Key result
During progressive arm exercise, lactate threshold at ~25% maximal work rate precedes intracellular pH decline.
Observational (n=12)
During progressive exercise, the threshold for blood lactate increase occurs significantly earlier than the threshold for intracellular pH decline, indicating lactic acidosis precedes the loss of intracellular biochemical homeostasis.
Lactate threshold dissociation from muscle pH during arm exercise warrants interpretive caution; leaves open mechanisms linking systemic lactate to intracellular homeostasis.
The purpose of this study was to compare the intramuscular and the intravascular events in relation to energy metabolism during progressive arm exercise. Twelve healthy untrained Japanese males participated in this study as subjects. They performed wrist flexion in a ramp incremental load of 0.14 W/min until exhaustion. 31P-MR spectra were obtained from wrist flexor muscle before and throughout the exercise. Venous blood was also sampled from antecubital vein with one minute interval during the exercise, and a change in plasma lactate concentration (La) was observed. Intracellular pH (pH) was calculated from a chemical shift between phosphocreatine (PCr) and inorganic phosphate (Pi) of the 31P-MR spectra. Change in pH showed a threshold behavior during exercise. Threshold points at decline in pH (pHT), increase in Pi/PCr (PT), and increase in La (LT) were determined by piecewise linear regression analysis of minutes-by-minutes data. Mean values of pHT, PT and LT were 43.0, 42.5, and 24.8% of maximal work rate, respectively. LT was significantly smaller than pHT and PT. This result suggests that lactic acidosis has already existed when pH is kept at resting level, and pHT reflects the capacity of remaining intracellular biochemical homeostasis, which might be one of the physiological indices of muscle fatigue.
No takes yet. Share an insight, caveat, or question.
Iwanaga et al. (1992) conducted an observational in Healthy (n=12). Progressive arm exercise was evaluated on Threshold points at decline in pH (pHT), increase in Pi/PCr (PT), and increase in plasma lactate concentration (LT). During progressive arm exercise, the lactate threshold (24.8% of maximal work rate) occurred significantly earlier than the thresholds for intracellular pH decline (43.0%) and Pi/PCr increase (42.5%).
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: