AnalyzeDirect

Adequate muscle activation and force are necessary to fulfill daily tasks, yet these exercises become increasingly difficult as a person ages. Skeletal muscle activity may be evaluated through electromyography (EMG), a tecnique performed to detect the electrical potential generated by muscle cells when they are electrically or neurologically activated. Studies using EMG show that spatial activation in muscles is not uniform and EMG potential distribution patters are affected by fatigue and muscle contractions levels.

Though EMG is a useful way to analyze muscle activation, certain extractable information is still limited. On the other hand, positron emission tomography (PET) scans with [¹⁸F]-fluorodeoxy-glucose ([¹⁸F]-FDG) tracers may provide data about muscle activation that EMG cannot detect, such as measurement of heterogeneity. These glucose tracers utilize a non-insulin dependent uptake in our working muscles, and the PET scan allows for a measure of heterogeneity within the muscle tissue. PET scans can measure glucose uptake from small 3D volume elements known as voxels. Thus, a muscle is virtually divided into small samples and the heterogeneity is calculated as the coefficient of variation of these [¹⁸F]-FDG uptake values of voxels within each muscle.

Researchers from Colorado State University performed a voxel by voxel analysis to ascertain whether or not glucose uptake heterogeneity, during isometric contractions, differs between younger and older men.

In this study, 6 younger and 6 older men were injected with [¹⁸F]-FDG and endurance tests were administered to evaluate muscle strength. Following these tests, subjects were placed in PET/CT scanners to measure their [¹⁸F]-FDG uptake in the selected muscles. Analyze software was used to process CT images, segmenting areas of bone, fat, muscle, and large blood vessels. The software also calculated the muscle volume value for each muscle analyzed.

The researchers found that the muscle volume of the knee extensors was much smaller in older men. This difference in muscle volume, which reflects age related morphological changes in skeletal muscle such as fiber atrophy and a decrease in the number of muscle fibers and motor units, strongly correlated with [¹⁸F]-FDG uptake heterogeneity. Age related changes in muscle fiber morphology hinder older adults from effectively recruiting more motor units during isomeric contractions. Thus, seniors will have greater skeletal muscle glucose uptake heterogeneity compared to younger men, due to their inability to activate the working muscle homogeneously.

This study provides greater information about the magnitude of the difference in muscle activity between younger and older men when performing isometric contractions and calls upon potential alternative paths to strengthen and prolong muscle use in older age.

Tags: Aging, Skeletal Muscle