Changes in intracellular pH of muscle during dynamic contraction.
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Exercise↗
Biomedical subjects
K Sairyo
Publications and source records attributed to K Sairyo.
[Changes in intracellular pH of working muscle during constant and stepwise incremental load exercise].
In this study, subjects performed wrist flexion in isokinetic manner by using CYBEX dynamometer while their right forearm was attached in a MR magnet. 31P-MR spectra were obtained from wrist flexor muscles before and throughout the exercise. Intracellular pH of muscle was calculated from the chemical shift between phosphocreatine (PCr) and inorganic phosphate (Pi). Fifteen Japanese males volunteered as subjects. They performed two experimental protocols, i. e. constant load test (CT) and stepwise incremental load test (IT). In CT, 10 of the subjects were participated. After 2 minutes rest, wrist flexion of 10, 20, 30, 40 or 50% of maximal voluntary contraction force (MVC) was performed at 2 seconds intervals for 15 minutes. In IT, 14 including 9 of CT were participated. They performed wrist flexion in incremental contraction force of 5 steps from 10% to 50% of MVC for 3 minutes in each step. Changes in intracellular pH of muscle against contraction level show non-linear relationships both in CT and IT. From this relationship we calculated the contraction level at which pH was 6.9 (%MVC6.9). Mean values of obtained %MVC6.9 by CT and by IT were 29.3 and 30.0% of MVC, respectively. And, significant correlation was found between %MVC6.9 by CT and by IT. This result shows that %MVC6.9 was a reproducible index independent of the type of exercise test, i. e. constant or incremental load test, and might reflect the physiological characteristics of the muscle.
Exercise↗
Thresholds for decrease in intracellular pH and increase in blood lactate during progressive exercise: 31P-MRS study.
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.
Adult↗
31P-MRS study of change in intracellular pH during sustained static contractions in human.
31P-MRS spectra were obtained from human first dorsal interosseous muscle during and after the voluntary static abduction of the index finger. Endurance tasks were performed at randomly assigned contraction levels of 15, 20, 30 and 40% of maximal voluntary contraction (MVC). Muscle pH was calculated according to Taylor et al. (1983) using chemical shift between inorganic phosphate (Pi) and phosphocreatine (PCr) on the 31P-MRS spectra. Mean values of endurance times of static contractions were 7.25, 5.33 and 3.08 minutes for 20, 30 and 40% MVC, respectively. At 15% MVC, all of the four subjects maintained contraction for 30 minutes, and the contractions were terminated at 30 minutes. Muscle pH at the onset of contractions were 7.12, 6.98, 7.01 and 7.08 for 15, 20, 30 and 40% MVC, respectively. At the end of contractions when the subject could not maintain the force level, muscle pH were 6.07, 5.97 and 5.94 for 20, 30 and 40% MVC, respectively. There was no significant difference in muscle pH at the end of contractions between three conditions by one-way ANOVA. In conclusion, there was a critical muscle pH of about 6.0 where static contractions could not be maintained.
Adult↗