Measuring Body Composition and Functional Strength: Implications for the Clinical Assessment of Skeletal Muscle

Abstract

Skeletal muscle represents the largest single component of the body, comprising up to 50% of total mass in healthy individuals. Body composition assessment has largely focused on overweight and obese individuals, but healthy skeletal muscle is also an important indicator of health and wellbeing. We hypothesized that estimates of lean body mass and empirical measures of functional strength should be directly correlated with one another. In the current study, we estimated body composition using two different field methods. Bioimpedance spectroscopy (BIS) employs 256 frequencies of low energy electrical current to estimate body composition. We used BIS (Impedimed SFB7) to determine percent body fat and fat free mass in physically active volunteers, ranging in age from 18 – 62 years. In addition, we used the Jackson and Pollock 3-site skin fold method to estimate these parameters from the same individuals. We also measured functional strength with a whole body dynamometer to determine mid-thigh pull strength, and a grip dynamometer to assess grip strength (Baseline Evaluation Instruments). Data collected from more than 75 men and women revealed significant correlations between fat-free mass (FFM) and both measures of functional strength. Interestingly, men and women fell along the same trend line, with women exhibiting similar strength for a given FFM. Moreover, functional strength standardized to FFM provides an objective measure of relative strength that was not different between men and women. The American Medical Association released a new policy statement about body mass index (BMI) in June of 2023, highlighting that BMI is an imprecise measure of body composition and recommending that alternative measures, such as more precise measurement of body composition, also be used. Indeed, we found that for individuals with a BMI of less than 30, there was direct relationship between FFM and functional strength. By contrast, percent body fat was not correlated with BMI within this range. We suggest that FFM and functional strength could be used to assess healthy weight, in conjunction with BMI. These measures could also be used to screen for sarcopenia, cachexia, and other conditions associated with significant muscle loss. Skeletal muscle represents an often underappreciated component of health and a more precise assessment of muscle mass and strength should be used as a measure of overall health. This work was supported by a Keenan Award at St. Bonaventure University. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.