The effect of exercise intensity on the post-exercise esophageal temperature response

On 2 separate days, nine volunteers aged 23.8 (2.0) years performed 15-min bouts of treadmill running in a temperature-controlled chamber at 29°C at a power output that elicited either 70% (moderate) or 93% (intense) of maximum oxygen consumption. Exercise was followed by a 45-min recovery period. End-exercise esophageal temperature (T _es) was elevated by 0.97°C and 2.17°C above baseline for the moderate and intense exercise trials, respectively. Post-exercise T _es achieved a sustained elevated value of 0.38°C and 0.79°C within 15 min of exercise cessation. Systolic blood pressure (SBP) for both exercise trials became hypotensive for the full recovery period, with the magnitude of the reduction being greater for the intense exercise (P<0.05). Diastolic blood pressure (DBP) was unaffected by exercise intensity and values were lower than baseline between 15 min and 30 min post-exercise (P<0.05). Mean arterial pressure (MAP) was reduced from baseline for both exercise trials, with intense exercise showing a greater decrement (P<0.05). It was shown that the increase in the post-exercise hypotensive response, induced by exercise of increasing intensity, was paralleled by an increase in the magnitude of the post-exercise elevation in T _es (i.e., a difference of 0.41°C between conditions). Electronic Publication     

The effect of a covert manipulation of ambient temperature on heat storage and voluntary exercise intensity

The modulation of sub-maximal voluntary exercise intensity during heat stress has been suggested as a behavioral response to maintain homeostasis; however, the relationship between thermophysiological cues and the associated response remains unclear. Awareness of an environmental manipulation may influence anticipatory planning before the start of exercise, making it difficult to isolate the dynamic integration of thermophysiological afferents during exercise itself. The purpose of the present study was to examine the direct real-time relationship between thermophysiological afferents and the behavioral response of voluntary exercise intensity. Participants were tasked with cycling at a constant rating of perceived exertion while ambient temperature (T(a)) was covertly changed from 20 °C to 35 °C and then back to 20 °C at 20-minute intervals. Overall, power output (PO) and heat storage, quantified using repeated measures ANOVA, changed significantly over 20-minute intervals (135 ± 39 W, 133 ± 46 W, 120 ± 45 W; 52.35 ± 36.15 W·m(-2), 66.34 ± 22.02 W·m(-2), -66.53 ± 56.01 W·m(-2)). The synchronicity of PO fluctuations with changes in thermophysiological status was quantified using Auto-Regressive Integrated Moving Average (ARIMA) time series analysis. Fluctuations in PO were not synchronized in real time with changes in T(a); heat storage; rectal, skin, or mean body temperature; or sweat rate (stationary-r(2) ≤ 0.10 and Ljung-Box statistic > 0.05 for all variables). We conclude that, while the thermal environment affects physiological responses and voluntary power output while cycling at a constant perceived effort, the behavioral response of voluntary exercise intensity did not depend on a direct response to real-time integration of thermal afferent inputs.     

The effect of exercise intensity and duration on the oxygen deficit and excess post-exercise oxygen consumption

Summary Nine males with mean maximal oxygen consumption ( ) =63.0 ml· kg^–1 · min^–1, SD 5.7 and mean body fat = 10.6%, SD 3.1 each completed nine counterbalanced treatments comprising 20, 50 and 80 min of treadmill exercise at 30, 50 and 70% . The OZ deficit, 8 h excess post-exercise oxygen consumption (EPOC) and EPOC:O₂ deficit ratio were calculated for all subjects relative to mean values obtained from 2 control days each lasting 9.3 h. The O₂ deficit, which was essentially independent of exercise duration, increased significantly (P<0.05) with intensity such that the overall mean values for the three 30%, 50% and 70% workloads were 0.83, 1.89 and 3.09 l, respectively. While there were no significant differences (P>0.05) between the three EPOCs after walking at 30% for 20 (1.01 l), 50 (1.43 l) and 80 min (1.041), respectively, the EPOC thereafter increased (P<0.05) with both intensity and duration such that the increments were much greater for the three 70% workloads (EPOC: 20 min=5.68 l; 50 min=10.04 l; 80 min= 14.59 l) than for the three 50% workload (EPOC: 20 min =3.14 l; 50 min=5.19 l; 80 min= 6.10 l). An analysis of variance indicated that exercise intensity was the major determinant of the EPOC since it explained five times more of the EPOC variance than either exercise duration or the intensity times duration interaction. The mean EPOC:O₂ deficit ratio ranged from 0.8 to 4.5 and generally increased with both exercise intensity and duration. These data imply that the EPOC is more than mere repayment of the O₂ deficit because metabolism is increasingly disturbed from resting levels as exercise intensity and duration increase due to other physiological factors occurring after the steady-state has been attained.     

Disturbance of thermal homeostasis during post-exercise hyperthermia

The response of core temperature to exercise was investigated during recovery in order to avoid the antagonistic competition between exercise and thermal reflexes for the same effector systems which control skin blood flow. Five healthy, non-training males [mean (SD) age, 23.8 (2.04) years] were habituated to 29° C at relative 50% humidity for more than 2 h and then exercised by treadmill running at about 75% maximum oxygen uptake for 18 min. They then remained at 29° C for up to 65 min of recovery. Oesophageal (T _es), rectal (T _re) and skin temperatures (T _sk) were recorded at 5-s intervals throughout. The abrupt fall of temperature gradient from the forearm to finger was used to identify the T _es for skin vessel dilatation (T _dil) during exercise. Mean (SE) Ts rose from a resting value of 36.67 (0.15)° C to 38.22 (0.24)° C, mean T _re rose from 37.09 (0.25)° C to 38.23 (0.15)° C, and T _dil occurred at 37.39 (0.32)° C. Within 10 min of recovery mean T _es fell to 37.31 (0.24)° C, where it remained a significant 0.64° C above its pre-exercise (PrEx) level (P0.018) but insignificantly different from T _dil for the remaining 55 min of recovery. Meanwhile, T _re fell gradually throughout recovery to 37.64 (0.18)° C. The T _sk at all non-acral sites except the thigh had recovered to PrEx levels by 20–30 min post-exercise (PoEx). The rapid PoEx fall of T _es to the level of T _dil and the subsequent plateau above PrEx values suggests that heat dissipation during recovery was primarily passive once T _es had fallen to T _dil, even though T _es and T _re were significantly elevated. The relationship of these results to the set-point and load error concepts of thermal control is discussed.These data have been presented at the Canadian Physiological Society Winter meeting, January 1993, but have not been previously published     

Skin temperature as a thermal controller of exercise intensity

This study examined the role of skin temperature on self-selected exercise intensity (i.e., power output). Eight well-trained, male cyclists completed two 60 min self-paced cycling bouts during which they completed as much work as possible. Using a liquid-perfused suit, skin temperature (T _Sk) was changed during the two trials such that T _Sk either started hot and was cooled (H to C) or started cold and was heated (C to H) throughout exercise. Pre-exercise core temperatures (T _C) and heart rates (HR) were similar between trials, while T _Sk, thermal comfort and thermal sensation were higher in H to C. The change in T _Sk was similar in magnitude during the two trials. Work completed was greatest in C to H, which was attributed to a higher initial power output. T _C was similar between trials. HR was similar until 35 min had elapsed, after which it became lower in H to C. The perception of effort increased similarly between the two trials, while thermal comfort and thermal sensation generally reflected the changes observed in T _Sk. These results indicate that upon exercise commencement T _Sk and the accompanying thermal perceptions are important inputs in the initial selection of exercise intensity.     

Effect of exercise intensity on post-exercise oxygen consumption and heart rate recovery

Purpose

There is some evidence that measures of acute post-exercise recovery are sensitive to the homeostatic stress of the preceding exercise and these measurements warrant further investigation as possible markers of training load. The current study investigated which of four different measures of metabolic and autonomic recovery was most sensitive to changes in exercise intensity.

Methods

Thirty-eight moderately trained runners completed 20-min bouts of treadmill exercise at 60, 70 and 80 % of maximal oxygen uptake (VO_2max) and four different recovery measurements were determined: the magnitude of excess post-exercise oxygen consumption (EPOC_MAG), the time constant of the oxygen consumption recovery curve (EPOCτ), heart rate recovery within 1 min (HRR_60s) and the time constant of the heart rate recovery curve (HRRτ) .

Results

Despite significant differences in exercise parameters at each exercise intensity, only EPOC_MAG showed significantly slower recovery with each increase in exercise intensity at the group level and in the majority of individuals. EPOCτ was significantly slower at 70 and 80 % of VO_2max vs. 60 % VO_2max and HRRτ was only significantly slower when comparing the 80 vs. 60 % VO_2max exercise bouts. In contrast, HRR_60s reflected faster recovery at 70 and 80 % of VO_2max than at 60 % VO_2max.

Conclusion

Of the four recovery measurements investigated, EPOC_MAG was the most sensitive to changes in exercise intensity and shows potential to reflect changes in the homeostatic stress of exercise at the group and individual level. Determining EPOC_MAG may help to interpret the homeostatic stress of laboratory-based research trials or training sessions.     

No effect of caffeine on exercise performance in high ambient temperature

Caffeine, an adenosine receptor antagonist, has shown to improve performance in normal ambient temperature, presumably via an effect on dopaminergic neurotransmission through the antagonism of adenosine receptors. However, there is very limited evidence from studies that administered caffeine and examined its effects on exercise in the heat. Therefore, we wanted to study the effects of caffeine on performance and thermoregulation in high ambient temperature. Eight healthy trained male cyclists completed two experimental trials (in 30°C) in a double-blind-randomized crossover design. Subjects ingested either placebo (6 mg/kg) or caffeine (6 mg/kg) 1 h prior to exercise. Subjects cycled for 60 min at 55% W (max), immediately followed by a time trial to measure performance. The significance level was set at p < 0.05. Caffeine did not change performance (p = 0.462). Rectal temperature was significantly elevated after caffeine administration (p < 0.036). Caffeine significantly increased B-endorphin plasma concentrations at the end of the time trial (p = 0.032). The present study showed no ergogenic effect of caffeine when administered 1 h before exercise in 30°C. This confirms results from a previous study that examined the effects of caffeine administration on a short (15 min) time trial in 40°C. However, caffeine increased core temperature during exercise. Presumably, the rate of increase in core temperature may have counteracted the ergogenic effects of caffeine. However, other factors such as interindividual differences in response to caffeine and changes in neurotransmitter concentrations might also be responsible for the lack of performance improvement of caffeine in high ambient temperature.     

The effect of post-exercise hydrotherapy on subsequent exercise performance and heart rate variability

We investigated the effect of hydrotherapy on time-trial performance and cardiac parasympathetic reactivation during recovery from intense training. On three occasions, 18 well-trained cyclists completed 60 min high-intensity cycling, followed 20 min later by one of three 10-min recovery interventions: passive rest (PAS), cold water immersion (CWI), or contrast water immersion (CWT). The cyclists then rested quietly for 160 min with R–R intervals and perceptions of recovery recorded every 30 min. Cardiac parasympathetic activity was evaluated using the natural logarithm of the square root of mean squared differences of successive R–R intervals (ln rMSSD). Finally, the cyclists completed a work-based cycling time trial. Effects were examined using magnitude-based inferences. Differences in time-trial performance between the three trials were trivial. Compared with PAS, general fatigue was very likely lower for CWI (difference [90% confidence limits; −12% (−18; −5)]) and CWT [−11% (−19; −2)]. Leg soreness was almost certainly lower following CWI [−22% (−30; −14)] and CWT [−27% (−37; −15)]. The change in mean ln rMSSD following the recovery interventions (ln rMSSD_Post-interv) was almost certainly higher following CWI [16.0% (10.4; 23.2)] and very likely higher following CWT [12.5% (5.5; 20.0)] compared with PAS, and possibly higher following CWI [3.7% (−0.9; 8.4)] compared with CWT. The correlations between performance, ln rMSSD_Post-interv and perceptions of recovery were unclear. A moderate correlation was observed between ln rMSSD_Post-interv and leg soreness [r = −0.50 (−0.66; −0.29)]. Although the effects of CWI and CWT on performance were trivial, the beneficial effects on perceptions of recovery support the use of these recovery strategies.     

The effect of ambient temperature on gross-efficiency in cycling

Time-trial performance deteriorates in the heat. This might potentially be the result of a temperature-induced decrease in gross-efficiency (GE). The effect of high ambient temperature on GE during cycling will be studied, with the intent of determining if a heat-induced change in GE could account for the performance decrements in time trial exercise found in literature. Ten well-trained male cyclists performed 20-min cycle ergometer exercise at 60% (power output at which VO_2max was attained) in a thermo-neutral climate (N) of 15.6 ± 0.3°C, 20.0 ± 10.3% RH and a hot climate (H) of 35.5 ± 0.5°C, 15.5 ± 3.2% RH. GE was calculated based on VO₂ and RER. Skin temperature (T _sk), rectal temperature (T _re) and muscle temperature (T _m) (only in H) were measured. GE was 0.9% lower in H compared to N (19.6 ± 1.1% vs. 20.5 ± 1.4%) (P < 0.05). T _sk (33.4 ± 0.6°C vs. 27.7 ± 0.7°C) and T _re (37.4 ± 0.6°C vs. 37.0 ± 0.6°C) were significantly higher in H. T _m was 38.7 ± 1.1°C in H. GE was lower in heat. T _m was not high enough to make mitochondrial leakage a likely explanation for the observed reduced GE. Neither was the increased T _re. Increased skin blood flow might have had a stealing effect on muscular blood flow, and thus impacted GE. Cycling model simulations showed, that the decrease in GE could account for half of the performance decrement. GE decreased in heat to a degree that could explain at least part of the well-established performance decrements in the heat.     

The effect of exercise intensity and duration on salivary immunoglobulin A

Summary Two experiments were performed to examine salivary immunoglobulin A (s-IgA) responses to varying levels of exercise intensity and duration. For experiment 1, 9 college men (mean age, SD=23.56, 1.64 years) completed treadmill runs of 15, 30, and 45 min at approximately 60% of maximum oxygen consumption (VO_2max). For experiment 2, 9 other college men (mean age, SD=23.67, 2.0 years) ran for 20 min at approximately 50, 65 and 80% of VO_2max. Unstimulated salivary samples were collected before, and immediately, 1 and 2 h after the exercise. Samples were assayed for s-IgA using an enzyme-linked immunosorbent assay. Mean s-IgA levels did not change significantly (P>0.05) at any of the post-exercise collection times when compared to pre-exercise levels. The results of this investigation indicated that running at intensities of 50–80% of VO_2max and for durations of 15–45 min did not affect s-IgA levels.     

Effect of ambient temperature on caffeine ergogenicity during endurance exercise

It is well established that caffeine ingestion during exercise enhances endurance performance. Conversely, the physiological and psychological strain that accompanies increased ambient temperature decreases endurance performance. Little is known about the interaction between environmental temperature and the effects of caffeine on performance. The purpose of this study was to compare the effects of ambient temperature (12 and 33°C) on caffeine ergogenicity during endurance cycling exercise. Eleven male cyclists (mean ± SD; age, 25 ± 6 years; [(V)\dot] \textO_2max , {\dot V \text{O}}_{2\max } , 58.7 ± 2.9 ml kg⁻¹ min⁻¹) completed four exercise trials in a randomized, double blind experimental design. After cycling continuously for 90 min (average 65 ± 7% [(V)\dot] \textO_2max {\dot V \text{O}}_{2\max } ) in either a warm (33 ± 1°C, 41 ± 5%rh) or cool (12 ± 1°C, 60 ± 7%rh) environment, subjects completed a 15-min performance trial (PT; based on total work accumulated). Subjects ingested 3 mg kg⁻¹ of encapsulated caffeine (CAF) or placebo (PLA) 60 min prior to and after 45 min of exercise. Throughout exercise, subjects ingested water so that at the end of exercise, independent of ambient temperature, their body mass was reduced 0.55 ± 0.67%. Two-way (temperature × treatment) repeated-measures ANOVA were conducted with alpha set at 0.05. Total work (kJ) during the PT was greater in 12°C than 33°C [P < 0.001, η² = 0.804, confidence interval (CI): 30.51–62.30]. When pooled, CAF increased performance versus PLA independent of temperature (P = 0.006, η² = 0.542 CI: 3.60–16.86). However, performance differences with CAF were not dependent on ambient temperature (i.e., non-significant interaction; P = 0.662). CAF versus PLA in 12 and 33°C resulted in few differences in other physiological variables. However, during exercise, rectal temperature (T _re) increased in the warm environment (peak T _re; 33°C, 39.40 ± 0.45; 12°C, 38.79 ± 0.42°C; P < 0.05) but was not different in CAF versus PLA (P > 0.05). Increased ambient temperature had a detrimental effect on cycling performance in both the CAF and PLA conditions. CAF improved performance independent of environmental temperature. These findings suggest that caffeine at the dosage utilized (6 mg/kg body mass) is a, legal drug that provides an ergogenic benefit in 12 and 33°C.     

The effect of exercise intensity on hematuria in healthy male runners

The purpose of this study were: (1) to establish the prevalence of exercise-induced hematuria in a group of otherwise healthy male runners (n?=?70), and (2) to investigate the role of exercise intensity in those runners who exhibited exercise-related hematuria (n?=?10) by evaluating the effect of running and cycling at high and low intensities. The identified and recruited subjects participated in four different exercise protocols: (1) a 60-min treadmill run (RUN) at 90% of anaerobic threshold (Th_ae), (2) a 60-min leg cycle ergometer ride (BIKE) at 90% of Th_ae, (3) a 3×400-m sprint (SPRINT), each followed by 4?min of rest or light walking, and (4) 3×60-Wingate leg cycle ergometry tests, each followed by 4?min of rest or light cycling. The study employed a 3×4 (time by protocol) within-subjects design and dependent variables were measured before exercise, 4?min after, and 1?h after exercise, and included measurements of hematuria, proteinuria, urinary pH, serum haptoglobin concentration, serum creatine phosphokinase activity, plasma lactate concentration, and hemoglobin. The 400-m sprint at maximal effort significantly increased both hematuria and proteinuria (P?P?P?相似文献   

Effects of exercise intensity and environmental stress on indices of oxidative stress and iron homeostasis during exercise in the horse

The effects of prolonged variable-intensity and short-term high-intensity exercise on indices of oxidative stress and iron homeostasis were compared in six fit horses under cool [20°C, 40% relative humidity (RH)] or hot/humid (30°C, 80% RH) environmental conditions. The exercise protocols were designed to simulate equine competition, including racing (intense exercise) or the speed and endurance phase of a 3-day event (prolonged exercise). Increased plasma concentrations of lipid hydroperoxides and haemolysate concentrations of oxidised glutathione (GSSG) were measured within 30 min of the completion of exercise, indicating production of reactive oxygen species (ROS) and lipid membrane peroxidation. The horses were unable to complete the prolonged exercise protocol at high temperature and humidity. This coincided with higher maximal values of lipid hydroperoxides [138.2 (17.7) M and GSSG [110.6 (18.2) M], compared to high-intensity [105.2 (14.9) M and 63.6 (8.6) M, respectively] or prolonged [100.7 (18.7) M and 86.2 (9.1) M, respectively] exercise performed under cooler environmental conditions. Significant correlations were found between the duration of the final stage of exercise during hot/humid environmental conditions and increased levels of lipid hydroperoxides (r = 0.85), GSSG (r = 0.94), xanthine (r = 0.92) and uric acid (r = 0.96). Excerise also decreased the iron (Fe)-binding antioxidant activity of the plasma and increased the total plasma Fe levels, although this was only significant for prolonged exercise in ambient conditions. There was no detectable free Fe in the plasma at any stage of exercise. Other changes in biochemical parameters had returned to pre-exercise levels within 24 h after exercise. The results show that exercise can induce changes in biochemical parameters that are indicative of oxidative stress in the fit horse and that this was, exacerbated during exercise at high temperature and humidity.     

Effects of caffeine and high ambient temperature on haemodynamic and body temperature responses to dynamic exercise.

Caffeine can enhance mean arterial blood pressure (MAP) and attenuate forearm blood flow (FBF) and forearm vascular conductance (FVC) during exercise in thermal neutral conditions without altering body temperature. During exercise at higher ambient temperatures, where a greater transfer of heat from the body core to skin would be expected, caffeine-induced attenuation of FBF (i.e. cutaneous blood flow) could attenuate heat dissipation and increase body temperature (T(re)). We hypothesized that during exercise at an ambient temperature of 38 degrees C, caffeine increases MAP, and attenuates FBF and FVC such that T(re) is increased. Eleven caffeine-naive, active men, were studied at rest and during exercise after ingestion of a placebo or 6 mg kg(-1) of caffeine. MAP, heart rate (HR), FBF, FVC, T(re) skin temperature (T(sk)) and venous lactate concentrations (lactate) were assessed sequentially during rest at room temperature, after 45 min of exposure to an ambient temperature of 38 degrees C, and during 35 min of submaximal cycling. Heat exposure caused increases in MAP, FBF, FVC and T(sk) that were not altered by caffeine. HR, T(re), and lactate were unaffected. During exercise, only MAP (95 +/- 2 vs. 102 +/- 2 mmHg), HR (155 +/- 10 vs. 165 +/- 10 beats min(-1)), and lactate (2.0 +/- 0.4 vs. 2.3 +/- 0.4 mmol l(-1)) were increased by caffeine. These data indicate that increases in cutaneous blood flow during exercise in the heat are not reduced by caffeine. This may be because of activation of thermal reflexes that cause cutaneous vasodilation capable of offsetting caffeine-induced reductions in blood flow. Caffeine-induced increases in lactate, MAP and HR during exercise suggest that this drug and high ambient temperatures increase production of muscle metabolites that cause reflex cardiovascular responses.     

The effect of moderate altitude on post-exercise blood lactate

Summary Post-exercise blood lactate levels were studied after a short exhaustive bicycle ride in 3 males at sea level control, at altitude (2300 m) and on return to sea level. The short exhaustive bicycle ride was performed at a work rate of 2730 kpm · min^–1 and ride times ranged from 55 to 105 sec. Compared to sea level controls, performance time of the tests at altitude were of similar intensity and duration. Although the changes were small, the oxygen uptakes during the ride and oxygen debts following the rides increased with each test. However, in comparison with sea level controls the blood lactate concentrations were reduced. The reduction on the average reached 44% after 4 days at altitude, and 51% after 22 days at altitude. This reduction in blood lactate concentration of the same subject at altitude as compared with his sea level values may indicate a decrease in the activity of the glycolytic pathway relative to the activity of the aerobic pathway. This appears to be a contradiction to what would be expected in the mild hypoxic conditions present at altitude.Work done while at the University of Michigan, Ann Arbor, Michigan.This study was supported in part by a grant from the Fitness and Amateur Sport Directorate, Ottawa, Canada.     

Fluid replacement drinks during high intensity exercise effects on minimizing exercise-induced disturbances in homeostasis

Summary The purpose of these experiments was to examine the influence of various fluid replacement drinks on exercise-induced disturbances in homeostasis during heavy exercise. Nine trained cyclists performed constant load exercise on a cycle ergometer to fatigue on three occasions with 1-week separating experiments. The work rate was set initially at 85% of (range 82–88%) with fatigue being defined as a 10% decline in power output below the initial value. During each experiment subjects consumed one of the following three beverages prior to and every 15 min during exercise: (1) non-electrolyte placebo (NEP; 31 mosmol · kg^–1); (2) glucose polymer drink containing electrolytes (GP; 7% CHO, 231 mosmol · kg^–1), and (3) electrolyte placebo drink without carbohydrate (EP; 48 mosmol · kg^–1). Both the GP and EP beverage contained sodium citrate/citric acid (C) as a flavoring agent while C was not contained in the NEP drink. Although seven of nine subjects worked longer during the GP and EP treatment when compared with the NEP trial, the difference was not significant (P>0.05). No differences (P>0.05) existed between the GP and EP treatments in performance time. Exercise changes in rectal temperature, heart rate, % plasma volume and plasma concentrations of total protein, free fatty acids, glucose, lactate, potassium, chloride, calcium, and sodium did not differ (P>0.05) between trials. In contrast, blood hydrogen ion concentration [H⁺] was significantly lower (P<0.05) at 30 min of exercise during the GP and EP treatment when compared with the NEP run. These data provide evidence that electrolyte drinks do not minimize exercise-induced disturbances in blood-electrolyte concentrations during heavy execrcise when compared with nonelectrolyte drinks; however, these results suggest that fluid replacement beverages containing buffers (i.e. C) and/or electrolytes may minimize blood alterations in [H⁺] during intense exercise. Additional research is required to determine if the buffering influence of these beverages has an ergogenic benefit during heavy exercise.