Kinetics of pulmonary oxygen uptake and muscle phosphates during moderate-intensity calf exercise

Abstract

The purpose of this study is to directly compare the dynamic responses of phosphocreatine (PCr) and P(i) to those oxygen uptake (VO2) measured at the lung during transitions to and from moderate-intensity exercise. Changes in PCr and P(i) were measured by 31P-nuclear magnetic resonance spectroscopy, and changes in VO2 were measured breath by breath by mass spectroscopy during transitions to and from moderate-intensity square-wave ankle plantar flexion exercise in 11 subjects (7 men and 4 women; mean age 27 yr). Three repeated transitions were averaged for improvement in signal-to-noise ratio of phosphate data, and 12 transitions were averaged for VO2 measurements. Averaged transitions were fit with a monoexponential curve for determination of the time constant (tau) of the responses. Mean tau values for on transients of PCr, P(i), and phrase 2 VO2 were 47.0, 57.7, and 44.5 s, respectively, whereas means tau values for off transients were 44.8, 42.1, and 33.4 s, respectively. There were no significant differences between tau values for phosphate- and VO2-measured transients or on and off transients. The similarity of on and off kinetics supports linear first-order respiratory control models. Measurement of phase 2 pulmonary VO2 kinetics to and from moderate-intensity small-muscle-mass exercise reflect muscle phosphate kinetics (and muscle oxygen consumption).

The effects of age on kinetics of oxygen uptake and phosphocreatine in humans during exercise

“…kinetics of cardiac output), rather than peripheral factors (blood flow redistribution, mitochondrial density), as is exercise of a smaller muscle mass such as the plantar flexors (Anderson & Saltin, 1985;Shephard, Bouhlel, Vandewalle & Monod, 1988). During exercise of a small muscle mass, it is unlikely that cardiovascular function is challenged, as perfusion is in excess of metabolic demand (Anderson & Saltin, 1985), while, in whole body exercise, demand for 02 may outstrip its supply (Shephard et al 1988 (McCreary et al 1996). Our results (Fig.…”

“…31P MRS 31p spectra collected during both the progressive resistance (ramp) and constant load (square wave) protocols were acquired at 1.5 T with a Siemens Helicon imaging and spectroscopy system and a dual tuned (31P and 'H) surface coil, which measured 5 cm in diameter. Placement of the surface coil over the belly of the lateral gastrocnemius was guided by transverse relaxation (T2) weighted images obtained previously (McCreary et al 1996). These images, along with surface electromyographic measurements indicated that the lateral gastrocnemius was the predominant muscle used during the plantar flexion protocol (McCreary et al 1996).…”

“…Placement of the surface coil over the belly of the lateral gastrocnemius was guided by transverse relaxation (T2) weighted images obtained previously (McCreary et al 1996). These images, along with surface electromyographic measurements indicated that the lateral gastrocnemius was the predominant muscle used during the plantar flexion protocol (McCreary et al 1996). The magnetic field homogeneity was adjusted until the proton signal from water produced a peak with a full width at a half-maximum of 20-30 Hz (0 3-0-4 p.p.m.)…”

Oxygen Uptake Kinetics During Exercise

“…O 2 kinetics reflect the kinetics of muscle PCr and thus the rate of muscle O 2 utilisation. Further support for this conclusion can be found in the data presented by McCreary et al [41] Their data showed that PCr and phase 2 V . O 2 kinetics, measured simultaneously during the same moderate exercise task (ankle plantar flexion), occurred at similar rate.…”

The effects of creatine supplementation on thermoregulation and physical (cognitive) performance: a review and future prospects

“…The coupling between PCr and O 2 kinetics at the onset of exercise until steady state has been well characterised (Binzoni et al 1992;Barstow et al 1994;McCreary et al 1996;Rossiter et al 1999;Rossiter et al 2001;Rossiter et al 2002;Korzeniewski and Zoladz 2006). The ratio of ATP/ADP and PCr/Cr are linked in the mitochondria to the creatine kinase (CK) reaction (Chance and Williams 1955;Meyer et al 1984;Mahler 1985;Balaban 1990).…”