Role for neurological and immunological resilience in the pathway of the aging muscle powerpenia: InCHIANTI study longitudinal results.

Abstract

The neuromuscular junction shows several degenerative changes with aging, resulting in a reduction of transmission efficacy. These changes, paired with low-grade chronic inflammation, were considered triggers of the aging muscle processes. The main objective of this study is to assess the role of leukocyte count-derived ratios, nerve conduction velocity (NCV), and compound muscle action potential (CMAP) in determining time-dependent reduction in lower limb muscle explosive strength, a condition that has been defined as powerpenia. The InCHIANTI study enrolled a representative sample from the registry lists of two towns in Tuscany, Italy. Baseline data were collected in 1998, with follow-up visits every 3 years. For the purpose of this analysis, we used 1229 subjects and 3814 follow-up assessments. Subjects with lower values of monocyte-to-lymphocyte ratio (ML-ratio) had higher nerve conduction velocity and higher proximal and distal action potential values; moreover, considering the interaction between age for ML-ratio effect, a statistically significant direct association is found with all the electromyography-parameters. Lower limb muscle power shows a gender dimorphism, male subjects having higher values at baseline, but experiencing steeper decline rate during the follow-up, compared to females. Muscle power was inversely associated with ML-ratio, proximal CMAP, distal CMAP, and NCV. Moreover, we found a direct and statistically significant second-order interaction (age for ML-ratio), meaning that at the same age, increasing ML-ratio increases lower limb muscle power. Lastly, also body composition variation across aging is directly associated with lower limb muscle power. Reduced immunological and neurological homeostasis affects the powerpenia phenotype in a large representative sample of Italian men and women.