Metabolic catecholamine, and endurance responses to caffeine during intense exercise

This study examined the possible effects of caffeine ingestion on muscle metabolism and endurance during brief intense exercise. We tested 14 subjects after they ingested placebo or caffeine (6 mg/kg) with an exercise protocol in which they cycled for 2 min, rested 6 min, cycled 2 min, rested 6 min, and then cycled to voluntary exhaustion. In each exercise the intensity required the subject's maximal O2 consumption. Eight subjects had muscle and venous blood samples taken before and after each exercise period. The caffeine ingestion resulted in a significant increase in endurance (4.12 +/- 0.36 and 4.93 +/- 0.60 min for placebo and caffeine, respectively) and resulted in a significant increase in plasma epinephrine concentration throughout the protocol but not in norepinephrine concentration. During the first two exercise bouts, the power and work output were not different; blood lactate concentrations were not affected significantly by caffeine ingestion, but during the exercise bouts muscle lactate concentration was significantly increased by caffeine. The net decrease in muscle glycogen was not different between treatments at any point in the protocol, and even at the time of fatigue there was at least 50% of the original glycogen concentration remaining. the data demonstrated that caffeine ingestion can be an effective ergogenic aid for exercise that is as brief as 4-6 min. However, the mechanism is not associated with muscle glycogen sparing. It is possible that caffeine is exerting actions directly on the active muscle and/or the neural processes that are involved in the activity.     

The use of drugs to improve athletic performance

In sports, medical drugs are applied for supposedly ergogenic effects. Forbidden drug use (doping) implies that the drug enhances performance, which is not always the case. Amphetamines are ergogenic particularly during short-term, explosive exercise. Amphetamines exert an ergolytic effect on high-intensity endurance exercise. Caffeine has an ergogenic effect on endurance performance in dosages of 3 to 6 mg/kg. Doping regulations allow a small amount of caffeine intake. Androgenic and anabolic steroids elicit an increase in muscle growth and strength. In females low doses appear to be ergogenic in all sport types. beta 2-adrenergic agonists appear to have a positive effect on strength and muscle growth. The effects on endurance performance are still unknown. Although growth hormone is used in sports, scientific studies show that compared with placebo no difference in strength and muscle volume is observed. Blood doping and administration of erythropoietin are effective in enhancing endurance performance.     

Caffeine counteracts the ergogenic action of muscle creatine loading

This study aimed to compare the effects of oral creatine (Cr) supplementation with creatine supplementation in combination with caffeine (Cr+C) on muscle phosphocreatine (PCr) level and performance in healthy male volunteers (n = 9). Before and after 6 days of placebo, Cr (0.5 g x kg-1 x day-1), or Cr (0.5 g x kg-1 x day-1) + C (5 mg x kg-1 x day-1) supplementation, 31P-nuclear magnetic resonance spectroscopy of the gastrocnemius muscle and a maximal intermittent exercise fatigue test of the knee extensors on an isokinetic dynamometer were performed. The exercise consisted of three consecutive maximal isometric contractions and three interval series of 90, 80, and 50 maximal voluntary contractions performed with a rest interval of 2 min between the series. Muscle ATP concentration remained constant over the three experimental conditions. Cr and Cr+C increased (P < 0.05) muscle PCr concentration by 4-6%. Dynamic torque production, however, was increased by 10-23% (P < 0.05) by Cr but was not changed by Cr+C. Torque improvement during Cr was most prominent immediately after the 2-min rest between the exercise bouts. The data show that Cr supplementation elevates muscle PCr concentration and markedly improves performance during intense intermittent exercise. This ergogenic effect, however, is completely eliminated by caffeine intake.     

Metabolic and exercise endurance effects of coffee and caffeine ingestion

Caffeine (Caf) ingestion increases plasma epinephrine (Epi) and exercise endurance; these results are frequently transferred to coffee (Cof) consumption. We examined the impact of ingestion of the same dose of Caf in Cof or in water. Nine healthy, fit, young adults performed five trials after ingesting (double blind) either a capsule (Caf or placebo) with water or Cof (decaffeinated Cof, decaffeinated with Caf added, or regular Cof). In all three Caf trials, the Caf dose was 4.45 mg/kg body wt and the volume of liquid was 7.15 ml/kg. After 1 h of rest, the subject ran at 85% of maximal O2 consumption until voluntary exhaustion (approximately 32 min in the placebo and decaffeinated Cof tests). In the three Caf trials, the plasma Caf and paraxanthine concentrations were very similar. After 1 h of rest, the plasma Epi was increased (P < 0.05) by Caf ingestion, but the increase was greater (P < 0.05) with Caf capsules than with Cof. During the exercise there were no differences in Epi among the three Caf trials, and the Epi values were all greater (P < 0.05) than in the other tests. Endurance was only increased (P < 0. 05) in the Caf capsule trial; there were no differences among the other four tests. One cannot extrapolate the effects of Caf to Cof; there must be a component(s) of Cof that moderates the actions of Caf.     

Creatine supplementation and exercise performance: an update

Creatine, a natural nutrient found in animal foods, is alleged to be an effective nutritional ergogenic aid to enhance sport or exercise performance. Research suggests that oral creatine monohydrate supplementation may increase total muscle creatine [TCr], including both free creatine [FCr] and phosphocreatine [PCr]. Some, but not all, studies suggest that creatine supplementation may enhance performance in high-intensity, short-term exercise tasks that are dependent primarily on PCr (i.e., < 30 seconds), particularly laboratory tests involving repeated exercise bouts with limited recovery time between repetitions; additional corroborative research is needed regarding its ergogenic potential in actual field exercise performance tasks dependent on PCr. Creatine supplementation has not consistently been shown to enhance performance in exercise tasks dependent on anaerobic glycolysis, but additional laboratory and field research is merited. Additionally, creatine supplementation has not been shown to enhance performance in exercise tasks dependent on aerobic glycolysis, but additional research is warranted, particularly on the effect of chronic supplementation as an aid to training for improvement in competitive performance. Short-term creatine supplementation appears to increase body mass in males, although the initial increase is most likely water. Chronic creatine supplementation, in conjunction with physical training involving resistance exercise, may increase lean body mass. However, confirmatory research data are needed. Creatine supplementation up to 8 weeks has not been associated with major health risks, but the safety of more prolonged creatine supplementation has not been established. Creatine is currently legal and its use by athletes is not construed as doping.     

Effect of caffeine on metabolism, exercise endurance, and catecholamine responses after withdrawal

In this study the effects of acute caffeine ingestion on exercise performance, hormonal (epinephrine, norepinephrine, insulin), and metabolic (free fatty acids, glycerol, glucose, lactate, expired gases) parameters during short-term withdrawal from dietary caffeine were investigated. Recreational athletes who were habitual caffeine users (n = 6) (maximum oxygen uptake 54.5 +/- 3.3 ml x kg-1 x min-1 and daily caffeine intake 761.3 +/- 11.8 mg/day) were tested under conditions of no withdrawal and 2-day and 4-day withdrawal from dietary caffeine. There were seven trials in total with a minimum of 10 days between trials. On the day of the exercise trial, subjects ingested either dextrose placebo or 6 mg/kg caffeine in capsule form 1 h before cycle ergometry to exhaustion at 80-85% of maximum oxygen uptake. Test substances were assigned in a random, double-blind manner. A final placebo control trial completed the experiment. There was no significant difference in any measured parameters among days of withdrawal after ingestion of placebo. At exhaustion in the 2- and 4-day withdrawal trials, there were significant increases in plasma norepinephrine in response to caffeine ingestion. Caffeine-induced increases in serum free fatty acids occurred after 4 days and only at rest. Subjects responded to caffeine with increases in plasma epinephrine (P < 0.05) at exhaustion and prolonged exercise time in all caffeine trials compared with placebo, regardless of withdrawal from caffeine. It is concluded that increased endurance is unrelated to hormonal or metabolic changes and that it is not related to prior caffeine habituation in recreational athletes.     

Relationship between nitric oxide and prostaglandins in carrageenin pleurisy

PURPOSE: To examine the effects of repeated bouts of exercise on the blood lactate [HLa]-ratings of perceived exertion (RPE) relation. METHODS: Six moderately trained males were studied on two occasions: a sequential exercise bouts day (SEB: 1000 h, 1130 h, and 1300 h) and a delayed exercise bouts day (DEB: 1000 h, 1400 h, and 1800 h). Each of the three exercise bouts within a given condition were 30 min in duration at the power output (PO) associated with 70% of VO2peak on a cycle ergometer. A standardized meal was provided at 0600 h. VO2, PO, HR, and RER were recorded every min during exercise and blood [HLa] and RPE were measured every 5 min during exercise. RESULTS: A 2 x 3 analysis of variance with repeated measures revealed that blood [HLa] decreased significantly with each repeated exercise bout (X +/- SEM: bout 1: SEB = 3.5 (0.3), DEB = 3.8 (0.4); bout 2: SEB = 2.6 (0.3), DEB = 2.8 (0.3); bout 3: SEB = 2.0 (0.2), DEB = 2.1 (0.4); mM). No differences were observed in the blood [HLa] response to repeated bouts of exercise between SEB and DEB. RPE-peripheral (legs, RPE-L) was higher during bout 3 compared with bout 1 (P <0.05) (bout 1: SEB = 11.8 (0.8), DEB = 12.3 (0.2); bout 2: SEB = 12.3 (0.5), DEB = 13.3 (0.4); bout 3: SEB = 13.5 (0.8), DEB = 14.0 (0.7); RPE-central (chest and breathing, RPE-C) was not affected by repeated bouts of exercise, whereas RPE-Overall (RPE-O) was higher during bout 3 compared with bouts 1 and 2 (P < 0.05) (bout 1: SEB = 12.5 (0.2), DEB = 12.3 (0.4); bout 2: SEB = 12.8 (0.4), DEB = 12.7 (0.4); bout 3: SEB = 13.7 (0.7), DEB = 13.2 (0.3)). No interaction for RPE x condition was observed. HR increased with repeated bouts of exercise with HR during exercise bout 3 being higher than HR during exercise bout 1 (164 vs. 156 bpm, P < 0.05). There was also a strong trend for HR during exercise bout 3 to be higher than HR during exercise bout 2 (P < 0.06). A trend for a reduction in VO2 with repeated exercise was observed (P < 0.07), with the reduction apparently related to the SEB condition (P < 0.12 for VO2 x condition). PO and kcal.min-1 were not affected by repeated bouts of exercise. RER decreased significantly with each repeated bout of exercise (from RER = 0.96 to RER = 0.89, P < 0.05) with no difference observed between SEB and DEB. CONCLUSIONS: We conclude that the blood [HLa]-RPE relation is altered by repeated bouts of exercise and that this alteration does not appear to be affected by recovery time between exercise bouts (up to 3.5 h of recovery). These data suggest that, after the first exercise bout, RPE should not be used to produce a specific blood [HLa] on subsequent exercise bouts.     

Postinjury magnesium sulfate treatment is not markedly neuroprotective for striatal medium spiny neurons after perinatal hypoxia/ischemia in the rat

PURPOSE: This experiment examined the influence of acute exercise on anxiety following caffeine-induced elevations in self-rated anxiety. METHODS: Eleven physically active, moderately fit males aged 25.1 +/- 3.8 yr completed four conditions in a within-subject, counterbalanced design involving 60 min of (1) cycling at 60% VO2peak or (2) quiet rest following placebo consumption (800 mg of lactose), as well as (3) cycling at 60% VO2peak and (4) quiet rest following 800 mg of caffeine. State anxiety and blood pressure were assessed 10 min before and 10 and 20 min after the conditions. RESULTS: A main effect for drug (caffeine vs placebo) determined by repeated measures ANOVA, (F(1,8) = 9.77; P = 0.01), indicated that state anxiety was elevated by caffeine. Drug effects were not obtained for blood pressure. Experimental hypotheses were tested by drug-by-condition (exercise vs quiet rest)-by-time (10 and 20 min postcondition) repeated measures ANOVA of change scores from the precondition baseline. A main effect for drug (F(1,8) = 5.81; P = 0.043) indicated that reductions in state anxiety were larger after caffeine ingestion. A condition-by-time effect (F(1,8) = 5.02; P = 0.055) indicated greater reductions in state anxiety 20 min after exercise compared with quiet rest. A condition effect for systolic blood pressure (F(1,10) = 4.56; P = 0.058) and condition-by-time interactions for diastolic (F(1,10) = 8.87; P = 0.014) and mean arterial blood pressures (F(1,10) = 8.46; P = 0.016) indicated reductions after exercise but not after quiet rest following both caffeine and placebo. CONCLUSIONS: We conclude that exercise can reduce anxiety elevated by a high dose of caffeine.     

Effects of high-intensity intermittent swimming on glucose transport in rat epitrochlearis muscle

Recently (K. Kawanaka, I. Tabata, and M. Higuchi. J. Appl. Physiol. 83: 429-433, 1997), we demonstrated that glucose transport activity after repeated 10-s-long in vitro tetani in rat epitrochlearis (Epi) muscle was negatively correlated with the postcontraction muscle glycogen concentration. Therefore, we examined whether high-intensity intermittent swimming, which depletes muscle glycogen to a lower level than that observed after ten 10-s-long in vitro tetani, elicits higher glucose transport than that observed after ten 10-s-long in vitro tetani, which has been regarded as the exercise-induced maximal stimulus for glucose transport. In male rats, 2-deoxy-D-glucose transport rate in Epi muscle after eight bouts of high-intensity intermittent swimming with a weight equal to 18% of body mass (exercise duration: 20 s, rest duration between exercise bouts: 40 s) was higher than that observed after the ten 10-s-long tetani (2.25 +/- 0.08 vs. 1.02 +/- 0.16 micromol . ml intracellular water-1 . 20 min-1). Muscle glycogen concentration in Epi after eight bouts of high-intensity intermittent swimming was significantly lower than that observed after ten 10-s-long in vitro tetani (7.6 +/- 0.5 vs. 14.8 +/- 1.4 micromol glucose/g muscle). These observations show that the high-intensity intermittent swimming increases glucose transport in rat Epi to a much higher level than that induced by ten 10-s-long in vitro tetani, which has been regarded as the exercise-related maximal stimulus for glucose transport. Furthermore, this finding suggests that the lower muscle glycogen level after high-intensity intermittent swimming than after in vitro tetani may play a role, because there was a significant negative correlation between glucose transport and muscle glycogen concentration in Epi after high-intensity swimming and in vitro tetani.     

Carbohydrate drinks delay fatigue during intermittent, high-intensity cycling in active men and women

The effects of ingesting carbohydrate drinks on fatigue during intermittent, high-intensity cycling in men and women were determined. Physically active but untrained women (n = 7) and men (n = 9) completed one practice trial and two experimental sessions separated by 1 week. Sessions consisted of repeated 1-min cycling bouts on a bicycle ergometer at 120-130% VO2max separated by 3 min rest until fatigue. Carbohydrate (CHO) or placebo (P) beverages (4 ml.kg body weight-1) were ingested immediately before exercise (18% CHO) and every 20 min during exercise (6% CHO). Plasma glucose and insulin were higher, RPE for the legs was lower, and time to fatigue was longer in CHO than P. Men's and women's responses were not different for any variable measured. These data suggest a beneficial role of CHO drinks on performance of intermittent, high-intensity exercise in men and women.     

First total synthesis of ganglioside GT1a alpha

Controversy still exists concerning the potential ergogenic benefit of caffeine (CAF) for exercise performance. The purpose of this study was to compare the effects of CAF ingestion on endurance performance during exercise on a bicycle ergometer at two different intensities, i.e., approximately 10% below and 10% above the anaerobic threshold (AT). Eight untrained males, non-regular consumers of CAF, participated in this study. AT, defined as the intensity (watts) corresponding to a lactate concentration of 4 mM, was determined during an incremental exercise test from rest to exhaustion on an electrically braked cycle ergometer. On the basis of these measurements, the subjects were asked to cycle until exhaustion at two different intensities, i.e., approximately 10% below and 10% above AT. Each intensity was performed twice in a double-blind randomized order by ingesting either CAF (5 mg/kg) or a placebo (PLA) 60 min prior to the test. Venous blood was analyzed for free fatty acid, glucose, and lactate, before, during, and immediately after exercise. Rating of perceived exertion and time to exhaustion were also measured during each trial. There were no differences in free fatty acids or lactate levels between CAF and PLA during and immediately after exercise for either intensity. Immediately after exercise glucose increased in the CAF trial at both intensities. Rating of perceived exertion was significantly lower (CAF = 14.1 +/- 2.5 vs PLA = 16.6 +/- 2.4) and time to exhaustion was significantly higher (CAF = 46.54 +/- 8.05) min vs PLA = 32.42 +/- 14.81 min) during exercise below AT with CAF. However, there was no effect of CAF treatment on rating of perceived exertion (CAF = 18.0 +/- 2.7 vs PLA = 17.6 +/- 2.3) and time to exhaustion (CAF = 18.45 +/- 7.28 min vs PLA = 19.17 +/- 4.37 min) during exercise above AT. We conclude that in untrained subjects caffeine can improve endurance performance during prolonged exercise performed below AT and that the decrease of perceived exertion can be involved in this process.     

Human muscle glycogen metabolism during exercise. Effect of carbohydrate supplementation

Carbohydrate (CHO) ingestion during exercise, in the form of CHO-electrolyte beverages, leads to performance benefits during prolonged submaximal and variable intensity exercise. However, the mechanism underlying this ergogenic effect is less clear. Euglycaemia and oxidation of blood glucose at high rates late in exercise and a decreased rate of muscle glycogen utilisation (i.e. glycogen 'sparing') have been proposed as possible mechanisms underlying the ergogenic effect of CHO ingestion. The prevalence of one or the other mechanism depends on factors such as the type and intensity of exercise, amount, type and timing of CHO ingestion, and pre-exercise nutritional and training status of study participants. The type and intensity of exercise and the effect of these on blood glucose, plasma insulin and catecholamine levels, may play a major role in determining the rate of muscle glycogen utilisation when CHO is ingested during exercise. The ingestion of CHO (except fructose) at a rate of > 45 g/h, accompanied by a significant increase in plasma insulin levels, could lead to decreased muscle glycogen utilisation (particularly in type I fibres) during exercise. Endurance training and alterations in pre-exercise muscle glycogen levels do not seem to affect exogenous glucose oxidation during submaximal exercise. Thus, at least during low intensity or intermittent exercise, CHO ingestion could result in reduced muscle glycogen utilisation in well trained individuals with high resting muscle glycogen levels. Further research needs to concentrate on factors that regulate glucose uptake and energy metabolism in different types of muscle fibres during exercise with and without CHO ingestion.     

Extended visual fixation in young infants: look distributions, heart rate changes, and attention

Feeding a high-carbohydrate (CHO) diet and administration of alkalinizing agents have both been shown to improve performance in high-intensity exercise. The effect of these treatments in combination was investigated in the present study. Six healthy male subjects exercised to exhaustion on an electrically braked cycle ergometer at a power output equivalent to 100% of their maximum oxygen uptake (VO2,max) on four separate occasions. Each subject consumed either a diet with the same composition as his normal diet (termed the experimental normal (N) diet; 54 +/- 7% CHO, 13 +/- 2% protein, 33 +/- 7% fat) or a high-CHO diet (81 +/- 2% CHO, 13 +/- 2% protein, 6 +/- 1% fat) that had the same energy and protein content for the 3 days prior to the exercise tests. Subjects then ingested either a placebo (CaCO3) or trisodium citrate (0.3 g (kg body mass)-1) 3 h before exercise. Time to fatigue was not different between experimental conditions. Consumption of the high-CHO diet had no effect on blood acid-base status, but the ingestion of sodium citrate induced a mild metabolic alkalosis after both the N diet and the high-CHO diet. This alkalinizing effect was also evident after exercise, since blood pH, plasma bicarbonate and blood base excess were higher (P < 0.05) after the ingestion of sodium citrate than under the placebo conditions. The changes in blood lactate, pyruvate and glucose and plasma glycerol after exercise were similar for all experimental conditions. Blood lactate, glucose and pyruvate and plasma glycerol concentrations increased from resting values (P < 0.01) following exercise but this increase was similar under all experimental conditions. These data demonstrate that when the energy and protein content of the diets is the same, exercise capacity and the metabolic response to intense exercise are similar following consumption either of a high-CHO diet or a more normal diet. Acute ingestion of sodium citrate prior to exercise resulted in a reduction in post-exercise acidosis despite a blood lactate concentration that was similar to that observed after the ingestion of a placebo, but did not affect exercise performance under the conditions of this study.     

The acute reversal of a diet-induced metabolic acidosis does not restore endurance capacity during high-intensity exercise in man

The present experiment was designed to investigate whether a diet-induced metabolic acidosis was a major factor in the earlier onset of fatigue during high-intensity exercise. Six healthy males cycled to exhaustion at a workload equivalent to 95 percent of maximum oxygen uptake on four separate occasions. Exercise tests were performed after an overnight fast and each test was preceded by one of four experimental conditions. Two experimental diets were designed, either to replicate each subject's own normal diet [N diet, mean (SD) daily energy intake (E) = 13 (0.7) MJ, 14.5 (0.8) percent protein (Pro), 37.5 (2.2) percent fat (Fat) and 47.5 (2.1) percent carbohydrate (CHO)], or a low-carbohydrate diet [E = 12.6 (0.8) MJ, 33.6 (1.3) percent Pro, 64.4 (1.5) percent Fat and 2.2 (0.4) percent CHO]. These diets were prepared and consumed within the department over a 3-day period. Over a 3-period prior to the exercise trial subjects ingested either NaHCO(3) or CaCO(3) (3.6 and 3.0 mmol*kg body mass), thus giving four experimental conditions: N diet and treatment, N diet and placebo, low-CHO diet and treatment and low-CHO diet and placebo. Treatments were assigned using a randomised protocol. Arterialised venous blood samples were taken for the determination of acid-base status and metabolite concentrations at rest prior to exercise and at intervals for 30 min following exhaustion. Consumption of the low-CHO diet induced a mild metabolic acidosis which was reversed by the ingestion of NaHCO(3). Blood pH, bicarbonate (HCO-(3)) and base excess (BE) were higher following NaHCO(3) ingestion after the normal diet than all of the other experimental conditions (P <0.01). Exercise time following the low-CHO diet was less than on the normal diet conditions (P <0.05): bicarbonate ingestion had no effect on exercise time on either of the diet conditions. Post-exercise blood pH, HCO-(3); and BE were higher following the ingestion of NaHCO(3) irrespective of the pre-exercise diet (P <0.05). Blood lactate concentration was higher 2 min after exercise following the N diet with NaHCO(3) when compared to the low-CHO diets with either NaHCO(3) or placebo (P <0.05). Plasma ammonia accumulation was not significantly different between experimental conditions. These data confirm previous data showing that the ingestion of a low-CHO diet reduces the capacity to perform high-intensity exercise, but it appears that the metabolic acidosis induced by the low-CHO diet is not the cause of the reduced exercise capacity observed during high-intensity exercise under these conditions.     

bcl-2 expression in plasma cells from neoplastic gammopathies and reactive plasmacytosis: a comparative study

OBJECTIVE: To review and summarize the current data on oral creatine supplementation regarding its potential efficacy in athletic performance, mechanism of action, and metabolism. DATA SOURCES AND STUDY SELECTION: Medline was searched using terms relating creatine supplementation to athletic performance. Studies that evaluated the effects of oral creatine supplementation on exercise performance in humans were selected for inclusion. Selected studies on muscle metabolism and exercise physiology were included if they provided useful information relative to creatine. Additional references were reviewed from the bibliographies of selected studies. DATA EXTRACTION AND SYNTHESIS: To summarize efficacy, extracted data were listed in table format, grouping studies together by type of activity and efficacy on performance. Whenever possible, the effect of creatine supplementation was quantified. Proposed explanations for creatine's efficacy or lack thereof in a particular type of activity were formulated. CONCLUSIONS: In laboratory settings, creatine supplementation is ergogenic in repeated 6-30-second bouts of maxima stationary cycling sprints. The data on a single sprint or first-bout sprint of any kind are inconsistent. The data regarding creatine's ergogenic effects on mass-dependent activities, such as running and swimming, are not convincing, perhaps because of the side effect of weight gain from water retention. Studies on weight lifting suggest that creatine improves strength possibly by increasing myofibrillar protein synthesis however, more study is needed to prove this. No ergogenic effects on submaximal or endurance exercise are evident Individual response to creatine supplementation can vary greatly.     

Determination of aspartame and its major decomposition products in foods

When exercise to exhaustion is performed using at least two different intensities, work to fatigue (Wlim) can be expressed as a linear function of time to fatigue (Tlim). Whereas the slope of this function is related to endurance ability, the y-intercept is associated with the potential to perform high intensity interval exercise. The purpose of the present investigation was to determine the influence of 8-wk intermittent high-intensity exercise training on the y-intercept derived from the Wlim-Tlim relationship. Eight healthy, untrained male students (19.1 +/- 0.6 yr) completed five 60-s bouts of maximal exercise on the cycle ergometer, three times a week, for 8 wk. Seven controls avoided regular activity for the same period. Prior to and immediately following the training period, the Wlim-Tlim relationship, VO2max, and total work completed in five 60-s exercise bouts on the cycle ergometer were determined. Correlational analysis established relationships between the y-intercept and total work accomplished in the interval test pre- (r = 0.90; P < 0.01; N = 15) and post-training (r = 0.92; P < 0.01; N = 15), confirming that the y-intercept is related to the ability to perform exercise of this nature. Moreover, the "anaerobic" energy yield, calculated from total work and oxygen consumed during the interval exercise, was also related to the y-intercept (r = 0.78; P < 0.01). Interval training significantly increased both the y-intercept (P = 0.0015) and total work accomplished in the interval test (P = 0.001), while the slope of the Wlim-Tlim relationship (critical power) remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship of blood pressure, heart rate and behavioral mood state to norepinephrine kinetics in younger and older men following caffeine ingestion

OBJECTIVE: To examine age-related differences in blood pressure, heart rate, behavioral mood state and norepinephrine kinetics after caffeine ingestion in younger and older men. DESIGN: Placebo-controlled, double-blind study. SETTING: General Clinical Research Center, University of Vermont. SUBJECTS: 10 older (O) (65-80 y) and 10 younger (Y) (19-26 y) healthy men who were moderate consumers of caffeine (Y= 126+/-30 mg/d; O = 160 44 mg/d:NS; mean +/- s.e.m.). INTERVENTION: All volunteers were characterized for fasting plasma glucose, insulin and caffeine levels, body composition, anthropometry, physical activity, and energy intake. Before and after placebo and caffeine ingestion (5 mg/kg fat-free mass) test days, the following variables were measured in all subjects: heart rate, blood pressure, mood state, and norepinephrine concentrations (NEconc), appearance (NEapp) and clearance (NEcl). MAIN OUTCOME MEASURES: Systolic and diastolic blood pressure, heart rate, mood state, and norepinephrine kinetic responses to placebo and caffeine ingestion. RESULTS: Following caffeine ingestion, plasma caffeine levels were similar in Y and O men. Systolic (SBP) and diastolic (DBP) blood pressure increased significantly (P < 0.01) from baseline by 9% (130+/-6 vs 142+/-6 mmHg) and 3% (75+/-3 vs 77+/-3 mmHg), respectively, in O men following caffeine ingestion, but remained unchanged in Y men. Self-reported feelings of tension (P < 0.05) and anger (P = 0.06) decreased in O men, while anger tended to increase in Y men (P < 0.06) following caffeine ingestion. Heart rates in both groups were unaltered following caffeine ingestion. No differences were noted at baseline between O and Y men for NEconc, NEapp and NEcl. After caffeine ingestion, NEconc were significantly greater in O than Y men, whereas NEapp and NEcl rates did not differ from baseline in either group. Blood pressure and subjective mood state effects of caffeine were not related to changes in norepinephrine kinetics. CONCLUSION: Age may play a role in augmenting blood pressure response and reducing subjective feelings of anger and tension following caffeine ingestion, suggesting that the elderly are more reactive to the pressor and less sensitive to the subjective effects of the drug. These effects do not appear to be mediated by changes in sympathetic nervous system activity.     

Thermoregulatory effects of caffeine ingestion during submaximal exercise in men

BACKGROUND: The exclusive effect of caffeine ingestion on exercise thermoregulation is unclear; data indicate that caffeine may have a positive effect, a negative effect, or no effect. METHODS: Rectal (TRE) and mean skin (TSK) temperatures, skin heat conductance (HSK), and sweat rate (MSW) were measured during 30 min of rest and subsequent 70 min of submaximal cycle-ergometer exercise (67% VO2PEAK) in 11 aerobically conditioned men (mean +/- SD 29 +/- 6 yr, 49 +/- 6 mL x min(-1) x kg(-1) VO2PEAK) under two conditions: a caffeine (10 mg x kg(-1) ingestion (CI) session and a noncaffeine ingestion (NCI) control session. RESULTS: There were no significant differences in physiological or thermoregulatory parameters during exercise: X (+/-SE) end exercise levels for the NCI and CI sessions, respectively, were VO2 = 2.50 +/- 0.09 vs. 2.55 +/- 0.09 L x min(-1); heart rate = 145 +/- 7 vs. 145 +/- 5 bpm; HSK = 30 +/- 3 vs. 28 +/- 3 kcal x m(-2) x h(-1) x degrees C(-1); MSW = 393 +/- 35 vs. 378 +/- 36 g x m(-2) x h(-1); and TRE = 38.3 +/- 0.2 vs. 38.4 +/- 0.1 degrees C. Control TSK was lower than that for CI by 0.4 to 0.5 degrees C at rest and during exercise. CONCLUSION: Ingestion of a high level (10 mg x kg(-1) of caffeine has no effect on skin heat conductance, sweating, or the rate of increase and final level of rectal temperature during moderate, submaximal leg exercise.     

Effect of carbohydrate ingestion on adipose tissue lipolysis during long-lasting exercise in trained men

To study whether sucrose administration acts on lipid mobilization during prolonged exercise, we used subcutaneous abdominal adipose tissue microdialysis in eight well-trained subjects submitted at random to two 100-min exercises (50% maximal aerobic power) on separate days. After 50 min of exercise, the subjects ingested either a sucrose solution (0.75 g/kg body wt) or water. By using a microdialysis probe, dialysate was obtained every 10 min from the subjects at rest, during exercise, and during a 30-min recovery period. During exercise without sucrose, plasma and dialysate glycerol increased significantly. With sucrose, the response was significantly lower for dialysate glycerol (P < 0.05). Plasma free fatty acid level was lower after sucrose than after water ingestion (P < 0.05). With water ingestion, plasma catecholamines increased significantly, whereas insulin fell (P < 0.05). With sucrose ingestion, the epinephrine response was blunted, whereas the insulin level was significantly increased. In conclusion, the use of adipose tissue microdialysis directly supports a lower lipid mobilization during exercise when sucrose is supplied, which confirms that the availability of carbohydrate influences lipid mobilization.     

Effect of carbohydrate ingestion on sprint performance following continuous and intermittent exercise

PURPOSE: This investigation was conducted to study the effects on sprint performance of glucose and fructose ingestion during a 15-min rest period half way through 90 min of continuous and intermittent exercise. On three occasions, eight subjects cycled at 76 +/- 2% VO2max for 90 min (continuous trials: CON trials) with a 15-min half-time break. METHODS: On another three occasions, they cycled for 90 min between moderate (65% VO2max) and high (100% VO2max) intensity (intermittent trials: INT trials) with the same half-time. In both trials, 90-min exercise was followed by a 40-s Wingate test to evaluate remaining sprint capacity. During half-time, they consumed either 20% glucose polymer (G), 20% fructose (F) or sweet placebo (P). Ingestion of G maintained plasma glucose levels, carbohydrate oxidation rate and lower value of ratings of perceived exertion (RPE) in both trials and indicated higher sprint performance compared with P (mean power of CON trials: 614.3 +/- 23.3 W vs 574.0 +/- 22.7 W, P < 0.001, INT trials: 629.5 +/- 27.6 W vs 596.3 +/- 25.5 W, P < 0.01). RESULTS: Ingestion of F showed similar effect in CON trials (603.8 +/- 26.1 W vs 574.0 +/- 22.7 W, P < 0.01) but had no positive effect in INT trials. Additionally, mean power of G was higher than F (629.5 +/- 27.6 W vs 598.4 +/- 34.2 W, P < 0.01) in INT trials. CONCLUSIONS: These results indicated that ingestion of G during half-time of 90-min exercise could maintain carbohydrate utilization and improve sprint performance in both CON and INT trials.