Inferences from pulmonary O₂ uptake with respect to intramuscular [phosphocreatine] kinetics during moderate exercise in humans

Abstract

In the non‐steady state of moderate intensity exercise, pulmonary O2 uptake (V̇p,O2) is temporally dissociated from muscle O2 consumption (V̇m,O2) due to the influence of the intervening venous blood volume and the contribution of body O2 stores to ATP synthesis. A monoexponential model of V̇p,O2 without a delay term, therefore, implies an obligatory slowing of V̇p,O2 kinetics in comparison to V̇m,O2. During moderate exercise, an association of V̇m,O2 and [phosphocreatine] ([PCr]) kinetics is a necessary consequence of the control of muscular oxidative phosphorylation mediated by some function of [PCr]. It has also been suggested that the kinetics of V̇p,O2 will be expressed with a time constant within 10 % of that of V̇m,O2. V̇p,O2 and intramuscular [PCr] kinetics were investigated simultaneously during moderate exercise of a large muscle mass in a whole‐body NMR spectrometer. Six healthy males performed prone constant‐load quadriceps exercise. A transmit‐receive coil under the right quadriceps allowed determination of intramuscular [PCr]; V̇p,O2 was measured breath‐by‐breath, in concert with [PCr], using a turbine and a mass spectrometer system. Intramuscular [PCr] decreased monoexponentially with no delay in response to exercise. The mean of the time constants (τPCr) was 35 s (range, 20–64 s) for the six subjects. Two temporal phases were evident in the V̇p,O2 response. When the entire V̇p,O2 response was modelled to be exponential with no delay, its time constant (τ′V̇p,O2) was longer in all subjects (group mean = 62 s; range, 52–92 s) than that of [PCr], reflecting the energy contribution of the O2 stores. Restricting the V̇p,O2 model fit to phase II resulted in matching kinetics for V̇p,O2 (group mean τV̇p,O2= 36 s; range, 20–68 s) and [PCr], for all subjects. We conclude that during moderate intensity exercise the phase II τV̇p,O2 provides a good estimate of τPCr and by implication that of V̇m,O2 (τV̇m,O2).

Oxygen uptake kinetics in trained adolescent females

“…Each dataset was interpolated second-bysecond between 0 -360 s; the two datasets were then ensemble averaged to produce a single response for each subject. The first 20 s of the ensemble dataset [cardiodynamic phase, (Rossiter et al 1999) were then removed. The remaining dataset (i.e.…”

Oxygen uptake kinetics as a determinant of sports performance

“…Fick principle (Grassi et al ., 1996;Koga et al ., 2005)] or indirect [i.e. 31 P-magnetic resonance spectroscopy (Rossiter et al ., 1999; Figure 2C] measurements of muscle V O 2 with simultaneous measurements of pulmonary V O 2 , is a qualified ''yes'' Á the qualification being that the time constant of the pulmonary V O 2 will reflect the muscle V O 2 time constant to within 910% (Barstow et al ., 1990). Given the variability in the measurements used (both at the pulmonary and muscle levels), this level of agreement is probably sufficient to use pulmonary V O 2 to reflect muscle V O 2 (but see Hughson, Tschakovsky, & Houston, 2001, for discussion).…”

Left Ventricular Diastolic Filling and Cardiovascular Functional Capacity in Older Men

“…In the former instance, the oxygen delivery does not keep pace with the cellular metabolic capacity for oxygen utilisation when a large muscle mass is recruited and driven to maximum (Rowell, 1993), while in the latter, the rapid increase in heart function and oxygen delivery overtakes the slower adjustment of the peripheral cellular response to the sudden power increase (Whipp & Ward, 1990;Rossiter et al 1999). Thus, there may be a different limit to ýOµ dependent upon the power output paradigm.…”