Effects of aerobic endurance training status and specificity on oxygen uptake kinetics during maximal exercise

The main purpose of this study was to analyze the effects of exercise mode, training status and specificity on the oxygen uptake (O₂) kinetics during maximal exercise performed in treadmill running and cycle ergometry. Seven runners (R), nine cyclists (C), nine triathletes (T) and eleven untrained subjects (U), performed the following tests on different days on a motorized treadmill and on a cycle ergometer: (1) incremental tests in order to determine the maximal oxygen uptake (O_2max) and the intensity associated with the achievement of O_2max (IO_2max); and (2) constant work-rate running and cycling exercises to exhaustion at IO_2max to determine the effective time constant of the O₂ response (O₂). Values for O_2max obtained on the treadmill and cycle ergometer [R=68.8 (6.3) and 62.0 (5.0); C=60.5 (8.0) and 67.6 (7.6); T=64.5 (4.8) and 61.0 (4.1); U=43.5 (7.0) and 36.7 (5.6); respectively] were higher for the group with specific training in the modality. The U group showed the lowest values for O_2max, regardless of exercise mode. Differences in O₂ (seconds) were found only for the U group in relation to the trained groups [R=31.6 (10.5) and 40.9 (13.6); C=28.5 (5.8) and 32.7 (5.7); T=32.5 (5.6) and 40.7 (7.5); U=52.7 (8.5) and 62.2 (15.3); for the treadmill and cycle ergometer, respectively]; no effects of exercise mode were found in any of the groups. It is concluded that O₂ during the exercise performed at IO_2max is dependent on the training status, but not dependent on the exercise mode and specificity of training. Moreover, the transfer of the training effects on O₂ between both exercise modes may be higher compared with O_2max.     

Comparison of fat oxidation in arm cranking in spinal cord-injured people versus ergometry in cyclists

The aim of our study was to establish the exercise intensity with the highest fat oxidation rate in spinal cord-injured (SCI) people compared with able-bodied subjects on a stationary ergometer in order to provide recommendations for ergometer training. Ten endurance-trained wheelchair athletes [O_{2peak,armcranking} 35.9 (5.7) ml kg^–1 min^–1; mean (SE)] and ten endurance-trained cyclists [O_{2peak,cycling} 62.3 (4.6) ml kg^–1 min^–1] were studied over 20 min at 55%, 65% and 75% O_{2peak,armcranking} or O_{2peak,cycling} on a cycling ergometer, respectively, in order to find the intensity with the highest fat oxidation. Total energy expenditure, and highest oxidation rate for fat and carbohydrate were highest at 75% O_{2peak,armcranking} and O_{2peak,cycling}. Relative fat oxidation was highest at 55% O_{2peak,armcranking} and O_{2peak,cycling}. Wheelchair athletes showed a tendency for higher lactate concentrations at each intensity compared to cyclists. Well-trained wheelchair athletes and cyclists reach the highest fat oxidation in arm cranking, respectively, in cycling on a stationary ergometer at the same relative intensity of 75% O_{2peak,armcranking} and O_{2peak,cycling}. We presume that well-trained wheelchair athletes can perform ergometer training on a stationary ergometer at 75% O_{2peak,armcranking}. Results are presented as mean (SE).     

Influence of mechanical and metabolic strain on the oxygen consumption slow component during forward pulled running

The possible influence of increased eccentric mechanical work on the increase in oxygen uptake (O₂) after 3 min of running (O₂) was investigated through forward pulled running. Ten subjects ran at individually predetermined constant velocity on a treadmill, while being pulled forward. Ground reaction forces, expired gas and EMGs from leg muscles were collected after 3 min and at the end of the run. O₂ and mechanical work were then calculated. The amplitude of O₂ was 138 (139) ml·min^–1 [mean (SD)]. Increased ventilation explained only 8% of O₂. Stride frequency slightly decreased, inducing a similar decrease in internal work and total mechanical work (all P<0.01), while integrated EMG showed no modifications. It was concluded that O₂ does not come from either an increase in mechanical work production or an increase in muscular activity. O₂ could come from a lower muscle efficiency that could be due to a modification of fibre type recruitment.     

Overshoot in <Emphasis Type="Italic">V̇</Emphasis>O<Subscript>2</Subscript> following the onset of moderate-intensity cycle exercise in trained cyclists

We have previously observed that following the onset of moderate intensity cycle ergometry, the pulmonary O₂ uptake (O₂) in trained cyclists often does not increase towards its steady-state value with the typical mono-exponential characteristics; rather, there is a transient overshoot. The purpose of this study was to systematically examine this phenomenon by comparing the O₂responses to two moderate-intensity work rates and one high-intensity work rate in trained and untrained subjects. Following a ramp exercise test to the limit of tolerance for the determination of the gas exchange threshold (GET) and O_2peak, seven trained cyclists [mean (SD); O_2peak 66.6 (2.5) ml·kg^–1·min^–1] and eight sedentary subjects [O_2peak 42.9 (5.1) ml·kg^–1·min^–1] completed six step transitions from baseline cycling to work rates requiring 60% and 80% GET and three step transitions from baseline cycling to a work rate requiring 50% of the difference between GET and O_2peak (50%). O₂ was measured breath-by-breath and modelled using standard techniques. The sedentary subjects did not overshoot the steady-state O₂ at any intensity. At 60% GET, six of the seven cyclists overshot the steady-state O₂ [by an integral volume of 164 (44) ml between ~45 and 125 s]. At 80% GET, four of the seven cyclists overshot the steady-state O₂ [by an integral volume of 185 (92) ml between ~55 and 140 s]. None of the cyclists showed an overshoot at 50%. These results indicate that trained cyclists evidence an overshoot in O₂ before steady-state is reached in the transition to moderate-intensity exercise. The mechanism(s) responsible for this effect remains to be elucidated, as does whether the overshoot confers any functional or performance benefit to the trained cyclist.     

Effects of priming exercise intensity on the dynamic linearity of the pulmonary V̇O2 response during heavy exercise

Prior heavy-intensity exercise facilitates the pulmonary oxygen uptake (O₂) response during subsequent exercise, such that its kinetics returns towards first-order. To better understand this priming phenomenon, we investigated the effect of priming exercise, over a range of intensities, on the O₂ response to heavy-intensity cycle ergometry at a work rate of 50% [halfway between lactate threshold (LT) and O_2max]. Eight subjects performed two consecutive 6-min bouts separated by 6 min at 20 W. The first bout was each of: no warm-up control (CON), sub-lactate threshold (LT) at 80% of LT, and three supra-LT conditions (20%, 40%, and 60%). The O₂ response during the subsequent bout was evaluated using the effective time constant (), and the O₂ difference between minutes 3 and 6 (O_2(6–3)). The goodness-of-fit, indicative of first-order kinetics, was determined by the residual profile, and the mean square of errors (MSEr). The heart rate and blood lactate concentration ([La]r) just prior to the second bout were also measured. Compared with CON, and O_2(6–3) were significantly reduced following all supra-LT priming bouts, while the goodness-of-fit was significantly improved following 40% exercise. O_2(6–3) and [La]r were negatively correlated (P<0.05), unlike HR. In conclusion, prior exercise just above, but not below, LT facilitated the O₂ response in a threshold-like manner. Supra-LT priming exercise influenced the O₂ response allowing it to return to within as little as 12% from first-order (compared to ~50% in CON). The associated increases in circulating lactate and/or related factors seem to be centrally involved in this phenomenon.     

Peak exercise oxygen uptake and left ventricular systolic and diastolic function and arterial mechanics in healthy young men

Echocardiography can be used to estimate myocardial contractility by the assessment of the circumferential end-systolic stress-corrected left ventricular (LV) fractional shortening measured at midwall level (stress-corrected MWS). Whether stress-corrected MWS at rest predicts exercise peak oxygen uptake (peak O₂) is unknown. Also, it is not known whether the propagation rate of the early LV filling wave (E wave propagation rate, _p), a new pre-load insensitive index of LV diastolic function, and echocardiographically assessed indices of arterial stiffness correlate to peak O₂. Accordingly, we performed echocardiographic studies and exercise tests with respiratory gas analysis in 15 young healthy male subjects (mean age 27 years, range 18–36). Neither stress-corrected-MWS (r=0.20, P=NS) nor ejection fraction (r=–0.05, P=NS) correlated significantly with peak O₂. Adjustment for age and resting heart rate had no effect on the results. In separate multiple regression models adjusting for standard covariates (age, LV size and heart rate), peak O₂ correlated with _p (beta=0.98, P<0.01), as well as with E/A (beta=0.85, P<0.01), and with the isovolumic relaxation time (indicator of LV relaxation) (beta=–0.59, P<0.05). Arterial stiffness indices showed no significant relation to peak O₂. We conclude that in young healthy male subjects, resting myocardial contractility and arterial stiffness are not significant correlates of peak O₂, whereas LV diastolic function, and in particular _p, influences the variability of peak O₂.     

The V̇O2 response for an exhaustive treadmill run at 800-m pace: a breath-by-breath analysis

Recent research in which data were averaged over 10 or 30 s suggests that the O₂ response of aerobically fit individuals plateaus below O_{2 max} in an exhaustive square-wave run lasting ~2 min. To investigate this phenomenon we examined the breath-by-breath O₂ response of trained runners to an exhaustive treadmill run at 800 m pace. Eight male competitive runners completed two treadmill tests on separate days: a ramp test to exhaustion and an exhaustive square-wave run at 800-m pace. For the ramp test, the breath-by-breath data were smoothed with a 15-s moving average and the highest of the smoothed values was taken as O_{2 peak} [mean (SD): 68.9 (5.6) ml kg^–1 min^–1]. For the square-wave, the breath-by-breath data were interpolated to give one value per second and modelled using a monoexponential function. Following a delay of 11.2 (1.5) s, O₂ increased quickly [phase-2 time constant of 10.7 (2.7) s] towards an asymptote that represented just 85 (6)% of O_{2 peak} from the ramp test. Expressed in ml kg^–1 min^–1, this asymptote was independent of O_{2 peak} (r=0.04, P=0.94). However, as a percentage of O_{2 peak} it was negatively correlated with O_{2 peak} itself (r=–0.96, P<0.001). It is concluded that in an exhaustive square-wave treadmill run lasting ~2 min the O₂ of aerobically fit runners increases quickly to plateau at a level that is lower than, but independent of, O_2max     

Peak oxygen uptake during running and arm cranking normalized to total and regional skeletal muscle mass measured by magnetic resonance imaging

The purposes of our study were to determine the peak oxygen uptake ( O_2peak) per total or regional skeletal muscle (SM) mass using magnetic resonance imaging (MRI) and to investigate the relationships between SM mass and O_2peak during running and arm cranking. Eight male college swimmers aged 18–22 years [mean (SD) age 20.0 (1.3) years] were recruited to participate in this study. O₂ during running and arm cranking were measured using an automated breath-by-breath mass spectrometry system. Contiguous MRI slices were obtained from the first vertebra cervicale to the malleolus lateralis (1.0-cm slice thickness, 0-cm inter-slice gap), resulting in a total of approximately 156 images for each subject. The absolute O_2peak and the O_2peak per body mass during running and arm cranking were 3.6 (0.6) l.min^-1, 54.4 (5.9) ml.min^-1.kg^-1 and 2.5 (0.5) l.min^-1, 36.9 (5.3) ml.min^-1.kg^-1, respectively. The absolute O_2peak was higher ( P <0.05) during running than during arm cranking, but not the O_2peak per regional area SM mass. The lower body SM mass was correlated to the O_2peak during running ( r =0.95, P <0.001). All measurements and calculated values were expressed as the mean (SD) for the eight subjects. To eliminate the influence of body mass and fat-free mass (FFM), a regression analysis was performed on the mass-residuals of the O_2peak during running and the lower body SM mass. The residuals of lower body SM mass were correlated to the residuals of O_2peak during running, with respect to body mass ( r =0.90, P <0.001) and FFM ( r =0.82, P <0.05). These results suggest that the MRI-measured lower body SM mass was closely associated to the absolute O_2peak during running, independently of body mass or FFM, and that the O_2peak per regional SM mass corresponded, regardless of the type of exercise (upper or lower body).     

Kinetics of oxygen uptake during arm cranking with the legs inactive or exercising at moderate intensities

The purpose of this study was to compare the kinetics of oxygen uptake (O₂) during arm cranking with the legs inactive or exercising. Each subject (n=8) performed three exercise protocols: 6-min arm cranking at an intensity of 60% of peak oxygen uptake (O_2peak, AC₆₀) and 6-min combined arm cranking and leg cycling in which AC₆₀ was added to on-going leg cycling at an intensity of 20% or 40% of O_2peak (LC₂₀ and LC₄₀: AC₆₀LC₂₀ and AC₆₀LC₄₀, respectively). After the onset of arm cranking, O₂ tended to increase until the end of arm cranking in all of the three exercise modes. The amplitudes of this increase in O₂ were 0.98 (0.18), 0.93 (0.16) and 0.84 (0.12) l.min^–1 during AC₆₀, AC₆₀LC₂₀ and AC₆₀LC₄₀, respectively, and there were significant differences between values for each exercise. The data are presented as means and standard deviations. There were no significant differences in the effective O₂ time constant, partial O₂ deficit, and the difference between the values of O₂ measured at 3 and 6 min in the three exercise modes. The present results indicate that the amplitude of the increase in O₂ is reduced during arm cranking with the legs exercising, that this reduction becomes greater with increases in the intensity of leg cycling, and that the rate of increase in O₂ is not affected by the additional muscle mass of the legs exercising below moderate intensities. The decrease in the amplitude of increase in O₂ might be caused by reduction in oxygen supply to the exercising arms due to large muscle mass and/or overlaps of activity of stabilizing muscles during combined arm and leg exercise.     

Effects of active recovery between series on performance during an intermittent exercise model in young endurance athletes

Abstract The purpose of our study was to compare time to exhaustion (t_lim) and time spent at a high level of oxygen uptake (O₂) during two high-intensity short intermittent exercises (30 s-30 s) realized with or without series. Eleven young endurance-trained athletes [16.6 (0.4) years] took part in three field tests until exhaustion: (1) a maximal graded test to measure their maximal aerobic velocity (MAV) and maximal oxygen uptake (O_2max); (2) and (3) two randomized intermittent exercises (30 s at 110% of MAV alternated with 30 s at 50% of MAV): one alternating repetitions non-stop (IE) and another including 4 min recovery every six repetitions (IEs). The mean t_lim measured during IEs was significantly longer than IE [respectively 960.0 (102.0) s vs 621.8 (56.2) s]. The time spent at O_2max(t_O2max) and the time spent above 90% of O_2max(t_90%O2max) did not differ significantly according to the type of exercise: with or without series [respectively t_O2max was 158.2 (59.7) s vs 178.0 (56.5) s and t_90%O2max was 290.4 (84.3) s vs 345.0 (61.6) s] but when expressed as a relative value, t_90%O2max during IEs was significantly lower than during IE [respectively 36.4 (10.4)% t_lim vs 58.3 (8.7)% t_lim]. Despite a significant decrease (P<0.005) of time to achieve 90% of O_2max at the start of each series during IEs [respectively 165.0 (43.1) s for the first series and 82.5 (15.8) s for the second series (n=6)] the time spent under 90% of O_2max limited the t_90%O2max during each series. In conclusion, our results showed that intermittent exercise with series does not permit an increase in the time spent at a high level of O₂; however, the athletes performed more repetitions of short intense exercise.     

A comparison of respiratory compensation thresholds of anaerobic competitors,aerobic competitors and untrained subjects

This study compared respiratory compensation thresholds (RCT) (CO₂ inflection point) of competitors in highly aerobic events (aerobic competitors, ARC) (n=16), competitors in highly anaerobic events (anaerobic competitors, ANC) (n=15), and untrained subjects (UT) (n=25). Maximal oxygen consumption (O_2max), respiratory compensation threshold as a percentage of O_2max (RCT), and O₂ at RCT (O_2RCT) were determined during a maximal Bruce treadmill protocol. O_2max (ml kg^–1 min^–1) was significantly greater (P<0.05) for ARC [67.2 (8.5)] than for ANC [50.0 (7.8)] and UT [43.8 (5.4)]. However, the difference between ANC and UT only approached significance (P=0.07). RCT was not significantly different between ARC [76.3 (8.7)] and ANC [80.7 (6.8)] but was significantly lower (P<0.05) for UT [62.5 (8.8)]. O_2RCT (ml kg^–1 min^–1) was significantly greater (P<0.05) for ARC [51.6 (11.0)] and ANC [40.2 (6.6)] than for UT [27.4 (5.4)], with a significant difference also between ARC and ANC. While used as a criterion for group assignment, greater O_2max, as well as RCT values in ARC (vs UT), reflect chronic aerobic training adaptations. ANC demonstrated O_2max values intermediate to ARC and UT, with RCT very comparable to those found in ARC. The results suggest subjects competitive in highly anaerobic events do not possess excessively high O_2max values. These individuals, however, demonstrate a high RCT when values are expressed relative to O_2max. Oxygen consumption at the RCT in this group is superior to that in UT but inferior to that in ARC, which likely has important implications regarding performance.     

Respiratory kinematics by optoelectronic plethysmography during exercise in men and women

Gender differences in resting pulmonary function are attributable to the smaller lung volumes in women relative to men. We sought to investigate whether the pattern of response in operational lung volumes during exercise is different between men and women of similar fitness levels. Breath-by-breath volume changes of the entire chest wall ( _CW) and its rib cage ( _Rc) and abdominal ( _Ab) compartments were studied by optoelectronic plethysmography in 15 healthy subjects (10 men) who underwent a symptom-limited ( W _peak) incremental bicycle test. The pattern of change in end-inspiratory and end-expiratory _CW ( _CW,EI and _CW,EE, respectively) did not differ between the sexes. With increasing workload the decrease in _CW,EE was almost entirely attributable to a reduction in end-expiratory _Ab, whereas the increase in _CW,EI was due to the increase in end-inspiratory _Rc in both sexes. In men, at W _peak tidal volume [ _T, 2.7 (0.2) l] and inspiratory capacity [IC, 3.4 (0.2) l] were significantly greater than in women [1.8 (0.2) and 2.6 (0.2) l, respectively]. However, after controlling for lung size using forced vital capacity (FVC) as a surrogate, the differences between men and women were eliminated [ _T /FVC 49 (3) and 45 (3) respectively, and IC/FVC 63 (2) and 65 (3) respectively]. All data are presented as mean (SE). In both men and women the contribution of the rib cage compartment to _T expansion was significantly greater than that of the abdominal compartment. We conclude that gender differences in operational lung volumes in response to progressive exercise are principally attributable to differences related to lung size, whereas compartmental chest wall kinematics do not differ among sexes.     

Effects of shortening velocity and of oxygen consumption on efficiency of contraction in dog gastrocnemius

Previous observations have shown that, in isolated perfused dog gastrocnemii in situ, stimulated to aerobic rhythmic isotonic tetanic contractions (at about 40% of maximal isometric force), only about 20% of the overall metabolic power (proportional to the rate of O₂ consumption, O₂) was converted into mechanical power (Ẇ). Here we report that, in the same preparation, the maximal velocity during the shortening phase of each tetanus (v, mm s^–1) increased with the rate of energy dissipation, as given by the difference between O₂ and Ẇ (W kg^–1). The relationship between these variables was described by: v=2.85(O₂–Ẇ)^1.24 (R ²=0.85; n=17). A mathematical analysis of this equation shows that the overall mechanical efficiency (=ẆO₂ ^–1) decreased with increasing v (at constant O₂), whereas it increased with increasing O₂ (at constant v). The net effect of this state of affairs was that the decrease of over the entire range of work intensities was relatively minor (from 0.22 to 0.15), in spite of a large increase of v, (from 40 to 120 mm s^–1), thanks to the concomitant increase of O₂ (from 10 to 25 W kg^–1). So, under these experimental conditions, the energetics of work performance seems to be governed by two conflicting needs. The need for a sufficiently high shortening speed (and hence power output), itself requiring a sufficiently large energy dissipation rate, which, however, brings about a fall in . This is counteracted by the increased O₂, which in turn leads to an increased efficiency at the expense of a fall in shortening speed.This article was published in Human Muscular Function during Dynamic Exercise, Marconnet P, Saltin B, Komi P, Poortmans J (eds) Med Sport Sci 41 (series editors: M. Hebbelink, R.J. Shephard) pp. 1–9, Karger, Basel, 1996. It is reproduced with minor editorial modifications. Permission from Karger is gratefully acknowledged.     

Dichloroacetate does not speed phase-II pulmonary V̇O2 kinetics following the onset of heavy intensity cycle exercise

We hypothesised that pharmacological activation of the pyruvate dehydrogenase enzyme complex (PDC) by dichloroacetate (DCA) would speed phase-II pulmonary O₂ uptake (O₂) kinetics following the onset of high-intensity, sub-maximal exercise. Eight healthy males (aged 19–33 years) completed two square-wave transitions of 6 min duration from unloaded cycling to a work-rate equivalent to ~80% of peak O₂ either with or without prior i.v. infusion of DCA (50 mg kg^–1 body mass in 50 ml saline). Pulmonary O₂ was measured breath-by-breath throughout all tests, and O₂ kinetics were determined using non-linear regression techniques from the averaged individual response to each of the conditions. Infusion of DCA resulted in significantly lower blood [lactate] during the baseline cycling period (means±SEM: control 0.9±0.1, DCA 0.5±0.1 mM; P<0.01) consistent with successful activation of PDC. However, DCA had no discernible effect on the rate at which O₂ increased towards the initially anticipated steady state following the onset of exercise as reflected in the time constant of the fundamental O₂ response (control 26.7±4.1, DCA 27.7±2.8 s). These results indicate that the principal limitation to oxidative metabolism following the onset of high-intensity, sub-maximal cycle exercise lies downstream from PDC and/or that muscle O₂ consumption is primarily under feedback control via the concentration of one or more of the reactants associated with ATP hydrolysis.     

The VO2 response to exhaustive square wave exercise: influence of exercise intensity and mode

We investigated the oxygen uptake (O₂) response to exhaustive square wave exercise of approximately 2, 5 and 8 min duration in cycling and running. Nine males completed a ramp test and three square wave tests on a motorised treadmill and the same four tests on a cycle ergometer, throughout which gas exchange was assessed (Douglas bag method). The peak O₂ from the ramp test was higher for running than for cycling [mean (SD): 58.4 (2.8) vs. 55.9 (3.7) ml.kg^–1.min^–1; P=0.04]. However O_2max (defined as the highest O₂ achieved in any of the four tests) did not differ between running and cycling [60.0 (2.9) vs. 58.5 (3.3) ml.kg^–1.min^–1; P=0.15]. The peak O₂ was similar (P>0.1) for the 5 and 8 min square wave tests [98.5 (1.8) and 99.2 (2.3) %O_2max for running; 97.0 (4.2) and 97.5 (2.0) %O_2max for cycling] but lower (P<0.001) for the 2-min test [91.8 (2.5) and 89.9 (5.5) %O_2max for running and cycling respectively]. O₂ increased over the final two 30-s collection periods of the 2-min test for cycling [O₂=0.18 (0.15) l.min^–1; P<0.01] but not running [O₂=0.00 (0.09) l.min^–1; P=0.98]. We conclude that in the aerobically fit the peak O₂ for square wave running or cycling at an intensity severe enough to result in exhaustion in approximately 2 min is below O_2max. In running, O₂ plateaus at this sub-maximal rate.     

Absence of long-term modulation of ventilation by dead-space loading during moderate exercise in humans

The stability of arterial PCO₂ (P_aCO₂) during moderate exercise in humans suggests a CO₂-linked control that matches ventilation (_E) to pulmonary CO₂ clearance (CO₂). An alternative view is that _E is subject to long-term modulation (LTM) induced by hyperpnoeic history. LTM has been reported with associative conditioning via dead-space (V_D) loading in exercising goats (Martin and Mitchell 1993). Whether this prevails in humans is less clear, which may reflect differences in study design (e.g. subject familiarisation; V_D load; whether or not _E is expressed relative to CO₂; choice of P_aCO₂ estimator). After familiarisation, nine healthy males performed moderate constant-load cycle-ergometry (20 W-80 W-20 W; <lactate threshold, _L): day 1, pre-conditioning, n=3; day 2, conditioning (V_D=1.59 l, doubling _E at 20 W and 80 W), n=8 with 10 min rest between tests; and, after 1 h rest, post-conditioning, n=3. Gas exchange was determined breath-by-breath. Post-conditioning, neither the transient [phase 1, phase 2 (1, 2)] nor steady-state _E exercise responses, nor their proportionality to CO₂, differed from pre-conditioning. For post-conditioning trial 1, steady-state _E was 28.1 (4.7) l min^–1 versus 29.1 (3.8) l min^–1 pre-conditioning, and mean-alveolar PCO₂ (a validated P_aCO₂ estimator) was 5.53 (0.48) kPa [41.5 (3.6) mmHg] versus 5.59 (0.49) kPa [41.9 (3.7) mmHg]; the 1 _E increment was 4.2 (2.9) l min^–1 versus 5.2 (1.9) l min^–1; the 2 _E time-constant () was 64.4 (24.1) s versus 64.1 (25.3) s; _E/CO₂ was 1.12 (0.04) versus 1.10 (0.04); and the _E-CO₂ slope was 21.7 (3.4) versus 21.2 (3.2). In conclusion, we could find no evidence to support ventilatory control during moderate exercise being influenced by hyperpnoeic history associated with dead-space loading in humans.     

Physiological responses to intermittent and continuous exercise at the same relative intensity in older men

We investigated the physiological responses in older men to continuous (CEx) and intermittent (IEx) exercise. Nine men [70.4 (1.2) years, O_2peak: 2.21 (0.20) l min^–1; mean (SE)] completed eight exercise tests (two CEx and six IEx) on an electronically braked cycle ergometer in random order. CEx and IEx were performed at 50% and 70% O_2peak. IEx was performed using 60sE:60sR, 30sE:30sR and 15sE:15sR exercise to rest ratios. The duration of exercise was adjusted so that the total amount of work completed was the same for each exercise test. Oxygen uptake (O₂), minute ventilation (_E) and heart rate (HR) were measured at the mid-point of each exercise test. Arterialised blood samples were obtained at rest and during exercise and analysed for pH and PCO₂. At the same relative intensity (50% or 70% O_2peak), IEx resulted in a significantly lower (P<0.01) O₂, _E and HR than CEx. There were no significant differences (P>0.05) in O₂, _E and HR measured at the mid point of the three exercise to rest ratios at 50% and 70% O_2peak. pH and PCO₂ during CEx and IEx at 50% O_2peak were not significantly different from rest. CEx performed at 70% O_2peak resulted in significant decreases (P<0.05) in pH and PCO₂. There was a significant decrease (P<0.05) in pH only during the 60sE:60sR IEx at 70% O_2peak. Changes in arterialised PCO₂ during the 60sE:60sR, 30sE:30sR and 15sE:15sR at both 50% and 70% O_2peak exercise tests were not significant. When exercising at the same percentage of O_2peak and with the total amount of work fixed, IEx results in significantly lower physiological responses than CEx in older men. All results are given as mean (SE).     

Non-linear cardiac output dynamics during ramp-incremental cycle ergometry

Published literature asserts that cardiac output (=O₂×1/C_(a-v)O₂) increases as a linear function of oxygen uptake with a slope of approximately 5–6 during constant work rate exercise. However, we have previously demonstrated that C_(a-v)O₂ has a linear relationship as a function of O₂ during progressively increasing work rate incremental exercise. Therefore, we hypothesized that may indeed have a non-linear relationship with respect to O₂ during incremental, non-steady state exercise. To investigate this hypothesis, we performed five maximal progressive work rate exercise studies in healthy human subjects. was determined every minute during exercise using measured breath-by-breath O₂, and arterial and pulmonary artery measurements of PO₂, hemoglobin saturation, and content. was plotted as a function of O₂ and the linear and non-linear (first order exponential and hyperbolic) fits determined for each subject. Tests for linearity were performed by assessing the significance of the quadratic terms added to the linear relation using least squares estimation in linear regression. Linearity was inadequate in all cases (group P<0.0001). We conclude that cardiac output is a non-linear function of O₂ during ramp-incremental exercise; the pattern of non-linearity suggests that while the kinetics of are faster than those of O₂ they progressively slow as work rate (and O₂) increases.     

Perceived speech difficulty during exercise and its relation to exercise intensity and physiological responses

The aim of this study was to establish how ratings of perceived speech production difficulty (PSPD) during exercise of varying intensities are correlated with various physiological responses, in order to determine whether the PSPD is suitable for prescribing exercise training intensity. An incremental running test was performed to establish the subjects maximal oxygen consumption (O_2max) and ventilatory anaerobic threshold (VAT). During the test, the subjects were asked to read a written text. The subjects graded their PSPD at each stage of the test using a 13-level PSPD scale. Throughout the test, various cardiopulmonary parameters were measured breath-by-breath. Regressions of O₂, heart rate (HR), and pulmonary ventilation ( _E), all as percentages of their respective measured maximal values, plotted as a function of PSPD showed that the overall associations among those variables are strong and statistically significant (P<0.05). However, the individual variability within each relative O₂, _E or HR was found to be rather large. The subjects distribution in relation to their PSPD at the VAT scattered widely across the PSPD scale. These results indicate that estimating exercise intensity by measuring speech difficulty is not valid. Thus it may be assumed that the talk test, in its present non-standardized form, is a questionable substitute for the anaerobic threshold, HR, or for any other objective physiological measure for prescribing individual training exercise intensity.     

Influence of muscle fibre type and pedal rate on the V̇O2-work rate slope during ramp exercise

We hypothesised that the ratio between the increase in oxygen uptake and the increase in work rate (O₂/WR) during ramp cycle exercise would be significantly related to the percentage type II muscle fibres at work rates above the gas exchange threshold (GET) where type II fibres are presumed to be active. We further hypothesised that ramp exercise at higher pedal rates, which would be expected to increase the proportional contribution of type II fibres to the total power delivered, would increase the O₂/WR slope at work rates above the GET. Fourteen healthy subjects [four female; mean (SD): age 25 (3) years, body mass 74.3 (15.1) kg] performed a ramp exercise test to exhaustion (25 W min^–1) at a pedal rate of 75 rev min^–1, and consented to a muscle biopsy of the vastus lateralis. Eleven of the subjects also performed two further ramp tests at pedal rates of 35 and 115 rev min^–1. The O₂/WR slope for exercise <GET (S ₁) was significantly correlated with O₂ peak in ml kg^–1 min^–1 (r=0.60; P<0.05), whereas the O₂/WR slope for exercise >GET (S ₂) was significantly correlated to percentage type II fibres (r=0.54; P=0.05). The ratio between the O₂/WR slopes for exercise above and below the GET (S ₂/S ₁) was significantly greater at the pedal rate of 115 rev min^–1 [1.22 (0.09)] compared to pedal rates of 35 rev min^–1 [0.96 (0.02)] and 75 rev min^–1 [1.09 (0.05), (P<0.05)]. The greater increase in S ₂ relative to S ₁ in subjects (1) with a high percentage type II fibres, and (2) at a high pedal rate, suggests that a greater recruitment of type II fibres contributes in some manner to the xs O₂ observed during ramp exercise.