Pre-exercise antioxidant enzyme activities determine the antioxidant enzyme erythrocyte response to exercise

Free radical production increases during exercise and oxidative damage occurs in several tissues. We examined the effects of three different exercise tests on the pattern of change of erythrocyte enzyme antioxidant activities. The tests were a short maximal exercise test, a submaximal prolonged exercise test and a cycling stage during competition. The participants were amateur and professional cyclists with different training statuses and different basal erythrocyte antioxidant enzyme activities. The maximal test produced no changes in the erythrocyte antioxidant enzyme activities of amateur sportsmen. The submaximal test, performed at 80% of maximal oxygen uptake, decreased erythrocyte catalase (12%), glutathione peroxidase determined with H₂O₂ (14%) and glutathione reductase (16%); superoxide dismutase activity increased by about 25%. The cycling stage performed by professional cyclists increased erythrocyte catalase (29%) and glutathione reductase (10%) activities. The in vivo changes in glutathione reductase activity were confirmed by in vitro measurements: hydrogen peroxide decreased and the presence of catalase increased the activity of this enzyme. In conclusion, we suggest that the different erythrocyte antioxidant enzyme responses to diverse exercise tests can be explained by the effects of hydrogen peroxide and the superoxide anion on the antioxidant enzyme activities in erythrocytes.     

Maximal strength and power, muscle mass, endurance and serum hormones in weightlifters and road cyclists

Maximal strength, power, muscle cross-sectional area, maximal and submaximal cycling endurance characteristics and serum hormone concentrations of testosterone, free testosterone and cortisol were examined in three groups of men: weightlifters (n = 11), amateur road cyclists (n = 18) and age-matched controls (n = 12). Weightlifters showed 45-55% higher power values than road cyclists and controls, whereas the differences in maximal strength and muscle mass were only 15% and 20%, respectively. These differences were maintained when average power output was expressed relative to body mass or relative to muscle cross-sectional area. Road cyclists recorded 44% higher maximal workloads, whereas submaximal blood lactate concentration was 50-55% lower with increasing workload than in controls and weightlifters. In road cyclists, workloads associated with blood lactate concentrations of 2 and 4 mmol.l-1 were 50-60% higher and occurred at a higher percentage of maximal workload than in weightlifters or controls. Basal serum total testosterone and free testosterone concentrations were lower in elite amateur cyclists than in age-matched weightlifters or untrained individuals. Significant negative correlations were noted between the individual values of maximal workload, workloads at 2 and 4 mmol.l-1 and the individual values of muscle power output (r = -0.37 to -0.49), as well as the individual basal values of serum total testosterone and free testosterone (r = -0.39 to -0.41). These results indicate that the specific status of the participants with respect to training, resistance or endurance is important for the magnitude of the neuromuscular, physiological and performance differences observed between weightlifters and road cyclists. The results suggest that, in cycling, long-term endurance training may interfere more with the development of muscle power than with the development of maximal strength, probably mediated by long-term cycling-related impairment in anabolic hormonal status.     

Redox status and antioxidant response in professional cyclists during training

Abstract

The aim of this study was to investigate whether different phases of training affect oxidative stress and antioxidant defences in professional cyclists. Ten professional cyclists, aged 21.8 ± 2.5 years, were enrolled in the study. They were classified into two groups of five athletes each one with similar nutritional intake excepting for the overload of vitamin C (1000 mg day^?1) and E (400 mg day^?1) supplementation in one of them. The cyclists of both groups performed the same exercise design, consisting of hard, tapering and recovery training periods. Total antioxidant capacity (TAC) of the diet, plasma oxygen radical absorption capacity (ORAC), lipid peroxidation (LPO), DNA damage (8-OHdG) and erythrocyte glutathione disulfide/glutathione ratio (GSSG:GSH^?1) were measured. During the intense exercise trainings, the cyclists without vitamin supplements had the TAC of diet significantly lower than the supplemented group. Plasma ORAC, LPO and 8-OHdG were similar in both groups of athletes. Athletes with supplements had a basal LPO:ORAC^?1 ratio lower than that without supplements, but this ratio converged to the same level at the end of the training in both groups of cyclists. Both groups of cyclists showed similar changes in GSSG:GSH^?1 ratio and in GSSG and GSH levels along the study. The data suggest that well-trained athletes with suitable ultra-endurance training volume and intensity do not require antioxidant vitamin supplements to adapt their endogenous antioxidant defenses to exercise-induced ROS.     

Physiological correlates to off-road cycling performance

The aim of this study was to examine the relationships between maximal and submaximal tests for aerobic fitness and performance in an off-road cross-country circuit race. Thirteen competitive off-road male cyclists participated in the study. Peak oxygen uptake (VO2peak), peak power output, and lactate thresholds corresponding to 1 mmol x l(-1) above baseline (lactate threshold) and to 4 mmol x l(-1) (onset of blood lactate accumulation) were measured during an incremental cycling test. Race time and final ranking within the same group of cyclists were determined during a cross-country off-road competition. All correlations between the measured parameters of aerobic fitness and off-road cycling performance were significant, particularly between race time and physiological parameters scaled to body mass0.79 (r = -0.68 to -0.94; P < 0.05) and between final ranking and physiological parameters expressed relative to body mass0.79 (r = -0.81 to - 0.96; P < 0.001). Moreover, there was a large difference (effect sizes = 1.12-1.70) in all measured parameters of aerobic fitness between the group of six cyclists with a race time above the median and the group of six cyclists with a race time below the median (P < 0.05). In conclusion, the results of this study provide empirical support to the widespread use of these maximal (VO2peak, peak power output) and submaximal (lactate thresholds) parameters of aerobic fitness in the physiological assessments of off-road cyclists. Furthermore, our results suggest body size should be taken into account when evaluating such athletes.     

Influence of leg preference on bilateral muscle activation during cycling

The purpose of this study was to investigate asymmetry of muscle activation in participants with different levels of experience and performance with cycling. Two separate experiments were conducted, one with nine cyclists and one with nine non-cyclists. The experiments involved incremental maximal and sub-maximal constant load cycling tests. Bilateral surface electromyography (EMG) and gross and net muscle efficiency were assessed. Analyses of variance in mixed linear models and t-tests were conducted. The cyclists in Experiment 1 presented higher gross efficiency (P < 0.05), whereas net efficiency did not differ between the two experiments (21.3 ± 1.4% and 19.8 ± 1.0% for cyclists and non-cyclists, respectively). The electrical muscle activity increased significantly with exercise intensity regardless of leg preference in both experiments. The coefficient of variation of EMG indicated main effects of leg in both experiments. The non-preferred leg of non-cyclists (Experiment 2) presented statistically higher variability of muscle activity in the gastrocnemius medialis and vastus lateralis. Our findings suggest similar electrical muscle activity between legs in both cyclists and non-cyclists regardless of exercise intensity. However, EMG variability was asymmetric and appears to be strongly influenced by exercise intensity for cyclists and non-cyclists, especially during sub-maximal intensity. Neural factors per se do not seem to fully explain previous reports of pedalling asymmetries.     

Antioxidant diet supplementation enhances aerobic performance in amateur sportsmen

The effects of antioxidant diet supplements on blood lactate concentration and on the aerobic and anaerobic thresholds and their adaptations to training were analysed. Fifteen amateur male athletes were randomly assigned to either a placebo group or an antioxidant-supplemented group (90 days supplementation with 500 mg x day(-1) of vitamin E and 30 mg x day(-1) of beta-carotene, and the last 15 days also with 1 g x day(-1) of vitamin C). Before and after the antioxidant supplements, the sportsmen performed a maximal exercise test on a cycle ergometer and maximal and submaximal physiological parameters were assessed together with blood lactate concentration. Maximal oxygen uptake (VO(2max)), maximal blood lactate concentration, and the maximal workload attained rose significantly in both groups after the 3 months of training. At the end of the study, maximal blood lactate concentration was lower in the group that took supplements than in the placebo group. The percentage of VO(2max) attained at the anaerobic threshold rose significantly in both groups after 3 months of training, although the final value in the supplemented group was higher than that in the placebo group. Antioxidant diet supplements induced lower increases in blood lactate concentration after a maximal exercise test and could improve the efficiency in which aerobic energy is obtained.     

耐力训练及限食对老龄大鼠骨骼肌线粒体氧化及抗氧化水平影响的比较研究

目的:观察长期耐力训练及限食对老龄大鼠骨骼肌线粒体氧化及抗氧化水平的影响,比较其单独及协同作用,为"线粒体衰老"学说提供一定的理论依据。方法:32只17月龄雄性SD大鼠分为4组:安静组(Control,C)、限食组(Caloric-Restricted,CR)、运动组(Exercise,E)和限食加运动组(Caloric-restricted and Exercise,E+CR),训练方式为跑台运动,中等运动强度(64%VO2max,15m/min,60分钟/天,每周5天),限食摄入的标准为正常摄入组的60%,共训练及限食12周,相同月龄对照组正常饲养。12周后于末次训练后取大鼠骨骼肌分别进行线粒体氧化损伤水平及抗氧化水平测定。结果:CR组、E组和CR+E组骨骼肌线粒体丙二醛(malondialdehyde,MDA)含量显著降低,锰超氧化物歧化酶(manganese-containing superoxide dismutase,MnSOD)活性显著增加,谷胱甘肽过氧化物酶(glutathion peroxidase,GSH-PX)活性显著增加;E组和CR+E组骨骼肌线粒体过氧化氢酶(catalase,CAT)活性显著增加。结论:耐力训练提高机体的抗氧化水平,同时使细胞机能节省化,耗氧量相对下降而减少了自由基的产生,限食减弱了机体的氧化应激,减少了自由基的产生,阻止了脂质过氧化,同时限食动员了一系列的适应性的网络防御机制,增加了抗氧化水平,加强了防御。耐力运动在机体抗氧化能力上明显强于限食作用,而耐力运动与限食的协同作用对某些抗氧化酶的影响强于其单独作用的影响。     

Non-exercise estimation of VO(2)max using the International Physical Activity Questionnaire

Non-exercise equations developed from self-reported physical activity can estimate maximal oxygen uptake (VO(2)max) as well as submaximal exercise testing. The International Physical Activity Questionnaire (IPAQ) is the most widely used and validated self-report measure of physical activity. This study aimed to develop and test a VO(2)max estimation equation derived from the IPAQ-Short Form (IPAQ-S). College-aged males and females (n = 80) completed the IPAQ-S and performed a maximal exercise test. The estimation equation was created with multivariate regression in a gender-balanced subsample of participants, equally representing five levels of fitness (n = 50) and validated in the remaining participants (n = 30). The resulting equation explained 43% of the variance in measured VO(2)max (SEE = 5.45 ml·kg(-1)·min(-1)). Estimated VO(2)max for 87% of individuals fell within acceptable limits of error observed with submaximal exercise testing (20% error). The IPAQ-S can be used to successfully estimate VO(2)max as well as submaximal exercise tests. Development of other population-specific estimation equations is warranted.     

服用姜黄素对过度运动大鼠部分组织及红细胞膜损伤保护研究

建立大鼠大强度跑台训练模型,测试了大鼠血清肌酸激酶(CK)、谷草转氨酶(SGOT)、谷丙转氨酶(SGPT)、乳酸脱氢酶(LDH)的活性和心肌、骨骼肌、肝组织超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)、过氧化氢酶(CAT)活性和丙二醛(MDA)含量以及大鼠红细胞膜的丙二醛(MDA)含量和钠、钾ATP酶(Na+、K+-ATPase)的活性,应用荧光探针法研究了姜黄素对自由基致鼠红细胞脱膜损伤的保护作用。结果表明,服用姜黄素使大强度运动大鼠血清CK、SGOT、SGPT、LDH活性显著性下降(P<0.05);服用姜黄素使运动大鼠心肌、骨骼肌、肝组织SOD、CAT、GSH-Px活性都有不同程度的升高、MDA含量显著降低(P<0.05);服用姜黄素大鼠红细胞膜GSH-Px活性显著升高(P<0.05),MDA含量有显著性降低(P<0.05),膜脂的流动性显著提高。结论:姜黄素对疲劳运动所致大鼠组织自由基的损伤具有保护作用。     

Athlete burnout in elite sport: A self-determination perspective

Abstract

The practice of exercise has shown to be beneficial to quality of life of individuals with HIV/AIDS. Thus, the present study analysed the effects of a combined exercise training in persons living with HIV/AIDS. Ten participants participated in the present study. The following variables were analysed: viral load and cell counts for TCD4+/TCD8; maximal oxygen consumption (VO_2max); total mass, absolute fat mass, relative fat mass, absolute lean mass, relative lean mass and body mass index; fasting glycaemia, fasting insulinaemia, homeostatic model assessment (HOMA) index (insulin resistance – homeostatic model assessment (IR-HOMA)); total cholesterol, triglycerides, high-density lipoprotein (HDL), very low-density lipoprotein (VLDL), low-density lipoprotein (LDL); superoxide dismutase, catalase, glutathione peroxidase activities; thiobarbituric acid reactive substances. The combined exercise training consisted of resistance exercises plus aerobic training (60 min · session^?1, three times per week, during 20 weeks). The number of TCD4+ cells, absolute lean mass and relative lean mass, muscle strength for the 45° leg press, seated row and triceps extension, HDL-c levels as well as VO_2max increased post-training. The activity of superoxide dismutase, catalase, glutathione peroxidase enzymes and thiobarbituric acid reactive substances levels were diminished post-training. Finally, it can be concluded that combined exercise training is able to change positively several variables related to health of individuals with HIV/AIDS, mainly the immune system as well as antioxidant mechanisms re-establishment.     

Oxidants,antioxidant nutrients and the athlete

Strenuous physical exercise induces oxidative stress. There may be a number of sources of this oxidative stress, including mitochondrial superoxide production, ischaemia-reperfusion mechanisms and auto-oxidation of catecholamines. Severe or prolonged exercise can overwhelm antioxidant defences, which include vitamins E and C and thiol antioxidants, which are interlinked in an antioxidant network, as well as antioxidant enzymes. Evidence for oxidative stress and damage during exercise comes from direct measurement of free radicals, from measurement of damage to lipids and DNA, and from measurement of antioxidant redox status, especially glutathione. There is little evidence that antioxidant supplementation can improve performance, but a large body of work suggests that bolstering antioxidant defences may ameliorate exercise-induced damage, suggesting that the benefits of antioxidant intervention may be for the long term rather than the short term.     

The effect of marathon running on carnitine metabolism and on some aspects of muscle mitochondrial activities and antioxidant mechanisms

Carnitine is an essential co-factor in the catabolism of fats as an energy source. The primary purpose of this study was to investigate the effect of running a marathon on the metabolism of carnitine by endurance-trained athletes, and to evaluate the effect of carnitine administration on the performance of such exercise. The effects of marathon running on mitochondrial enzymes and cellular anti-oxidants were also examined to assess whether the expression of these activities is altered by exercise. Subjects were 10 experienced male marathon runners aged between 19 and 25 years. Running a marathon caused a fall in the plasma content of unesterified carnitine (37%) and an increase in the level of acetylcarnitine present (288%). Loading of the athletes with L-carnitine for 10 days before running a marathon abolished the exercise-induced fall in plasma-free carnitine (P less than 0.05) whilst amplifying the production of acetylcarnitine (P less than 0.05). Carnitine loading of the athletes studied made no detectable improvement in performance of the marathon (P greater than 0.05). Cytochrome oxidase, succinate cytochrome C reductase and superoxide dismutase activities present in skeletal muscle were unaltered by marathon running. However, such exercise caused a large increase in the tissue content of oxidized glutathione (189%) at the expense of reduced glutathione (-18%).     

优秀短距离自行车运动员无氧代谢能力特征研究

目的:比较不同性别和训练水平运动员无氧能力的差异,探讨短距离自行车运动员高能磷酸原供能、糖酵解供能和混合无氧供能能力的特征。方法:对16名优秀短距离自行车运动员进行10s(女)、15s(男)、30s和60s的无氧功测定,测定运动后即刻、运动后3min恢复心率和血乳酸。结果:1)磷酸原代谢能力表现出明显的性别差异,男运动员最大功率、相对最大功率、平均功率、相对平均功率、最大圈数都明显高于女运动员;2)30s和60s两种测试中,运动员爆发力表现出相同水平,但糖酵解代谢持续供能能力随运动时间的延长而明显下降;3)男子优秀运动员组15s无氧功最大功率、平均功率明显高于普通组。男、女最大圈数大于普通组,达到最大圈数时间小于或等于普通组;4)男子优秀组运动员30s、60s平均功率高于普通运动员组。女子优秀运动员组30s、60s平均功率、最大圈数明显高于普通运动员组,60s最大功率明显高于普通运动员组(P<0.05)。结论:1)优秀短距离自行车运动员具有较强的磷酸原代谢能力,男运动员明显强于女运动员;2)较强的糖酵解代谢能力是短距离自行车运动员无氧代谢能力的特征;3)评定磷酸原系统能力时,男、女运动员都使用10s无氧功测试为好;4)不同水平运动员的无氧代谢能力表现出明显差异,优秀运动员组强于普通运动员组。     

Physiological characteristics of successful mountain bikers and professional road cyclists

The aims of this study were to compare the physiological and anthropometric characteristics of successful mountain bikers and professional road cyclists and to re-examine the power-to-weight characteristics of internationally competitive mountain bikers. Internationally competitive cyclists (seven mountain bikers and seven road cyclists) completed the following tests: anthropometric measurements, an incremental cycle ergometer test and a 30 min laboratory time-trial. The mountain bikers were lighter (65.3+/-6.5 vs 74.7+/-3.8 kg, P= 0.01; mean +/- s) and leaner than the road cyclists (sum of seven skinfolds: 33.9+/-5.7 vs 44.5+/-10.8 mm, P = 0.04). The mountain bikers produced higher power outputs relative to body mass at maximal exercise (6.3+/-0.5 vs 5.8+/-0.3 W x kg(-1), P= 0.03), at the lactate threshold (5.2+/-0.6 vs 4.7+/-0.3 W x kg(-1), P= 0.048) and during the 30 min time-trial (5.5+/-0.5 vs 4.9+/-0.3 W x kg(-1), P = 0.02). Similarly, peak oxygen uptake relative tobody mass was higher in the mountain bikers (78.3+/-4.4 vs 73.0+/-3.4 ml x kg(-1) x min(-1), P = 0.03). The results indicate that high power-to-weight characteristics are important for success in mountain biking. The mountain bikers possessed similar anthropometric and physiological characteristics to previously studied road cycling uphill specialists.     

Physiological characteristics of successful mountain bikers and professional road cyclists

The aims of this study were to compare the physiological and anthropometric characteristics of successful mountain bikers and professional road cyclists and to re-examine the power-to-weight characteristics of internationally competitive mountain bikers. Internationally competitive cyclists (seven mountain bikers and seven road cyclists) completed the following tests: anthropometric measurements, an incremental cycle ergometer test and a 30 min laboratory time-trial. The mountain bikers were lighter (65.3 - 6.5 vs 74.7 - 3.8 kg, P = 0.01; mean - s ) and leaner than the road cyclists (sum of seven skinfolds: 33.9 - 5.7 vs 44.5 - 10.8 mm, P = 0.04). The mountain bikers produced higher power outputs relative to body mass at maximal exercise (6.3 - 0.5 vs 5.8 - 0.3 W·kg -1 , P = 0.03), at the lactate threshold (5.2 - 0.6 vs 4.7 - 0.3 W·kg -1 , P = 0.048) and during the 30 min time-trial (5.5 - 0.5 vs 4.9 - 0.3 W·kg -1 , P = 0.02). Similarly, peak oxygen uptake relative to body mass was higher in the mountain bikers (78.3 - 4.4 vs 73.0 - 3.4 ml·kg -1 ·min -1 , P = 0.03). The results indicate that high power-to-weight characteristics are important for success in mountain biking. The mountain bikers possessed similar anthropometric and physiological characteristics to previously studied road cycling uphill specialists.     

Individual differences in the interleukin-6 response to maximal and submaximal exercise tasks

Abstract

The inflammatory responsive cytokine interleukin-6 (IL-6) helps regulate immune responses to exercise. Evidence suggests that increases in IL-6 are related to exercise duration and intensity. However, the moderating effect of sex and underlying mediators have received limited attention. We compared plasma IL-6 responses to two cycling tasks with a resting control in young male (n = 12) and female (n = 12) recreationally active adults. Both 45 min tasks comprised an incremental test, either maximal or submaximal, followed by steady-state exercise at 55% peak power output. Interleukin-6 was elevated above baseline immediately after the maximal but not the submaximal task. Compared with the control condition, IL-6 was increased at 30 and 60 min after both exercise tasks. The IL-6 response was greater in women than men at 60 min after maximal exercise. Cortisol increased in both tasks compared with the control condition, the increase being greater after maximal than submaximal exercise. No associations were found between IL-6 responses and cortisol, heart rate, fitness or body mass index. The results show that 45 min of moderate-intensity exercise can increase IL-6 and suggest that the inclusion of maximal effort may accelerate this response. The finding that women showed a greater IL-6 response to maximal exercise may reflect a gender dimorphism in the immune response to stress.     

Measurement Invariance of Expectancy-Value Questionnaire in Physical Education

The study was designed to determine the effect of upright-posture (UP) versus semirecumbent (SR) cycling on commonly used measures of maximal and submaximal exercise capacity. Nine healthy, untrained men (M age = 27 years, SD = 4.8 years) underwent steady-state submaximal aerobic testing followed by a ramped test to determine maximal oxygen consumption (V_O2max). Anaerobic peak and average power and total work were assessed with the Wingate test. All tests were performed in both SR and UP positions, in random order. Oxygen consumption (V_O2) and ventilation (V_E) at the maximum workrate were lower in the SR position (p < .05). At submaximal workrates (50 W and 100 W), V_O2 and V_E were equivalent in the UP and SR positions, despite differences in tidal volume and respiratory rate (p < .05). There was no difference in peak or average anaerobic power in the two positions. In summary, SR exercise was associated with a reduced V_O2max and a significantly altered ventilatory response to aerobic exercise, with no change in anaerobic power output.     

Individual differences in the interleukin-6 response to maximal and submaximal exercise tasks

The inflammatory responsive cytokine interleukin-6 (IL-6) helps regulate immune responses to exercise. Evidence suggests that increases in IL-6 are related to exercise duration and intensity. However, the moderating effect of sex and underlying mediators have received limited attention. We compared plasma IL-6 responses to two cycling tasks with a resting control in young male (n = 12) and female (n = 12) recreationally active adults. Both 45 min tasks comprised an incremental test, either maximal or submaximal, followed by steady-state exercise at 55% peak power output. Interleukin-6 was elevated above baseline immediately after the maximal but not the submaximal task. Compared with the control condition, IL-6 was increased at 30 and 60 min after both exercise tasks. The IL-6 response was greater in women than men at 60 min after maximal exercise. Cortisol increased in both tasks compared with the control condition, the increase being greater after maximal than submaximal exercise. No associations were found between IL-6 responses and cortisol, heart rate, fitness or body mass index. The results show that 45 min of moderate-intensity exercise can increase IL-6 and suggest that the inclusion of maximal effort may accelerate this response. The finding that women showed a greater IL-6 response to maximal exercise may reflect a gender dimorphism in the immune response to stress.     

Effects of dietary antioxidants on training and performance in female runners

Abstract

Exercise-induced oxidative stress is implicated in muscle damage and fatigue which has led athletes to embark on antioxidant supplementation regimes to negate these effects. This study investigated the intake of vitamin C (VC) (1 g), blackcurrant (BC) juice (15 mg VC, 300 mg anthocyanins) and placebo in isocaloric drink form on training progression, incremental running test and 5-km time-trial performance. Twenty-three trained female runners (age, 31±8 y; mean±SD) completed three blocks of high-intensity training for 3 wks and 3 days, separated by a washout (~3.7 wks). Changes in training and performance with each treatment were analysed with a mixed linear model, adjusting for performance at the beginning of each training block. Markers of oxidative status included protein carbonyl, malondialdehyde (in plasma and in vitro erythrocytes), ascorbic acid, uric acid and erythrocyte enzyme activity of superoxide dismutase, catalase and glutathione peroxidase were analysed. There was a likely harmful effect on mean running speed during training when taking VC (1.3%; 90% confidence limits ±1.3%). Effects of the two treatments relative to placebo on mean performance in the incremental test and time trial were unclear, but runners faster by 1 SD of peak speed demonstrated a possible improvement on peak running speed with BC juice (1.9%; ±2.5%). Following VC, certain oxidative markers were elevated: catalase at rest (23%; ±21%), protein carbonyls at rest (27%; ±38%) and superoxide dismutase post-exercise (8.3%; ±9.3%). In conclusion, athletes should be cautioned about taking VC chronically, however, BC may improve performance in the elite.     

The effect of caffeine ingestion on human neutrophil oxidative burst responses following time-trial cycling

Following fixed-duration exercise of submaximal intensity, caffeine ingestion is associated with an attenuation of the exercise-induced decline in N-formyl-methionyl-phenyl-alanine (f-MLP) stimulated neutrophil oxidative burst. However, the response following high-intensity exhaustive exercise is unknown. Nine endurance-trained male cyclists ingested 6 mg caffeine or placebo per kilogram of body mass 60 min before cycling for 90 min at 70% of maximal oxygen consumption (VO2max) and then performing a time-trial requiring an energy expenditure equivalent to 30 min cycling at 70% maximum power output. Time-trial performance was 4% faster in the caffeine than in the placebo trial (P = 0.043). Caffeine was associated with an increased plasma adrenaline concentration after 90 min of exercise (P = 0.046) and immediately after the time-trial (P = 0.02). Caffeine was also associated with an increased serum caffeine concentration (P < 0.01) after 90 min of exercise and immediately after the time-trial, as well as 1 h after the time-trial. However, the f-MLP-stimulated neutrophil oxidative burst response fell after exercise in both trials (P = 0.002). There was no effect of caffeine on circulating leukocyte or neutrophil counts, but the lymphocyte count was significantly lower on caffeine (20%) after the time-trial (P = 0.003). Our results suggest that high-intensity exhaustive exercise negates the attenuation of the exercise-induced decrease in neutrophil oxidative burst responses previously observed when caffeine is ingested before exercise of fixed duration and intensity. This may be associated with the greater increase in adrenaline concentration observed in the present study.