Maximal Oxygen Uptake Is Achieved in Hypoxia but Not Normoxia during an Exhaustive Severe Intensity Run.

Highly aerobically trained individuals are unable to achieve maximal oxygen uptake ([Formula: see text]) during exhaustive running lasting ~2 min, instead [Formula: see text] plateaus below [Formula: see text] after ~1 min. Hypoxia offers the opportunity to study the ([Formula: see text]) response to an exhaustive run relative to a hypoxia induced reduction in [Formula: see text]. The aim of this study was to explore whether there is a difference in the percentage of [Formula: see text] achieved (during a 2 min exhaustive run) in normoxia and hypoxia. Fourteen competitive middle distance runners (normoxic [Formula: see text] 67.0 ± 5.2 ml.kg-1.min-1) completed exhaustive treadmill ramp tests and constant work rate (CWR) tests in normoxia and hypoxia (F i O2 0.13). The [Formula: see text] data from the CWR tests were modeled using a single exponential function. End exercise normoxic CWR [Formula: see text] was less than normoxic [Formula: see text] (86 ± 6% ramp, P < 0.001). During the hypoxic CWR test, hypoxic [Formula: see text] was achieved (102 ± 8% ramp, P = 0.490). The phase II time constant was greater in hypoxia (12.7 ± 2.8 s) relative to normoxia (10.4 ± 2.6 s) (P = 0.029). The results demonstrate that highly aerobically trained individuals cannot achieve [Formula: see text] during exhaustive severe intensity treadmill running in normoxia, but can achieve the lower [Formula: see text] in hypoxia despite a slightly slower [Formula: see text] response.

An exploratory study of cardiac function and oxygen uptake during cycle ergometry in overweight children.

OBJECTIVE: Obesity has been proposed to negatively impact cardiac function in overweight (OW) individuals. The relationship between diastolic dysfunction and oxygen uptake (Vo(2)) kinetics is equivocal. This exploratory investigation evaluated the relationship between resting left ventricular function and Vo(2) kinetics during cycle ergometry in OW and non-overweight (NO) children and adolescents. RESEARCH METHODS AND PROCEDURES: Fourteen OW (>85 percentile for BMI for age and gender) children, 10 boys and 4 girls (age, 11.7 +/- 1.9 years; body mass, 80.6 +/- 45.5 kg) and 10 NO children (4 boys, 6 girls) volunteered to participate in the study (age, 12.5 +/- 2.1 years; body mass, 45.8 +/- 13.8 kg). Resting cardiovascular structure and function were assessed using spectral Doppler echocardiography. All subjects underwent two sub-maximal exercise stages on a cycle ergometer (3 minutes unloaded and 5 minutes at 50 W, both at a cadence of 50 rpm). Respiratory data were measured on a breath-by-breath basis at both workloads and the mean response time (MRT) was calculated. RESULTS: Analysis of the MRT data demonstrated that there were no significant differences between OW and NO (OW, 52.6 +/- 11.7 seconds vs. NO, 45.6 +/- 7.4 seconds). Significant correlations (p < 0.05) were obtained between MRT Vo(2) and echocardiographic-derived mitral valve inflow pressure half-time (r = 0.55) and between MRT Vo(2), and mitral valve inflow deceleration time (r = 0.55). DISCUSSION: The evidence from this research suggests a possible link between left ventricular diastolic function at rest and oxygen uptake kinetics during sub-maximal exercise in OW and NO children and adolescents.

The effect of prior moderate- and heavy-intensity running on the VO2 response to exhaustive severe-intensity running.

We tested the hypothesis that prior heavy-intensity exercise reduces the difference between asymptotic oxygen uptake (VO2) and maximum oxygen uptake (VO2max) during exhaustive severe-intensity running lasting ?2 minutes. Ten trained runners each performed 2 ramp tests to determine peak VO2 (VO2peak) and speed at ventilatory threshold. They performed exhaustive square-wave runs lasting ?2 minutes, preceded by either 6 minutes of moderate-intensity running and 6 minutes rest (SEVMOD) or 6 minutes of heavy-intensity running and 6 minutes rest (SEVHEAVY). Two transitions were completed in each condition. VO2 was determined breath by breath and averaged across the 2 repeats of each test; for the square-wave test, the averaged VO2 response was then modeled using a monoexponential function. The amplitude of the VO2 response to severe-intensity running was not different in the 2 conditions (SEVMOD vs SEVHEAVY; 3925 +/- 442 vs 3997 +/- 430 mL/min, P = .237), nor was the speed of the response (?; 9.2 +/- 2.1 vs 10.0 +/- 2.1 seconds, P = .177). VO2peak from the square-wave tests was below that achieved in the ramp tests (91.0% +/- 3.2% and 92.0% +/- 3.9% VO2peak, P < .001). There was no difference in time to exhaustion between conditions (110.2 +/- 9.7 vs 111.0 +/- 15.2 seconds, P = .813). The results show that the primary VO2 response is unaffected by prior heavy exercise in running performed at intensities at which exhaustion will occur before a slow component emerges.

Age-related changes in maximal power and maximal heart rate recorded during a ramped test in 114 cyclists age 15-73 years.

This study assessed age-related changes in power and heart rate in 114 competitive male cyclists age 15-73 years. Participants completed a maximal Kingcycle ergometer test with maximal ramped minute power (RMPmax, W) recorded as the highest average power during any 60 s and maximal heart rate (HRmax, beats/min) as the highest value during the test. From age 15 to 29 (n = 38) RMPmax increased by 7.2 W/year (r = .53, SE 49 W, p < .05). From age 30 to 73 (n = 78) RMPmax declined by 2.4 W/year (r = - .49, SE 49 W, p < .05). Heart rate decreased across the full age range by 0.66 beats . min( -1 ) . year( -1 ) (r = -.75, SE 9 beats/min, p < .05). Age accounted for only 25% of the variance in RMPmax but 56% in HRmax. RMPmax was shown to peak at age 30, then decline with age, whereas HRmax declined across the full age range.

Oxygen uptake kinetics in children and adults after the onset of moderate-intensity exercise.

The literature suggests that the oxygen uptake (VO2) response to the onset of moderate-intensity exercise may be both mature from childhood and independent of sex. Yet the cardiorespiratory response to exercise and the metabolic profile of the muscle appear to change with growth and development and to differ between the sexes. The aim of this study was to investigate further changes in the VO2 kinetic response with age and sex. Participants completed a series of no less than four step change transitions, from unloaded pedalling to a constant work rate corresponding to 80% of their previously determined ventilatory threshold. Each participant's breath-by-breath responses were interpolated to 1 s intervals, time aligned and then averaged. A single exponential model that included a time delay was used to analyse the averaged response following phase 1 (15 s). Participants with parameter confidence intervals more than +/- 5 s were removed from the sample; the results for the remaining 13 men and 12 women (age 19-26 years), 12 boys and 11 girls (age 11-12 years) were used for statistical analysis. Children had a significantly shorter time constant than adults, both for males (19.0+/-2.0 and 27.9+/-8.6 s respectively; P<0.01) and females (21.0+/-5.5 and 26.0+/-4.5 s respectively; P<0.05). There were no significant differences in the time constant between the sexes for either adults or children (P>0.05). A significant relationship between the time constant and peak VO2 was found only in adult males (P<0.05). A shorter time constant in children may reflect an enhanced potential for oxidative metabolism.