Muscle hypertrophy in prediabetic men after 16 wk of resistance training

Abstract

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. 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.

Resistance exercise stimulates mixed muscle protein synthesis in lean and obese young adults

“…More recently, Stuart et al. () reported that although 16 weeks of resistance exercise training led to an increase in muscle strength and muscle fiber cross‐sectional area within obese, prediabetic men there were no improvements in fasting glucose or insulin concentrations or clamp‐derived measures of insulin sensitivity (so resistance exercise training was only partially effective). Unfortunately, none of these studies included a healthy‐weight control group, so it is not clear if the magnitude of response (i.e., the effectiveness of training) would have been different had the training been undertaken by nonobese individuals.…”

Impact of Endurance and Resistance Training on Skeletal Muscle Glucose Metabolism in Older Adults

“…Six weeks of one-legged strength training (three times per week) in aged, non-obese, type 2 diabetics increased skeletal muscle GLUT4 in the exercised leg (~40%), but not in healthy controls [93]. In support of these findings, 16 weeks of resistance training increased skeletal muscle GLUT4 protein content in middle-aged (30–54 years) prediabetic, obese men [95] and increased the hypomethylation (promotes gene transcription) of the GLUT4 promoter in middle-aged morbidly obese Maori and Pacific Islanders diagnosed with type 2 diabetes [96]. In contrast to these findings, no changes in skeletal muscle GLUT4 were observed in healthy, non-obese, aged individuals in response to 6 weeks of one-legged strength training [93] or 12 weeks of whole body resistance training [2].…”

Exercising for Insulin Sensitivity – Is There a Mechanistic Relationship With Quantitative Changes in Skeletal Muscle Mass?

“…However, difficult they are to identify, a certain number of studies have postulated a divergence between SM hypertrophy per se , and intrinsic changes in SM IS or have pointed out a lack of clarity around the mechanisms involved ( Holten et al, 2004 ; Bird and Hawley, 2017 ; Pesta et al, 2017 ). Furthermore, the relationship between relative or absolute FFM and glucose homeostasis is inconsistent across studies ( Gippini et al, 2002 ; Goulet et al, 2007 ; Glouzon et al, 2015 ; Perreault et al, 2016 ; Stuart et al, 2017 ). Amongst these studies, Brochu et al (2008) have shown in non-diabetic postmenopausal women matched for fat mass that those displaying a larger FFM had higher fasting insulin and glucose compared to those with lower FFM ( Brochu et al, 2008 ).…”