Oxidative stress responses in physical education students during 8 weeks aerobic training

AIM: This study aimed to evaluate responses of selected markers of oxidative stress in physical education students during aerobic training. METHODS: Twenty male students were randomly assigned into either a control (mean+/-SD: age 23.5+/-1.4 years, height 1.72+/-0.06 m, body mass 68.9+/-5.8 kg, n=10) or an aerobic training (mean+/-SD: age 23.8+/-1.8 years, height 1.66+/-0.03 m, body mass 65.5+/-4.8 kg, n=10, 3 training sessions per week, 8 weeks, running at 75-80% of HR(max)) group. Plasma samples, collected at rest and after exercise to exhaustion before and after 8 weeks, were analysed for the determination of selected markers of oxidative stress (malondialdehyde MDA, carbonylated proteins CP, and creatine kinase CK). RESULTS: Aerobic training caused a 10% increase in maximal oxygen consumption (VO(2max)) and a 9% increase in exercise time to exhaustion (P<0.05). The aerobic training did not significantly change (P>0.05) MDA and CP levels at rest and after exercise to exhaustion. An exhaustive exercise caused a substantial increase (P<0.05) of CK in both groups independent of treatment and time of measurement. However, aerobic training did not prevent serum CK from increasing after exercise to exhaustion (P>0.05). CONCLUSIONS: It can be concluded that this pattern of moderate aerobic exercise training did not have any effect on oxidative stress levels in moderately trained physical education students, whereas it enhanced their functional performance and aerobic power of these physical education students.     

Hormone and metabolite response to weight-lifting training sessions

Eleven weight-trained athletes (age X +/- SD = 33 +/- 5 yrs, weight = 72 +/- 10 kg) with a maximal performance in bench press at the beginning of the study (116 +/- 19 kg) were studied at rest, after a standardized submaximal training session, and after a maximal session once a month for 4 months to study the blood metabolites and hormonal changes during weight lifting. The submaximal load was six series of eight bench presses at 70% of maximal performance presses, and the maximal load was the maximal number of repetitions at the same work load. The levels of several metabolites (lactate, glycerol, triglycerides, beta-OH-butyrate) and hormones (norepinephrine and epinephrine) increased (P less than 0.05) after submaximal work and more after maximal work. Glucose, FFA, acetoacetate, insulin, testosterone, and cortisol did not change significantly or consistently. Lactate after maximal work was higher after the 4th training month (P less than 0.05). Other variables did not change much with training while the maximal number of repetitions in the last series increased slightly (P less than 0.05). In general, the changes observed were smaller than the ones reported for endurance or interval running, which use larger muscle groups. Nevertheless, weight lifting induced changes in blood metabolites which reflect a mobilization of both carbohydrates and lipids stores for energy.     

Exercise performance in hypoxia after novel erythropoiesis stimulating protein treatment

Maximal aerobic power at high altitude (<4000 m) does not increase with altitude acclimatization. In order to investigate the isolated effects of increased arterial oxygen content (CaO2) on maximal oxygen uptake (VO2max) in hypoxia, we studied 10 subjects during exercise in acute exposure to 12.6% O2 before and after novel erythropoiesis stimulating protein (NESP) induced increases in CaO2. Over a period of 1 month, weekly NESP treatment increased resting hemoglobin (Hb) from 13.8+/-0.9 to 16.2+/-0.5 g/dL, hematocrit from 42.1+/-0.6% to 49.0+/-1.5%, and CaO2 from 189.7+/-3.0 to 218.6+/-5.7 mL/L. At maximal exercise CaO2 was increased from 172.3+/-3.7 to 191.5+/-3.8 mL/L with NESP treatment, and although maximal heart rate was similar in both conditions (178.4+/-2.6 and 180.9+/-2.5 b.p.m.) VO2max remained unaltered, the values being 3.12+/-2.0 and 3.12+/-2.0, before and after NESP treatment, respectively. NESP-injections in human subjects causes Hb and accordingly CaO2 to increase both in normoxia and hypoxia. Despite increases in CaO2 at maximal exercise in hypoxia VO2max is not increased.     

The effects of supplemental carbohydrate ingestion on intermittent isokinetic leg exercise.

BACKGROUND: The purpose of this investigation was to examine the effects of carbohydrate (CHO) supplementation on isokinetic leg extension/flexion exercise performance, blood glucose responses, blood free fatty acid (FFA) responses, and blood lactate (La) responses. METHODS: Eight resistance trained males (mean+/-SEM, age: 23.7+/-1.3 yrs, height: 180.0+/-3.5 cm, bodymass: 94.9+/-4.9 kg) participated in a randomized, double blind protocol with testing sessions separated by 7-d. Subjects were given CHO or placebo (P) while performing 16 sets of 10 repetitions at 120 degrees x s(-1) on a Cybex isokinetic dynamometer. Performance variables measured were; total work (TW), average work (AW), peak torque (PT) and average torque (AT). Plasma glucose (PG), FFA, and La were measured prior to testing (PRE), after set 8 (MID), and 16 (POST). RESULTS: Results indicated that the CHO treatment elicited significantly (p<0.05) more TW (CHO: 41.1+/-3.9 kJ; P: 38.1+/-3.9 kJ) and AW (CHO: 2.6+/-0.2 kJ; P: 2.4+/-0.2 kJ). There were no differences (p<0.05) between treatments for PT of the hamstrings (CHO: 91.6+/-6.5 Nm; P: 87.4+/-8.5 Nm) and quadriceps (CHO: 129.7+/-9.5 Nm; P: 123.0+/-10.6 Nm). The AT of the hamstrings (CHO: 77.8+/-5.2 Nm; P: 75.7+/-8.7 Nm) and quadriceps (CHO: 116.9+/-8.9 Nm; P: 110.0+/-8.5 Nm) were not statistically different (p>0.05) between the treatments. PG was significantly higher at the POST blood draw in the CHO treatment. No significant differences (p>0.05) were observed between the treatments for FFA and La concentrations. CONCLUSIONS: The data from this investigation indicate that the use of CHO supplementation during isokinetic leg exercise allows for the performance of more work.     

Effect of ubidecarenone oral treatment on aerobic power in middle-aged trained subjects

BACKGROUND: Coenzyme Q10 (CoQ10) plays an important role in oxidative mithocondrial phosphorylation and prevents lipid peroxidation in biological membranes. During sustained physical exercise, reactive oxygen species (ROS) production increase through several mechanism; one of them is the purine nucleotide cycle activation by shifting xanthine-dehydrogenase to xanthine-oxidase during AMP breakdown. The aim of this study was to evaluate the effect of CoQ10 treatment on aerobic power. METHODS: Experimental design: according to a single blind study design, 28 health male cyclists were randomized into two groups (CoQ10 or placebo) and remained on treatments for eight weeks; there were 5 drop-outs and only 23 subjects were completely evaluated. Before and at the end of the eight weeks, cyclists underwent cardiopulmonary exercise testing. Measures: a software system performed the necessary calculations to obtain the following parameters: oxygen uptake, CO2 production, minute ventilation, oxygen ventilatory equivalent, carbon dioxide ventilatory equivalent, oxygen pulse. Finally oxygen peak and anaerobic threshold were determined. Moreover blood inosine, hypoxanthine, xanthine, lactate and CoQ10 levels were measured before and immediately after each test. RESULTS: The results of this study showed that at the end of the eight weeks there was no difference between the two groups concerning physiological and metabolic parameters, but muscular exhaustion was reached at higher workloads in the CoQ10 group. CONCLUSIONS: In our experience ubidecarenone oral treatment does not improve aerobic power. The little improvement of tolerance to higher workloads may be due to the antioxidant activity of CoQ10.     

Myocardial perfusion after marathon running

We investigated the effects of acute prolonged exercise (marathon running) on cardiac function and myocardial perfusion. Cardiac dimensions and function were measured in seven endurance-trained men using echocardiography before and repeatedly after marathon (42.2 km) running (at 10 min, 150 min, and 20 h). Myocardial perfusion and perfusion resistance were measured using positron emission tomography and 15O-H2O before and 85-115 min after running. Echocardiographic indices showed only mild and clinically non-significant changes in cardiac function after running. Rate-pressure-corrected basal myocardial perfusion (0.89+/-0.13 vs. 1.20+/-0.32 mL min(-1) g(-1), P=0.04) was increased after running. Also, adenosine-stimulated perfusion tended to be higher (3.67+/-0.81 vs. 4.47+/-0.52 mL min(-1) g(-1), P=0.12) and perfusion resistance during adenosine stimulation was significantly lower after running (26+/-6 vs. 18+/-3 mmHg min g mL(-1), P=0.03). Plasma free fatty acid (FFA) concentration was significantly increased after running. These results show that marathon running does not cause marked changes in cardiac function in healthy men. Basal perfusion was increased after exercise, probably reflecting changes in fuel preferences to increased use of FFAs. Strenuous exercise also seems to enhance coronary reactivity, which could thereby serve as a protective mechanism to vascular events after exercise.     

Metabolic demands of intense aerobic interval training in competitive cyclists

PURPOSE: To investigate the metabolic demands of a single session of intense aerobic interval training in highly trained competitive endurance cyclists. METHODS: Seven cyclists (peak O2 uptake [VO2 peak] 5.14 +/- 0.23 L x min(-1), mean +/-SD) performed 8 x 5 min work bouts at 86 +/- 2% of VO2 peak with 60-s recovery. Muscle biopsies were taken from the vastus lateralis immediately before and after the training session, whereas pulmonary gas exchange and venous blood were sampled at regular intervals throughout exercise. RESULTS: Muscle glycogen concentration decreased from 501 +/- 91 to 243 +/- 51 mmol x kg (-1) dry mass (P < 0.01). High rates of total carbohydrate oxidation were maintained throughout exercise (340 micromol.kg(-1).min(-1)), whereas fat oxidation increased from 16 +/- 8 during the first to 25 +/- 13 micromol x kg(-1) x min(-1) during the seventh work bout (P < 0.05). Blood lactate concentration remained between 5 and 6 mM throughout exercise, whereas muscle lactate increased from 6 +/- 1 at rest to 32 +/- 12 mmol x kg(-1) d.m. immediately after the training session (P < 0.01). Although muscle pH decreased from 7.09 +/- 0.06 at rest to 7.01 +/- 0.03 at the end of the session (P < 0.01), blood pH was similar after the first and seventh work bouts (7.34). Arterial oxygen saturation (% S(P)O2) fell to 95.6 +/- 1% during the first work bout and remained at 94% throughout exercise: the 60-s rest intervals were adequate to restore % S(P)O2) to 97%. CONCLUSION: Highly trained cyclists are able to sustain high steady state aerobic power outputs that are associated with high rates of glycogenolysis and total energy expenditure similar to those experienced during a 60-min competitive ride.     

The effect of prolonged intermittent exercise, combined with food deprivation, on plasma metabolite concentration.

To examine the effect of continuous fasting combined with prolonged, intermittent exercise on glucose homeostasis, 16 endurance-trained subjects, ranging in age from 18-21 years, were completely deprived of food during 81 h of field maneuvers. Water was supplied to avoid dehydration. Participants marched 10 h each night at an estimated intensity of 35-45% of mean VO2 max covering a total distance of 105 km, and had a relative rest during day time. Blood was sampled prior to the beginning of the march, at the end of 81 h, and after 24 h of recovery. Samples were analyzed for plasma glucose, insulin, alanine, free fatty acids (FFA), and 3-hydroxybutyrate (3-HB). Body weight decreased from a mean (+/- S.E.M.) of 73.0 +/- 0.6 kg at pre-march to 66.5 +/- 0.6 kg at 81 h of fasting (p less than 0.05), and remained unchanged at 24 h after march termination. Glucose, insulin, and alanine decreased, whereas FFA and 3-HB increased significantly at 81 h fast (p less than 0.05). Within 24 h of recovery all parameters changed significantly (p less than 0.05), approaching baseline values. The results indicate that in trained individuals under extreme survival conditions, as in the present study, blood glucose is maintained above hypoglycemic levels at the expense of fat and fat-derived substrates that become the main energy sources utilized.     

Creatine enhances oxygen uptake and performance during alternating intensity exercise

PURPOSE: The main purpose of the present study was to measure the total oxygen consumed, accumulation of blood metabolites, and performance during alternating intensity exercise before and after a period of creatine (Cr) loading in well-trained humans. METHODS: Fourteen males were randomly assigned to two groups of seven males and were tested before and after 5 d of placebo (PL) or Cr monohydrate (CR) loading (20 g x d(-1)). Oxygen uptake was measured using a breath-by-breath system during bicycle exercise alternating every 3 min between bouts at 30%(-30%) and 90% (-90%) of the maximal power output to exhaustion. Blood samples were also obtained at rest, before the end of each cycling load, at exhaustion, and 5-min postexercise. RESULTS: The oxygen consumed during 1-90% (5.08 +/- 0.39 L) and 2-90% (5.32 +/- 0.30 L) was larger after CR (5.67 +/- 0.34 and 5.78 +/- 0.35 L, P < 0.01 and P < 0.05, respectively). Blood ammonia accumulation at the end of 1-90% (23.1 +/- 6.5 micromol x L(-1)) and 3-30% (64.7 +/- 15.2 micromol x L(-1)) was lower after CR (P < 0.05), whereas plasma uric acid accumulation was lower at exhaustion (P < 0.05) and 5-min postexercise (P < 0.01). Time to exhaustion increased (P < 0.05) from 29.9 +/- 3.8 to 36.5 +/- 5.7 min after CR, whereas it remained the same after PL. CONCLUSIONS: The results indicate that Cr feeding increases the capacity of human muscle to perform work during alternating intensity contraction, possibly as a consequence of increased aerobic phosphorylation and flux through the creatine kinase system.     

High-intensity dynamic human muscle performance enhanced by a metabolic intervention

PURPOSE: The purpose of this study was to quantify the effects of a metabolic treatment on human muscle dynamic performance (strength, work, and fatigue) measured under conditions of acute, exhaustive high-intensity anaerobic isokinetic exercise. METHODS: Unilateral prefatigue and postfatigue peak torque and work values were measured in the quadriceps femoris of 13 subjects using a computer-controlled isokinetic dynamometer, over a 23-d interval. The two experimental treatments were: 1) a glycine and L-arginine salt of alpha-ketoisocaproic acid calcium ("GAKIC"); and 2) isocaloric sucrose (control). Based on a randomized double-blind cross-over repeated measures design, measurements were made before and during an exhaustive anaerobic fatigue protocol to calculate a Fatigue Resistance Index (FRI = [peri-exhaustion torque]\[baseline peak torque]), as well as total work. RESULTS: The FRI and total work for each of the exhaustion sets measured at 0, 5, and 15 min after oral GAKIC treatment were greater than values obtained for isocaloric control treatment (P < 0.02). GAKIC treatment increased the mean resistance to fatigue (FRI) up to 28% over isocaloric control. Overall gain in total muscle work attributable to GAKIC was 10.5 +/- 0.8% greater than control, sustained for at least 15 min. After 24 h, both GAKIC and control concentric forces returned to the same absolute values (P > 0.05): mean FRI = 0.42 +/- 0.05 and mean total work = 4600 +/- 280 J. There were no significant differences attributable to random order of testing. CONCLUSIONS: Compared with isocaloric carbohydrate, oral GAKIC treatment increased muscle torque and work sustained during intense acute anaerobic dynamic exercise; additionally, it increased overall muscle performance by delaying muscle fatigue during the early phases of anaerobic dynamic exercise.     

Few adverse effects of long-term creatine supplementation in a placebo-controlled trial

Although oral creatine supplementation is very popular among athletes, no prospective placebo-controlled studies on the adverse effects of long-term supplementation have yet been conducted. We performed a double-blind, placebo-controlled trial of creatine monohydrate in patients with the neurodegenerative disease amyotrophic lateral sclerosis, because of the neuroprotective effects it was shown to have in animal experiments. The purpose of this paper is to compare the adverse effects, and to describe the effects on indirect markers of renal function of long-term creatine supplementation. 175 subjects (age = 57.7 +/- 11.1 y) were randomly assigned to receive creatine monohydrate 10 g daily or placebo during an average period of 310 days. After one month, two months and from then on every fourth month, adverse effects were scored using dichotomous questionnaires, plasma urea concentrations were measured, and urinary creatine and albumin concentrations were determined. No significant differences in the occurrence at any time of adverse effects due to creatine supplementation were found (23 % nausea in the creatine group, vs. 24 % in the placebo group, 19 % gastro-intestinal discomfort in the creatine group, vs. 18 % in the placebo group, 35 % diarrhoea in the creatine group, vs. 24 % in the placebo group). After two months of treatment, oedematous limbs were seen more often in subjects using creatine, probably due to water retention. Severe diarrhoea (n = 2) and severe nausea (n = 1) caused 3 subjects in the creatine group to stop intake of creatine, after which these adverse effects subsided. Long-term supplementation of creatine did not lead to an increase of plasma urea levels (5.69 +/- 1.47 before treatment vs. 5.26 +/- 1.44 at the end of treatment) or to a higher prevalence of micro-albuminuria (5.4 % before treatment vs. 1.8 % at the end of treatment).     

Arterial stiffness and wave reflection following exercise in resistance-trained men

PURPOSE: Resistance training increases arterial stiffness and pressure wave reflection. We tested the hypothesis that potentially greater tonic arterial stiffness in resistance-trained (RT) men may alter the vascular response to an acute exercise stressor. METHODS: Thirty participants (age 22 +/- 0.5 yr; 15 highly RT men and 15 sedentary non-RT men) underwent measures of central (carotid femoral) and peripheral (femoral dorsalis pedis) pulse wave velocity (PWV) and augmentation index (AIx; index of central pressure wave reflection derived from radial artery applanation tonometry and pulse wave analysis) before and 10, 20, and 30 min after maximal aerobic exercise. RESULTS: RT men were significantly stronger (bench press 143 +/- 7 vs 85 +/- 2 kg, P < 0.05) and heavier (93 +/- 3 vs 82 +/- 3 kg, P < 0.05) than sedentary men. Groups did not differ in resting central/peripheral PWV or in AIx. AIx was not changed at 10 min after maximal aerobic exercise in both groups and was reduced similarly in both groups at 20 and 30 min after maximal aerobic exercise (P < 0.05). Peripheral PWV decreased similarly at all time points after maximal aerobic exercise in both groups and was not recovered by 30 min (P < 0.05). There was no change in central PWV after maximal aerobic exercise. CONCLUSIONS: The arterial response to maximal aerobic exercise was similar in highly RT and non-RT men. There was no change in intensity of central pressure wave reflection 10 min after exercise, despite significant reductions in peripheral muscular artery stiffness. Arterial reactivity to an acute exercise stressor is not impaired in young, highly RT men.     

The Biomechanical effects of treadmill training on running performance

The biomechanics of overground running were compared before and after a month training period which comprised 16 thirty-minute sessions of short duration (5 seconds work, 10 seconds rest) high intensity (4.69 m/sec 20-25% grade) interval treadmill work. For the eight subjects filmed there were no significant changes in support and non support time, stride length or stride rate while running at 3.58 m/sec that could be attributed to the treadmill training regime. This training programme produced significant gains in aerobic and anaerobic metabolism but was not an effective developer of speed.     

Influence of endurance exercise on respiratory muscle performance

PURPOSE: During high-intensity, exhaustive, constant-load exercise above 85% of maximal oxygen consumption, the diaphragm of healthy subjects can fatigue. Although a decrease in trans-diaphragmatic pressure is the most objective measure of diaphragmatic fatigue, possible extra-diaphragmatic muscle fatigue would not be detected by this method. The aim of the present study was to investigate the impact of exhaustive, constant-load cycling exercise at different intensities on global respiratory performance determined by the time to exhaustion while breathing against a constant resistance. METHODS: Ten healthy, male subjects performed an exhaustive cycling endurance test at 65, 75, 85, and 95% of peak oxygen consumption (VO2peak). Before cycling (to) as well as at 10 min (t10) and 45 min (t45) after cycling, respiratory performance was determined. RESULTS: Breathing endurance was equivalently reduced after exhaustive cycling at either 65% (8.4 +/- 4.1 min [t0] vs 3.9 +/- 2.8 min [t10]), 75% (9.9 +/- 6.1 vs 4.4 +/- 2.8 min), 85% (9.3 +/- 6.0 vs 3.8 +/- 2.9 min), or 95% VO2peak (8.5 +/- 5.1 vs 4.0 +/- 2.5 min) and, therefore, was independent of exercise intensity. CONCLUSION: This result contradicts previous findings, possibly due to the fact that extra-diaphragmatic muscles are tested in addition to the diaphragm during resistive breathing.     

Effects of an intrahospital exercise program intervention for children with leukemia

PURPOSE: The purpose was to investigate the effect of a 16-wk intrahospital supervised conditioning program including both resistance and aerobic training and a 20-wk detraining period on measures of aerobic fitness, muscular strength, functional mobility, ankle range of motion, and quality of life (QOL) in children receiving treatment for acute lymphoblastic leukemia (ALL). METHODS: Seven children (four boys, three girls; age: 5.1 +/- 1.2 yr, body mass: 24.0 +/- 5.8 kg, height: 114.6 +/- 7.7 cm) in the maintenance phase of treatment against ALL performed three sessions per week for 16 wk of resistance (one set of 8-15 repetitions of 11 exercises) and aerobic training (30 min at > 70% HRmax) followed by 20 wk of detraining where no structured exercise program was performed. Before training, after training, and after detraining, a treadmill test determining .VO2peak and ventilator threshold (VT), muscular strength (6RM), functional mobility (timed up and down stairs test, time up and go 3-m and 10-m tests), passive and dynamic ankle range of motion, and self-reported quality of living were determined. RESULTS: After training, significant increases in .VO2peak, VT, upper- and lower-body muscular strength, and all measures of functional mobility were shown (P < 0.05). Muscular strength was well maintained (significantly greater than before training and no significant decrease from after training) during detraining, whereas .VO2peak, VT, and functional mobility (not significantly different from before training but no significant decrease from after training) were only partially retained. CONCLUSION: Young children in the maintenance phase of treatment against ALL can safely perform both aerobic and resistance training. Training results in significant increases in measures of aerobic fitness, strength, and functional mobility. During detraining, strength and functional mobility are well maintained, whereas .VO2peak and VT are partially maintained.     

Low-intensity training dissociates metabolic from aerobic fitness

This study investigated the effect of prolonged whole-body low-intensity exercise on blood lipids, skeletal muscle adaptations and aerobic fitness. Seven male subjects completed a 32-day crossing of the Greenland icecap on cross-country skies and before and after this arm or leg cranking was performed on two separate days and biopsies were obtained from arm and leg muscle, and venous blood was sampled. During the crossing, subjects skied for 342+/-42 min/day and body mass was decreased by 7.1+/-0.7 kg. Peak leg oxygen uptake (4.6+/-0.2 L/min) was decreased (P<0.05) by 7% whereas peak arm oxygen uptake (3.0+/-0.2 L/min) remained unchanged. Total and low-density lipoprotein cholesterol (5.0+/-0.2 and 3.20.2 mmol/L) were decreased by 8% and 20%, respectively. Muscle beta-hydroxy-acyl-CoA dehydrogenase activity was increased with 22% in arm (P=0.08) and remained unchanged in leg muscle. Hormone sensitive lipase activity was similar in arm and leg muscle prior to the expedition and was not significantly affected by the crossing. In conclusion, an improved blood lipid profile and thus metabolic fitness was present after prolonged low-intensity training and this occurred in spite of a decreased aerobic fitness and an unchanged arm and leg muscle hormone-sensitive lipase activity.     

Potential benefits of maximal exercise just prior to return from weightlessness

The purpose of this study was to determine whether performance of a single maximal bout of exercise during weightlessness within hours of return to earth would enhance recovery of aerobic fitness and physical work capacities under a 1G environment. Ten healthy men (36-51 yr) underwent maximal supine exercise followed by upright maximal exercise before and after a 10-d bedrest period in the 6 degrees headdown position. A graded maximal supine cycle ergometer test was performed before and at the end of bedrest to simulate exercise during weightlessness. Following 3 h of resumption of the upright posture from the supine exercise test, a second maximal exercise test was performed on a treadmill to measure work capacity under conditions of 1G. Compared to before bedrest, peak VO2 decreased (p less than 0.05) by 8.7% and peak HR increased (p less than 0.05) by 5.6% in the supine cycle test at the end of bedrest. However, there were no significant changes in peak VO2 and peak HR in the upright treadmill test following bedrest. These data, based on a simulation, suggest that one bout of maximal leg exercise prior to return from 10 d of weightlessness may be adequate to restore preflight aerobic fitness and physical work capacity.     

Neuromuscular fatigue following constant versus variable-intensity endurance cycling in triathletes.

The aim of this study was to determine whether or not variable power cycling produced greater neuromuscular fatigue of knee extensor muscles than constant power cycling at the same mean power output. Eight male triathletes (age: 33+/-5 years, mass: 74+/-4 kg, VO2max: 62+/-5 mL kg(-1) min(-1), maximal aerobic power: 392+/-17 W) performed two 30 min trials on a cycle ergometer in a random order. Cycling exercise was performed either at a constant power output (CP) corresponding to 75% of the maximal aerobic power (MAP) or a variable power output (VP) with alternating +/-15%, +/-5%, and +/-10% of 75% MAP approximately every 5 min. Maximal voluntary contraction (MVC) torque, maximal voluntary activation level and excitation-contraction coupling process of knee extensor muscles were evaluated before and immediately after the exercise using the technique of electrically evoked contractions (single and paired stimulations). Oxygen uptake, ventilation and heart rate were also measured at regular intervals during the exercise. Averaged metabolic variables were not significantly different between the two conditions. Similarly, reductions in MVC torque (approximately -11%, P<0.05) after cycling were not different (P>0.05) between CP and VP trials. The magnitude of central and peripheral fatigue was also similar at the end of the two cycling exercises. It is concluded that, following 30 min of endurance cycling, semi-elite triathletes experienced no additional neuromuscular fatigue by varying power (from +/-5% to 15%) compared with a protocol that involved a constant power.     

Cardiac function after exhaustive open-sea swimming

AIM: The present study examined the acute effects of exhaustive 25-km open-sea swimming on left ventricular (LV) function and morphology. METHODS: Twenty elite male swimmers (22.3+/-4.1 years) participated in this study. Two-dimensionally guided M-mode echocardiograms, and electrocardiographic, phonocardiographic and carotid pulse tracings were performed simultaneously before and immediately after prolonged exhaustive swimming to evaluate the LV function and morphology, and the cardiac sympathetic outflow. Blood samples were also collected before and after the race to determine the hematocrit and the plasma concentrations of K+, Na+, Ca2+, a-ANP, renin, myoglobulin, CPK-MB, and lactate. RESULTS: Exhaustive swimming was associated with a significant reduction in LV fractional shortening (-13%), ejection fraction (-11%), stroke volume (-25%), and LV internal diastolic diameter (-7%). In contrast, cardiac index was increased by 31%, total peripheral resistance was increased by 7%, and LV circumferential and meridional wall stresses were increased by 101% and 102%, respectively. Significant relationships were found between the increases in total peripheral resistance and LV circumferential wall stress and the decrease in ejection fraction. On the contrast, no significant relationship was found between the increased hematocrit and decreased ejection fraction. Furthermore, the pre-ejection period increased by 11%, the pre-ejection period to LV ejection time ratio increased by 15%, and the electrical to electromechanical systole relationship increased from -8 to 10 ms. Immediately after the race, there were significant increases in hematocrit (9%), and plasma concentrations of a-ANP (211%), renin (161%) and lactate (72%), myoglobulin (421%), and CPK-MB (141%) compared to pre-race values. CONCLUSIONS: In elite athletes, prolonged exhaustive swimming is associated with depressed LV function, as suggested by reduced stroke volume, ejection fraction, and LV fractional shortening. This alteration is mainly due to increased afterload.     

Effect of pre-exercise fructose ingestion on endurance performance in fed men

Twelve trained males, in a fed state, were studied to examine the effect of pre-exercise fructose ingestion on endurance capacity during prolonged cycling exercise. Sixty minutes prior to exercise, subjects ingested either 60 or 85 g fructose or a sweet placebo. Mean exercise intensity initially required 62% of the maximal aerobic power and thereafter increased to elicit 72 and 81% of maximal aerobic power at 90 and 120 min of exercise, respectively. Exercise time (mean +/- SE) to exhaustion was significantly increased after fructose ingestion, as compared to placebo ingestion (145 +/- 4 vs 132 +/- 3 min, P less than 0.01). During the exercise, no differences were observed between both trials for oxygen uptake, heart rate, or perceived exertion. Serum glucose and insulin levels between both trials were not significantly different throughout the experiment. There were also no significant differences in serum-free fatty acids and glycerol levels as well as respiratory exchange ratio between fructose and placebo trials during the exercise. The results suggest that fructose ingestion is of benefit before prolonged exercise, because it provides a carbohydrate source to contracting muscles without transient hypoglycemia and a depression of fat utilization, and thereby delays the fatigue.