Skeletal Muscle Quality: Concordant Findings from Two Practical Non‐Invasive Approaches

Abstract

Phase angle (θ), derived from bioelectrical impedance analysis (BIA) resistance and reactance, decreases with adult age and is associated with changes in nutritional status and skeletal muscle (SM) function. Another measure of SM quality is the light fraction (LF) measured with ultrasound (US) followed by image processing; echogenic light SM is produced with fat and fibrous tissue infiltration of normally dark SM. While the BIA system automatically measures θ, technical training is needed for operation of the US system and subsequent image analysis. The aim of this study was to examine the associations between these two age-related measures of SM quality: θ at 50 KHz using an 8-electrode multifrequency BIA system (MC980, Tanita Corp., Tokyo, Japan); US (GE LOGIC e, Milwaukee, Wisconsin; Nikon NIS Elements Advanced Research 3.22.11, Melville, NY). Subjects were 165 males and females, ages 5-80 yrs, with US measures of biceps, triceps, calf, and thigh muscles; and θ measures of each arm and leg. Significant correlations (p<0.05) were present for key associations, including: bicep LF and arm θ; triceps LF and arm θ; thigh LF and leg θ; age and biceps and thigh LF, and leg θ. Our findings thus show concordant relations between the two different measures of SM quality, θ and LF. Measurement of θ may be a simple, practical, and clinically-useful measure of age-related changes in SM quality.