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1.
The aim of this study was to determine the influence of breathing frequency and tidal volume on resting heart rate variability in children aged 9 years (n = 29) and 16 years (n = 19). Heart rate variability was measured in four conditions: (1) without the control of ventilation followed at random by (2) a fixed breathing frequency of 12 breaths x min(-1), (3) a breathing frequency of 12 breaths x min(-1) but with a fixed tidal volume of 30% vital capacity and (4) a fixed breathing frequency of 6 breaths x min(-1) and a tidal volume of 30% vital capacity. A total of 128 RR intervals (the time between two spikes in the heart rate) were detected and absolute high- and low-frequency spectral components were calculated using autoregressive modelling. The younger children were unable to control ventilation to achieve conditions 3 and 4; therefore, a 2 x 2 (group x condition) analysis of variance was used to analyse conditions 1 and 2. There were significant interactions between group and heart rate variability conditions for the low-frequency component and the ratio of low to high frequencies (P < 0.001). The main effect for condition showed that at 12 breaths x min(-1) with no fixed tidal volume there was a significantly higher standard deviation of the RR interval, total power and high-frequency (P< 0.01) and low-frequency spectral components (P < 0.05) than in the condition with no ventilatory control. Across the four breathing conditions for the older participants, the high-frequency spectral component was significantly higher in the condition at 6 breaths x min(-1) with a fixed tidal volume than in that with no ventilatory control (P < 0.005); the ratio of high to low frequencies was significantly lower for the spontaneous condition than those performed at 12 breaths x min(-1) (P < 0.001). The results provide evidence of the need for ventilatory control when assessing short-term resting heart rate variability in children.  相似文献   

2.
The aim of this study was to establish the validity of the breakpoint in breathing frequency for the assessment of the lactate threshold and the ventilatory threshold during incremental running exercise. Twelve trained runners (mean +/- s: age 29 +/- 8 years; body mass 68.7 8.8 kg; V O 2m ax 57.9 +/- 4.1 ml . kg -1 . min -1 ) performed randomly assigned incremental treadmill tests on separate days. In addition to the assessment of the V O 2m ax (Test 1), the subjects performed two standard multi-stage treadmill tests (4-min stages) for the assessment of the lactate threshold while wearing (Test 2) and not wearing (Test 3) a standard mouthpiece and noseclip arrangement. Breathing frequency was measured by a thermistor, which was positioned in the back of the mouthpiece for Test 2, and fixed 3 cm in front of the mouth using a headband and flexible wiring for Test 3. All exercise tests were recorded on videotape and mean breathing frequency and stride rate were calculated for the last minute of each stage from real-time playback of the videotapes. The breathing frequency breakpoint was determined in six subjects only for Test 2 and in five subjects only for Test 3. For Test 2, there were no differences between the breakpoint in breathing frequency (14.7 +/- 0.9 km . h - 1), the lactate threshold (14.7 +/- 0.9 km . h -1 ) and the ventilatory threshold (14.7 +/- 1.1 km . h -1 ). For Test 3, the breakpoint in breathing frequency (14.0 +/- 1.0 km . h -1 ) was not appreciably different from the lactate threshold (14.7 +/- 1.2 km . h -1 ). Hey plots showed marked interindividual differences in the responses of breathing frequency and tidal volume to exercise. In four subjects, the ventilatory threshold was mediated by a non-linear increase in tidal volume, with breathing frequency either increasing in a linear manner (n = 1) or remaining constant owing to entrainment of breathing frequency to cadence (n = 3). We conclude that the breakpoint in breathing frequency does not provide a valid method for the field-based assessment of the lactate or ventilatory thresholds in most subjects for running exercise.  相似文献   

3.
The aim of this study was to assess the influence of three imposed crank rates on the attainment of peak oxygen consumption ( V O 2peak ) and other physiological responses during incremental arm crank ergometry. Twenty physically active, although non-specifically trained, males volunteered for the study. They completed an exercise protocol using an electrically braked arm ergometer (Lode Angio, Groningen, Netherlands) at crank rates of 60, 70 and 80 rev·min -1 . The order of tests was randomized and they were separated by at least 2 days. Peak V O 2 was significantly higher ( P ? 0.05) at 70 and 80 rev·min -1 than at 60 rev·min -1 . Peak ventilation volume increased as a function of crank rate and was higher ( P ? 0.05) at 80 than at 60 rev·min -1 . Peak heart rate was higher ( P ? 0.05) at 70 and 80 rev·min -1 than at 60 rev·min -1 . Furthermore, 70 and 80 rev·min -1 resulted in an extended test time compared with 60 rev·min -1 . The greater physiological responses observed during the tests at the two faster crank rates might have been the result of a postponement of acute localized neuromuscular fatigue, allowing for more work to be completed. We recommend, therefore, that an imposed crank rate between 70 and 80 rev·min -1 should be used to elicit V O 2peak and other physiological responses in arm crank ergometry.  相似文献   

4.
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·s -1 ) under three wet bulb globe temperature conditions (25°C, 17°C and 12°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·h -1 ; mean - s) were greater (P? 0.05) than in the cool (0.47 - 0.13 l·h -1 ) but not the moderate (0.54 - 0.26 l·h -1 ) trial. Each volume replaced 63%, 68% and 73% of total sweat losses in each condition, respectively, and kept dehydration below ~3% of body mass. After the initial 30 min of exercise, rectal temperature was maintained well below 39°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   

5.
The aim of this study was to compare the effects of nasal splinting during different modes of breathing on breathing patterns and cardiorespiratory responses. Ten healthy subjects (4 males, 6 females) performed five maximal treadmill tests while breathing through the nose, nose + dilator, mouth, nose + mouth, and nose + mouth + dilator. Repeated-measures analysis of variance and Tukey HSD revealed no significant differences between trials for maximal oxygen consumption, minute ventilation at an oxygen consumption of 30 ml.kg-1.min-1, carbon dioxide production, respiratory exchange ratio, tidal volume, dead space to tidal volume ratio, or completed treadmill stages to exhaustion. No significant difference was found in subjective dyspnoea ratings between stages of nose versus nose + dilator breathing. Minute ventilation, ventilatory equivalent for oxygen, and breath frequency for nose and nose + dilator versus mouth, nose + mouth, and nose + mouth + dilator were significantly lower. Ventilatory equivalent for carbon dioxide was significantly lower for nose versus mouth, and nose + dilator versus nose + mouth + dilator breathing. End-tidal carbon dioxide was significantly higher in nose versus mouth, nose + mouth, and nose + mouth + dilator breathing, and in nose + dilator versus mouth breathing. Nose breathing revealed a significantly lower heart rate versus nose + dilator, mouth, nose + mouth, and nose + mouth + dilator breathing. These results suggest that nasal splinting during exercise has minimal effects when nasal breathing and no effects when oronasal breathing.  相似文献   

6.
The aim of the present study was to examine the relationship between the performance heart rate during an ultra-endurance triathlon and the heart rate corresponding to several demarcation points measured during laboratory-based progressive cycle ergometry and treadmill running. Less than one month before an ultra-endurance triathlon, 21 well-trained ultra-endurance triathletes (mean +/- s: age 35 +/- 6 years, height 1.77 +/- 0.05 m, mass 74.0 +/- 6.9 kg, = 4.75 +/- 0.42 l x min(-1)) performed progressive exercise tests of cycle ergometry and treadmill running for the determination of peak oxygen uptake (VO2peak), heart rate corresponding to the first and second ventilatory thresholds, as well as the heart rate deflection point. Portable telemetry units recorded heart rate at 60 s increments throughout the ultra-endurance triathlon. Heart rate during the cycle and run phases of the ultra-endurance triathlon (148 +/- 9 and 143 +/- 13 beats x min(-1) respectively) were significantly (P < 0.05) less than the second ventilatory thresholds (160 +/- 13 and 165 +/- 14 beats x min(-1) respectively) and heart rate deflection points (170 +/- 13 and 179 +/- 9 beats x min(-1) respectively). However, mean heart rate during the cycle and run phases of the ultra-endurance triathlon were significantly related to (r = 0.76 and 0.66; P < 0.01), and not significantly different from, the first ventilatory thresholds (146 +/- 12 and 148 +/- 15 beats x min(-1) respectively). Furthermore, the difference between heart rate during the cycle phase of the ultra-endurance triathlon and heart rate at the first ventilatory threshold was related to marathon run time (r = 0.61; P < 0.01) and overall ultra-endurance triathlon time (r = 0.45; P < 0.05). The results suggest that triathletes perform the cycle and run phases of the ultra-endurance triathlon at an exercise intensity near their first ventilatory threshold.  相似文献   

7.
The aim of this study was to establish a graded exercise test protocol for determining the peak physiological responses of female outrigger canoeists. Seventeen trained female outrigger canoeists completed two outrigger ergometer graded exercise test protocols in random order: (1) 25 W power output for 2 min increasing by 7.5 W every minute until exhaustion; and (2) 25 W power output for 2 min increasing by 15 W every 2 min to exhaustion. Heart rate and power output were recorded every 15 s. Expired air was collected continuously and sampled for analysis at 15-s intervals, while blood lactate concentration was measured immediately after and 3, 5, and 7 min after exercise. The peak physiological and performance variables examined included peak oxygen uptake (VO2peak), minute ventilation, tidal volume, ventilatory thresholds 1 and 2, respiratory rate, respiratory exchange ratio, heart rate, blood lactate concentration, power output, performance time, and time to VO2peak. There were no significant differences in peak physiological responses, ventilatory thresholds or performance variables between the two graded exercise test protocols. Despite no significant differences between protocols, due to the large limits of agreement evident between protocols for the peak physiological responses, it is recommended that the same protocol be used for all comparison testing to minimize intra-individual variability of results.  相似文献   

8.
To examine the activity profile and physiological demands of top-class soccer refereeing, we performed computerized time-motion analyses and measured the heart rate and blood lactate concentration of 27 referees during 43 competitive matches in the two top Danish leagues. To relate match performance to physical capacity and training, several physiological tests were performed before and after intermittent exercise training. Total distance covered was 10.07 - 0.13 km (mean - s x ), of which 1.67 - 0.08 km was high-intensity running. High-intensity running and backwards running decreased (P ? 0.05) in the second half. Mean heart rate was 162 - 2 beats· min -1 (85 - 1% of maximal heart rate) and the mean blood lactate concentration was 4.9 - 0.3 (range 1.7-14.0) mmol·l -1 . The amount of high-intensity running during a match was related to the Yo-Yo intermittent recovery test ( r 2 = 0.57; P ? 0.05) and the 12 min run ( r 2 = 0.21; P ? 0.05). After intermittent training ( n = 8), distance covered during high-intensity running was greater (2.06 - 0.13 vs 1.69 - 0.08 km; P ? 0.05) and mean heart rate was lower (159 - 1 vs 164 - 2 beats· min -1 ; P ? 0.05) than before training. The results of the present study demonstrate that: (1) top-class soccer referees have significant aerobic energy expenditure throughout a game and episodes of considerable anaerobic energy turnover; (2) the ability to perform high-intensity running is reduced towards the end of matches; (3) the Yo-Yo intermittent recovery test can be used to evaluate referees' match performance; and (4) intense intermittent exercise training improves referees' performance capacity during a game.  相似文献   

9.
The aim of this study was to devise a laboratory-based protocol for a motorized treadmill that was representative of work rates observed during soccer match-play. Selected physiological responses to this soccer-specific intermittent exercise protocol were then compared with steady-rate exercise performed at the same average speed. Seven male university soccer players (mean - s : age 24 - 2 years, height 1.78 - 0.1 m, mass 72.2 - 5.0 kg, VO 2max 57.8 - 4 ml·kg -1 ·min -1 ) completed a 45-min soccer-specific intermittent exercise protocol on a motorized treadmill. They also completed a continuous steady-rate exercise session for an identical period at the same average speed. The physiological responses to the laboratory-based soccer-specific protocol were similar to values previously observed for soccer match-play (oxygen consumption approximately 68% of maximum, heart rate 168 - 10 beats·min -1 ). No significant differences were observed in oxygen consumption, heart rate, rectal temperature or sweat production rate between the two conditions. Average minute ventilation was greater ( P ? 0.05) in intermittent exercise (81.3 - 0.2l·min -1 ) than steady-rate exercise (72.4 - 11.4l·min -1 ). The rating of perceived exertion for the session as a whole was 15 - 2 during soccer-specific intermittent exercise and 12 - 1 for continuous exercise ( P ? 0.05). The physiological strain associated with the laboratory-based soccer-specific intermittent protocol was similar to that associated with 45 min of soccer match-play, based on the variables measured, indicating the relevance of the simulation as a model of match-play work rates. Soccer-specific intermittent exercise did not increase the demands placed on the aerobic energy systems compared to continuous exercise performed at the same average speed, although the results indicate that anaerobic energy provision is more important during intermittent than during continuous exercise at the same average speed.  相似文献   

10.
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°C?=?30±1°C and 18°C?=?18±1°C wet bulb globe temperature (WBGT)]. The participants were requested to maintain a cadence of 60 rev?·?min?1 with the intensity individualized at ～ 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°C (1380±325?ml?·?h?1) was significantly greater (P<0.05) than at 18°C (632±311?ml?·?h?1). Sweat lactate concentration was significantly greater (P<0.05) at each time point during the 18°C trial, with values between trials tending to converge across time. During the 30°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°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°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   

11.
Abstract

The aim of this study was to establish a graded exercise test protocol for determining the peak physiological responses of female outrigger canoeists. Seventeen trained female outrigger canoeists completed two outrigger ergometer graded exercise test protocols in random order: (1) 25 W power output for 2 min increasing by 7.5 W every minute until exhaustion; and (2) 25 W power output for 2 min increasing by 15 W every 2 min to exhaustion. Heart rate and power output were recorded every 15 s. Expired air was collected continuously and sampled for analysis at 15-s intervals, while blood lactate concentration was measured immediately after and 3, 5, and 7 min after exercise. The peak physiological and performance variables examined included peak oxygen uptake ([Vdot]O2peak), minute ventilation, tidal volume, ventilatory thresholds 1 and 2, respiratory rate, respiratory exchange ratio, heart rate, blood lactate concentration, power output, performance time, and time to [Vdot]O2peak. There were no significant differences in peak physiological responses, ventilatory thresholds or performance variables between the two graded exercise test protocols. Despite no significant differences between protocols, due to the large limits of agreement evident between protocols for the peak physiological responses, it is recommended that the same protocol be used for all comparison testing to minimize intra-individual variability of results.  相似文献   

12.
  相似文献   

13.
Power output and heart rate were monitored for 11 months in one female (V(.)O(2max): 71.5 mL · kg?1 · min?1) and ten male (V(.)O(2max): 66.5 ± 7.1 mL · kg?1 · min?1) cyclists using SRM power-meters to quantify power output and heart rate distributions in an attempt to assess exercise intensity and to relate training variables to performance. In total, 1802 data sets were divided into workout categories according to training goals, and power output and heart rate intensity zones were calculated. The ratio of mean power output to respiratory compensation point power output was calculated as an intensity factor for each training session and for each interval during the training sessions. Variability of power output was calculated as a coefficient of variation. There was no difference in the distribution of power output and heart rate for the total season (P = 0.15). Significant differences were observed during high-intensity workouts (P < 0.001). Performance improvements across the season were related to low-cadence strength workouts (P < 0.05). The intensity factor for intervals was related to performance (P < 0.01). The variability in power output was inversely associated with performance (P < 0.01). Better performance by cyclists was characterized by lower variability in power output and higher exercise intensities during intervals.  相似文献   

14.
ABSTRACT

The aim of this study is to investigate whether the change in (sub)maximal heart rate after intensified training is associated with the change in performance. Thirty subjects were recruited who performed cardiopulmonary exercise tests to exhaustion 2 weeks before (pre), 1 week after (post) and 5 weeks after (follow-up) an 8-day non-competitive amateur cycling event (TFL). The exercise volume during the TFL was 7.7 fold the volume during the preparation period. Heart rate and cardiopulmonary parameters were obtained at standardised absolute submaximal workloads (low, medium and high intensity) and at peak level each test. Subjects were classified as functionally overreached (FOR) or acute fatigued (AF) based on the change in performance. No differences between FOR and AF were observed for heart rate (P?=?.51). On total group level (AF?+?FOR), post-TFL heart rate decreased significantly at low (?4.4 beats·min?1, 95% CI [?8.7, ?0.1]) and medium (?5.5 beats·min?1 [?8.5, ?2.4]), but not at high intensity. Peak heart rate decreased ?3.4 beats·min?1 [?6.1, ?0.7]. O2pulse was on average 0.49?ml O2·beat?1 [0.09, 0.89] higher at all intensities after intensified training. No changes in ?O2 (P?=?.44) or the ventilatory threshold (P?=?.21) were observed. Pearson’s correlation coefficients revealed negative associations between heart rate and O2pulse at low (r?=??.56, P?<?.01) and medium intensity (r?=??.54, P?<?.01), but not with ?O2 or any other submaximal parameter. (Sub)maximal heart rate decreased after the TFL. However, this decrease is unrelated to the change in performance. Therefore, heart rate seems inadequate to prescribe and monitor intensified training.  相似文献   

15.
Abstract

We hypothesised that experienced runners would select a stride frequency closer to the optimum (minimal energy costs) than would novice runners. In addition, we expected that optimal stride frequency could simply be determined by monitoring heart rate without measuring oxygen consumption (V?O2). Ten healthy males (mean±s: 24±2 year) with no running training experience and 10 trained runners of similar age ran at constant treadmill speed corresponding to 80% of individual ventilatory threshold. For two days, they ran at seven different stride frequencies (self-selected stride frequency±18%) imposed by a metronome. Optimal stride frequency was based on the minimum of a second-order polynomial equation fitted through steady state V?O2 at each stride frequency. Running cost (mean±s) at optimal stride frequency was higher (P < 0.05) in novice (236±31 ml O2·kg?1.km?1) than trained (189±13 ml O2·kg?1.km?1) runners. Self-selected stride frequency (mean±s; strides.min?1) for novice (77.8±2.8) and trained runners (84.4±5.3) were lower (P < 0.05) than optimal stride frequency (respectively, 84.9±5.0 and 87.1±4.8). The difference between self-selected and optimal stride frequency was smaller (P < 0.05) for trained runners. In both the groups optimal stride frequency established with heart rate was not different (P > 0.3) from optimal stride frequency based on V?O2. In each group and despite limited variation between participants, optimal stride frequencies derived from V?O2 and heart rate were related (r > 0.7; P < 0.05). In conclusion, trained runners chose a stride frequency closer to the optimum for energy expenditure than novices. Heart rate could be used to establish optimal stride frequency.  相似文献   

16.
T'ai Chi Chuan (TCC) is a widely practiced Chinese martial art said to physically develop balance and coordination as well as enhance emotional and mental health. TCC consists of a series of postures combined into a sequential movement providing a smooth, continuous, low-intensity activity. The purpose of this study was to examine the ventilatory and cardiovascular responses to the Long Form of Yang's style TCC. In addition, the subjects' TCC responses were compared to their ventilatory and cardiovascular responses during cycle ergometry at an oxygen consumption (VO2) equivalent to the mean TCC VO2. Six experienced (M = 8.3 yrs) male TCC practitioners served as subjects with data collected during the Cloud H and movement of the TCC exercise. Significantly (p less than .05) lower responses for ventilatory frequency (Vf) (11.3 and 15.7 breaths.min-1), ventilatory equivalent (VE/VO2) (23.47 and 27.41), and the ratio of dead space ventilation to tidal volume (VD/VT) (20 and 27%) were found in TCC in comparison to cycle ergometry. The percentage of minute ventilation used for alveolar ventilation was significantly higher during TCC (p less than .03) than cycle ergometry, with mean values of 81.1% and 73.1%, respectively. Cardiac output, stroke volume, and heart rate were not significantly different between TCC exercise and cycle ergometry at the same oxygen consumption. We concluded that, during TCC, expert practitioners show significantly different ventilatory responses leading to more efficient use of the ventilatory volume than would be expected from comparable levels of exertion on a cycle ergometer.  相似文献   

17.
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   

18.
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°C, 43.9 ± 10.1% relative humidity; mean ± s) and warm (31.5 &± 0.6°C, 48.9 - 8.4% relative humidity) conditions. Aural temperature increased from rest by 0.7 ± 0.7°C (P ? 0.05) during exercise in cool conditions and by 1.6 ± 0.7°C during exercise in warm conditions (P ? 0.05). During exercise in cool conditions, calf skin temperature decreased (1.5 ± 1.3°C), whereas an increase was observed during exercise in warm conditions (3.0 ± 1.7°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·g-1 ·°C-1, 1.3 ± 0.5 kg and 1038 ± 356 ml, respectively) than in cool conditions (1.35 ± 0.23 J·g-1·°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   

19.
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   

20.
In this study, we examined the effects of upper-body pre-cooling before intermittent sprinting exercise in a moderate environment. Seven male and three female trained cyclists (age 26.8±5.5 years, body mass 68.5±9.5?kg, height 1.76±0.13?m, [Vdot]O2peak 59.0±11.4?mL?·?kg?1?·?min?1; mean±s) performed 30?min of cycling at 50% [Vdot]O2peak interspersed with a 10-s Wingate cycling sprint test at 5?min intervals. The exercise was performed in a room controlled at 22oC and 40% relative humidity. In the control session, the participants rested for 30?min before exercise. In the pre-cooling session, the participants wore the upper segment of a liquid conditioning garment circulating 5oC coolant until rectal temperature decreased by 0.5oC. Rectal temperature at the start of exercise was significantly lower in the pre-cooling (36.5±0.3oC) than in the control condition (37.0±0.5oC), but this difference was reduced to a non-significant 0.4oC throughout exercise. Mean skin temperature was significantly lower in the pre-cooling (30.7±2.3oC) than in the control condition (32.5±1.6oC) throughout exercise. Heart rate during submaximal exercise was similar between the two conditions, although peak heart rate after the Wingate sprints was significantly lower in the pre-cooling condition. With pre-cooling, mean peak power (909±161?W) and mean overall power output (797±154?W) were similar to those in the control condition (peak 921±163?W, mean 806±156?W), with no differences in the subjective ratings of perceived exertion. These results suggest that upper-body pre-cooling does not provide any benefit to intermittent sprinting exercise in a moderate environment.  相似文献   

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