/- 0.2 kg and 530 +/- 284 ml, respectively; P < 0.05). The results of this study indicate that the increasing thermal strain with constant thermal stress in warm conditions is due to heat storage within the lower body. These results may aid in understanding thermoregulatory control mechanisms of populations with a thermoregulatory dysfunction, such as those with spinal cord injuries.  相似文献   

11.
Ad libitum fluid intakes and thermoregulatory responses were compared in eight female marathon runners during a 30 km treadmill run at individual best marathon race pace (range = 2.45-4.07 m x s(-1)) under three wet bulb globe temperature conditions (25 degrees C, 17 degrees C and 12 degrees C, corresponding to hot, moderate and cool conditions, respectively). Rectal temperature, mean skin temperature and heart rate were recorded at 10 min intervals and expired air was collected every 5 km during exercise. Simulated water stations were also provided at 5 km intervals with voluntary fluid intake being recorded. Blood was drawn before and after exercise for the determination of plasma volume changes and osmolarity. Ad libitum fluid intakes in the hot trial (0.70+/-0.31 l x h(-1); mean+/-s) were greater (P< 0.05) than in the cool (0.47+/-0.13 l x h(-1)) but not the moderate (0.54+/-0.26 l x h(-1)) trial. Each volume replaced 63%, 68% and 73% of total sweat losses in each condition, respectively, and kept dehydration below approximately 3% of body mass. After the initial 30 min of exercise, rectal temperature was maintained well below 39 degrees C for > 2 h of continuous running. The results demonstrate that the thermoregulatory responses of female distance runners to exercise in variable, but compensable, weather conditions is well maintained when ad libitum fluid intakes replace approximately 60-70% of sweat losses.  相似文献   

12.
Sweat lactate reflects eccrine gland metabolism. However, the metabolic tendencies of eccrine glands in a hot versus thermoneutral environment are not well understood. Sixteen male volunteers completed a maximal cycling trial and two 60-min cycling trials [30 degrees C = 30 +/- 1 degrees C and 18 degrees C = 18 +/- 1 degrees C wet bulb globe temperature (WBGT)]. The participants were requested to maintain a cadence of 60 rev min(-1) with the intensity individualized at approximately 90% of the ventilatory threshold. Sweat samples at 10, 20, 30, 40, 50 and 60 min were analysed for lactate concentration. Sweat rate at 30 degrees C (1380 +/- 325 ml x h(-1)) was significantly greater (P < 0.05) than at 18 degrees C (632 +/- 311 ml x h(-1)). Sweat lactate concentration was significantly greater (P < 0.05) at each time point during the 18 degrees C trial, with values between trials tending to converge across time. During the 30 degrees C trial, both heart rate (20, 30, 40, 50 and 60 min) and rectal temperature (30, 40, 50 and 60 min) were significantly higher than in the 18 degrees C trial. Higher sweat lactate concentrations coupled with lower sweat rates may indicate a greater relative contribution of oxygen-independent metabolism within eccrine glands during exercise at 18 degrees C. Decreases in sweat lactate concentration across time suggest either greater dilution due to greater sweat volume or increased reliance on aerobic metabolism within eccrine glands. The convergence of lactate concentrations between trials may indicate that time-dependent modifications in sweat gland metabolism occur at different rates contingent partially on environmental conditions.  相似文献   

13.
In this study, we examined thermoregulatory responses to ingestion of separate aliquots of drinks at different temperatures during low-intensity exercise in conditions of moderate heat stress. Eight men cycled at 50% (s = 3) of their peak oxygen uptake (VO2peak) for 90 min (dry bulb temperature: 25.3 degrees C, s = 0.5; relative humidity: 60%, s = 5). Four 400-ml aliquots of flavoured water at 10 degrees C (cold), 37 degrees C (warm) or 50 degrees C (hot) were ingested after 30, 45, 60, and 75 min of exercise. Immediately after the 90 min of exercise, participants cycled at 95% VO2peak to exhaustion to assess exercise capacity. There were no differences between trials in rectal temperature at the end of the 90 min of exercise (cold: 38.11 degrees C, s = 0.30; warm: 38.10 degrees C, s = 0.33; hot: 38.21 degrees C, s = 0.30; P = 0.765). Mean skin temperature between 30 and 90 min tended to be influenced by drink temperature (cold: 34.49 degrees C, s = 0.64; warm: 34.53 degrees C, s = 0.69; hot: 34.71 degrees C, s = 0.48; P = 0.091). Mean heart rate from 30 to 90 min was higher in the hot trial (129 beats . min(-1), s = 7; P < 0.05) than on the cold (124 beats . min(-1), s = 9) and warm trials (126 beats . min(-1), s = 8). Ratings of thermal sensation were higher on the hot trial than on the cold trial at 35 and 50 min (P < 0.05). Exercise capacity was similar between trials (P = 0.963). The heat load and debt induced by periodic drinking resulted in similar body temperatures during low-intensity exercise in conditions of moderate heat stress due to appropriate thermoregulatory reflexes.  相似文献   

14.
The aim of the present study was to determine the combined effects of pre-cooling and water ingestion on thermoregulatory responses and exercise capacity at 32 degrees C and 80% relative humidity. Nine untrained males exercised for 60 min on a cycle ergometer at 60% maximal oxygen uptake (VO2max) (first exercise bout) under four separate conditions: No Water intake, Pre-cooling, Water ingestion, and a combination of pre-cooling and water ingestion (Combined). To evaluate the efficacy of these conditions on exercise capacity, the participants exercised to exhaustion at 80% VO2max (second exercise bout) following the first exercise bout. Rectal and mean skin temperatures before the first exercise bout in the Pre-cooling and Combined conditions were significantly lower than in the No Water and Water conditions. At the end of the first exercise bout, rectal temperature was lower in the Combined condition (38.5 +/- 0.1 degrees C) than in the other conditions (No Water: 39.1 +/- 0.1 degrees C; Pre-cooling: 38.7 +/- 0.1 degrees C; Water: 38.8 +/- 0.1 degrees C) (P < 0.05). Heat storage was higher following pre-cooling than when there was no pre-cooling (P < 0.05). The final rectal temperature in the second exercise bout was similar between the four conditions (39.1 +/- 0.1 degrees C). However, exercise time to exhaustion was longer (P < 0.05) in the Combined condition than in the other conditions. Total sweat loss was less following pre-cooling than when there was no pre-cooling (P < 0.001). Evaporative sweat loss in the Water and Combined conditions was greater (P < 0.01) than in the No Water and Pre-cooling conditions. Our results suggest that the combination of pre-cooling and water ingestion increases exercise endurance in a hot environment through enhanced heat storage and decreased thermoregulatory and cardiovascular strain.  相似文献   

15.
Abstract

The capturing of movements by means of wearable sensors has become increasingly popular in order to obtain sport performance measures during training or competition. The purpose of the current study was to investigate the feasibility of using body worn accelerometers to identify previous highlighted performance related biomechanical changes in terms of substantial differences across skill levels and skating phases. Twenty-two ice hockey players of different caliber were equipped with two 3D accelerometers, located on the skate and the waist, as they performed 30 m forward skating sprints on an ice rink. Two measures of the temporal stride characteristics (contact time and stride time) and one measure of the propulsive power (stride propulsion) of a skating stride were calculated and checked for discriminating effects across (i) skill levels and (ii) sprint phases as well as for their (iii) strength of association with the sprint performance (total sprint time). High caliber players showed an increased stride propulsion (+22%, P?<?0.05) and shorter contact time (?5%, P?<?0.05). All three analysed variables highlighted substantial biomechanical differences between the accelerative and constant velocity phases (P?<?0.05). Stride propulsion of acceleration strides primarily correlated to total sprint time (r?=??0.57, P?<?0.05). The results demonstrate the potential of accelerometers to assess skating technique elements such as contact time or elements characterizing the propulsive power such as center of mass acceleration, to gauge skating performance. Thus, the findings of this study might contribute to establishing wearable sensors for in-field ice hockey skating performance analysis.  相似文献   

16.
The aim of this study was to determine the effect of 10 days of heat acclimation with and without pre-cooling on intermittent sprint exercise performance in the heat. Eight males completed three intermittent cycling sprint protocols before and after 10 days of heat acclimation. Before acclimation, one sprint protocol was conducted in control conditions (21.8 ± 2.2°C, 42.8 ± 6.7% relative humidity) and two sprint protocols in hot, humid conditions (33.3 ± 0.6°C, 52.2 ± 6.8% relative humidity) in a randomized order. One hot, humid condition was preceded by 20 min of thigh pre-cooling with ice packs (-16.2 ± 4.5°C). After heat acclimation, the two hot, humid sprint protocols were repeated. Before heat acclimation, peak power output declined in the heat (P < 0.05) but pre-cooling prevented this. Ten days of heat acclimation reduced resting rectal temperature from 37.8 ± 0.3°C to 37.4 ± 0.3°C (P < 0.01). When acclimated, peak power output increased by ～2% (P < 0.05, main effect) and no reductions in individual sprint peak power output were observed. Additional pre-cooling offered no further ergogenic effect. Unacclimated athletes competing in the heat should pre-cool to prevent reductions in peak power output, but heat acclimate for an increased peak power output.  相似文献   

17.
Nine males cycled at 53% (s = 2) of their peak oxygen uptake (VO(2peak)) for 90 min (dry bulb temperature: 25.4 degrees C, s = 0.2; relative humidity: 61%, s = 3). One litre of flavoured water at 10 (cold), 37 (warm) or 50 degrees C (hot) was ingested 30 - 40 min into exercise. Immediately after the 90 min of exercise, participants cycled at 95%VO(2peak) to exhaustion to assess exercise capacity. Rectal and mean skin temperatures and heart rate were recorded. The gradient of rise in rectal temperature was influenced (P < 0.01) by drink temperature. Mean skin temperature was highest in the hot trial (cold trial: 34.2 degrees C, s = 0.5; warm trial: 34.4 degrees C, s = 0.5; hot trial: 34.7 degrees C, s = 0.6; P < 0.01). Significant differences were observed in heart rate (cold trial: 132 beats . min(-1), s = 13; warm trial: 134 beats . min(-1), s = 12; hot trial: 139 beats . min(-1), s = 13; P < 0.05). Exercise capacity was similar between trials (cold trial: 234 s, s = 69; warm trial: 214 s, s = 52; hot trial: 203 s, s = 53; P = 0.562). The heat load and debt induced via drinking resulted in appropriate thermoregulatory reflexes during exercise leading to an observed heat content difference of only 33 kJ instead of the predicted 167 kJ between the cold and hot trials. These results suggest that there may be a role for drink temperature in influencing thermoregulation during exercise.  相似文献   

18.
Six games players (GP) and six endurance-trained runners (ET) completed a standardized multiple sprint test on a non-motorized treadmill consisting of ten 6-s all-out sprints with 30-s recovery periods. Running speed, power output and oxygen uptake were determined during the test and blood samples were taken for the determination of blood lactate and pH. Games players tended to produce a higher peak power output (GP vs ET: 839 +/- 114 vs 777 +/- 89 W, N.S.) and higher peak speed (GP vs ET: 7.03 +/- 0.3 vs 6.71 +/- 0.3 m s-1, N.S.), but had a greater decrement in mean power output than endurance-trained runners (GP vs ET: 29.3 +/- 8.1% vs 14.2 +/- 11.1%, P less than 0.05). Blood lactate after the test was higher for the games players (GP vs ET: 15.2 +/- 1.9 vs 12.4 +/- 1.7 mM, P less than 0.05), but the decrease in pH was similar for both groups (GP vs ET: 0.31 +/- 0.08 vs 0.28 +/- 0.08, N.S.). Strong correlations were found between peak blood lactate and peak speed (r = 0.90, P less than 0.01) and between peak blood lactate and peak power fatigue (r = 0.92, P less than 0.01). The average increase in oxygen uptake above pre-exercise levels during the sprint test was greater for endurance-trained athletes than for the games players (ET vs GP: 35.0 +/- 2.2 vs 29.6 +/- 3.0 ml kg-1 min-1, P less than 0.05), corresponding to an average oxygen uptake per sprint (6-s sprint and 24 s of subsequent recovery) of 67.5 +/- 2.9% and 63.0 +/- 4.5% VO2 max respectively (N.S.). A modest relationship existed between the average increase in oxygen uptake above pre-exercise values during the sprint test and mean speed fatigue (r = -0.68, P less than 0.05). Thus, the greater decrement in performance for the games players may be related to higher glycolytic rates as reflected by higher lactate concentrations and to their lower oxygen uptake during the course of the 10 sprints.  相似文献   

19.
AbstThis study examined the relationship between intensity of training and changes in hydration status, core temperature, sweat rate and composition and fluid balance in professional football players training in the heat. Thirteen professional football players completed three training sessions; "higher-intensity" (140 min; HI140), "lower-intensity" (120 min; LI120) and "game-simulation" (100 min; GS100). Movement demands were measured by Global Positioning System, sweat rate and concentration were determined from dermal patches and body mass change. Despite similar environmental conditions (26.9 ± 0.1 °C and 65.0 ± 7.0% relative humidity [Rh]), higher relative speeds (m · min(-1)) and increased perceptions of effort and thermal strain were observed in HI140 and GS100 compared with LI120 (P < 0.05). Significantly (P < 0.05) greater sweat rate (L · h(-1)) and electrolyte losses (g) were observed in HI140 and GS100 compared with LI120. Rate of rise in core temperature was correlated with mean speed (r = 0.85), session rating of perceived exertion (sRPE) (r = 0.61), loss of potassium (K+) (r = 0.51) sweat rate (r = 0.49), and total sweat loss (r = 0.53), with mean speed the strongest predictor. Sodium (Na+) (r = 0.39) and K+ (r = 0.50) losses were associated with total distance covered. In hot conditions, individualised rehydration practices should be adopted following football training to account for differences in sweat rate and electrolyte losses in response to intensity and overall activity within a session.  相似文献   

20.
The aim of this study was to assess the effect of time of day on physiological responses to running at the speed at the lactate threshold. After determination of the lactate threshold, using a standard incremental protocol, nine male runners (age 26.3 +/- 5.7 years, height 1.77 +/- 0.07 m, mass 73.1 +/- 6.5 kg, lactate threshold speed 13.6 +/- 1.6 km x h(-1); mean +/- s) completed a standardized 30 min run at lactate threshold speed, twice within 24 h (07:00-09:00 h and 18:00-21:00 h). Core body temperature, heart rate, minute ventilation, oxygen uptake, carbon dioxide expired, respiratory exchange ratio and capillary blood lactate were measured at rest, after a warm-up and at 10, 20 and 30 min during the run. In addition, the rating of perceived exertion was reported every 10 min during the run. Significant diurnal variation was observed only for body temperature (36.9 +/- 0.9 degrees C vs 37.3 +/- 0.3 degrees C) and respiratory exchange ratio at rest (0.86 +/- 0.01 vs 0.89 +/- 0.07) (P < 0.05). Diurnal variation persisted for body temperature throughout the warm-up (37.1 +/- 0.2 degrees C vs 37.5 +/- 0.3 degrees C) and during exercise (36.2 +/- 0.6 degrees C vs 38.6 +/- 0.4 degrees C), but only during the warm-up for the respiratory exchange ratio (0.85 +/- 0.05 vs 0.87 +/- 0.02) (P < 0.05). The rating of perceived exertion was significantly elevated during the morning trial (12.7 +/- 0.9 vs 11.9 +/- 1.2) (P < 0.05). These findings suggest that, despite the diurnal variation in body temperature, other physiological responses to running at lactate threshold speed are largely unaffected. However, a longer warm-up may be required in morning trials because of a slower increase in body temperature, which could have an impact on ventilation responses and ratings of perceived exertion.  相似文献   

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