Effects of acute exercise on the soleus H-reflex and self-reported anxiety after caffeine ingestion

The effects of moderate intensity cycling exercise on the soleus H-reflex and state anxiety were examined among 16 individuals whose anxiety was experimentally manipulated by consumption of a large dose of caffeine. The soleus H-reflex and state anxiety were measured before and 1 h after consuming caffeine or placebo and then again 10 min after 30 min of either cycling at an intensity of 60% VO(2peak) or quiet rest. We found that (1) caffeine consumption did not influence the amplitude of the soleus H-reflex, but it did increase state anxiety; (2) acute exercise reduced the soleus H-reflex after consumption of either caffeine or placebo, but it reduced state anxiety only after consumption of caffeine; and (3) there was no evidence of a relationship between changes in the soleus H-reflex and state anxiety. Exercise-induced anxiolysis does not appear to underlie the postexercise reduction of the soleus H-reflex.     

The acute effects of exercise and glucose ingestion on circulating angiotensin-converting enzyme in humans

Angiotensin-converting enzyme (ACE) activity has been suggested as a determinant of some exercise phenotypes via some studies that have associated the ACE gene with exercise performance, although several studies provide conflicting evidence regarding the influence of the ACE gene. The relationships between ACE phenotype (ACE activity) and various exercise parameters should also be examined. An early step in this process is to determine whether common environmental stimuli such as exercise and diet have acute effects on ACE activity. In this study, the acute effects of aerobic exercise, resistance exercise and glucose ingestion on circulating ACE activity were examined. On three separate occasions, 20 healthy adult volunteers (9 female and 11 male) performed 20 min of submaximal cycle exercise at 70–80% of maximal heart rate, four sets of ten repetitions of unilateral leg extension resistance exercise at ten-repetition maximum load, or ingested 1 g kg^–1 glucose. Circulating ACE activity was assessed for 1 h after each intervention using a modified fluorometric method. Pre-intervention ACE activity remained remarkably stable across test days (difference 1.8%). Furthermore, there was no significant change in circulating ACE activity following any of the interventions (difference from pre-intervention values 6.8% when unadjusted for plasma volume changes, 4.5% when adjusted for plasma volume changes). These results suggest that acute exercise and glucose ingestion interventions as used here do not affect circulating ACE activity. These findings are an early step in illuminating the relationships between ACE activity and various exercise parameters.     

Benefits of caffeine ingestion on sprint performance in trained and untrained swimmers

Summary The influence of specific training on benefits from caffeine (Caf) ingestion was examined during a sprint test in a group of highly trained swimmers (T) and compared with the response of a group of untrained occasional swimmers (UT). Seven T and seven UT subjects swam freestyle two randomly assigned 2 × 100 m distances, at maximal speed and separated by 20 min of passive recovery, once after Caf (250 mg) and once after placebo (Pla) ingestion. Anaerobic capacity was assessed by the mean velocity (meters per second) during each 100 m and blood was sampled from the fingertip just before and 1, 3, 5, 7, and 9 min after each 100 m for resting and maximal blood lactate concentration ([1a^–]_{b, max}) determination. The [[1a^–]_{b, max} was significantly enhanced by Caf in both T and UT subjects (P<0.01). However, only T subjects exhibited significant improvement in their swimming velocity (P<0.01) after Caf or any significant impairment during the second 100 m. In light of these results, it appears that specific training is necessary to benefit from the metabolic adaptations induced by Caf during supramaximal exercise requiring a high anaerobic capacity.     

Cardiac vagal tone, exercise performance and the effect of respiratory training

Heart rate variability (HRV) at rest and heart rate recovery after exercise reflect cardiac vagal activity. The aim of this study was to determine whether increasing HRV during involuntary respiratory training induced by rebreathing air using a Hepburn heart and lung exerciser (HHALE) could, like exercise, improve vagal tone. Eighteen subjects (36–88 years) underwent a 6-week control period, then a 6-week training period with the HHALE following which half continued training for 6 weeks and half ceased training. Measurements were made of HRV, work at 60% predicted heart rate max for 15 min, heart rate recovery after exercise, resting blood pressure, heart rate, vital capacity and forced expiratory volume. After the first 6-week HHALE training, there was a significant increase of 13.2±5.7 in the high frequency peak of the power spectrum of HRV at rest, whereas, the low frequency peak decreased. Similarly, exercise performance showed a significant improvement of 0.031±0.012 J per heartbeat from a pre-training 0.128±0.022. Also, heart rate recovery after exercise significantly faster (drop in the first 20 s improving by 3.3±1.5 beats from a pre-training 12.9±1.6). The subgroup that continued training maintained or slightly improved these values. In those that ceased training the speed of heart rate recovery at the end of the exercise test returned to pre-trained levels, whereas, other responses were either maintained or decreased slightly. We conclude that training with the HHALE can, without additional exercise, increase cardiac vagal tone and exercise performance.     

Effect of prior ingestion of glucose or fructose on the performance of exercise of intermediate duration

The metabolic responses induced by the ingestion of a beverage containing glucose (G), fructose (F) or placebo (W) 30 min before exercise of high intensity and intermediate duration have been investigated; in these conditions the energy processes are mostly dependent on aerobic reactions. A group of 11 male recreational sportsmen ran on a treadmill, at an intensity corresponding to 82% of peak oxygen consumption, until exhaustion on three different occasions (after ingestion of a beverage containing 75 g of G, 75 g of F or W). Plasma glucose, insulin, and lactic acid concentrations were determined just prior to the ingestion of the beverages, 30 min afterwards and 10 and 30 min after completion of the exercise. The mean endurance time was 644 (SD 261) s after the ingestion of G, 611 (SD 227) s after the ingestion of F and 584 (SD 189) s after the ingestion of the W (P < 0.05 between G and W). No differences in the oxygen uptake, respiratory quotient or lactate concentrations between the three trials were observed. Both plasma glucose and insulin concentrations determined in samples obtained immediately before the onset of exercise were higher when G was ingested than when F (P < 0.05 andP < 0.05, respectively) or W (P < 0.001 and P < 0.005, respectively) were ingested. These findings would suggest that the ingestion of G prior to an effort of intermediate duration may improve physical performance.     

Effect of altered pre-exercise carbohydrate availability on selection and perception of effort during prolonged cycling

This study assessed the effect of altered carbohydrate (CHO) availability on self-selected work rate during prolonged time-trial cycling. Eight endurance-trained men undertook two experimental cycling time-trials after glycogen-depleting exercise and 2 days of: (a) high (9.3 ± 0 g CHO kg⁻¹ day⁻¹) (HC) and (b) low CHO intakes (0.6 ± 0.1 g CHO kg⁻¹ day⁻¹) (LC), via a double-blinded crossover design. All feedback regarding performance was removed during both exercise trials. Self-selected external power output was not different during the first 2 h of exercise between experimental conditions (P > 0.05), despite reported sensations of increased tiredness before and during exercise, significantly reduced whole body CHO oxidation (P < 0.05), plasma lactate concentrations (P < 0.05) and earlier onset of fatigue during exercise in LC versus HC. Perceived exertion was not different throughout exercise between conditions (P > 0.05). Mean power output declined significantly in LC versus HC (P < 0.05) after ∼ 2 h of exercise, and was associated with significant reductions in cadence, heart rate and plasma glucose concentration (P < 0.05). These results demonstrate that when compared with time-trial cycling performed after a HC diet, reduced CHO availability does not initially alter self-selected work rate in endurance athletes who are deceived of their CHO status prior to exercise. This finding suggests that reduced work rate during exercise following lowered CHO intake may, in part, be a consequence of the subject’s awareness of dietary CHO restriction rather than solely a physiologically mediated action. Further research is required to distinguish the influence of circulating glucose and peripheral glycogen availability on pacing strategy during prolonged exercise.     

Effect of prolonged physical exercise on the fibrinolytic system

Summary The effect of a test marathon race on plasma fibrinolytic activity (FA) was studied in 16 endurance athletes before, immediately after, 3 h, and 31 h after the run. Tissue plasminogen activator (t-PA) activity increased about 31-fold immediately after the run. Similar increases were found in t-PA antigen concentration. Plasminogen activator inhibitor (PAI) was not detectable immediately after the race and was significantly decreased 3 h (P < 0.05) and 31 h (P < 0.01) later. B_15–42 peptide increased by 0.63 pmol · ml^–1 (P<0.001),d-dimer by 68.3 ng · ml^–1 (P< 0.05). Euglobulin lysis time (ELT) was reduced from 109 to 18 min (P<0.001). The increased t-PA activity and t-PA antigen concentration disappeared in the course of the first 3 h after exertion. ELT also reached its pre-exercise levels at this time. Thirty-one hours after the race ELT and t-PA antigen levels were slightly but significantly reduced (P<0.05), whereas B_15–42 peptide remained increased (P<0.05). t-PA activity was unchanged compared with pre-exercise values. It seems that the exercise-induced FA is mainly caused by the marked increase of t-PA antigen and t-PA activity.     

Leptin response to acute prolonged exercise after training in rowers

The aim of this study was to determine if there is a training effect on leptin levels at rest or after prolonged exercise during an 8-month training season of rowers. Eleven trained rowers were evaluated at three sessions (control, early and late) during the season. At the early and late sessions, leptin and insulin concentrations were measured before and after 90 min of rowing exercise (70–75% maximal oxygen consumption, O₂max), 120 min and 24 h afterwards. Anthropometrics data were collected at each session. Energy balance was determined on the days of exercise sessions. Resting leptin levels were not modified over the season and were in correlation with weight and body fat (P<0.05). At exercise sessions, a delayed reducing effect of acute exercise on leptin levels appeared (P<0.01 compared to pre-exercise). After 24 h of recovery, leptin levels remained lower at early (P<0.001) but not at late sessions, and a training effect appeared between early and late sessions (P<0.001). Leptin levels were correlated with energy balance at early and late sessions (P<0.05). At the two training sessions, insulin levels were decreased immediately post-exercise and at 120 min of recovery compared to pre-exercise (P<0.01 and P<0.001 respectively for the two sessions). A training effect on insulin levels appeared at 24 h of recovery (P<0.05 between early and late sessions). We concluded that rowing training over a season did not alter resting leptin levels but it attenuated the exercise-induced reduction in leptin. This could be attributed to an alteration in energy balance, although an influence of training on insulin may also be involved in the leptin response to acute exercise.An erratum to this article can be found at     

Effects of caffeine ingestion on endurance racing in heat and humidity

A hot and humid environment can be detrimental to race performance. Caffeine, on the other hand, has been shown to be an ergogenic aid for improving endurance performance. To examine the influence of caffeine ingestion on race performance during high heat stress, seven endurance trained competitive road racers aged between 23 and 51 years (five men, two women) performed three maximal effort 21-km road races outdoors in hot and humid conditions. The caffeine dose, randomly assigned in a double-blind fashion, consisted of either 0, 5, or 9 mg · kg⁻¹ body mass. During each run, the subjects were allowed to drink waterad libitum at each 5-km point. Blood samples were obtained immediately before and after each run and analysed for changes in concentrations of Na⁺, K⁺, glucose, lactate, and hematocrit. Pre and postrun data were also collected for body mass and tympanic membrane temperature. Race times were not significantly different among the races or caffeine doses, with the average times within 1.1% of each other. In addition, none of the other variables measured varied significantly among the races or caffeine doses. In summary, caffeine intake did not affect race performance. Therefore it was concluded from our study that caffeine is not of ergogenic benefit in endurance races during high heat stress.     

Dynamic changes of deleted mitochondrial DNA in human leucocytes after endurance exercise

We examined the time course of the appearance and disappearance of deleted mitochondrial DNA (mtDNA) in human leucocytes after endurance exercise. Five untrained healthy females [aged 20.2 (0.4) years] exercised for 30 min at 50–60 W at 60 rpm on a cycle ergometer for 2 or 3 consecutive days. Blood samples were collected immediately before exercise, and on three occasions after the end of the last exercise bout. Levels of mtDNA were analyzed using the nested polymerase chain reaction method. Prior to exercise, a common mtDNA deletion was identified in all subjects. This common deletion was again identified in all subjects 1 day after completion of the exercise regime. However, mtDNA with this common deletion was found to have disappeared 2 days after exercise in three subjects, and after 4 days in the other two subjects. The deletion then reappeared 5 or 6 days after the final exercise bout in three of the five subjects. These findings demonstrate that a common deletion in leucocytes disappears over a period of several days after endurance exercise and reappears a number of days thereafter. Therefore, the status of the appearance and disappearance of common mtDNA deletion in leucocytes is highly dynamic. Electronic Publication     

Effects of exercise on vasodilatory capacity in endurance- and resistance-trained men

To determine vasodilatory responsiveness we measured forearm blood flow (FBF) following reactive hyperemia (RH), prior to and following a bout of maximal aerobic exercise in endurance- (n=14) and resistance-trained men (n=10). Both groups were similar in height, body mass, and percentage body fat. Using strain-gauge plethysmography, resting FBF was higher in the resistance-trained group [4.82 (0.84) vs 3.33 (1.17) ml min⁻¹ 100 ml⁻¹ of tissue; P<0.05]. However, the resistance-trained group had a 17%–29% lower pre-exercise FBF response to RH for the first 45 s (P<0.05). Following the maximal exercise bout there were no group differences in FBF. Post-exercise FBF was higher compared to pre-exercise values in both the endurance- (P<0.001) and resistance- (P<0.01) trained groups. Endurance-trained men appear to have a greater peak vasodilatory capacity compared to resistance-trained men, and acute maximal exercise increased the vasodilatory capacity in both groups. Acute exercise also equalized the peak vasodilatory response between the endurance- and resistance-trained groups, suggesting the potential for flow-mediated vasodilatation was similar for both groups. Electronic Publication     

Glucose ingestion before and during exercise does not enhance performance of daily repeated endurance exercise

Summary The effect of glucose (Glc) ingestion before and during daily, repeated, prolonged exercise on metabolism and performance was tested. Seven young, healthy males performed cycling exercise in two series, with 1 month interval. Each exercise series consisted of 1 h/day on 3 successive days. On the 3rd day, exercise was continued until exhaustion. The intensity was 73.4 (7.7) % [mean (SD)] of maximal oxygen uptake ( ). Glucose (Glc) or placebo (P) drink was ingested 15 min before the start, and at 15 and 45 min of each daily exercise. The total amount of Glc ingested was 43.1 (4.2) g. During exercise, blood Glc concentrations were significantly higher (P<0.05) when Glc was ingested than when P was ingested [Glc 5.14 (0.32) and P 4.12 (4.17) mmol · 1^–1 at exhaustion]. However, Glc ingestion did not improve performance time to exhaustion [Glc 92.05 (29.55) and P 98.07 (27.33) min]. Free fatty acid concentrations were significantly lower when Glc was ingested than when P was ingested [Glc 0.63 (0.21) and P 1.39 (0.46) mmol · l^–1 at exhaustion]. There were no significant differences in exercise heart rate, , respiratory exchange ratio, blood lactate concentrations or rating of perceived exertion between the conditions nor were there any significant differences in these parameters on different days of exercise. It seems that ingestion of small amounts of Glc does not increase the metabolism of carbohydrate or improve the performance of intensive endurance exercise of poorly trained subjects, even when the exercise is repeated daily.     

Effects of L-carnitine supplementation on physical performance and energy metabolism of endurance-trained athletes: a double-blind crossover field study

A double-blind crossover field study was performed to investigate the effects of acute L-carnitine supplementation on metabolism and performance of endurance-trained athletes during and after a marathon run. Seven male subjects were given supplements of 2 g L-carnitine 2 h before the start of a marathon run and again after 20 km of the run. The plasma concentration of metabolites and hormones was analysed 1 h before, immediately after and 1 h after the run, as well as the next morning after the run. In addition, the respiratory exchange ratio (R) was determined before and at the end of the run, and a submaximal performance test was completed on a treadmill the morning after the run. The administration of L-carnitine was associated with a significant increase in the plasma concentration of all analysed carnitine fractions (i.e. free carnitine, short-chain acylcarnitine, long-chain acylcarnitine, total acid soluble carnitine, total carnitine) but caused no significant change in marathon running time, in R, in the plasma concentrations of carbohydrate metabolites (glucose, lactate, pyruvate), of fat metabolites (free fatty acids, glycerol, -hydroxybutyrate), of hormones (insulin, glucagon, cortisol), and of enzyme activities (creatine kinase, lactate dehydrogenase). Moreover, there was no difference in the result of the submaximal performance test the morning after the run. In conclusion, acute administration of L-carnitine did not affect the metabolism or improve the physical performance of the endurance-trained athletes during the run and did not alter their recovery.     

Reduced plasma free fatty acid availability during exercise: effect on gene expression

Endurance exercise transiently increases the mRNA of key regulatory proteins involved in skeletal muscle metabolism. During prolonged exercise and subsequent recovery, circulating plasma fatty acid (FA) concentrations are elevated. The present study therefore aimed to determine the sensitivity of key metabolic genes to FA exposure, assessed in vitro using L6 myocytes and secondly, to measure the expression of these same set of genes in vivo, following a single exercise bout when the post-exercise rise in plasma FA is abolished by acipimox. Initial studies using L6 myotubes demonstrated dose responsive sensitivity for both PDK4 and PGC-1α mRNA to acute FA exposure in vitro. Nine active males performed two trials consisting of 2 h exercise, followed by 2 h of recovery. In one trial, plasma FA availability was reduced by the administration of acipimox (LFA), a pharmacological inhibitor of adipose tissue lipolysis, and in the second trial a placebo was provided (CON). During the exercise bout and during recovery, the rise in plasma FA and glycerol was abolished by acipimox treatment. Following exercise the mRNA abundance of PDK4 and PGC-1α were elevated and unaffected by either acipimox or placebo. Further analysis of skeletal muscle gene expression demonstrated that the CPT I gene was suppressed in both trials, whilst UCP-3 gene was only modestly regulated by exercise alone. Acipimox ingestion did not alter the response for both CPT I and UCP-3. Thus, this study demonstrates that the normal increase in circulating concentrations of FA during the later stages of exercise and subsequent recovery is not required to induce skeletal muscle mRNA expression of several proteins involved in regulating substrate metabolism.     

Metabolic effects of testosterone during prolonged physical exercise and fasting

Summary Previous studies have shown a decrease in plasma testosterone during prolonged physical exercise and 72 h fasting in rats.To determine whether this hormonal change has an influence upon energy metabolism, two experiments were carried out, in which the plasma levels of testosterone were elevated during prolonged physical exercise and fasting in male wistar rats.The effects of acute and chronic increases in the levels of circulating testosterone were studied, on the one hand after human chorionic gonadotropin (H.C.G.) injection, and on the other by prolonged testosterone perfusion with an osmotic minipump. Blood and tissue sampling were performed to evaluate blood glucose, alanine, and lactate, and tissue glycogen. The results in fed and rest control rats showed no changes in blood parameters under the effect of hypertestosteronemia but there was an increase in muscle glycogen after testosterone perfusion.In 72 h fasted rats both types of hypertestosteronemia were associated with a decrease in blood alanine and lactate ranging from 25% to 35%. Only testosterone perfusion was associated with higher concentrations of muscle glycogen.After 7 h of treadmill running, testosterone perfusion and H.C.G. injection induced a 35% decrease in blood alanine and a slight decrease in blood glucose, with no change in other parameters.Whereas an elevation in the level of testosterone can induce muscle glycogen compensation in the fed resting state, it cannot counteract the exhaustion of muscle glycogen during running.     

The critical power model for intermittent exercise

This paper develops and illustrates the critical power model for intermittent work. Model theoretic development reveals that total endurance time is always a step function of one or more of the four independent variables: work interval power output (P _w), rest interval power output (P _r), work interval duration (t _w), and rest interval duration (t _r). Six endurance-trained male athletes recorded their best performances during the season in 3-, 5-, and 10-km races, and performed three different intermittent running tests to exhaustion in random order, recording their total endurance times. These data were used to illustrate the model and compare anaerobic distance capacities () and critical velocities () estimated from each type of exercise. Good fits of the model to data were obtained in all cases: 0.954<R ²<0.999. Critical velocity was found to be significantly less when estimated using an intermittent versus continuous running protocol.     

The effects of two levels of caffeine ingestion on excess postexercise oxygen consumption in untrained women

Summary The effects of two levels of caffeine ingestion (5 mg·kg ^–1, CAF1, and 10 mg·kg ^–1, CAF2) on postexercise oxygen consumption was investigated in six untrained women aged 20.5 (SEM 0.5) years. After a test to determine maximal oxygen consumption (VO_2max) each subject underwent three test sessions at 55% VO_2max either in a control condition (CON) or with the CAF1 or CAF2 dose of caffeine. During exercise, oxygen consumption was found to be significantly higher in the CAM and CAF2 trials, compared to CON (P<0.05). During the hour postexercise, oxygen consumption in CAF1 and CAF2 remained significantly higher than in CON (P<0.05). At all times throughout the exercise, free fatty acid (FFA) concentrations were significantly higher in the caffeine trials than in CON. The FFA concentrations 1 h postexercise (+ 60 min) were further elevated above resting values for all three trials. Caffeine ingestion caused the greatest elevation above resting levels being 1.89 (SEM 0.19) mmol·l^–1 and 1.96 (SEM 0.22) mmol·1^–1 for the CAF1 and CAF2 trials, respectively. This was significantly higher (P<0.0001) than the CON level which was 0.97 (SEM 0.19) mmol·l^–1. Respiratory exchange ratio (R) values became significantly lower (P<0.05) in CAF1 and CAF2 compared to CON at the onset of exercise and continued to decrease during the activity. Throughout the recovery period, R values were significantly lower for both caffeine trials compared to CON. The results of this study would suggest that caffeine is useful in significantly increasing metabolic rate above normal levels in untrained women during, as well as after, exercising at 55% VO_2max.     

The effect of ammonium chloride and sodium bicarbonate ingestion on the physical working capacity at the fatigue threshold

Summary The purpose of this investigation was to examine the effect of ammonium chloride (NH₄Cl) and sodium bicarbonate (NaHCO₃) ingestion on the physical working capacity at the fatigue threshold (PWC_FT). Eighteen adult males (mean age, SD=23, 2 years) volunteered for two experiments (experiment 1,n=9 ; experiment 2,n=9). In both experiments, the subjects orally ingested 0.3 g · kg^–1 body weight of NH₄Cl and NaHCO₃ over a 3-h period in random order on days separated by 72 h or more. In experiment 1, following ingestion of the substance, the subjects performed a discontinuous incremental cycle ergometer test to the onset of PWC_FT which was estimated from integrated electromyography voltages at the vastus lateralis muscle. In experiment 2, the subjects performed a continuous PWC_FT test. The results of these experiments indicated that NH₄Cl and NaHCO₃ ingestion had no significant (P>0.05) effect on PWC_FT (experiment 1: NH₄Cl=257, SD 26 W; NaHCO₃=256, SD 22 W;t=0.06;r=0.866; experiment 2: NH₄Cl=231, 14 W; NaHCO₃=216, 16 W;t=1.78;r=0.857).