Muscle fiber type is associated with obesity and weight loss

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Abstract
The purpose of this study was to test the hypothesis that muscle fiber type is related to obesity. Fiber type was compared 1 ) in lean and obese women, 2 ) in Caucasian (C) and African-American (AA) women, and 3 ) in obese individuals who lost weight after gastric bypass surgery. When lean (body mass index 24.0 ± 0.9 kg/m2, n = 28) and obese (34.8 ± 0.9 kg/m2, n = 25) women were compared, there were significant ( P < 0.05) differences in muscle fiber type. The obese women possessed fewer type I (41.5 ± 1.8 vs. 54.6 ± 1.8%) and more type IIb (25.1 ± 1.5 vs. 14.4 ± 1.5%) fibers than the lean women. When ethnicity was accounted for, the percentage of type IIb fibers in obese AA was significantly higher than in obese C (31.0 ± 2.4% vs. 19.2 ± 1.9%); fewer type I fibers were also found in obese AA (34.5 ± 2.8% vs. 48.6 ± 2.2%). These data are consistent with the higher incidence of obesity and greater weight gain reported in AA women. With weight loss intervention, there was a positive relationship ( r = 0.72, P < 0.005) between the percentage of excess weight loss and the percentage of type I fibers in morbidly obese patients. These findings indicate that there is a relationship between muscle fiber type and obesity.