Effects of skin blood flow and temperature on bioelectric impedance after exercise

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To examine the effects of increased skin blood flow (BFsk) and skin temperature (Tsk) on bioelectric impedance (BIA), 30 young males participated as subjects. All subjects underwent the following measurements: 1) BFsk and Tsk for the chest, biceps, thigh, and calf; 2) body composition using the BIA prediction equations and underwater weighing (UW); and 3) triceps skinfold (SFtri) thickness. After the baseline studies (M1) the subjects exercised for 30 min at approximately 83% of maximal heart rate. The above measurements were repeated immediately after exercise (M2), and at 1-h recovery from exercise (M3). Repeated measures ANOVA showed that mean Tsk and BFsk, and for the four measured sites were significantly increased from M1 to M2 (P < 0.05) and decreased from M2 to M3 (P < 0.05). These changes did not affect BIA measurement for resistance (R) and reactance between M1 and M2 (P > 0.05), and between M2 and M3 (P > 0.05). With regression analysis the following independent variables were identified as strong contributing factors for predicting fat-free mass (FFM): 1) SFtri and total body water for M1 and M3; and 2) WT, SFtri, and Tsk of the chest for M2. Two FFM equations have little multicolinearity (M1 and M2), e.g., they have low root mean square errors (≤2.6 kg), very high values for R2 (≤0.94), and relatively low values for coefficient of variations (≥5.65%). Differences (P < 0.05) were observed between the UW method and the Lukaski equation for estimating FFM for M1 and M3, but not for M2. Using the Guo equation for estimating percent body fat (%BF), statistical difference (P < 0.05) was observed for M2 only. We conclude that: 1) exercise-induced changes in BFsk and Tsk do not influence the BIA study; and 2) after exercise the following independent variables were strong predictors for estimating FFM: S2/R, SFtri, weight, and Tsk of the chest.

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