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 8 wk of resistance 
training found that 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 male 
volunteers to progressive resistance training for a total of 16 wk. In these 
studies, weight loss was discouraged so that muscle changes would be attributed 
to the training alone. Detailed assessments included comparisons of histological 
examinations of needle biopsies of vastus lateralis muscle pretraining and at 8 
and 16 wk. Prolonging the training from 8 to 16 wk 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 and mTOR. Muscle GLUT4 expression increased, 
although insulin receptor and IRS-1 expression did not change. We conclude that 
resistance training of prediabetic obese subjects is effective at changing 
muscle, resulting in fiber hypertrophy and increased type IIx fiber content, and 
these changes continue up to 16 wk of training.NEW & NOTEWORTHY Obese, 
insulin-resistant men responded to 16 wk of progressive resistance training with 
muscle hypertrophy and increased strength and a shift in muscle fiber 
composition toward fast-twitch, type IIx fibers. Activation of muscle mTOR was 
increased by 8 wk but did not increase further at 16 wk despite continued 
augmentation of peak power and rate of force generation.