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     

Sweat lactate response between males with high and low aerobic fitness

Sweat lactate indirectly reflects eccrine gland metabolism. However the potential influence of aerobic fitness on sweat lactate is not well-understood. Six males with high aerobic fitness [peak oxygen consumption (O₂peak): 61.6 (2.5) ml·kg^–1·min^–1] and seven males with low aerobic fitness [O₂peak: 41.8 (6.4) ml·kg^–1·min^–1] completed a maximal exertion cycling trial followed on a different day by 60 min of cycling (60 rev·min^–1) in a 30°C wet bulb globe temperature environment. Intensity was individualized at 90% of the ventilatory threshold ( _E/O₂ increase with no concurrent _E/CO₂ increase). Sweat samples were collected from the lumbar region every 10 min and analyzed for lactate concentration. Sweat rate (SR) was significantly greater (p<0.05) for subjects with a high [1445 (254) ml·h^–1] versus a low [1056 (261) ml·h^–1] fitness level. Also, estimated total lactate excretion (SR×mean sweat lactate concentration) was marginally greater (p=0.2) in highly fit males. However, repeated measures ANOVA showed no significant differences (p>0.05) between groups for sweat lactate concentration at any time point. Current results show highly fit (vs. low fitness level) males have a greater sweat rate which is consistent with previous literature. However aerobic fitness and subsequent variations in SR do not appear to influence sweat lactate concentrations in males.     

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.     

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).     

Differences in the energy cost between children and adults during front crawl swimming

There is little information available about the swimming economy of children. The aim of this study was to examine any possible differences in swimming economy in children and adults, swimming front crawl submaximally. Swimming economy was compared in adults [n=13, aged 21.4 (3.7) years] and children [n=10, aged 11.8 (0.8) years] tested at four submaximal 6-min workloads. Oxygen consumption (O₂) was measured with Douglas bags in a 25-m pool and pacer lights were used to control the velocities. Swimming economy was scaled to body size using mass (BM), body surface area (BSA) and body length (BL). Children had lower O₂ (litres per minute) at a given velocity than the adults, with 1.86 (0.28) and 2.39 (0.20) l min^–1 respectively (at 1.00 m s^–1). When scaling for size, children had higher O₂ measured in litres per square metre per minute and millilitres per kilogram per minute (divided by BSA and BM) than adults. The O₂ divided by BL was found not to differ between the two groups. The O₂ cost of swimming 1 m at a velocity of 1.00 m s^–1 was lower in the children [31.0 (4.6) ml m^–1] than in the adults [39.9 (3.3) ml m^–1 P<0.01], probably due to a lower total drag in the children. The results also showed that for children a relationship between swimming velocity cubed and O₂ exists as shown earlier for adults. It is concluded that, when scaling for BSA and BM, children are less economical than adults, when scaling for BL, children are equally economical, and when considering energy cost per metre and absolute O₂, children are more economical than the adults.     

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.     

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 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.     

Velocity at V̇O2 max and peak treadmill velocity are not influenced within or across the phases of the menstrual cycle

Velocity at VO_{2 max} (vO_{2 max}) and peak treadmill velocity (PTV) are variables highly predictive of endurance performance. However, how these variables are affected by the menstrual cycle is unknown. The aim of this study was to assess the effect of the menstrual cycle on vO_{2 max} and PTV. Ten, female runners were studied across three menstrual cycles. Training, menstrual history and mood states were assessed for 2 months, with daily salivary samples taken to detect menstrual phases. During the third menstrual cycle, participants completed a maximal test to determine O_{2 max}, vO_{2 max} and PTV in the early follicular phase, late follicular phase, early luteal phase, late luteal phase and menses. Progesterone increased at the onset of the luteal phase [mean (SEM); 490 (73.6) pmol l^–1] compared to the follicular phase [344.6 (59.7) pmol l^–1). No significant differences in the psychological mood states between the phases of the menstrual cycle were found (P>0.05). No significant differences in vO_{2 max} (P=0.611), or PTV (P=0.472) were found between the phases of the menstrual cycle. Thus, vO_{2 max} and PTV are not affected by the monthly menstrual cycle in female endurance runners.     

Prediction of sprint triathlon performance from laboratory tests

This study investigated whether sprint triathlon performance can be adequately predicted from laboratory tests. Ten triathletes [mean (SEM), age 21.8 (0.3) years, height 179 (2) cm, body mass 67.5 (2.5) kg] performed two graded maximal exercise test in random order, either on their own bicycle which was mounted on an ergometer or on a treadmill, to determine their peak oxygen consumption (O₂peak). Furthermore, they participated in two to three 30-min constant-load tests in both swimming, cycling and running to establish their maximal lactate steady state (MLSS) in each exercise mode. Swim tests were performed in a 25-m swimming pool (water temperature 27°C). During each test heart rate (HR), power output (PO) or running/swimming speed and blood lactate concentration (BLC) were recorded at regular intervals. Oxygen uptake (O₂) was continuously measured during the graded tests. Two weeks after the laboratory tests all subjects competed in a triathlon race (500 m swim, 20-km bike, 5-km run) [1 h 4 min 45 s (1 min 38 s)]. Peak HR was 7 beats·min^–1 lower in the graded cycle test than in the treadmill test (p<0.05) at similar peak BLC (~10 mmol·l^–1) and O₂peak (~5 L·min^–1). High correlations were found between O₂peak during cycling (r=–0.71, p<0.05) or running (r=–0.69, p<0.05) and triathlon performance. Stepwise multiple regression analysis showed that running speed and swimming speed at MLSS, together with BLC in running at MLSS, yielded the best prediction of performance [1 h 5 min 18 s (1 min 49 s)]. Thus, our data indicate that exercise tests aimed to determine MLSS in running and swimming allow for a precise estimation of sprint triathlon performance.     

Gender difference in the metabolic response to prolonged exercise with [13C]glucose ingestion

The metabolic response to a 120-min cycling exercise with ingestion of [¹³C]glucose (3 g kg^–1) was compared in women in the follicular phase of the cycle [n=6; maximum rate of oxygen uptake (O_2max) 44.7 (2.6) ml kg^–1 min^–1] and in men [n=6; O_2max 54.2 (4.3) ml kg^–1 min^–1] working at the same relative workload (~65% O_2max: 107 and 179 W in women and men, respectively). We hypothesized that the contribution of endogenous substrate oxidations (indirect respiratory calorimetry corrected for protein oxidation) to the energy yield will be similar in men and women, but that women will rely more than men on exogenous glucose oxidation. Over the exercise period, the respective contributions of protein, lipid and carbohydrate oxidation to the energy yield, were similar in men [3.7 (0.9), 21.7 (2.9) and 74.6 (3.5)%] and women [3.4 (0.8), 21.5 (2.2), 75.1 (2.5)%]. The rate of exogenous glucose oxidation was ~45% lower in women than men (0.5 and 0.6 g min^–1 vs 0.7 and 0.9 g min^–1, between min 40 and 80, and min 80 and 120, respectively). However, when the ~39% difference in absolute workload and energy expenditure was taken into account, the contribution of exogenous glucose oxidation to the energy yield was similar in men and women: 22.5 vs 24.2% between min 40 and 80, and 25.7 and 28.5% between min 80 and 120, respectively. These data indicate that when fed glucose, the respective contributions of the oxidation of the various substrates to the energy yield during prolonged exercise at the same %O_2max are similar in men and in women in the follicular phase of the cycle.     

Interleukin-6 response to exercise during acute and chronic hypoxia

Prolonged exercise is associated with increased plasma levels of the cytokine interleukin-6 (IL-6). Both circulating catecholamine levels and exercise intensity have been related to the exercise-derived IL-6. During hypoxia and acclimatization, changes in sympathetic activity is seen, and also a given workload becomes more intense in hypoxia. Therefore, hypoxia offers a unique opportunity to study the effect of catecholamines and intensity on exercise-derived IL-6. In the present study, eight Danish sea-level residents performed 60 min of cycle ergometer exercise at sea level (SL) (154 W, 45% maximal O₂ consumption, O₂max), in acute (AH) and chronic hypoxia (CH), at the same absolute (_abs) (AH_abs=154 W, 54% O₂max; CH_abs=154 W, 59% O₂max) and same relative (_rel) (AH_rel=130 W, 46% O₂max; CH_rel=120 W, 44% O₂max) workload. We hypothesized that the IL-6 response to exercise at the same absolute workload would be augmented during hypoxia compared with sea level, and that these changes would not correlate with changes in catecholamines. In AH_abs (2.35 pg·ml^–1) and CH_abs (3.34 pg·ml^–1) the IL-6 response to exercise was augmented (p<0.05) compared with that at sea level (0.78·ml^–1). In addition, after 60 min of bicycling at sea level, AH_rel (1.02 pg·ml^–1) and CH_rel (1.31 pg·ml^–1) resulted in similar IL-6 responses. The augmented IL-6 response during AH_abs and CH_abs did not match changes in circulating catecholamine levels when comparing all trials. We conclude that the plasma IL-6 concentration during exercise in hypoxia is intensity dependent, and that factors other than catecholamine levels are more important for its regulation.     

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.     

Integrated characterization of the human chemoreflex system controlling ventilation,using an equilibrium diagram

The chemoreflex system controlling ventilation consists of two subsystems, i.e., the central controller (controlling element), and peripheral plant (controlled element). We developed an integral framework to quantitatively characterize individual ventilatory regulation by experimental determination of an equilibrium diagram using a modified metabolic hyperbola and the CO₂ response curve. In 13 healthy males, the steady-state arterial CO₂ pressure (P_aCO₂) and minute ventilation (_e) were measured. To characterize the central controller, we changed fraction of inspired CO₂ (0, 3.5, 5 and 6% CO₂ in 80% oxygen with nitrogen balance) and measured the P_aCO₂–_e relation. To characterize the peripheral plant, we altered _e by hyper- or hypoventilation using a visual feedback method, which made it possible to control both tidal volume and breathing frequency, and measured the _e–P_aCO₂ relation. The intersection between the two relationship lines gives the operating point. The relationship between P_aCO₂ and _e for the central controller was reasonably linear in each subject (r²=0.808~0.995). The peripheral plant approximated a modified metabolic hyperbolic curve (r²=0.962~0.996). The operating points of the system estimated from the two relationship lines were in good agreement with those measured under the closed-loop condition. The gain of the central controller was 1.9 (1.0) l min^–1 mmHg^–1 and that of the peripheral plant was 3.0 (0.5) mmHg l^–1 min^–1. The total loop gain, the product of the two gains, was 5.3 (2.5). We conclude that human ventilatory regulation by the respiratory chemoreflex system can be quantitatively characterized using an equilibrium diagram. This framework should be useful for understanding the mechanisms responsible for abnormal ventilation under various pathophysiological conditions.     

Aerobic determinants of the decline in preferred walking speed in healthy, active 65- and 80-year-olds

The preferred walking speed is a common measure of mobility that declines with age and has been related to maximal oxygen uptake (O_2,max). The present study determined whether this decline is associated with a higher percentage of the ventilatory threshold in older adults walking at their preferred speed. We compared the preferred walking speed and O₂ at this speed in relation to both O_2,max and O₂ corresponding to the ventilatory threshold (T _VE) in healthy, physically active sexagenarians (G65, n=10) and octogenarians (G80, n=10) walking on a treadmill. The preferred walking speed was lower in G80 (1.16±0.09 m·s^–1) than in G65 (1.38±0.09 m·s^–1; P<0.001). Energy expenditure and the energy cost of walking at the preferred walking speed were not significantly different between the two groups. G80 subjects exhibited significantly higher fractions of O_2,max (60.8±8.0%) and T _VE (74.2±7.9%) at the preferred walking speed than G65 (42.9±5.0 and 53.2±5.7% respectively; P<0.001). Multiple regression analysis showed that the fraction of T _VE was the main determinant, with a small contribution of height, in the decline in the preferred walking speed in healthy and active elderly subjects (R ²=64%; P<0.001). These findings show that with age, walking at the preferred speed requires a higher fraction of T _VE. This increase in the relative physiological effort at preferred walking speed could explain the reduction in this gait speed in healthy older subjects.     

Physiology of difficult rock climbing

The purpose of this review is to explore existing research on the physiological aspects of difficult rock climbing. Findings will be categorized into the areas of an athlete profile and an activity model. An objective here is to describe high-level climbing performance; thus the focus will primarily be on studies that involve performances at the 5.11/6c (YDS/French) level of difficulty or higher. Studies have found climbers to be small in stature with low body mass and low body fat. Although absolute strength values are not unusual, strength to body mass ratio is high in accomplished climbers. There is evidence that muscular endurance and high upper body power are important. Climbers do not typically possess extremely high aerobic power, typically averaging between 52–55 ml·kg^–1·min^–1 for maximum oxygen uptake. Performance time for a typical ascent ranges from 2 to 7 min and oxygen uptake (O₂) averages around 20–25 ml·kg^–1·min^–1 over this period. Peaks of over 30 ml·kg^–1·min^–1 for O₂ have been reported. O₂ tends to plateau during sustained climbing yet remains elevated into the post-climb recovery period. Blood lactate accumulates during ascent and remains elevated for over 20 min post-climbing. Handgrip endurance decreases to a greater degree than handgrip strength with severe climbing. On the basis of this review, it appears that a specific training program for high-level climbing would include components for developing high, though not elite-level, aerobic power; specific muscular strength and endurance; ATP–PC and anaerobic glycolysis system power and capacity; and some minimum range of motion for leg and arm movements.     

Measurement of exercise cardiac output by thoracic impedance in healthy children

The purpose of this study was to track changes in stroke volume during exercise by impedance cardiography in order to validate the method, and to obtain such data in a large number of healthy children for reference purposes. One hundred and fifteen healthy children (aged 7–19 years) performed progressive exercise to voluntary exhaustion with work increments every minute on a cycle ergometer. Oxygen uptake (O₂) was measured on a breath-by-breath system. Cardiac output was measured with an ICG-M501 impedance cardiograph. Stroke volume was normalized for body surface area and expressed as stroke volume index. Cardiac output was regressed against O₂, and differences between stroke volume index at rest and exercise were assessed by repeated measures analysis of variance. Cardiac output increased linearly with O₂ in all subjects: individual slopes and intercepts averaged 5.16 (1.56) lmin^–1 per lmin^–1 O₂, and 4.25 (1.92) lmin^–1, respectively [mean (SD)]. Stroke volume index rose by an average of 29% from rest to exercise, reaching a maximum of 52 mlm^–2 in boys and girls. Most subjects demonstrated a continuous, gentle rise in stroke volume index with increasing work rate, though a minority demonstrated a falling index as work increased above the anaerobic threshold, despite rising cardiac output. Impedance cardiography accurately tracks cardiac output and can be a useful clinical and research tool in pediatric cardiology and exercise physiology.     

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 anthropometrical and physiological characteristics of elite water polo players

In order to examine the physical and physiological demands of water polo, we assessed the profile of elite water polo players. Nineteen male professional water polo players (age: 25.5±5.0 years, height: 184.5±4.3 cm body mass: 90.7±6.4 kg) underwent body composition assessment by dual-energy X-ray absorptiometry. We also evaluated peak oxygen consumption O_2peak, lactate threshold (LT), energy cost of swimming (C_s), anaerobic capacity and isokinetic shoulder strength. Body fat (%) was 16.8±4.4, lean mass (LM) 75.1±4.9 kg and bone mineral density (BMD) 1.37±0.07 g·cm^–2 . O_2peak was 57.9±7 ml·kg^–1· min^–1 . LT was identified at 3.9±0.7 mmol·l^–1 at a swimming velocity (v) of 1.33±0.05 m·s^–1 with a heart rate of 154±7 bpm, corresponding to an intensity of 83±9 of O_2peak. The average C_s of swimming at the LT was 1.08±0.04 kJ·m^–1 . C_s at LT was correlated to body mass index (BMI) (r=0.22, P=0.04) and to swimming performance at 400 m (r=0.86, P=0.01) and 4×50 m (r=0.84, P<0.01). Internal rotator muscles were stronger compared to the external rotators by a 2:1 ratio. This study provides a quantitative representation of both physical and physiological demands of water polo and proposes a comprehensive battery of tests that can be used for assessing the status of a team.     

Cardiac output and oxygen release during very high-intensity exercise performed until exhaustion

Our objectives were firstly, to study the patterns of the cardiac output () and the arteriovenous oxygen difference [(a–)O₂] responses to oxygen uptake (O₂) during constant workload exercise (CWE) performed above the respiratory compensation point (RCP), and secondly, to establish the relationships between their kinetics and the time to exhaustion. Nine subjects performed two tests: a maximal incremental exercise test (IET) to determine the maximal O₂ ( V ̇O₂peak), and a CWE test to exhaustion, performed at p 50 (intermediate power between RCP and O₂peak). During CWE, V ̇O₂ was measured breath-by-breath, Q ̇ was measured beat-by-beat with an impedance device, and blood lactate (LA) was sampled each minute. To calculate ( a–v ̄)O₂, the values of V ̇O₂ and Q ̇ were synchronised over 10 s intervals. A fitting method was used to describe the V ̇O₂, Q ̇ and ( a–v ̄)O₂ kinetics. The ( a–v ̄)O₂ difference followed a rapid monoexponential function, whereas both V ̇O₂ and Q ̇ were best fitted by a single exponential plus linear increase: the time constant () V ̇O₂ [57 (20 s)] was similar to ( a–v ̄)O₂, whereas for Q ̇ was significantly higher [89 (34) s, P <0.05] (values expressed as the mean and standard error). LA started to increase after 2 min CWE then increased rapidly, reaching a similar maximal value as that seen during the IET. During CWE, the rapid component of O₂ uptake was determined by a rapid and maximal ( a–)O₂ extraction coupled with a two-fold longer Q ̇ increase. It is likely that lactic acidosis markedly increased oxygen availability, which when associated with the slow linear increase of Q ̇, may account for the V ̇O₂ slow component. Time to exhaustion was larger in individuals with shorter time delay for ( a–v ̄)O₂ and a greater for .