Andrew D. Fields, Katherine Sullivan, Casey Metoyer, Jacob Broeckel, Madelyn K. Simmang, Mary Lovelady, Maddy Schwing, Michael V. Fedewa, Michael R. Esco, FACSM. University of Alabama, Tuscaloosa, AL.

BACKGROUND: It is commonly accepted that body composition is related to physical activity (PA) and muscular fitness (MF). However, it is not as well understood if metrics of PA and MF can explain the variance in both fat mass (FM) and fat-free mass (FFM). PURPOSE: The purpose of this investigation was to determine the extent of variation in FM and FFM that can be explained by specific components of PA and MF. METHODS: A convenience sample of participants was recruited for this study (n=37, 27.03% Female, 22.35±3.76 yrs.). All metrics were assessed during a single visit to the Exercise Physiology Lab. Body mass (BM) was measured to the nearest 0.1 kg with a calibrated digital scale (Tanita BWB-800, Tanita Corporation, Tokyo, Japan). Results from the International Physical Activity Questionnaire (IPAQ) Short-Form were converted to calculate the intensity and amount of weekly PA in MET-minutes per week (MET-min/wk). Intensities were categorized into vigorous, moderate, and walking based on IPAQ standards. FM was estimated using brightness-mode ultrasound (Philips iU22, Philips Medical Systems, Andover, MA, USA) across seven standardized sites. FFM was derived from subtracting FM from BM. Handgrip strength (HGS) was assessed on dominant hand via a hydraulic hand dynamometer (Alphamed Inc., Lakewood, NJ, USA) as a metric of muscular strength, and a maximum-rep push-up test was administered to quantify muscular endurance. The correlations between PA, MF, FM, and FFM were assessed using Pearson’s r, and described as weak, moderate, or strong (r=0.2, 0.5, or 0.8, respectively). Data are presented as mean±standard deviation, with an alpha level set to p<0.05. RESULTS: There were no significant correlations found between FM and any of the PA or MF measures, (r=-0.28 to 0.24, all p>0.05). FFM was moderately correlated with vigorous MET-min/wk (r=0.34, p=0.04) and walking MET-min/wk, (r=-0.37, p=0.02), and strongly correlated with and HGS (r=0.80, p<0.001). Stepwise regression analysis showed that only HGS and vigorous MET-min/wk were included in the model that explained the variance in FFM (R2=0.74, p<0.001). DISCUSSION: The results indicate that muscular strength and vigorous PA have stronger relationships with FFM than muscular endurance or other, lower-intensity metrics of PA. FM does not appear to be related to either MF parameters or IPAQ-derived PA.

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