Showing papers by "David A. Jones published in 1997"
TL;DR: This study supports the possible central modulation of exercise tolerance by serotonergic pathways, although a role for dopamine cannot be excluded.
Abstract: Male subjects exercised at 80% maximal rate of O2 uptake (VO2,max) following oral administration of either placebo or the partial 5-HT1A agonist buspirone (45 mg), using a paired design. Ratings of perceived exertion were higher following buspirone and time to volitional fatigue (median and inter-quartile range) fell significantly by approximately a third from 26 min (24-30 min) on placebo to 16 min (11-19 min) following buspirone. Serum prolactin was significantly elevated following buspirone administration, indicating increased hypothalamic 5-HT1A receptor stimulation. There were no significant differences in blood lactate or serum glucose between the trials. This study supports the possible central modulation of exercise tolerance by serotonergic pathways, although a role for dopamine cannot be excluded.
62 citations
TL;DR: A model for phosphocreatine (PCr) resynthesis is proposed based on a simple electric circuit, where the PCr store in muscle is likened to the stored charge on the capacitor, and the solution to the second-order differential equation that describes the potential around the circuit is given.
Abstract: A model for phosphocreatine (PCr) resynthesis is proposed based on a simple electric circuit, where the PCr store in muscle is likened to the stored charge on the capacitor. The solution to the second-order differential equation that describes the potential around the circuit suggests the model for PCr resynthesis is given by PCr(t) = R - [d1.exp(-k1.t) +/- d2.exp(-k2.t)], where R is PCr concentration at rest, d1, d2, k1, and k2 are constants, and t is time. By using nonlinear least squares regression, this double-exponential model was shown to fit the PCr recovery data taken from two studies involving maximal exercise accurately. In study 1, when the muscle was electrically stimulated while occluded, PCr concentrations rose during the recovery phase to a level above that observed at rest. In study 2, after intensive dynamic exercise, PCr recovered monotonically to resting concentrations. The second exponential term in the double-exponential model was found to make a significant additional contribution to the quality of fit in both study 1(P < 0.05) and study 2(P < 0.01).
42 citations
TL;DR: The results of the present study indicate that there is little difference in the muscle concentration of PCr estimated by the two methods, but that there are differences in the estimates of ATP, pH and lactate changes during contraction.
Abstract: Five subjects underwent twenty electrically evoked maximal isometric contractions of the anterior tibialis muscle of both legs (n = 10), with limb blood flow occluded. Measurements of muscle high-energy phosphates (ATP, ADP and phosphocreatine (PCr)), lactate and pH were made using both 31P magnetic resonance spectroscopy (MRS) and the biochemical analysis of biopsy samples obtained from directly below the MRS surface coil. The resting PCr concentration determined using MRS was similar to that measured in the biopsy material. Following contraction, MRS showed a greater decrease in ATP concentration compared with biochemical analysis (P 0.05). The results of the present study indicate that there is little difference in the muscle concentration of PCr estimated by the two methods, but that there are differences in the estimates of ATP, pH and lactate changes during contraction. This latter discrepancy may lead to greater estimates of ATP turnover being made as a result of MRS analysis.
17 citations