Effect of glycogen depletion on the oxygen uptake slow component in humans

Previous studies have indicated that the (.-)VO(2) slow component is related to the recruitment of type II muscle fibres. We therefore hypothesised that an exercise and dietary regimen designed to deplete type I muscle fibres of glycogen would result in a greater contribution of type II muscle fibres to the exercise power output and therefore a larger amplitude of the (.-)VO(2) slow component. Eight male subjects took part in this study. On day 1, the subjects reported to the laboratory at 8 a.m., and completed a 9 min constant-load cycling test at a work rate equivalent to 85 % (.-)VO(2) peak. On day 2 at 12 p.m., the subjects were fed a 4200 kJ meal (60 % protein, 40 % fat); at 6 p.m. they completed a 2 h cycling test at 60 % (.-)VO(2) peak. On day 3 at 8 a.m., the subjects performed an exercise test identical to that of day 1. Metabolic and respiratory measurements indicated that our experimental design was effective in reducing the muscle glycogen content. (.-)VO(2) was significantly higher (by approximately 140 ml x min (-1)) throughout exercise following glycogen depletion but no appreciable changes in (.-)VO(2) kinetics were found: neither the time constant of the primary response (from 35.4 +/- 2.5 to 33.2 +/- 4.4 s) nor the amplitude of the slow component (from 404 +/- 95 to 376 +/- 81 ml x min (-1)) was significantly altered. Therefore, we suggest that the increased (.-)VO(2) throughout exercise and the unaltered (.-)VO(2) slow component following glycogen depletion might be explained by a shift towards a greater reliance on fat metabolism in type I muscle fibres with no appreciable change in fibre type recruitment patterns.     

Effect of different pedal rates on oxygen uptake slow component during constant-load cycling exercise

AIM: We hypothesized that an extremely high pedal rate would induce much more type II muscle fibers recruitment even at an early phase of the same absolute work rate compared with normal pedal rates, and would result in changed amplitude of the pulmonary oxygen uptake slow component (VO(2)SC) during heavy constant-load exercise. METHODS: Two square-wave transitions of constant-load exercise were carried out at an exercise intensity corresponding to a VO(2) of 130% of the ventilatory threshold. The amplitude of the VO(2)SC in phase III during heavy constant-load exercise was determined at normal (60 rpm) and extremely high pedal rates (110 rpm). The VO(2) kinetics were analyzed by nonlinear regression. RESULTS: Although the absolute work rates were almost identical in the two pedal rates cycling exercise, the amplitude of the VO(2) in phase II (phase II amplitude), end-exercise VO(2) (EEVO(2)) and blood lactate accumulation ([La]) were significantly greater at 110 rpm than at 60 rpm (2 260+/-242 vs 1.830+/-304 mL.min(-1) for phase II amplitude; P<0.01, 2 350+/-265 vs 1 709+/-342 mL.min(-1) for EEVO(2); P<0.01, 6.4+/-1.3 vs 3.2+/-1.3 mmol.L(-1) for [La]; P<0.01, respectively). The amplitude of the VO(2)SC in phase III also revealed a significantly higher value at 110 rpm compared with 60 rpm (416+/-73 vs 201+/-89 mL.min(-1), P<0.01). In spite of the appearance of greater VO(2)SC at 110 rpm, no corresponding changes in integrals of the electromyography (EMG) signal and mean power frequency were observed. CONCLUSIONS: The results of this study indicate that the amplitude of the VO(2)SC was greater in higher pedal rate during the same work rate constant-load cycling exercise, which might be associated with a progressive increase in the adenosine triphosphate requirement of already recruited muscle fibers in exercising muscle.     

Effects of a carbohydrate-protein beverage on cycling endurance and muscle damage

INTRODUCTION: The purpose of this study was to determine whether endurance cycling performance and postexercise muscle damage were altered when consuming a carbohydrate and protein beverage (CHO+P; 7.3% and 1.8% concentrations) versus a carbohydrate-only (CHO; 7.3%) beverage. METHODS: Fifteen male cyclists (mean (.-)VO(2peak) = 52.6 +/- 10.3 mL x kg x min) rode a cycle ergometer at 75% (.-)VO(2peak) to volitional exhaustion, followed 12 - 15 h later by a second ride to exhaustion at 85% (.-)VO(2peak). Subjects consumed 1.8 mL x kg BW of randomly assigned CHO or CHO+P beverage every 15 min of exercise, and 10 mL x kg BW immediately after exercise. Beverages were matched for carbohydrate content, resulting in 20% lower total caloric content per administration of CHO beverage. Subjects were blinded to treatment beverage and repeated the same protocol seven to 14 d later with the other beverage. RESULTS: In the first ride (75% (.-)VO(2peak)), subjects rode 29% longer (P < 0.05) when consuming the CHO+P beverage (106.3 +/- 45.2 min) than the CHO beverage (82.3 +/- 32.6 min). In the second ride (85% (.-)VO(2peak)), subjects performed 40% longer when consuming the CHO+P beverage (43.6 +/- 12.5 min) than when consuming the CHO beverage (31.2 +/- 8.7 min). Peak postexercise plasma CPK levels, indicative of muscle damage, were 83% lower after the CHO+P trial (216.3 +/- 122.0 U x L) than the CHO trial (1318.1 +/- 1935.6 U x L). There were no significant differences in exercising levels of (.-)VO(2), ventilation, heart rate, RPE, blood glucose, or blood lactate between treatments in either trial. CONCLUSION: A carbohydrate beverage with additional protein calories produced significant improvements in time to fatigue and reductions in muscle damage in endurance athletes. Further research is necessary to determine whether these effects were the result of higher total caloric content of the CHO+P beverage or due to specific protein-mediated mechanisms.     

Inspiratory muscle training fails to improve endurance capacity in athletes

PURPOSE: The purpose of this study was to examine the effects of specific inspiratory muscle training (IMT) on respiratory muscle strength and endurance and whole-body endurance exercise capacity in competitive endurance athletes. METHODS: Seven collegiate distance runners (5 male/2 female; VO2max = 59.9 +/- 11.7 mL.kg-1.min-1) were recruited to participate in this study. Initial testing included maximal oxygen consumption (VO2max), sustained maximal inspiratory mouth pressure (MIP), breathing endurance time (BET) at 60% MIP, and endurance run time (ERT) at 85% VO2max. Heart rate (HR), minute ventilation (VE), oxygen consumption (VO2), and ratings of perceived dyspnea (RPD) were recorded at 5-min intervals and during the last minute of the endurance run. Blood lactate concentration (BLC) was also obtained immediately before and at 2 min after the endurance run. All testing was repeated after 4 wk of IMT (50-65% MIP, approximately 25 min x d(-1), 4-5 sessions/week, 4 wk). RESULTS: After 4 wk of IMT, MIP and BET were significantly increased compared with pretraining values (P < 0.05). No significant differences between pre and post values were observed in VO2max or ERT at 85% VO2max after IMT. No significant differences between pre and post values were detected in HR, VE, VO2, or RPD during the endurance run as measured at steady state and end of the test after IMT. BLC was not significantly different before or at 2 min after the endurance run between pre and post IMT. CONCLUSION: These results suggest that IMT significantly improves respiratory muscle strength and endurance. However, these improvements in respiratory muscle function are not transferable to VO2max or endurance exercise capacity as assessed at 85% VO2max in competitive athletes.     

Effects of respiratory muscle endurance training on ventilatory and endurance performance of moderately trained cyclists

This study examined the effects of respiratory muscle endurance training (RMET) on ventilatory and endurance performance among moderately trained, male cyclists. Nine subjects initially completed two cycling VO2 max tests, two endurance cycling tests for time at 95% VO2 max, a 15-s MVV test, and an endurance breathing test for time at 100% MVV. Four subjects then underwent 3 weeks of strenuous RMET while five served as controls. Mean posttest 15-s MVV and endurance breathing time were significantly higher in the RMET group (243 +/- 14 l X min-1 and 804 +/- 94 s) than in the control group (205 +/- 6 l X min-1 and 48 +/- 8 s). No significant group differences in VO2 max or endurance cycling time at 95% VO2 max were observed following RMET. Results of this exploratory study indicated that RMET improved ventilatory power and endurance, but did not alter VO2 max or endurance cycling performance among moderately trained, male cyclists.     

Endurance training reduces end-exercise VO2 and muscle use during submaximal cycling

INTRODUCTION: End-exercise VO2 during heavy, constant-load exercise is reduced after endurance training, due to an attenuated VO2 slow component. PURPOSE/METHODS: To determine whether the training-induced reduction in end-exercise VO2 was associated with reduced muscle use, we measured VO2 and T2 changes in magnetic resonance images in the final minute of two 15-min constant-load cycle rides, one above lactate threshold and the other below lactate threshold. These measures were repeated after a 4-wk period in eight subjects who trained on a cycle ergometer and seven controls. RESULTS: There were no changes in end-exercise VO2 or active muscle after training in either group during low-intensity cycling, in which no VO2 slow component was present. During high-intensity cycling, in which there was a slow component before training, the training group experienced a significant reduction (P < 0.05) in end-exercise VO2 (2625 +/- 673; 2567 +/- 605 mL.min (-1) and the T2 of the vastus lateralis (35.6 +/- 1.4; 34.5 +/- 0.9 ms). CONCLUSION: These results support the hypothesis that reduction in end-exercise VO2 (and the VO2 slow component) after training is due to reduced muscle use during heavy, constant load cycling.     

The effect of prior high-intensity cycling exercise on the VO2 kinetics during high-intensity cycling exercise is situated at the additional slow component

In previous studies conclusions about the effect of prior exercise on VO2 kinetics of subsequent high-intensity exercise are generally based on observed changes in the overall VO2 response without considering the effects on the VO2 fast and slow component. The aim of the present study was to examine the effect on the VO2 fast and slow component separately. Therefore 10 subjects performed an exercise protocol consisting of an initial 3 min period of unloaded cycling followed by two constant-load work bouts at a work rate corresponding to 90% VO2peak, separated by 3 min of rest and 3 min of unloaded cycling. VO2 was measured on a breath-by-breath basis, and the response curves were analysed by a biexponential model. To increase signal-to-noise ratio, subjects performed four repetitions of the exercise protocol, each separated by at least one day. There was no significant alteration in VO2 kinetic parameters of the primary, fast component after high-intensity exercise. However, there was a significant effect of prior high-intensity exercise on the VO2 kinetic parameters of the slow component. The time constant and the amplitude of the slow component were reduced by respectively 44% (from 231.0 +/- 111.7 s to 130.1 +/- 50.4 s) and 49% (from 824 +/- 270 ml x min(-1) to 417 +/- 134 ml x min(-1)). The results of this study indicate that the effect of high-intensity exercise on the VO2 kinetics of a subsequent high-intensity exercise is probably limited to an effect on the slow component.     

The oxygen uptake response of sprint- vs. endurance-trained runners to severe intensity running.

We compared the oxygen uptake (VO2) response of sprint- and endurance-trained runners for an exhaustive square wave run lasting approximately 2 minutes. Six sprinters and six middle- and long-distance runners each performed two exhaustive square wave runs lasting approximately 2 min and two exhaustive ramp tests. VO2 was determined breath-by-breath (QP9000; Morgan Medical, Rainham, UK) and averaged across the two repeats of each test; for the square wave test, the averaged VO2 response (excluding the first 15 s) was then modelled using a monoexponential function. Both VO2peak for the ramp test (67.5+/-3.3 vs. 54.5+/-8.5 mlxkg(-1)xmin(-1); P= 0.006) and the asymptotic VO2 for the square wave run (59.6+/-2.7 vs. 50.7+/-4.6 mlxkg(-1)xmin(-1); P= 0.002) were higher for the endurance than for the sprint group. However, as a percentage of VO2peak, this asymptotic VO2 did not differ between the groups (90.1+/-3.2% (endurance) vs. 96.2+/-9.0% (sprint); P= 0.145). Across all 12 subjects, the %VO2peak attained in the square wave run was negatively correlated with VO2peak (Pearson's r= -0.811, P= 0.001). We conclude that VO2max is more important than training history as a determinant of the %VO2max attained in exhaustive square wave running lasting approximately 2 min.     

Effect of sodium bicarbonate on muscle metabolism during intense endurance cycling

INTRODUCTION: Sodium bicarbonate (NaHCO3) ingestion has been shown to increase both muscle glycogenolysis and glycolysis during brief submaximal exercise. These changes may be detrimental to performance during more prolonged, exhaustive exercise. This study examined the effect of NaHCO3 ingestion on muscle metabolism and performance during intense endurance exercise of approximately 60 min in seven endurance-trained men. METHODS: Subjects ingested 0.3 g.kg-1 body mass of either NaHCO3 or CaCO3 (CON) 2 h before performing 30 min of cycling exercise at 77 +/- 1% .VO(2peak) followed by completion of 469 +/- 21 kJ as quickly as possible (approximately 30 min, approximately 80% .VO(2peak)). RESULTS: Immediately before, and throughout exercise, arterialized-venous plasma HCO3- concentrations were higher (P < 0.05) whereas plasma and muscle H+ concentrations were lower (P < 0.05) in NaHCO3 compared with CON. Blood lactate concentrations were higher (P < 0.05) during exercise in NaHCO3, but there was no difference between trials in muscle glycogen utilization or muscle lactate content during exercise. Reductions in PCr and ATP and increases in muscle Cr during exercise were also unaffected by NaHCO3 ingestion. Accordingly, exercise performance time was not different between treatments. CONCLUSION: NaHCO3 ingestion resulted in a small muscle alkalosis but had no effect on muscle metabolism or intense endurance exercise performance in well-trained men.     

The VO2 slow component: relationship between plasma ammonia and EMG activity

PURPOSE: An increased recruitment of type II muscle fibers has been suggested as a major cause of the slow component of O(2) uptake (VO(2)) kinetics. Furthermore, the rise in plasma ammonia (NH(3)) during high-intensity exercise, where a slow component is observed, has been associated with the activation of type II muscle fibers. Therefore, the purpose of this study was to examine the relationship between the VO(2) slow component, plasma NH3 concentration, and electromyography (EMG) responses during constant-load cycling. METHODS: Eight healthy adults (mean age +/- SEM: 21.4 +/- 1.0 yr) performed 7 min of heavy constant-load exercise. The breath-by-breath VO(2) response was characterized using a two-term exponential model. Plasma NH(3) concentration was measured at rest, following 3 min of unloaded cycling and at 3 and 7 min of constant-load exercise. Surface EMG activity of the right vastus lateralis muscle was measured during the final 10 s of every minute of exercise. RESULTS: The amplitude of the slow component was 561 +/- 52 mL.min(-1), and occurred 132 +/- 11 s following the onset of constant-load exercise. Plasma NH(3) concentration increased significantly from 3 to 7 min of constant-load exercise by 32.2 +/- 2.9 micromol.L(-1). The rise in plasma NH(3) concentration correlated significantly with the amplitude of the slow component (r = 0.79, P < 0.05). The mean power frequency of the EMG increased significantly while the integrated EMG/VO(2) ratio remained constant over the duration of the slow component. CONCLUSION: The rise in NH(3) concentration and the amplitude and spectral components of the EMG are consistent with a progressive increase in the recruitment of type II muscle fibers during the slow component phase of exercise.     

Effects of leg press training on cycling, leg press, and running peak cardiorespiratory measures

Six males and seven females trained 3 d per wk (30 min at 80 to 85% heart rate reserve) for 20 wk on a leg press apparatus. A progressive exercise test was administered on a cycle ergometer, leg press apparatus, and treadmill before and after training. Before training, peak oxygen consumption (VO2, ml X kg-1 X min-1) during the leg press test was higher for the males (23.9 +/- 1.60, mean +/- SE) compared to the females (19.5 +/- 2.40, P less than or equal to 0.05). Peak VO2 during the cycling (males = 36.6 +/- 2.65, females = 28.5 +/- 2.35) and treadmill (males = 39.8 +/- 2.04, females = 33.2 +/- 2.64) tests was also different between the sexes, and 30 to 40% higher than during the leg press test (P less than or equal to 0.05). Peak heart rate (beats X min-1) was not different between the sexes (P greater than 0.05), yet was 11% lower during the leg press test (165 +/- 3.5) compared to the cycling (184 +/- 2.8) and treadmill (187 +/- 1.3) tests (P less than or equal to 0.05). After training, peak VO2 during the cycling and treadmill tests increased 10 to 15%, compared to 35% during the leg press test (P less than or equal to 0.05). The only change in peak heart rate was a 6% increase during the leg press test (P less than or equal to 0.05). Although peak VO2 on the leg press apparatus was lower than on the cycle ergometer and treadmill, leg press exercise elicited a sufficient stimulus for increasing peak VO2 on the three testing modes.     

Prior heavy exercise enhances performance during subsequent perimaximal exercise

PURPOSE: To test the hypothesis that prior heavy exercise increases the time to exhaustion during subsequent perimaximal exercise. METHODS: Seven healthy males (mean +/- SD 27 +/- 3 yr; 78.4 +/- 0.7 kg) completed square-wave transitions from unloaded cycling to work rates equivalent to 100, 110, and 120% of the work rate at VO2peak (W-[VO2peak) after no prior exercise (control, C) and 10 min after a 6-min bout of heavy exercise at 50% Delta (HE; half-way between the gas exchange threshold (GET) and VO2peak), in a counterbalanced design. RESULTS: Blood [lactate] was significantly elevated before the onset of the perimaximal exercise bouts after prior HE (approximately 2.5 vs approximately 1.1 mM; P < 0.05). Prior HE increased time to exhaustion at 100% (mean +/- SEM. C: 386 +/- 92 vs HE: 613 +/- 161 s), 110% (C: 218 +/- 26 vs HE: 284 +/- 47 s), and 120% (C: 139 +/- 18 vs HE: 180 +/- 29 s) of W-VO2peak, (all P < 0.01). VO2 was significantly higher at 1 min into exercise after prior HE at 110% W-VO2peak (C: 3.11 +/- 0.14 vs HE: 3.42 +/- 0.16 L x min(-1); P < 0.05), and at 1 min into exercise (C: 3.25 +/- 0.12 vs HE: 3.67 +/- 0.15; P < 0.01) and at exhaustion (C: 3.60 +/- 0.08 vs HE: 3.95 +/- 0.12 L x min(-1); P < 0.01) at 120% of W-VO2peak. CONCLUSIONS: This study demonstrate that prior HE, which caused a significant elevation of blood [lactate], resulted in an increased time to exhaustion during subsequent perimaximal exercise presumably by enabling a greater aerobic contribution to the energy requirement of exercise.     

Effects of phosphatidylserine on exercise capacity during cycling in active males

PURPOSE: The purpose of the study was to investigate the effects of 750 mg of soybean-derived phosphatidylserine, administered daily for 10 d, on exercise capacity, oxygen uptake kinetic response, neuroendocrine function, and feeling states during exhaustive intermittent exercise. METHODS: Following preliminary testing, fourteen active males completed a staged intermittent exercise protocol on two further occasions (T1 and T2) separated by 16 +/- 1 d. The protocol consisted of three 10-min stages of cycling at 45, 55, and 65% VO2max, followed by a final bout at 85% VO2max that was continued until exhaustion. Approximately 5 d after T1 the subjects were assigned, in a double-blind manner, to either phosphatidylserine (PS) or placebo (P). Breath-by-breath respiratory data and heart rate were continually recorded throughout the exercise protocol, and blood samples were obtained at rest, during the rest periods within the protocol (Post-55, Post-65), at the end of exercise (Post-85), 20 min after the completion of exercise (postexercise), and the day following exercise (Post-24 h). RESULTS: The main finding of this study was that supplementation had a significant effect on exercise time to exhaustion at 85% VO2max (P = 0.005). The exercise time to exhaustion in PS increased following supplementation (7:51 +/- 1:36 to 9:51 +/- 1:42 min:s, P = 0.001), whereas P remained unchanged (8:09 +/- 0:54 to 8:02 +/- 0:54 min:s, P = 0.670). Supplementation did not significantly affect oxygen kinetic mean response times (MRT(on) and MRT(off)), serum cortisol concentrations, substrate oxidation, and feeling states during the trial. CONCLUSION: This is the first study to report improved exercise capacity following phosphatidylserine supplementation. These findings suggest that phosphatidylserine might possess potential ergogenic properties.     

The decrease in VO(2) slow component induced by prior exercise does not affect the time to exhaustion

In previous studies decreases in the VO(2) slow component were observed after prior heavy exercise. The observed effects after prior low-intensity exercise were rather controversial. The purpose of the present study was to more thoroughly examine the effects of prior low-intensity exercise on the VO(2) slow component. Furthermore, it has been suggested that the VO(2) slow component may be a determinant of exercise tolerance. Therefore we tested the hypothesis whether an attenuated VO(2) slow component induced by prior exercise could affect the time to exhaustion. Ten subjects performed four exercise protocols consisting of heavy cycling exercise (95 % VO(2)peak) until exhaustion. This constant-load exercise was performed without prior exercise (protocol NPE), or was preceded by 6 min heavy cycling exercise (protocol 6HPE), 12 min low-intensity cycling exercise (protocol 12LPE) or 6 min low-intensity cycling exercise (protocol 6LPE). The VO(2) slow component quantified as Delta VO(2 (end-2)) (669 +/- 90 ml x min (-1) in NPE) was significantly reduced after heavy as well as low-intensity exercise (respectively 47 %, 29 % and 17 % in 6HPE, 12LPE and 6LPE). This reduction lead to a significantly lower end VO(2) in 6HPE and 12LPE. The time to exhaustion (594 +/- 139 s in NPE), however, was unaffected by prior exercise rejecting our hypothesis that the attenuated VO(2) slow component could improve the capability to sustain exercise performance.     

Evaluation of fitness level by the oxygen uptake efficiency slope after a short-term intermittent endurance training

Several indicators are used as indices of cardiorespiratory reserve. Among them, oxygen uptake (VO(2)) at peak and ventilatory threshold (VAT) levels are the most common used. In the present study, endurance training was used to evaluate and compare the usefulness of a new index, the Oxygen Uptake Efficiency Slope (OUES) as an alternative to the previous ones. Fifteen physical education student women participated in the study (8 as a trained group [T: age (mean +/- SD) 21.9 +/- 3.3 y, height 165.1 +/- 5.5 cm, weight 60.4 +/- 3.3 kg] and 7 as a control group [C: age 21.7 +/- 1.9 y, height 165.4 +/- 7.2 cm, weight 59.6 +/- 8.6 kg]). Before and after 6 weeks of the Square-Wave Endurance Exercise Test (SWEET) training program or daily activities, they performed an incremental test (30 W/3 min) on a cycle ergometer to determined VO(2), power output and parameters associated with breathing efficiency (the respiratory equivalents, and the ventilatory dead space to tidal volume ratio [Vd/Vt]) at peak- and VAT-levels. The slope of the relationship between ventilation and carbon dioxide production was also calculated. OUES, derived from the logarithmic relationship between VO(2) and minute ventilation (V(E)), was determined at 75 % (OUES75), 90 % (OUES90) and 100 % (OUES100) of exercise duration. After endurance training in T, VO(2) and power output were significantly improved at peak- and VAT-levels while all breathing efficiency indices remained unchanged. No changes were observed in C after 6 weeks. Despite significant correlation between OUES values and VO(2) at peak- and VAT-levels, OUES75, OUES90 and OUES100 did not significantly change after endurance training. While VO(2) and power output at peak- and VAT-levels increased in all T, training-induced changes in OUES appeared more variable. We concluded that OUES was not sufficiently sensitive to highlight improvement of cardiorespiratory reserve after endurance training whereas VO(2) at peak and VAT levels did.     

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.     

No effect of 5% hypohydration on running economy of competitive runners at 23 degrees C

PURPOSE: Although running economy (RE) is recognized as an integral component of successful endurance performance and is affected by numerous factors, little is known about the influence of body water loss on RE. This investigation examined the effects of hypohydration (HY) on RE and associated physiological responses. METHODS: Ten highly trained collegiate distance runners (mean +/- SD; age, 20 +/- 3 yr; height, 178.5 +/- 6.3 cm; body mass, 66.7 +/- 5.4 kg; VO2max, 66.5 +/- 4.1 mL x kg(-1) x min(-1)) participated in four experiments on separate days, twice in a euhydrated (EU) and twice in a HY state (-5.5 and -5.7% body mass loss achieved during 24 h). At each hydration level, subjects performed one 10-min treadmill run per day (23 degrees C environment), at either 70% VO2max (EU 70% or HY 70%) or 85% VO2max (EU 85% or HY 85%) in a randomized, repeated-measures design. Cardiopulmonary, metabolic, thermal, hormonal, and perceptual variables were measured. RESULTS: No between-treatment differences existed for RE (EU 70%, 46.3 +/- 3.2; HY 70%, 47.2 +/- 3.8; EU 85%, 58.6 +/- 2.8; HY 85%, 58.9 +/- 4.1 mL x kg(-1) x min(-1)), postexercise plasma lactate concentration (EU 70%, 1.9 +/- 0.6; HY 70%, 1.8 +/- 0.6; EU 85%, 6.5 +/- 3.5; HY 85%, 6.4 +/- 3.5 mmol x L(-1)), or rating of perceived exertion. HY resulted in a greater (P < 0.05 to 0.001) heart rate (HR), rectal temperature, and plasma norepinephrine concentration (NE), concurrent with reduced cardiac output, stroke volume, and respiratory exchange ratio. CONCLUSION: HY did not alter the RE or lactate accumulation of endurance athletes during 10 min of exercise at 70 and 85% VO2max. These findings indicate that HY had no effect on RE, but that it increased physiological strain in a 23 degrees C environment.     

Oxygen-uptake efficiency slope as a determinant of fitness in overweight adolescents

PURPOSE: Peak oxygen uptake (VO2peak) is frequently difficult to assess in overweight individuals; therefore, submaximal measures that predict VO2peak are proposed as substitutes. Oxygen uptake efficiency slope (OUES) has been suggested as a submaximal measurement of cardiorespiratory fitness that is independent of exercise intensity. There are few data examining its value as a predictor of V O2peak in severely overweight adolescents. METHODS: One hundred seven severely overweight (BMI Z 2.50 +/- 0.34) and 43 nonoverweight (BMI Z 0.13 +/- 0.84) adolescents, performed a maximal cycle ergometer test with respiratory gas-exchange measurements. OUES was calculated through three exercise intensities: lactate inflection point (OUES LI), 150% of lactate inflection point (OUES 150), and VO2peak (OUES PEAK). RESULTS: When adjusted for lean body mass, VO2peak and OUES at all exercise intensities were lower in overweight subjects (VO2peak: 35.3 +/- 6.4 vs 46.8 +/- 7.9 mL.kg(-1) LBM.min(-1), P < 0.001; OUES LI: 37.9 +/- 10.0 vs 43.7 +/- 9.2 mL.kg(-1) LBM.min(-1).logL(-1) P < 0.001; OUES 150: 41.6 +/- 9.0 vs 49.8 +/- 11.1 mL.kg(-1) LBM.min(-1).logL(-1) P < 0.001; and OUES PEAK: 45.1 +/- 8.7 vs 52.8 +/- 9.6 mL.kg(-1) LBM.min(-1).logL(-1) P < 0.001). There was a significant increase in OUES with increasing exercise intensity in both groups (P < 0.001). OUES at all exercise intensities was a significant predictor of VO2peak for both groups (r2 = 0.35-0.83, P < 0.0001). However, limits of agreement for predicted VO2peak relative to actual VO2peak were wide (+/- 478 to +/- 670 mL.min(-1)). CONCLUSIONS: OUES differs significantly in overweight and nonoverweight adolescents. The wide interindividual variation and the exercise intensity dependence of OUES preclude its use in clinical practice as a predictor of VO2peak.     

Effects of respiratory muscle endurance training on wheelchair racing performance in athletes with paraplegia: a pilot study.

OBJECTIVE: Respiratory muscle endurance training (RMET) has been shown to improve both respiratory muscle and cycling exercise endurance in able-bodied subjects. Since effects of RMET on upper extremity exercise performance have not yet been investigated, we evaluated the effects of RMET on 10-km time-trial performance in wheelchair racing athletes. DESIGN: Pilot study, controlled before and after trial. SETTING: Spinal cord injury research center. PARTICIPANTS: 12 competitive wheelchair racing athletes. INTERVENTIONS: The training group performed 30 sessions of RMET for 30 min each. The control group did no respiratory muscle training. MAIN OUTCOME MEASUREMENTS: Differences in 10-km time-trial performance pre- versus postintervention. RESULTS: In the training group, the time of the 10-km time-trial decreased significantly from before versus after intervention (27.1 +/- 9.0 vs. 24.1 +/- 6.6 min); this did not occur in the control group (23.3 +/- 2.8 vs. 23.2 +/- 2.4 min). No between groups difference was present (P = 0.150). Respiratory muscle endurance increased significantly within the training group (9.1 +/- 7.2 vs. 39.9 +/- 17.8 min) and between groups, but not within the control group (4.3 +/- 2.9 vs. 6.6 +/- 7.0 min) before versus after intervention. CONCLUSION: There was a strong trend, with a large observed effect size of d = 0.87, towards improved performance in the 10-km time-trial after 6 weeks of RMET.