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).     

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.     

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.     

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     

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.     

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.     

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.     

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.     

New acquisitions in the assessment of breath-by-breath alveolar gas transfer in humans

We summarise recent results obtained in testing some of the algorithms utilised for estimating breath-by-breath (BB) alveolar O₂ transfer (VO_2A) in humans. VO_2A is the difference of the O₂ volume transferred at the mouth minus the alveolar O₂ stores changes. These are given by the alveolar volume change at constant O₂ fraction (F _AiO₂ V _Ai) plus the O₂ alveolar fraction change at constant volume [V _Ai–1(F _Ai–F _Ai–1)O₂], where V _Ai–1 is the alveolar volume at the beginning of the breath i. All these quantities can be measured BB, with the exception of V _Ai–1, which is usually set equal to the subjects functional residual capacity (FRC) (Auchincloss algorithm, AU). Alternatively, the respiratory cycle can be defined as the time elapsing between two equal O₂ fractions in two subsequent breaths (Grønlund algorithm, GR). In this case, F _AiO₂=F _Ai–1O₂ and the term V _Ai–1(F _Ai–F _Ai–1)O₂ disappears. BB alveolar gas transfer was first determined at rest and during exercise at steady-state. AU and GR showed the same accuracy in estimating alveolar gas transfer; however GR turned out to be significantly more precise than AU. Secondly, the effects of using different V _Ai–1 values in estimating the time constant of alveolar O₂ uptake (O_2A) kinetics at the onset of 120 W step exercise were evaluated. O_2A was calculated by using GR and by using (in AU) V _Ai–1 values ranging from 0 to FRC +0.5 l. The time constant of the phase II kinetics (₂) of O_2A increased linearly, with V _Ai–1 ranging from 36.6 s for V _Ai–1=0 to 46.8 s for V _Ai–1=FRC+0.5 l, whereas ₂ amounted to 34.3 s with GR. We concluded that, when using AU in estimating O_2A during step exercise transitions, the ₂ value obtained depends on the assumed value of V _Ai–1.     

Estimation of<Emphasis Type="Italic"> V̇</Emphasis>O<Subscript>2max</Subscript> from the ratio between HR<Subscript>max </Subscript>and HR<Subscript>rest</Subscript> – the Heart Rate Ratio Method

The effects of ̇raining and/or ageing upon maximal oxygen uptake (O_2max) and heart rate values at rest (HR_rest) and maximal exercise (HR_max), respectively, suggest a relationship between O_2max and the HR_max-to-HR_rest ratio which may be of use for indirect testing of O_2max. Fick principle calculations supplemented by literature data on maximum-to-rest ratios for stroke volume and the arterio-venous O₂ difference suggest that the conversion factor between mass-specific O_2max (ml·min^–1·kg^–1) and HR_max·HR_rest ^–1 is ~15. In the study we experimentally examined this relationship and evaluated its potential for prediction of O_2max. O_2max was measured in 46 well-trained men (age 21–51 years) during a treadmill protocol. A subgroup (n=10) demonstrated that the proportionality factor between HR_max·HR_rest ^–1 and mass-specific O_2max was 15.3 (0.7) ml·min^–1·kg^–1. Using this value, O_2max in the remaining 36 individuals could be estimated with an SEE of 0.21 l·min^–1 or 2.7 ml·min^–1·kg^–1 (~4.5%). This compares favourably with other common indirect tests. When replacing measured HR_max with an age-predicted one, SEE was 0.37 l·min^–1 and 4.7 ml·min^–1·kg^–1 (~7.8%), which is still comparable with other indirect tests. We conclude that the HR_max-to-HR_rest ratio may provide a tool for estimation of O_2max in well-trained men. The applicability of the test principle in relation to other groups will have to await direct validation. O_2max can be estimated indirectly from the measured HR_max-to-HR_rest ratio with an accuracy that compares favourably with that of other common indirect tests. The results also suggest that the test may be of use for O_2max estimation based on resting measurements alone.An erratum to this article can be found at     

Effect of order of exercise intensity upon cardiorespiratory,metabolic, and perceptual responses during exercise of mixed intensity

Exercise of mixed intensities can be of benefit in many different ways. However, whether physiological interaction exists between exercises of different intensity is questionable. As such, the primary aim of this study was to examine the effect of order of exercise intensity upon cardiorespiratory, metabolic, and perceptual responses during exercise of mixed intensity. Eight males and four females volunteered to serve as subjects for the study. They were informed of the purpose of the experiment and gave their written consent to participate. Each subject completed a peak oxygen uptake (O_2peak) test and two submaximal exercises of mixed intensity on three separate laboratory visits. During each submaximal exercise trial, subjects performed a 15-min (high intensity) exercise at 70%O_2peak that was followed by another 15-min (low intensity) exercise at 50%O_2peak (high/low, H/L), or a 15-min exercise at 50%O_2peak that was followed by another 15-min exercise at 70%O_2peak (low/high, L/H). Oxygen uptake (O₂), respiratory exchange ratio (R), expired ventilation (_E), heart rate (HR) and ratings of perceived exertion (RPE) were measured every 5 min throughout exercise. Energy expenditure and carbohydrate and fat oxidation were calculated from O₂ adjusted for substrate metabolism using R and then accumulated for each phase of exercise intensity as well as for the entire exercise session. O₂ and HR were higher (P<0.05), while R was lower (P<0.05) at the lower intensity in H/L than in L/H. _E and RPE were lower (P<0.05) at the higher intensity in H/L than in L/H. While no differences in caloric expenditure and carbohydrate oxidation between the two trials were observed, fat oxidation was higher (P<0.05) both at the lower intensity and for the entire trial in H/L than in L/H. It appears that during exercise of mixed intensity, placing some periods of moderate intensity exercise prior to a milder one is a more favorable sequence in that it can elicit a greater fat oxidation while being felt less stressful.     

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.     

Analysis of alveolar PCO 2 control during the menstrual cycle

We attempted to analyze how is regulated during progesterone-induced hyperventilation in the luteal phase. A model for the CO₂ control loop was constructed, in which the function of the CO₂ exchange system was described as and that of the CO₂ sensing system as . Using this model, we estimated (1) the primary increase in produced by progesterone stimulation and (2) the effectiveness (E) of the loop to regulateP _{A CO 2}, defined as P _{A CO 2} (op)/P _{A CO 2} (cl) in which op signifies open-loop and cl, closed-loop. These respiratory variables were investigated throughout the menstrual cycle in 8 healthy women. During the luteal phase, on average, increased by 9.4% andP _{A CO 2},B andH decreased by 0.33 kPa (2.5 mm Hg), 0.47 kPa (3.5 mm Hg) and 13.6%, respectively, whileS and did not change significantly. (op) increased progressively on successive days of the luteal phase whileE remained unchanged at a value of 7.9, thus there was a progressive decrease inP _{A CO 2}. The decrease inH was considered to lessen P _{A CO 2} (op) and so reduce the final deviation ofP _{A CO 2} (P _{A CO 2} (cl)) during the luteal phase. The decrease inB was found to be dependent on (op).     

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.     

Test–retest errors and the apparent heterogeneity of training response

Published reports have shown large apparent inter-individual differences of gains in maximal oxygen intake (O_2max) in response to a standard 20-week programme of aerobic conditioning that progressed to 75% of the individuals initial O_2max. The observed gains of O_2max ranged from 0 to 1,000 ml min^–1, with a coefficient of variation (CV) of 8.4%. The present analysis evaluates the potential contribution of test–retest errors to these apparent large inter-individual differences in training response. The 2-day test–retest CV for O_2max readings in 742 healthy adults was initially 5.0%, dropping to 4.1% after training. Published training responses were estimated from the mean of paired measurements obtained before and after training if readings agreed by <5%, but from the highest of paired values if these differed by >5%. Taking account of the relative proportions of single and paired observations, the weighted O_2max data for the entire sample had an effective 2-day CV of 4.3% before and 3.4% after training. Assumption 1: if the 20-week test–retest error remained similar to the 2-day figure, measurement error would contribute a CV of 5.5% to apparent training responses, or (for the stated initial mean O_2max of 2,409 ml min^–1) an SD of 132 ml min^–1. Assumption 2: if the 20-week CV was similar to that in other long-term studies (~5%), measurement error would contribute a CV of 6.1%, or a SD of 146 ml min^–1. The published data show a total SD of 202 ml min^–1 for apparent inter-individual differences in training response, with age, gender, race and baseline O_2max accounting for only 11% of this variance. After estimating the likely effect of test–retest measurement errors, the SD due to inter-individual differences would decrease to 138 ml minO_2max (assumption 1) or 123 ml min^–1 (assumption 2). We conclude that when estimating the extent of inter-individual differences in training response, allowance must be made not only for the minor effects of recognized covariates (age, gender, race and initial fitness), but also for the larger influence of test-retest measurement errors. Nevertheless, substantial inter-individual differences persist after making such adjustments. The most likely explanation of these differences is a familial aggregation of training responses.     

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.     

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.     

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.     

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).     

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.