The Influence of Age and Obesity-Altered Muscle Tissue Composition on Muscular Dimensional Changes: Impact on Strength and Function.

The purpose of this study was to determine if muscular dimensional changes with increases in torque production are influenced by age and obesity-related increases in intramuscular fat, and its relationship to percent body fat (%BF), echo intensity (EI), strength, and maximum walking speed. Sixty-six healthy men were categorized into three groups based on age and BMI status [young normal weight (YNW), older normal weight (ONW), and older obese (OB)]. Participants underwent %BF assessments, resting ultrasonography to determine muscle size (CSA) and EI of the superficial quadriceps, and a 10-m maximum walking speed assessment. Maximal and submaximal (rest-100%MVC in 10% increments) isometric leg extension strength was assessed while changes in rectus femoris (RF) CSA, width, and depth were obtained with ultrasonography. EI and %BF were different among all groups (P≤0.007), with the YNW and OB groups exhibiting the lowest and highest %BF and EI values, respectively. The RF increased in depth and decreased in width with increases in torque intensity for all groups. The ONW group demonstrated no change (-0.08%) in RF CSA across torque intensities, whereas the YNW group (-11.5%) showed the greatest decrease in CSA, and the OB group showed a more subtle decrease (-4.6%). Among older men, a greater change in RF CSA was related to poorer EI (r=-0.355) and higher %BF (r=-0.346), while a greater decrease in RF width was associated with faster walking speeds (r=-0.431). Examining muscular dimensional changes during contraction is a unique model to investigate the influence of muscle composition on functional performance.