Muscle Hypertrophy in Pre-Diabetic Men after Sixteen Weeks of Resistance Training

Resistance training of healthy young men typically results in muscle hypertrophy and a shift in vastus lateralis composition away from type IIx fibers to an increase in IIa fiber content. Our previous studies of eight weeks of resistance training found many metabolic syndrome men and women paradoxically increased IIx fibers with a decrease in IIa fibers. To confirm the hypothesis that obese subjects might have muscle remodeling after resistance training very different from healthy lean subjects, we subjected a group of nine obese men volunteers to progressive resistance training for a total of sixteen weeks. In these studies, weight loss was discouraged so that muscle changes would be attributed to the training alone. Detailed assessments included comparisons of histologic examinations of needle biopsies of vastus lateralis muscle pre-training and at eight and sixteen weeks. Prolonging the training from eight to sixteen weeks resulted in increased strength, improved body composition and more muscle fiber hypertrophy, but euglycemic clamp-quantified insulin responsiveness did not improve. Similar to prior studies, muscle fiber composition shifted toward more fast-twitch type IIx fibers (23% to 42%). Eight weeks of resistance training increased the muscle expression of phosphorylated AKT2, AMPK, and mTOR. Muscle GLUT4 expression increased although insulin receptor and IRS-1 expression did not change. We conclude that resistance training of pre-diabetic obese subjects is effective at changing muscle, resulting in fiber hypertrophy and increased type IIx fiber content, and these changes continue up to 16 weeks of training.

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