Anaerobic and aerobic relative contribution to total energy release during supramaximal effort in patients with left ventricular dysfunction.

Energetic metabolism during effort is impaired in patients with left ventricular dysfunction (Dysf), but data have been lacking up to now on the relative anaerobic vs. aerobic contribution to total energy release during supramaximal effort. Recently, the maximal accumulated oxygen deficit (MAOD) has been shown to be measurable in Dysf patients, making it possible to evaluate the anaerobic/aerobic interaction under conditions of maximal stress of both anaerobic and aerobic metabolic pathways in this population. Nineteen Dysf patients and 17 normal patients (N) underwent one ramp cardiopulmonary, three moderate-intensity constant-power, and three supramaximal constant-power (1- to 2-min, 2- to 3-min, and 3- to 4-min duration) exercise tests. MAOD was the difference between accumulated O(2) demand (accO(2)dem; estimated from the moderate-intensity O(2) uptake/watt relationship) and uptake during supramaximal tests. Percent anaerobic (%Anaer) and aerobic (%Aer) energetic release were [(MAOD/accO(2)dem).100] and 100 - %Anaer, respectively. MAOD did not vary between 1-2, 2-3, and 3-4 min supramaximal tests, whereas accO(2)dem increased significantly with and was linearly related to test duration in both Dysf and N. Consequently, %Anaer and %Aer decreased and increased, respectively, with increasing test duration but did not differ between Dysf and N in 1-2 min, 2-3 min, and 3-4 min tests. Our study demonstrates a similar relative anaerobic vs. aerobic contribution to total energy release during supramaximal effort in Dysf and N. This finding indicates that energetic metabolism during supramaximal exercise is exercise tolerance independent and that relative anaerobic vs. aerobic contribution in this effort domain remains the same within the physiology- or pathology-induced limits to individual peak exercise performance.     

Oxygen deficits incurred during 45, 60, 75 and 90-s maximal cycling on an air-braked ergometer

The aims of this study were to determine the most appropriate duration for the measurement of the maximal accumulated O₂ deficit (MAOD), which is analogous to the anaerobic capacity, to ascertain the effects of mass, fat free mass (FFM), leg volume (V _leg) and lower body volume (V _1b) on anaerobic test performance, to examine the reproducibility for peak power output ( ) or maximal anaerobic power using an air-braked cycle ergometer and to produce approximations for the percentages of aerobic and anaerobic metabolism during exercise of short duration but high intensity. A group of 12 endurance trained cyclists [mean age 25.1 (SD 4.6) years; mean body mass 73.43 (SD 7.12) kg; mean maximal oxygen consumption 5.12 (SD 0.35) l·min^–1; mean body fat 12.5 (SD 4.1) %] accordingly performed four counterbalanced treatments of 45, 60, 75 and 90 s of maximal cycling on an air-braked ergometer. The mean O₂ deficit of 3.52 l for the 45-s treatment was significantly less (P < 0.01) than those for the 60 (3.75 l), 75 (3.80 l) and 90-s (3.75 l) treatments. These data therefore indicate that in predominantly aerobically trained subjects the O₂ deficit attains a plateau after 60 s of maximal cycling on an air-braked ergometer. Statistically significant interclass correlation coefficients (P<0.05) between the anthropometric variables (mass, FFM, V _leg and V_1b) and or maximal anaerobic power (0.624–0.748) and MAOD (ml) or anaerobic capacity (0.666–0.772) furthermore would suggest the relevance of taking into account muscle mass during anaerobic tests. Intraclass correlation coefficients (0.935–0.946; all P<0.001) would indicate a high degree of reliability for the measurement of . The relative importance of anaerobic work decreased from 60% for the 45-s test to 40% for the 90-s one. Hence our study showed that both aerobic and anaerobic metabolism contributed significantly during all-out tests of 45–90 s duration.     

Time to exhaustion and time spent at a high percentage of VO2max in severe intensity domain in children and adults

The aim of the study was to compare time spent at a high percentage of VO2max (>90% of VO2max) (ts90%), time to achieve 90% of VO2max (ta90%), and time to exhaustion (TTE) for exercise in the severe intensity domain in children and adults. Fifteen prepubertal boys (10.3 ± 0.9 years) and 15 men (23.5 ± 3.6 years) performed a maximal graded exercise to determine VO2max, maximal aerobic power (MAP) and power at ventilatory threshold (PVTh). Then, they performed 4 constant load exercises in a random order at PVTh plus 50 and 75% of the difference between MAP and PVTh (PΔ50 and PΔ75) and 100 and 110% of MAP (P100 and P110). VO2max was continuously monitored. The P110 test was used to determine maximal accumulated oxygen deficit (MAOD). No significant difference was found in ta90% between children and adults. ts90% and TTE were not significantly different between children and adults for the exercises at PΔ50 and PΔ75. However, ts90% and TTE during P100 (p < 0.05 and p < 0.01, respectively) and P110 (p < 0.001) exercises were significantly shorter in children. Children had a significantly lower MAOD than adults (34.3 ± 9.4 ml · kg vs. 53.6 ± 11.1 ml · kg). A positive relationship (p < 0.05) was obtained between MAOD and TTE values during the P100 test in children. This study showed that only for intensities at, or higher than MAP, lower ts90% in children was linked to a reduced TTE, compared to adults. Shorter TTE in children can partly be explained by a lower anaerobic capacity (MAOD). These results give precious information about exercise intensity ranges that could be used in children's training sessions. Moreover, they highlight the implication of both aerobic and anaerobic processes in endurance performances in both populations.     

Comparison between a 30-s all-out test and a time-work test on a cycle ergometer

The relationship between the amount of work (Wlim) performed at the end of constant-power exhausting exercise and exhaustion time (tlim) has been studied for supramaximal exercise [105%, 120%, 135% and 150% of the individual maximal aerobic power, (MAP)] performed on a Monark cycle ergometer in nine men. The Wlim--tlim relationship was described by a linear relationship (Wlim = a + b . tlim). Intercept a was roughly equivalent to the work produced during a 1-min exercise performed at MAP. Slope b was equal to 79% of MAP. Intercept a has been correlated with the total amount of work (AW) performed during a 30-s all-out test supposed to assess anaerobic capacity. Intercept a was significantly (p less than 0.05) correlated with AW. The anaerobic capacity was not depleted at the end of the all-out test, as the mechanical power at the 30th s of this test was approximately equal to twice MAP. However, AW was significantly higher than intercept a. It was likely that the value of intercept a was an underestimation of the maximal anaerobic capacity because of the inertia of the aerobic metabolism. Indeed, an exponential model of the Wlim--tlim relationship, which takes the interia of the aerobic metabolism into account, shows that a linear approximation of the Wlim--tlim relationship yields a systematic underestimation of the anaerobic capacity. Consequently, intercept a of the Wlim--tlim relationship is not a more accurate estimation of the anaerobic capacity than the AW performed during a 30-s all-out test.(ABSTRACT TRUNCATED AT 250 WORDS)     

Potassium and ventilation during incremental exercise in trained and untrained men.

The present investigation was undertaken to examine the relationship between plasma potassium (K+) and ventilation (VE) during incremental exercise. Blood lactate (La-) was also measured, and its relationship with VE was similarly examined. Eight endurance-trained triathletes (ET) and eight active but untrained men (UT) performed an incremental cycling test to volitional fatigue. Maximal oxygen uptake (VO2max) and oxygen uptake (VO2) at lactate threshold (LT) were higher (P < 0.05) in ET (VO2max 4.60 +/- 0.10 l/min, LT 2.77 +/- 0.85 l/min) than in UT (VO2max 3.79 +/- 0.11 l/min, LT 1.94 +/- 0.60 l/min). There were significant (P < 0.05) correlations between VE and K+ (UT 0.87, ET 0.77) and between VE and La- (UT 0.88, ET 0.85). In ET compared with UT, VE was lower (P < 0.05) at 330 W, K+ was lower at 300 and 330 W, and La- was lower at all work loads > 90 W. These results suggest that K+ may make an important contribution to the regulation of ventilation during incremental exercise and that endurance training attenuates the K+ response to that exercise.     

Anaerobic energy provision does not limit Wingate exercise performance in endurance-trained cyclists.

The aim of this study was to evaluate the effects of severe acute hypoxia on exercise performance and metabolism during 30-s Wingate tests. Five endurance- (E) and five sprint- (S) trained track cyclists from the Spanish National Team performed 30-s Wingate tests in normoxia and hypoxia (inspired O(2) fraction = 0.10). Oxygen deficit was estimated from submaximal cycling economy tests by use of a nonlinear model. E cyclists showed higher maximal O(2) uptake than S (72 +/- 1 and 62 +/- 2 ml x kg(-1) x min(-1), P < 0.05). S cyclists achieved higher peak and mean power output, and 33% larger oxygen deficit than E (P < 0.05). During the Wingate test in normoxia, S relied more on anaerobic energy sources than E (P < 0.05); however, S showed a larger fatigue index in both conditions (P < 0.05). Compared with normoxia, hypoxia lowered O(2) uptake by 16% in E and S (P < 0.05). Peak power output, fatigue index, and exercise femoral vein blood lactate concentration were not altered by hypoxia in any group. Endurance cyclists, unlike S, maintained their mean power output in hypoxia by increasing their anaerobic energy production, as shown by 7% greater oxygen deficit and 11% higher postexercise lactate concentration. In conclusion, performance during 30-s Wingate tests in severe acute hypoxia is maintained or barely reduced owing to the enhancement of the anaerobic energy release. The effect of severe acute hypoxia on supramaximal exercise performance depends on training background.     

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

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 x 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 ([la-]b,max) determination. The [la-]bmax was significantly enhanced by Caf in both T and UT subjects (P less than 0.01). However, only T subjects exhibited significant improvement in their swimming velocity (P less than 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.     

Electromyographic activity and rate of muscle fatigue of the quadriceps femoris during cycling exercise in the severe domain

This study compared the activation pattern and the fatigue rate among the superficial muscles of the quadriceps femoris (QF) during severe cycling exercise. Peak oxygen consumption (VO(2)peak) and maximal accumulated oxygen Deficit (MAOD) were established by 10 well-trained male cyclists (27.5 ± 4.1 years, 71.0 ± 10.3 kg, 173.4 ± 6.6 cm, mean VO(2)peak 56.7 ± 4.4 ml·kg·min(-1), mean MAOD 5.7 ± 1.1 L). Muscle activity (electromyographic [EMG] signals) was obtained during the supramaximal constant workload test (MAOD) and expressed by root mean square (RMS) and median frequency (MF slope). The RMS of the QF, vastus lateralis (VL) and vastus medialis (VM) muscles were significantly higher than at the beginning after 75% of exercise duration, whereas for the rectus femoris (RF), this was observed after 50% of exercise duration (p ≤ 0.05). The slope of the MF was significantly higher in the RF, followed by the VL and VM (-3.13 ± 0.52 vs. -2.61 ± 0.62 vs. -1.81 ±0.56, respectively; p < 0.05). We conclude that RF may play an important role in limiting performance during severe cycling exercise.     

Fatigue depresses maximal in vitro skeletal muscle Na(+)-K(+)-ATPase activity in untrained and trained individuals.

This study investigated whether fatiguing dynamic exercise depresses maximal in vitro Na(+)-K(+)-ATPase activity and whether any depression is attenuated with chronic training. Eight untrained (UT), eight resistance-trained (RT), and eight endurance-trained (ET) subjects performed a quadriceps fatigue test, comprising 50 maximal isokinetic contractions (180 degrees /s, 0.5 Hz). Muscle biopsies (vastus lateralis) were taken before and immediately after exercise and were analyzed for maximal in vitro Na(+)-K(+)-ATPase (K(+)-stimulated 3-O-methylfluoroscein phosphatase) activity. Resting samples were analyzed for [(3)H]ouabain binding site content, which was 16.6 and 18.3% higher (P < 0.05) in ET than RT and UT, respectively (UT 311 +/- 41, RT 302 +/- 52, ET 357 +/- 29 pmol/g wet wt). 3-O-methylfluoroscein phosphatase activity was depressed at fatigue by -13.8 +/- 4.1% (P < 0.05), with no differences between groups (UT -13 +/- 4, RT -9 +/- 6, ET -22 +/- 6%). During incremental exercise, ET had a lower ratio of rise in plasma K(+) concentration to work than UT (P < 0.05) and tended (P = 0.09) to be lower than RT (UT 18.5 +/- 2.3, RT 16.2 +/- 2.2, ET 11.8 +/- 0.4 nmol. l(-1). J(-1)). In conclusion, maximal in vitro Na(+)-K(+)-ATPase activity was depressed with fatigue, regardless of training state, suggesting that this may be an important determinant of fatigue.     

Relationship in humans between spontaneously chosen crank rate and power output during upper body exercise at different levels of intensity

The aim of this study was to assess the relationship between spontaneously chosen crank rate (SCCR) and power output during two upper body exercise tests: firstly, an incremental maximal aerobic power test (T1), with an initial intensity of 50 W followed by 15-W increases at each subsequent 90-s stage and secondly, a test (T2) with consecutive exercise periods set at 50%, 60%, 70%, 80%, 110% and 120% of maximal power (Pmax) separated by passive recovery periods. Eight nationally and internationally ranked kayakers, aged 20 (SD 2) years, performed the tests. During both T1 and T2, mean SCCR values were correlated (r = 1) and increased significantly (P < 0.05) in association with the increases in power output. The finding that the subjects consistently increased their crank rate as the power output increased in different tests, i.e. at submaximal, maximal and supramaximal intensities, strongly suggests that SCCR depended on power output and not on the type of exercise (incremental or rectangular exercise). Moreover, the equation relating crank rate and power output determined from T1 suggests that it may be used to predict the crank rate which will be chosen in upper body exercise, whatever the intensity. Finally, the results of testing at 110% and 120% of Pmax would suggest that a high crank rate (>90 rpm) should be used during the test procedure using supramaximal exercises where accumulated oxygen deficit is calculated, and more particularly when exercise is performed using the upper body.     

Enhanced endurance in trained cyclists during moderate intensity exercise following 2 weeks adaptation to a high fat diet

These studies investigated the effects of 2 weeks of either a high-fat (HIGH-FAT: 70% fat, 7% CHO) or a high-carbohydrate (HIGH-CHO: 74% CHO, 12% fat) diet on exercise performance in trained cyclists (n = 5) during consecutive periods of cycle exercise including a Wingate test of muscle power, cycle exercise to exhaustion at 85% of peak power output [90% maximal oxygen uptake ( O_2max), high-intensity exercise (HIE)] and 50% of peak power output [60% O_2max, moderate intensity exercise (MIE)]. Exercise time to exhaustion during HIE was not significantly different between trials: nor were the rates of muscle glycogen utilization during HIE different between trials, although starting muscle glycogen content was lower [68.1 (SEM 3.9) vs 120.6 (SEM 3.8) mmol · kg ^–1 wet mass, P < 0.01] after the HIGH-FAT diet. Despite a lower muscle glycogen content at the onset of MIE [32 (SEM 7) vs 73 (SEM 6) mmol · kg ^–1 wet mass, HIGH-FAT vs HIGH-CHO, P < 0.01], exercise time to exhaustion during subsequent MIE was significantly longer after the HIGH-FAT diet [79.7 (SEM 7.6) vs 42.5 (SEM 6.8) min, HIGH-FAT vs HIGH-CHO, P<0.01]. Enhanced endurance during MIE after the HIGH-FAT diet was associated with a lower respiratory exchange ratio [0.87 (SEM 0.03) vs 0.92 (SEM 0.02), P<0.05], and a decreased rate of carbohydrate oxidation [1.41 (SEM 0.70) vs 2.23 (SEM 0.40) g CHO · min^–1, P<0.05]. These results would suggest that 2 weeks of adaptation to a high-fat diet would result in an enhanced resistance to fatigue and a significant sparing of endogenous carbohydrate during low to moderate intensity exercise in a relatively glycogen-depleted state and unimpaired performance during high intensity exercise.     

Effects of isokinetic training of the knee extensors on high-intensity exercise performance and skeletal muscle buffering

Twenty-three subjects isokinetically trained the right and left quadriceps femoris, three times per week for 16 weeks; one group (n=13) trained at an angular velocity of 4.19 rad · s^–1 and a second group (n=10), at 1.05 rad · s^–1. A control group (n=10) performed no training. Isometric endurance time at 60% quadriceps maximum voluntary contraction (MVC), mean power output and work done (W) during all-out cycling, and the muscle buffer value (B) and carnosine concentration of biopsy samples from the vastus lateralis, were all assessed before and after training. The two training groups did not differ significantly from each other in their training response to any of these variables (P < 0.05). No significant difference in either 60% MVC endurance time or impulse [(endurance time × force) at 60% MVC] was observed for any group after the 16 week period (P > 0.05). However, the post-training increase (9%) in W during high-intensity cycling was greater in the training group than in the control group (P=0.04). NeitherB nor carnosine concentration showed any significant change following training (P=0.56 andP=0.37, respectively). It is concluded that 16 weeks of isokinetic training of the knee extensors enables subjects to do more work during high-intensity cycling. Although the precise adaptations responsible for the improved performance have yet to be identified, they are unlikely to include an increase inB.     

Increases in maximal accumulated oxygen deficit after high-intensity interval training are not gender dependent.

Gender differences in maximal accumulated oxygen deficit (MAOD) were examined before and after 4 and 8 wk of high-intensity interval training. Untrained men (n = 7) and women (n = 7) cycled at 120% of pretraining peak oxygen uptake (VO2 peak) to exhaustion (MAOD test) pre-, mid-, and posttraining. A posttraining timed test was also completed at the MAOD test power output, but this test was stopped at the time to exhaustion achieved during the pretraining MAOD test. The 14.3 +/- 5.2% increase in MAOD observed in men after 4 wk of training was not different from the 14.0 +/- 3.0% increase seen in women (P > 0.05). MAOD increased by a further 6.6 +/- 1.9% in men, and this change was not different from the additional 5.1 +/- 2.3% increase observed in women after the final 4 wk of training. VO2 peak measured during incremental cycling increased significantly (P < 0.01) in male but not in female subjects after 8 wk of training. Moreover, the accumulated oxygen (AO2) uptake was higher in men during the posttraining timed test compared with the pretraining MAOD test (P < 0.01). In contrast, the AO2 uptake was unchanged from pre- to posttraining in female subjects. The increase in MAOD with training was not different between men and women, suggesting an enhanced ability to produce ATP anaerobically in both groups. However, the increase in VO2 peak and AO2 uptake obtained in male subjects after training indicates improved oxidative metabolism in men but not in women. We conclude that there are basic gender differences that may predispose men and women to specific metabolic adaptations after a period of intense interval training.     

Parasympathetic reactivation after repeated sprint exercise

The purpose of this study was to examine the effects of muscular power engagement, anaerobic participation, aerobic power level, and energy expenditure on postexercise parasympathetic reactivation. We compared the response of heart rate (HR) after repeated sprinting with that of exercise sessions of comparable net energy expenditure and anaerobic energy contribution. Fifteen moderately trained athletes performed 1) 18 maximal all-out 15-m sprints interspersed with 17 s of passive recovery (RS), 2) a moderate isocaloric continuous exercise session (MC) at a level of mean oxygen uptake similar to that of the RS trial, and 3) a high-intensity intermittent exercise session (HI) conducted at a level of anaerobic energy expenditure similar to that of the RS trial. Subjects were immediately seated after the exercise trials, and beat-to-beat HR was recorded for 10 min. Parasympathetic reactivation was evaluated through 1) immediate postexercise HR recovery, 2) the time course of the root mean square for the successive R-R interval difference between successive 30-s segments (RMSSD(30s)) and 3) HR variability vagal-related indexes calculated for the last 5-min stationary period of recovery. RMSSD(30s) increased during the 10-min period after the MC trial, whereas RMSSD(30s) remained depressed after both the RS and HI trials. Parasympathetic reactivation indexes were similar for the RS and HI trials but lower than for the MC trial (P < 0.001). When data of the three exercise trials were considered together, only anaerobic contribution was related to HR trial-derived indexes. Parasympathetic reactivation is highly impaired after RS exercise and appears to be mainly related to anaerobic process participation.     

Circulating plasma VEGF response to exercise in sedentary and endurance-trained men.

The skeletal muscle capillary supply is an important determinant of maximum exercise capacity, and it is well known that endurance exercise training increases the muscle capillary supply. The muscle capillary supply and exercise-induced angiogenesis are regulated in part by vascular endothelial growth factor (VEGF). VEGF is produced by skeletal muscle cells and can be secreted into the circulation. We investigated whether there are differences in circulating plasma VEGF between sedentary individuals (Sed) and well-trained endurance athletes (ET) at rest or in response to acute exercise. Eight ET men (maximal oxygen consumption: 63.8 +/- 2.3 ml x kg(-1) x min(-1); maximum power output: 409.4 +/- 13.3 W) and eight Sed men (maximal oxygen consumption: 36.3 +/- 2.1 ml x kg(-1) x min(-1); maximum power output: 234.4 +/- 13.3 W) exercised for 1 h at 50% of maximum power output. Antecubital vein plasma was collected at rest and at 0, 2, and 4 h postexercise. Plasma VEGF was measured by ELISA analysis. Acute exercise significantly increased VEGF at 0 and 2 h postexercise in ET subjects but did not increase VEGF at any time point in Sed individuals. There was no difference in VEGF between ET and Sed subjects at any time point. When individual peak postexercise VEGF was analyzed, exercise did increase VEGF independent of training status. In conclusion, exercise can increase plasma VEGF in both ET athletes and Sed men; however, there is considerable variation in the individual time of the peak VEGF response.     

Altered single cell force-velocity and power properties in exercise-trained rat myocardium.

Myocardial function is enhanced by endurance exercise training, but the cellular mechanisms underlying this improved function remain unclear. The ability of the myocardium to perform external work is a critical aspect of ventricular function, but previous studies of myocardial adaptation to exercise training have been limited to measurements of isometric tension or unloaded shortening velocity, conditions in which work output is zero. We measured force-velocity properties in single permeabilized myocyte preparations to determine the effect of exercise training on loaded shortening and power output. Female Sprague-Dawley rats were divided into sedentary control (C) and exercise trained (T) groups. T rats underwent 11 wk of progressive treadmill exercise. Myocytes were isolated from T and C hearts, chemically skinned, and attached to a force transducer. Shortening velocity was determined during loaded contractions at 15 degrees C by using a force-clamp technique. Power output was calculated by multiplying force times velocity values. We found that unloaded shortening velocity was not significantly different in T vs. C myocytes (T = 1.43 muscle lengths/s, n = 46 myocytes; C = 1.12 muscle lengths/s, n = 43 myocytes). Training increased the velocity of loaded shortening and increased peak power output (peak power = 0.16 P/P(o) x muscle length/s for T myocytes; peak power = 0.10 P/P(o) x muscle length/s for C myocytes, where P/P(o) is relative tension). We found no effect of training on myosin heavy chain isoform content. These results suggest that training alters power output properties of single cardiac myocytes and that this adaptation may improve the work capacity of the myocardium.     

The effect of one-legged sprint training on intramuscular pH and nonbicarbonate buffering capacity

To determine the effect of one-legged sprint training on muscle pH and nonbicarbonate buffering capacity (BC), 9 subjects completed 15 to 20 intervals at 90 RPM, 4 days a week for 7 weeks on a bicycle ergometer adapted for one-legged pedaling. Needle biopsies from the vastus lateralis and blood samples from an antecubital vein were taken at rest and twice during recovery (1 and 4 minutes) from a 60 s one-legged maximal power test on a cycle ergometer. pH one minute after exercise in both the trained and untrained legs following the training period was not different but both were higher than before training. BC increased from 49.9 to 57.8 mumol HCl x g-1 x pH-1 after training (p less than 0.05). Blood lactate levels after exercise were significantly higher for the trained leg when compared to the untrained leg after spring training. Peak and average power output on the 60 s power test increased significantly after training. One-legged aerobic power (VO2max) was significantly increased in the untrained and trained legs. Two-legged VO2max also improved significantly after training. These data suggest that nonbicarbonate buffering capacity and power output can be enhanced with one-legged sprint training. Also, small but significant improvements in VO2max were also observed.     

Baroreflex function in endurance- and static exercise-trained men

The effect of exercise training mode on reflex cardiovascular control was studied in a cross-sectional design. We examined the cardiovascular responses to progressive incremental phenylephrine (PE) infusion to maximal rates of 120 micrograms/min and the delta heart rate/delta blood pressure responses to lower body negative pressure (LBNP) to -50 Torr in 30 men who were either endurance exercise trained (ET), untrained (UT), or weight trained (WT). During PE infusion, measures of blood pressures, forearm blood flow, heart rate and cardiac output, and calculations of forearm vascular resistance, stroke volume, and peripheral vascular resistance were made at each infusion rate when steady-state blood pressure was attained. No significant differences (P less than 0.05) in forearm blood flow or resistance were observed between the groups at any dose of PE, suggesting that the vasoconstrictor response was similar among the groups. Regression analyses of heart rate against mean blood pressure during the PE infusion were performed to evaluate baroreflex function. A linear model was used and correlation coefficients ranging from 0.82 to 0.96 were obtained (P less than 0.05). The slope of the line of best fit for the ET subjects (-0.57) was significantly less (P less than 0.05) than the slopes obtained for either the UT (-0.91) or WT (-0.88) subjects. In addition, the delta heart rate/delta blood pressure measurements obtained during LBNP reflected a similarly significant attenuation of reflex chronotropic control in the ET subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influences of Normobaric Hypoxia Training on Physical Fitness and Metabolic Risk Markers in Overweight to Obese Subjects

Previous studies suggested that hypoxia and exercise may have a synergistic effect on cardiovascular and metabolic risk factors. We conducted a single blind study in overweight to obese subjects to test the hypothesis that training under hypoxia (HG, n = 24, FiO₂ = 15%) results in similar or even greater improvement in body weight and metabolic risk markers compared with exercise under normoxia (NG, n = 21, FiO₂ = 21%). After an initial metabolic evaluation including incremental exercise testing, subjects trained in normoxic or hypoxic conditions thrice weekly over a 4‐week period at a heart rate corresponding to 65% of maximum oxygen uptake (VO_2max). The experimental groups were similar at the start of the investigation and weight stable during the training period. Subjects in the hypoxia group trained at a significantly lower workload (P < 0.05). Yet, both groups showed similar improvements in VO_2max and time to exhaustion. Respiratory quotient and lactate at the anaerobic threshold as well as body composition improved more in the hypoxia group. We conclude that in obese subjects, training in hypoxia elicits a similar or even better response in terms of physical fitness, metabolic risk markers, and body composition at a lower workload. The fact that workload and, therefore, mechanic strain can be reduced in hypoxia could be particularly beneficial in obese patients with orthopedic comorbidities.     

Effect of varying light intensity on maximal power production and selected metabolic variables

This study was designed to examine the effect of exposure to two levels of light intensity (bright; 5000 lux, dim; 50 lux) prior to supramaximal cycle exercise on performance and metabolic alterations. The exercise was performed after bright and dim light exposure for 90 minutes. Ten male long-distance runners volunteered to take part in the study. They performed 45-sec supramaximal exercise using a cycle ergometer in a 500-lux. Mean power output was measured during the exercise. Lactate and ammonia in the blood and epinephrine and norepinephrine concentrations in plasma were measured at rest immediately after bright and dim light exposures and after the exercise. Bright and dim light exposure prior to exercise did not significantly affect the power output during the exercise. Blood glucose concentration immediately after exercise and plasma epinephrine during the resting period were significantly lower after bright light exposure compared with dim light exposure (p < 0.05). No significant difference was found in blood lactate, ammonia, or plasma norepinephrine levels after exercise following bright and dim light exposures. This study demonstrated that bright light stimulation prior to supramaximal exercise decreases glucose and epinephrine levels, but is not related to physical performance.