Phase I and Phase II Oxygen Uptake Kinetics During Atrioventricular Dyssynchrony in Chronotropically Competent Pacemaker Patients

This study used priming exercise in young boys to investigate (i) how muscle oxygen delivery and oxygen utilization, and muscle activity modulate oxygen uptake kinetics during exercise; and (ii) whether the accelerated oxygen uptake kinetics following priming exercise can improve exercise tolerance. Seven boys that were aged 11.3 ± 1.6 years completed either a single bout (bout 1) or repeated bouts with 6 min of recovery (bout 2) of very heavy-intensity cycling exercise. During the tests oxygen uptake, muscle oxygenation, muscle electrical activity and exercise tolerance were measured. Priming exercise most likely shortened the oxygen uptake mean response time (change, ±90% confidence limits; –8.0 s, ±3.0), possibly increased the phase II oxygen uptake amplitude (0.11 L·min−1, ±0.09) and very likely reduced the oxygen uptake slow component amplitude (–0.08 L·min−1, ±0.07). Priming resulted in a likely reduction in integrated electromyography (–24% baseline, ±21% and –25% baseline, ±19) and a very likely reduction in Δ deoxyhaemoglobin/Δoxygen uptake (–0.16, ±0.11 and –0.09, ±0.05) over the phase II and slow component portions of the oxygen uptake response, respectively. A correlation was present between the change in tissue oxygenation index during bout 2 and the change in the phase II (r = –0.72, likely negative) and slow component (r = 0.72, likely positive) oxygen uptake amplitudes following priming exercise, but not for muscle activity. Exercise tolerance was likely reduced (change –177 s, ±180) following priming exercise. The altered phase II and slow component oxygen uptake amplitudes in boys following priming exercise are linked to an improved localised matching of muscle oxygen delivery to oxygen uptake and not muscle electrical activity. Despite more rapid oxygen uptake kinetics following priming exercise, exercise tolerance was not enhanced.

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Pulmonary O2 uptake on-kinetics in sprint- and endurance-trained athletes

Applied Physiology Nutrition and Metabolism ◽

10.1139/h06-109 ◽

2007 ◽

Vol 32 (3) ◽

pp. 383-393 ◽

Cited By ~ 25

Author(s):

Nicolas J.A. Berger ◽

Andrew M. Jones

Keyword(s):

Oxygen Uptake ◽

Phase Ii ◽

Exercise Performance ◽

Slow Component ◽

Oxygen Uptake Kinetics ◽

Uptake Kinetics ◽

Anaerobic Exercise ◽

Moderate Intensity ◽

Peak Power Output ◽

Severe Intensity

Pulmonary O2 uptake kinetics during “step” exercise have not been characterized in young, sprint-trained (SPT), athletes. Therefore, the objective of this study was to test the hypotheses that SPT athletes would have (i) slower phase II kinetics and (ii) a greater oxygen uptake “slow component” when compared with endurance-trained (ENT) athletes. Eight sub-elite SPT athletes (mean ( ± SD) age = 25 (±7) y; mass = 80.3 (±7.3) kg) and 8 sub-elite ENT athletes (age= 28 (±4) y; mass = 73.2 (±5.1) kg) completed a ramp incremental cycle ergometer test, a Wingate 30 s anaerobic sprint test, and repeat “step” transitions in work rate from 20 W to moderate- and severe-intensity cycle exercise, during which pulmonary oxygen uptake was measured breath by breath. The phase II oxygen uptake kinetics were significantly slower in the SPT athletes both for moderate (time constant, τ; SPT 32 (±4) s vs. ENT 17 (±3) s; p < 0.01) and severe (SPT 32 (±12) s vs. ENT 20 (±6) s; p < 0.05) exercise. The amplitude of the slow component (derived by exponential modelling) was not significantly different between the groups (SPT 0.55 (±0.12) L·min–1 vs. ENT 0.50 (±0.22) L·min–1), but the increase in oxygen uptake between 3 and 6 min of severe exercise was greater in the SPT athletes (SPT 0.37 (±0.08) L·min–1 vs. ENT 0.20 (±0.09) L·min–1; p < 0.01). The phase II τ was significantly correlated with indices of aerobic exercise performance (e.g., peak oxygen uptake (moderate-intensity r = –0.88, p < 0.01; severe intensity r = –0.62; p < 0.05), whereas the relative amplitude of the oxygen uptake slow component was significantly correlated with indices of anaerobic exercise performance (e.g., Wingate peak power output; r = 0.77; p < 0.01). Thus, it could be concluded that sub-elite SPT athletes have slower phase II oxygen uptake kinetics and a larger oxygen uptake slow component compared with sub-elite ENT athletes. It appears that indices of aerobic and anaerobic exercise performance differentially influence the fundamental and slow components of the oxygen uptake kinetics.

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