Dynamic Responses of Oxygen Uptake at the Onset and End of Moderate and Heavy Exercise in Trained Subjects

Inconsistencies about dynamic asymmetry between the on- and off-transient responses in [Formula: see text] are found in the literature. Therefore the purpose of this study was to examine [Formula: see text]on-and off-transients during moderate- and heavy-intensity cycling exercise in trained subjects. Ten men underwent an initial incremental test for the estimation of ventilatory threshold (VT) and, on different days, two bouts of square-wave exercise at moderate (< VT) and heavy (> VT) intensities. [Formula: see text] kinetics in exercise and recovery were better described by a single exponential model (< VT), or by a double exponential with two time delays (> VT). For moderate exercise, we found a symmetry of [Formula: see text] kinetics between the on- and off-transients (i.e., fundamental component), consistent with a system manifesting linear control dynamics. For heavy exercise, a slow component superimposed on the fundamental phase was expressed in both the exercise and recovery, with similar parameter estimates. But the on-transient values of the time constant were appreciably faster than the associated off-transient, and independent of the work rate imposed (< VT and > VT). Our results do not support a dynamically linear system model of [Formula: see text] during cycling exercise in the heavy-intensity domain. Key words: oxygen uptake kinetics, on- and off-transients, slow component

Regulation of Blood Flow at the Onset of Exercise by Feed Forward and Feedback Mechanisms

Blood flow adapts quickly after the onset of exercise to meet the metabolic demands of skeletal muscle. This review approaches the issue of how rapidly blood flow adapts and what the mechanisms for adaptation are primarily from a control theory perspective. Several recent papers have suggested that O2 transport proceeds at a rate that anticipates the metabolic demand over a very wide range of work rates. When considered from a control theory perspective, this implies involvement of feed forward control. Although there is one very important feed forward mechanism in the muscle pump that is activated with the onset of exercise, other evidence suggests that adjustment of blood flow to match the metabolic demand relies on feedback control from local dilator factors released in proportion to the metabolic demand. These distinct mechanisms with different onset times mean that blood flow adapts to the exercise demand with at least two distinct phases. The time course of the adaptation varies greatly between work rates, showing that blood flow control cannot be described by a linear control system and that the mechanisms responsible for vasodilation are dependent on work rate. Key words: oxygen uptake, kinetics, vasodilation, muscle metabolism

Dynamic Responses of O2 Uptake at the Onset and End of Exercise in Trained Subjects

Inconsistencies about dynamic asymmetry between the on- and off-transient responses in [Formula: see text] are found in the literature. Therefore the purpose of this study was to examine [Formula: see text]on- and off-transients during moderate- and heavy-intensity cycling exercise in trained subjects. Ten men underwent an initial incremental test for the estimation of ventilatory threshold (VT) and, on different days, two bouts of square-wave exercise at moderate (< VT) and heavy (> VT) intensities. [Formula: see text] kinetics in exercise and recovery were better described by a single exponential model (< VT), or by a double exponential with two time delays (> VT). For moderate exercise, we found a symmetry of [Formula: see text] kinetics between the on- and off-transients (i.e., fundamental component), consistent with a system manifesting linear control dynamics. For heavy exercise, a slow component superimposed on the fundamental phase was expressed in both the exercise and recovery, with similar parameter estimates. But the on-transient values of the time constant were appreciably faster than the associated off-transient, and independent of the work rate imposed (< VT and > VT). Our results do not support a dynamically linear system model of [Formula: see text] during cycling exercise in the heavy-intensity domain. Key words: oxygen uptake kinetics, on- and off-transients, slow component

Field Testing of in Cross-Country Skiers With Portable Breath-by-Breath System

Peak aerobic exercise responses were determined in 8 competitive cross-country skiers during field-testing and during an incremental treadmill test (TM) to determine peak oxygen uptake [Formula: see text], heart rate, and oxygen pulse. Field testing consisted of maximal effort roller skiing using diagonal stride (DS) and double poling (DP) techniques. [Formula: see text] was measured during roller skiing by the portable Cosmed K4b2 breath-by-breath system. The portable system was compared against a standard laboratory mixing box system, and no differences were found across the full range of [Formula: see text]. During DS, [Formula: see text] and oxygen pulse were not different from TM, whereas peak HR was lower. With DP, [Formula: see text] and oxygen pulse were less than DS or TM, whereas peak HR was less than with TM but not different from DS. These results demonstrate the validity and utility of the portable breath-by-breath system for measurement of aerobic energy demand of athletes as they carry out their normal activity. Key words: oxygen uptake, oxygen pulse, Cosmed K4b2, athlete

Physiological Correlates of Simulated Wheelchair Racing in Trained Quadriplegics

This study examined the physiological responses during a 7.5-km simulated wheelchair race (SR) performed on rollers by 8 male quadriplegic marathon racers and analyzed the factors associated with SR time. Cardiac output (Q) was estimated during the SR using carbon dioxide rebreathing, from which stroke volume (SV) and [Formula: see text] were calculated. Subjects raced at 90 and 93% of peak oxygen uptake [Formula: see text] and peak heart rate, respectively. SR time was inversely related (p < 0.05) to peak [Formula: see text], and [Formula: see text], Q, and SV during the SR, but not [Formula: see text], age, and lesion level. Multiple regression analysis included only absolute SR [Formula: see text] in the equation to predict SR time: Y = −29.7X + 65.9; SE = 5.8. SR [Formula: see text] was significantly (p < 0.05) related to Q and SV but not to [Formula: see text]. These descriptive data suggest that SR performance in trained male quadriplegics might be limited by central, as opposed to peripheral, factors that determine [Formula: see text]. Key words: oxygen uptake, cardiac output, spinal cord injury

Design and evaluation of an automated oxygen uptake rate measurement system

The design and operating procedure for a newly developed automatic oxygen uptake rate (OUR) measurement apparatus is presented. This unit, with the aid of a microcomputer, is capable of collecting a volume of sample, aerating the sample, measuring the oxygen concentration at preselected times, and calculating the oxygen uptake rate on a routine basis. The OUR unit was evaluated using three different performance testing procedures. These were (1) a calibration and general performance test, (2) a long-term performance test, and (3) a detailed comparative performance test. The results of each of these tests are presented. The value and alternative uses of routine monitoring of OUR are discussed along the possible applications such as detection of toxic compounds entering the plant and adjustment of sludge return rates to match OUR values. Key words: oxygen uptake rate, activated sludge, microcomputer, process control, oxygen consumption.