31P-MRS-Measured Phosphocreatine Recovery Kinetics in Human Muscles in Health and Disease-A Systematic Review and Meta-Analysis.

The noninvasive, in vivo measurement of postexercise phosphocreatine (PCr) recovery kinetics using 31-phosphorus magnetic resonance spectroscopy (³¹P-MRS) is a highly prevalent method for assessing skeletal muscle energetics. However, ³¹P-MRS methodology is notoriously laboratory-specific, leading to uncertainty about the normal range of PCr recovery kinetics among healthy individuals, as well as relationships with disease and demographic factors. This systematic review and meta-analysis characterized the normal range of PCr recovery kinetics from ³¹P-MRS in human skeletal muscles across the lifespan, differences between healthy and those with muscle-related diseases, and relationships between intermuscular PCr recovery measurements and demographic factors. PubMed, Web of Science, Cochrane, and Google Scholar databases were searched for PCr recovery studies, which resulted in a final set of 128 studies eligible for meta-analysis. Studies were categorized into three muscle groups (forearm, upper leg, and lower leg) and further subdivided into three groups: diseased, control (the comparator group in studies of disease), and healthy (those recruited into studies that lacked a disease group). Only English-language studies were included. All statistical analysis was performed using Stata 17 software. Forest plots showed significant heterogeneity across PCr recovery time estimates and outlier study removal significantly reduced this heterogeneity. Greater age was associated with longer PCr recovery in upper leg muscles among both healthy (ρ = 0.387, p < 0.05) and diseased (ρ = 0.733, p < 0.05) individuals. Additionally, longer PCr recovery time was correlated with more acidic end-of-exercise pH in all three muscle groups among healthy individuals. In conclusion, skeletal muscle energetics as indexed by ³¹P-MRS-based PCr recovery time is similar across three different skeletal muscle groups among healthy people. Common diseases significantly prolong PCr recovery times. Methodological heterogeneity has a significant impact on PCr recovery time measurements in this literature. Greater age and more acidic pH increase PCr recovery time among healthy people.