Effects of exercise‐induced intracellular acidosis on the phosphocreatine recovery kinetics: a ³¹P MRS study in three muscle groups in humans

Abstract

Little is known about the metabolic differences that exist among different muscle groups within the same subjects. Therefore, we used (31)P-magnetic resonance spectroscopy ((31)P-MRS) to investigate muscle oxidative capacity and the potential effects of pH on PCr recovery kinetics between muscles of different phenotypes (quadriceps (Q), finger (FF) and plantar flexors (PF)) in the same cohort of 16 untrained adults. The estimated muscle oxidative capacity was lower in Q (29 ± 12 mM min(-1), CV(inter-subject) = 42%) as compared with PF (46 ± 20 mM min(-1), CV(inter-subject) = 44%) and tended to be higher in FF (43 ± 35 mM min(-1), CV(inter-subject) = 80%). The coefficient of variation (CV) of oxidative capacity between muscles within the group was 59 ± 24%. PCr recovery time constant was correlated with end-exercise pH in Q (p < 0.01), FF (p < 0.05) and PF (p < 0.05) as well as proton efflux rate in FF (p < 0.01), PF (p < 0.01) and Q (p = 0.12). We also observed a steeper slope of the relationship between end-exercise acidosis and PCr recovery kinetics in FF compared with either PF or Q muscles. Overall, this study supports the concept of skeletal muscle heterogeneity by revealing a comparable inter- and intra-individual variability in oxidative capacity across three skeletal muscles in untrained individuals. These findings also indicate that the sensitivity of mitochondrial respiration to the inhibition associated with cytosolic acidosis is greater in the finger flexor muscles compared with locomotor muscles, which might be related to differences in permeability in the mitochondrial membrane and, to some extent, to proton efflux rates.

Skeletal muscle ATP synthesis and cellular H+ handling measured by localized 31P-MRS during exercise and recovery

“…Calculated Q max values are broadly within the range of previous reports471516. With protocol A, no significant difference of Q max was found between the two muscles, although measurements using protocol B showed higher values of Q max in SOL.…”

Interrelations of muscle functional MRI, diffusion‐weighted MRI and 31P‐MRS in exercised lower back muscles

“…We observed load‐induced changes of T 2 of approximately 10% confirming recent findings , changes in high‐energy phosphate metabolism (PCr depletion of about 30% and Pi accumulation of approximately 130%), again in line with previous work , and increases in vascular tissue perfusion of up to 3 percentage points.…”

Combined spiroergometry and 31P–MRS of human calf muscle during high‐intensity exercise

“…Vandenborne et al also reported similar low pH values with a slowed recovery towards resting pH after a repeated plantar flexion exercise over 2 min with 30% maximum voluntary contraction (MVC) and maximum frequency. Previously, negative correlations between pH values at the end of exercise and PCr recovery times have been reported in finger, plantar flexor muscles, quadriceps muscles and calf muscles . This association was confirmed in our in vivo cohort (see Figure a), and reflects the alterations in inhibited mitochondrial respiration as a result of H + accumulation and release in muscles.…”