Lean body mass (LBM) and its estimated measure of skeletal muscle mass (SKMM) is ~30 to ~40 % of total body weight. Measuring SKMM is an important assessment for both exercise and nutritional research. There is biological variation in dual X-ray absorptiometry (DXA) estimates related to subject presentation, changes in tissue hydration, as well as GI tract contents. PURPOSE: The purpose of this study is to examine how normal activities (e.g. eating, sleeping, exercise) influence LBM and SKMM measures using DXA in college students. METHODS: (Mean ± SEM; n = 42; Age: 26.9 ± 0.4 y; ht: 169.2 ± 1.3 cm; wt: 73.0 ± 2.5 kg; body fat 27.0 ± 1.5 %; LBM: 51.3 ± 1.7 kg; appendicular lean soft tissue (ALST): 23.9 ± 0.9 kg). Each participant underwent an AM (0600-0800 h) and PM (1800-2000 h) DXA (Lunar Prodigy; GE Healthcare, Madison, WI), BIA (720; InBody, Cerriritos, CA) scan, Ultrasonography (LOGIQ e, GE Healthcare, Wauwtosa, WI) of the right vastus lateralis (VL), and completed a 3-day dietary recall using Myfitnesspal. RESULTS: Differences were found between AM and PM in LBM (+275.2 ± 89.6 g; p = .003), ASLT (+226.1 ± 65.7 g; p = .001), SKMM (+274.8 ± 78.9 g). No difference was found in muscle thickness measures (MT). There was an increase found in extracellular body water (+176 ± 86.2 g; p = .04) Daily carbohydrate (CHO) intake (-47.5 ± 13.5 g; p = .001), fat (FAT) intake (-15.23 ± 3.8 g; p = .0004), protein (PRO) intake (-22.2 ± 5.3 g; p = .0002), and Kcal intake (-413.3 ± 85.5 g; p = <.00001) were found less on assessment day. CONCLUSION: Currently, our results suggest that there may be minimal increases in SKMM and LBM indices during intra-day composition assessments, which can not be explained by Kcalorie intake.



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