Negative accumulated oxygen deficit during heavy and very heavy intensity cycle ergometry in humans

The concept of the accumulated O₂ deficit (AOD) assumes that the O₂ deficit increases monotonically with increasing work rate (WR), to plateau at the maximum AOD, and is based on linear extrapolation of the relationship between measured steady-state oxygen uptake (O₂) and WR for moderate exercise. However, for high WRs, the measured O₂ increases above that expected from such linear extrapolation, reflecting the superimposition of a "slow component" on the fundamental O₂ mono-exponential kinetics. We were therefore interested in determining the effect of the O₂ slow component on the computed AOD. Ten subjects [31 (12) years] performed square-wave cycle ergometry of moderate (40%, 60%, 80% and 90% ), heavy (40%), very heavy (80%) and severe (110% O_{2 peak}) intensities for 10–15 min, where is the estimated lactate threshold and is the WR difference between and O_{2 peak}. O₂ was determined breath-by-breath. Projected "steady-state" O₂ values were determined from sub- tests. The measured O₂ exceeded the projected value after ~3 min for both heavy and very heavy intensity exercise. This led to the AOD actually becoming negative. Thus, for heavy exercise, while the AOD was positive [0.63 (0.41) l] at 5 min, it was negative by 10 min [–0.61 (1.05) l], and more so by 15 min [–1.70 (1.64) l]. For the very heavy WRs, the AOD was [0.42 (0.67) l] by 5 min and reached –2.68 (2.09) l at exhaustion. For severe exercise, however, the AOD at exhaustion was positive in each case: +1.69 (0.39) l. We therefore conclude that the assumptions underlying the computation of the AOD are invalid for heavy and very heavy cycle ergometry (at least). Physiological inferences, such as the "anaerobic work capacity", are therefore prone to misinterpretation.     

Effects of moderate hyperoxia on oxygen consumption during submaximal and maximal exercise

The present study examined the effect of hyperoxia on oxygen uptake (V˙O₂) and on maximal oxygen uptake (V˙O_2max) during incremental exercise (IE) and constant work rate exercise (CWRE). Ten subjects performed IE on a bicycle ergometer under normoxic and hyperoxic conditions (30% oxygen). They also performed four 12-min bouts of CWRE at 40, 55, 70 and 85% of normoxic V˙O_2max (ex1, ex2, ex3 and ex4, respectively) in normoxia and in hyperoxia. V˙O_2max was significantly improved by 15.0 (15.2)% under hyperoxia, while performance (maximum workload, W _max) was improved by only +4.5 (3.0)%. During IE, the slope of the linear regression relating V˙O₂ to work rate was significantly steeper in hyperoxia than in normoxia [10.80 (0.88) vs 10.06 (0.66) ml·min^–1·W^–1]. During CWRE, we found a higher V˙O₂ at ex1, ex2, ex3 and ex4, and a higher V˙O₂ slow component at ex4 under hyperoxia. We have shown that breathing hyperoxic gas increases V˙O_2max, but to an extent that is difficult to explain by an increase in oxygen supply alone. Changes in metabolic response, fibre type recruitment and V˙O₂ of non-exercising tissue could explain the additional V˙O₂ for a given submaximal work rate under hyperoxia. Electronic Publication     

Lactate disposal in resting trained and untrained forearm skeletal muscle during high intensity leg exercise

Summary At a given oxygen uptake ( O₂) and exercise intensity blood lactate concentrations are lower following endurance training. While decreased production of lactate by trained skeletal muscle is the commonly accepted cause, the contribution from increased lactate removal, comprising both uptake and metabolic disposal, has been less frequently examined. In the present study the role of resting skeletal muscle in the removal of an arterial lactate load (approximately 11 mmol·-l^–1) generated during high intensity supine leg exercise (20 min at approximately 83% maximal oxygen uptake) was compared in the untrained (UT) and trained (T) forearms of five male squash players. Forearm blood flow and the venoarterial lactate concentration gradient were measured and a modified form of the Fick equation used to determine the relative contributions to lactate removal of passive uptake and metabolic disposal. Significant lactate uptake and disposal were observed in both forearms without any change in forearm O₂. Neither the quantity of lactate taken up [UT, 344.2 (SEM 118.8) mol·100 ml^–1; T, 330.3 (SEM 85.3) mol·100 ml^–1] nor the quantity disposed of [UT, 284.0 (SEM 123.3) mol·100 ml^–1, approximately 83% of lactate uptake; T, 300.8 (SEM 77.7) mol·100 ml^–1, approximately 91% of lactate uptake] differed between the two forearms. It is concluded that while significant lactate disposal occurs in resting skeletal muscle during high intensity exercise the lower blood lactate concentrations following endurance training are unlikely to result from an increase in lactate removal by resting trained skeletal muscle.     

Ventilatory response during incremental exercise tests in weight lifters and endurance cyclists

Summary The effect of a progressively increasing work rate (15 W·min^–1) up to exhaustion on the time course of O₂ uptake ( ), ventilation ( ) and heart rate (HR) has been studied in weight lifters (WL) in comparison to endurance cyclists (Cycl) and sedentary controls (Sed). and were measured as average value of 30-s intervals by a semiautomatic open circuit method. was 2.55±0.33; 4.29±0.53 and 2.86±0.19·min^–1 in WL, Cycl and Sed respectively. With time and work rate, while and HR increased linearly, changed its slope at two levels. The 1st change occured at a work load corresponding to a mean (± SD) of 1.50±0.26; 1.93±0.34; and 1.23±0.14 l·min^–1 in WL, Cycl, and Sed respectively. values corresponding to the second change of slope were 2.18±0.32 in WL; 3.48±0.53 in Cycl and 2.17±0.28 l·min^–1 in Sed. The first change of slope might be the consequence of the different readjustment of on-response and hence of early lactate in the different subjects. The second change seems to be comparable to the conventional anaerobic threshold and is achieved in all subjects when vs time slope is 7–10 l·min^–1/min of exercise.This work has been supported in part by a grant from the Italian National Research Council (CNR)     

In humans the oxygen uptake slow component is reduced by prior exercise of high as well as low intensity

The aim of the study was to examine to what extent prior high- or low-intensity cycling, yielding the same amount of external work, influenced the oxygen uptake (V˙O₂) slow component of subsequent high-intensity cycling. The 12 subjects cycled in two protocols consisting of an initial 3 min period of unloaded cycling followed by two periods of constant-load exercise separated by 3 min of rest and 3 min of unloaded cycling. In protocol 1 both periods of exercise consisted of 6 min cycling at a work rate corresponding to 90% peak oxygen uptake (V˙O_2peak). Protocol 2 differed from protocol 1 in that the first period of exercise consisted of a mean of 12.1 (SD 0.8) min cycling at a work rate corresponding to 50% V˙O_2peak. The difference between the 3rd min V˙O₂ and the end V˙O₂ (ΔV˙O₂₍₆₋₃₎) was used as an index of the V˙O₂ slow component. Prior high-intensity exercise significantly reduced ΔV˙O₂₍₆₋₃₎. The ΔV˙O₂₍₆₋₃₎ was also reduced by prior low-intensity exercise despite an unchanged plasma lactate concentration at the start of the second period of exercise. The reduction was more pronounced after prior high- than after prior low-intensity exercise (59% and 28%, respectively). The results of this study show that prior exercise of high as well as low intensity reduces the V˙O₂ slow component and indicate that a metabolic acidosis is not a necessary condition to elicit a reduction in ΔV˙O₂₍₆₋₃₎. Accepted: 8 July 2000     

Effects of prolonged cycle ergometer exercise on maximal muscle power and oxygen uptake in humans

Summary The mechanical power (W_tot, W·kg^–1) developed during ten revolutions of all-out periods of cycle ergometer exercise (4–9 s) was measured every 5–6 min in six subjects from rest or from a baseline of constant aerobic exercise [50%–80% of maximal oxygen uptake (VO_2max)] of 20–40 min duration. The oxygen uptake [VO₂ (W·kg^–1, 1 ml O₂ = 20.9 J)] and venous blood lactate concentration ([la]_b, mM) were also measured every 15 s and 2 min, respectively. During the first all-out period, W_tot decreased linearly with the intensity of the priming exercise (W_tot = 11.9–0.25·VO₂). After the first all-out period (i greater than 5–6 min), and if the exercise intensity was less than 60% VO_2max, W_tot, VO₂ and [la]_b remained constant until the end of the exercise. For exercise intensities greater than 60% VO_2max, VO₂ and [la]_b showed continuous upward drifts and W_tot continued decreasing. Under these conditions, the rate of decrease of W_tot was linearly related to the rate of increase of V [(d W_tot/dt) (W·kg^–1·s^–1) = 5.0·10^–5 –0.20·(d VO₂/dt) (W·kg^–1·s^–1)] and this was linearly related to the rate of increase of [la]_b [(d VO₂/dt) (W·kg^–1·s^–1) = 2.310^–4 + 5.910^–5·(d [la]_b/dt) (mM·s^–1)]. These findings would suggest that the decrease of W_tot during the first all-out period was due to the decay of phosphocreatine concentration in the exercising muscles occurring at the onset of exercise and the slow drifts of VO₂ (upwards) and of W_tot (downwards) during intense exercise at constant W_tot could be attributed to the continuous accumulation of lactate in the blood (and in the working muscles).     

The aerobic-anaerobic transition: re-examination of the threshold concept including an electromyographic approach

Summary The surface electromyogram (EMG) from the vastus lateralis muscle and the metabolic and respiratory parameters were studied simultaneously during an incremental exercise in order to identify EMG signal modifications during the aerobic-anaerobic transition. Subjects performed an incremental test on the bicycle ergometer from an initial work load of 175 W to exhaustion by steps of 25 W. Ventilatory flow ( _E), oxygen uptake ( ) and carbon dioxide flow ( ) were recorded continuously. For lactate concentration determination, venous blood samples were collected during the final 30 s of each step. EMG signals were stored on magnetic tape. They were then converted into successive spectra to allow the study of EMG total power (PEMG) and mean power frequency (MPF) evolutions. A non linear increase in blood lactate reflected by a breaking point at 250 W was observed. A change in ratio occured at 275 W. PEMG value showed a non linear increase reflected by a breaking point at 275 W. MPF value increased from the first to the seventh step with a tendency to decrease at the last step. A great interindividual variance of EMG data was observed indicating the difficulty of correlating mean values of EMG parameters with mean values of blood lactate in order to explain sudden lactate increase by fast twitch fibre recruitment. However, comparison of individual EMG data suggests a progressive recruitment of fast twitch fibres as work load increases.     

Effect of cycling position on oxygen uptake and preferred cadence in trained cyclists during hill climbing at various power outputs

Numerous researchers have studied the physiological responses to seated and standing cycling, but actual field data are sparse. One open issue is the preferred cadence of trained cyclists while hill climbing. The purpose of this study, therefore, was to examine the affect of cycling position on economy and preferred cadence in trained cyclists while they climbed a moderate grade hill at various power outputs. Eight trained cyclists (25.8 ± 7.2 years, 68.8 ± 5.0 ml kg⁻¹ min⁻¹, peak power 407.6 ± 69.0 W) completed a seated and standing hill climb at approximately 50, 65 and 75% of peak power output (PPO) in the order shown, although cycling position was randomized, i.e., half the cyclists stood or remained seat on their first trial at each power output. Cyclists also performed a maximal trial unrestricted by position. Heart rate, power output, and cadence were measured continuously with a power tap; ventilation , BF and cadence were significantly higher with seated climbing at all intensities; there were no other physiological differences between the climbing positions. These data support the premise that trained cyclists are equally economical using high or low cadences, but may face a limit to benefits gained with increasing cadence.     

Cardiorespiratory adaptation with short term training in older men

Summary The purpose of this study was to assess the rate of training-induced cardiorespiratory adaptations in older men [mean (SD), 66.5 (1.2) years]. The eight subjects trained an average of 4.3 (0.3) times each week. The walk/jog training was in two phases with 4 weeks (phase 1) at a speed to elicit 70% of pre-training maximal oxygen consumption ( ), and 5 weeks (phase 2) at 80%. Maximal exercise treadmill tests and a standardized submaximal protocol were performed prior to training, at weekly intervals during the training programme, and after training. (ml·kg^–1·min^–1) increased significantly over both phases: 6.6% after the first 4 weeks, and an additional 5.2% after the final 5 weeks. The weekly changes in over phase 1 were well fitted by an exponential association curve (r=0.75). The half-time for the rate of adaptation was 13.8 days, or 8.3 training sessions. Over phase 2, the change in did not plateau and a time course could not be determined. Submaximal exercise heart rate (f _c ) was reduced a significant 10 beats · min^–1 after the first 4 weeks, and a further 6 beats · min^–1 over the final 5 weeks. Thef _c reductions showed half-times of 9.1 days (phase 1) and 9.8 days (phase 2) (or 5-6 training sessions). The anaerobic ventilation threshold was increased 13.9% over the 9 weeks of training and the respiratory exchange ratio during constant load heavy exercise was significantly reduced; however, these changes could not be described by an exponential time course. Thus, short-term exercise training of older men resulted in significant and rapid cardiorespiratory improvements.     

Automatic detection of maximal oxygen uptake and ventilatory threshold

Maximal oxygen uptake () and ventilatory threshold (VT) are the most common measurements in exercise physiology laboratories for the objective characterization of the physiologic state of metabolic and respiratory systems. Several techniques for their identification were proposed in the literature: the aim of the present study was to review them and assess their performance when applied to experimental data.In the present study, the criteria to detect and VT from respiratory gas-exchange data were analysed and automatic procedures for the identification of these parameters were implemented. These procedures were then applied to experimental data in order to assess the verifiability, repeatability and sensitivity to measurement noise of each proposed method.The results suggest plateau- and RISE-105- as the most reliable automatic procedures for determining , while respiratory exchange ratio-, ventilatory equivalent for O₂- and P_ET,O2-criteria appear to be the most reliable automatic procedures for estimating VT.     

The relationship between lactate and ventilatory thresholds: coincidental or cause and effect?

Summary To determine if blood lactate (LA) is the stimulus responsible for breakaway ventilation (V_E), the lactate (LT) and ventilation (VT) thresholds were monitored during one-legged cycling exercise. Ten healthy volunteer male subjects (Mean 2-legged =4.27 l·min^–1) performed prior exercise (PE) to reduce muscle glycogen stores by cycling at 75–85% of maximal heart rate (HR max) for 60–75 min, followed by a 30 h low carbohydrate diet. Pre- and post- LT and VT tests were performed on a cycle ergometer employing a continuous protocol with increments of 16 W every 3 min. Muscle biopsies were taken from the vastus lateralis muscle before the PE ride, prior to the threshold test 24 h later, and before testing the non-exercised (NE) leg. An I.V. catheter placed in the antecubital vein was used for serial blood samples taken at rest, and during the final 30 s of each progressive load. Gas analysis was calculated every 30 s (Beckman Metabolic Measurement Cart). Biopsies (N=3) showed that the exercise and diet regimen elicited glycogen reduction which significantly (p<0.05) reduced R and the blood LA concentration in both the PE (2.62 to 1.99 mmol·l^–1) and NE (2.87 to 2.26 mmol·l^–1) legs at LT. At VT, LA concentrations were also significantly reduced in the PE (3.35 to 2.56 mmol·l^–1) and NE (3.59 to 2.74 mmol·^–1) legs. and V_E, however, were similar between pre- and post- tests. Results of this study suggest that plasma LA accumulation is not responsible for breakaway ventilation during progressive exercise and that LT and VT are not a cause and effect relationship.     

Reproducibility of aerobic and anaerobic thresholds in 20–50 year old men

Summary The reproducibility of the aerobic (AerT) and the anaerobic (AnT) threshold was studied in 33 men aged 20–50 years. They completed two maximal exercise tests on a bicycle ergometer. The thresholds, as (l·min^–1), were determined visually by two investigators using both the blood lactate and the respiratory indices. The respiratory variables were measured with a computerized breath-by-breath method; samples of venous blood were drawn every 2nd min and analysed enzymatically for lactate. The reproducibility of the AerT (r=0.94) and of the AnT (r=0.96) were equally good. The AnT can be determined either from blood lactate concentrations (AnT_La) or from ventilatory and gas exchange response (AnT_r) during a 2-min incremental exercise test. They both also showed similar reproducibility:r=0.93 for the AnT_La andr=0.95 for the AnT_r. The work rate and the measured physiological variables at the AerT and AnT, except for the blood lactacte concentration, were very reproducible. Age did not affect the reproducibility of the thresholds. The poor reproducibility of blood lactate concentration of the AnT confirmed our previous opinion that the fixed blood lactate levels of 2 and 4 mmol·l^–1 are poor indicators of AerT and AnT.     

The effects of training on the metabolic and respiratory profile of high-intensity cycle ergometer exercise

Summary The tolerable work duration (t) for high-intensity cycling is well described as a hyperbolic function of power (W):W=(W'·t ⁻¹)+W _a , whereW _a is the upper limit for sustainable power (lying between maximumW and the threshold for sustained blood [lactate] increase,Θ _lac), andW' is a constant which defines the amount of work which can be performed >W _a . As training increases the tolerable duration of high-intensity cycling, we explored whether this reflected an alteration ofW _a ,W' or both. Before and after a 7-week regimen of intense interval cycle-training by healthy males, we estimated (^)Θ _lac and determined maximum O₂ uptake ;W _a ;W'; and the temporal profiles of pulmonary gas exchange, blood gas, acid-base and metabolic response to constant-load cycling at and aboveW _a . Although training increased (24%), (15%) andW _a (15%),W' was unaffected. For exercise atW _a , a steady state was attained for , [lactate] and pH both pre- and post-training, despite blood [norepinephrine] and [epinephrine] ([NE], [E]) and rectal temperature continuing to rise. For exercise >W _a , there was a progressive increase in (resulting in at fatigue), [lactate], [NE], [E] and rectal temperature, and a progressive decrease for pH. We conclude that the increased endurance capacity for high-intensity exercise following training reflects an increasedW asymptote of theW−t relationship with no effect on its curvature; consequently, there is no appreciable change in the amount of work which can be performed aboveW _a . Furthermore, regardless of training status,W _a represents the upper power limit at which , blood [lactate] and blood pH can eventually be stabilized. Exercise >W _a , in contrast, is characterized by a steadily increasing and blood [lactate], a falling blood pH and consequently, imminent fatigue. Supported in part by a UCLA Graduate Division Doctoral Research Award     

Maximal accumulated oxygen deficit expressed relative to the active muscle mass for cycling in untrained male and female subjects

The purpose of the present study was to determine if gender differences exist in the maximal accumulated oxygen deficit (MAOD) or in the blood lactate (Lac^?) and catecholamine responses to the MAOD test (120% peak oxygen uptake to exhaustion). The MAOD for cycling was measured in ten untrained male and ten untrained female subjects using the method described by Medbø et?al. (Anaerobic capacity determined by maximal accumulated oxygen deficit. J Appl Physiol 64: 50–60, 1988). Blood Lac^? and catecholamine concentrations were measured at rest, exhaustion and for 30?min following the MAOD test. Dual-energy X-ray absorptiometry was used to measure lean body mass (LBM) and to estimate the active muscle mass (AMM) for cycling. Males achieved a significantly higher MAOD than females following correction for AMM [126.3 (5.6) versus 108.3 (6.1)?ml?·?kg AMM^?1, P=0.04]. The peak blood lactate concentration ([Lac^?]) in males [13.6 (0.9)?mmol?·?l^?1] was significantly higher than in females [10.0 (1.0)?mmol?·?l^?1]. Males obtained a 68% higher peak epinephrine concentration ([Epi]) than females, but the difference was not significant [1268 (188)?pg?·?ml^?1 versus 755 (179)?pg?·?ml^?1, P=0.066]. However, plasma [Epi] was significantly higher for males than females at 1?min [824 (116) versus 489 (116)?pg?·?ml^?1, P=0.036] and 3?min [330 (52) versus 179 (42)?pg?·?ml^?1, P=0.039] into the recovery period. No gender-dependent differences in the norepinephrine concentration were observed at any time. Peak [Lac^?] was significantly correlated with MAOD (ml?·?kg AMM^?1) in females (r=0.75), but not in males (r=0.09). The peak plasma [Epi] was not significantly correlated with MAOD (ml?·?kg AMM^?1) or peak [Lac^?] in either group. These findings suggest that there are gender-dependent differences in MAOD even when expressed relative to the AMM for cycling. The higher blood [Lac^?] in males compared to females obtained after supramaximal exercise was not caused by enhanced secretion of Epi. The greater MAOD in untrained males was not caused by a greater ability to produce Lac^? or by enhanced secretion of Epi.     

The amplitude of the slow component of oxygen uptake is related to muscle contractile properties

During constant-load exercise above the lactate threshold, oxygen-uptake kinetics deviate from the pattern seen below the threshold, with an additional, delayed component superimposed on the monoexponential pattern. It was hypothesised that this slow component is due to the progressive recruitment of type II muscle fibres. Oxygen uptake was measured for six male power athletes (group P) and six male endurance athletes (group E) during constant-load knee extension exercise tests in order to determine slow component amplitude. In addition, an electrical stimulation protocol was employed in order to assess the functional contractile profile and fatiguability of the knee extensors. The amplitude of the slow component during exercise was significantly (P<0.05) greater in group P than in group E when expressed as an absolute value [mean (SEM)=77 (17) ml min^–1 and 24 (16) ml min^–1] and when normalised to end-exercise oxygen uptake,O₂ [8.2 (0.5)% and 2.6 (1.8)%]. Group differences were observed for percentage force loss during the electrical stimulation protocol [50.0 (3.4)% and 31.5 (3.7)% for groups P and E, respectively], increase in relaxation time from start to end of the fatigue test [87.9 (15.5)% and 31.1 (11.9)%], and relaxation time for fresh muscle [32.4 (1.0) ms and 40.6 (2.1) ms]. These contractile parameters may indicate a higher proportion of type II fibres in group P compared with group E. These experiments have shown evidence of a relationship between the amplitude of the slow component and muscle contractile properties, indicating that the origin of the slow component may lie in the pattern of different muscle fibre types.     

Tricarboxylic acid cycle intermediates accumulate at the onset of intense exercise in man but are not essential for the increase in muscle oxygen uptake

It was proposed that a contraction-induced increase in tricarboxylic acid cycle intermediates (TCAI) is obligatory for the increase in muscle oxygen uptake at the start of exercise. To test this hypothesis, we measured changes in muscle TCAI during the initial seconds of intense exercise and used dichloroacetate (DCA) in an attempt to alter the level of TCAI. Five men performed strenuous leg kicking exercise (64±8 W) under noninfused control (CON) and DCA-supplemented conditions; biopsies (vastus lateralis) were obtained at rest and after 5, 15, and 180 s of exercise. In CON, the total concentration of three measured TCAI (ΣTCAI: citrate, malate, and fumarate) increased (p<0.05) by 71% during the first 15 s of exercise. The ΣTCAI was lower (p<0.05) in DCA than in CON at rest [0.18±0.02 vs 0.64±0.09 mmol kg⁻¹ dry weight (d.w.)], after 5 s (0.30±0.07 vs 0.85±0.14 mmol kg⁻¹ d.w.), and 15 s of exercise (0.60±0.07 vs 1.09±0.16 mmol kg⁻¹ d.w.), but not different after 3 min (3.12±0.53 vs 3.23±0.55 mmol kg⁻¹ d.w.). Despite differences in the level of muscle TCAI, muscle phosphocreatine degradation was similar in DCA and CON during the first 15 s of exercise (17.5±3.3 vs 25.6±4.1 mmol kg⁻¹ d.w.). Taken together with our previous observation that DCA does not alter muscle oxygen uptake during the initial phase of intense leg kicking exercise (Bangsbo et al. Am J Physiol 282:R273–R280, 2002), the present data suggest that muscle TCAI accumulate during the initial seconds of exercise; however, this increase is not essential for the contraction-induced increase in mitochondrial respiration.     

The effects of specificity of training on rating of perceived exertion at the lactate threshold

Summary To determine the effects of cycle and run training on rating of perceived exertion at the lactate threshold (LT), college men completed a 40-session training program in 10 weeks (n=6 run training,n=5 cycle training,n=5 controls). Pre-and post-training variables were measured during graded exercise tests on both the bicycle ergometer and treadmill. ANOVA on the pre- and post-training difference scores resulted in similar improvements in for both testing protocols, regardless of training mode. The run training group increased at the LT by 58.5% on the treadmill protocol and by 20.3% on the cycle ergometer. Cycle trainers increased LT only during cycle ergometry (+38.7%). No changes were observed in the control group. No differences for RPE at the LT were found before or after training, or between testing protocols for any group. Perception of exercise intensity at the LT ranged from “very light” to “light”. The relationship between RPE and was altered by the specific mode of training, with trained subjects having a lower RPE at a given (no change in RPE at max.). It was concluded that RPE at the LT was not affected by training, despite the fact that after training the LT occurs at a higher work rate and was associated with higher absolute and relative metabolic and cardiorespiratory demands.     

Association between anaerobic components of the maximal accumulated oxygen deficit and 30-second Wingate test

The purpose of this study was to analyze the relationship between the anaerobiccomponents of the maximal accumulated oxygen deficit (MAOD) and of the 30-secondWingate anaerobic test (30-WAnT). Nine male physical education students performed: a)a maximal incremental exercise test; b) a supramaximal constant workload test todetermine the anaerobic components of the MAOD; and c) a 30-WAnT to measure the peakpower (PP) and mean power (MP). The fast component of the excess post-exercise oxygenconsumption and blood lactate accumulation were measured after the supramaximalconstant workload test in order to determine the contributions made by alactic(AL_MET) and lactic (LA_MET) metabolism. Significantcorrelations were found between PP and AL_MET (r=0.71; P=0.033) and betweenMP and LA_MET (r=0.72; P=0.030). The study results suggested that theanaerobic components of the MAOD and of the 30-WAnT are similarly applicable in theassessment of AL_MET and LA_MET during high-intensityexercise.     

The acute effects of low-intensity exercise on plasma lipids in endurance-trained and untrained young adults

Summary The acute effects of low-intensity exercise on plasma lipids were assessed in 22 healthy, normolipidaemic volunteers [mean age (SEM) 21.1 (0.2) years] of whom 11 were untrained and 11 endurance trained. Each subject walked for 2 h on a treadmill at a speed selected to elicit 30% [29.8 (3.9)%] of his or her maximal oxygen uptake. All subjects consumed a similar diet, i.e. 48% of energy from carbohydrate, for 2 days prior to the test. Pre-exercise, high-density lipoprotein (HDL) cholesterol concentration was higher in the trained group than in the untrained group [0.88 (0.06) mmol · 1^–1 vs 0.73 (0.09) mmol · 1^–1,P< 0.05]. The walk elicited an increase in blood lactate concentration (P<0.01) but glucose homeostasis was well maintained by both groups. After 2 h of walking total cholesterol had increased by 13 (0.6)% (P<0.05). HDL cholesterol concentration increased by 17 (1.6)%, so that the ratio of total to HDL cholesterol was lower after the walk than pre-exercise (P<0.05). In the endurance-trained group HDL cholesterol concentration increased progressively, being 7.9 (2.4)% higher after 1 h and 19.7 (1.6)% higher after 2h. A different response was evident in the untrained group where a rise after the 1st h [25.1 (2.3)%] was followed by a decrease towards pre-exercise values. These results show that one prolonged bout of low-intensity exercise modifies lipoprotein metabolism and hold out the interesting possibility that this response may differ in trained and untrained individuals.     

The effects of one- and two-legged exercise on the lactate and ventilatory threshold

Summary The purpose of this investigation was to compare differences between one- and two-legged exercise on the lactate (LT) and ventilation (VT) threshold. On four separate occasions, eight male volunteer subjects (1-leg =3.36 l · min^–1; 2-leg =4.27 l · min^–1) performed 1- and 2-legged submaximal and maximal exercise. Submaximal threshold tests for 1- and 2-legs, began with a warm-up at 50 W and then increased every 3 minutes by 16 W and 50 W, respectively. Similar increments occurred every minute for the maximal tests. Venous blood samples were collected during the last 30 s of each work load, whereas noninvasive gas measures were calculated every 30 s. No differences in (l · min^–1) were found between 1- and 2-legs at LT or VT, but significant differences (p<0.05) were recorded at a given power output. Lactate concentration ([LA]) was different (p<0.05) between 1-and 2-legs (2.52 vs. 1.97 mmol · l^–1) at LT. This suggests it is rather than muscle mass which affects LT and VT. for 1-leg exercise was 79% of the 2-leg value. This implies the central circulation rather than the peripheral muscle is limiting to .Supported by NSERC A7555