Resistance training, insulin sensitivity & metabolic health

[摘要] Skeletal muscle is the largest organ in the human body, comprising 40%-50% of total body weight and more than 600 skeletal muscles in a human body performing common functions such as body movements, maintaining posture, storing protein and glycogen and generating heat. Approximately 0.8% skeletal muscle mass declines per year a process known as sarcopenia. On top of that, ageing also results in a decrease in muscle strength, at a rate of approximately 1-3% per year (Keller & Engelhardt, 2013).Skeletal muscle is the major organ responsible for glucose uptake under insulin stimulated conditions, accounting for ~80% of total glucose disposal and low muscle strength and mass likely contribute to metabolic dysregulation seen in Type 2 diabetes. Research has shown that resistance exercise training can increase strength, muscle size, fat-free mass, connective tissue thickness, decrease body fat, reduce blood pressure and improve insulin sensitivity and VO2max(Croymans et al., 2013; Ozaki et al., 2013;Abdul & Defronzo, 2010). In order to monitor efficacy of such resistance training interventions it is important to be able to accurately quantify skeletal muscle mass and several methods exist for this purpose, although many require expensive equipment making them not always possible to use. The aim of chapter 2 was to investigate the repeatability and validity of a relatively cheap and portable A-mode ultrasound device. This chapter has found that A mode ultrasound is a repeatable measure of muscle thickness (CV of 4.6%) and that both A and B mode ultrasound provide valid measures of muscle volume, as compared to the gold standard MRI (r=0.96).Following this, the aim of chapter 3 wasto determine if this A-mode ultrasound device is able to detect changes in muscle thickness in response to resistance exercise training and to determine its validity. Findings in this Chapter 3 have shown that the A-mode ultrasound can detect increases in muscle thickness of 6.2 ± 5.4%, alongside a 26 ± 7.3% increase in 1RM after 8 weeks of resistance exercise training. However, it was also shown that both A and B mode measures of ultrasound muscle thickness were not valid measures of the resistance exercise induced changes in muscle volume (r=0.30 A-mode & r=0.04 B-mode)Resistance exercise is known as the most efficacious method to increase muscle strength and mass. It has been demonstrated recently that if exercise is performed to volitional failure then gains in muscle mass, and to a lesser extent strength, are similar regardless of the load at which exercise is performed. The aims of chapter 4, were to investigate the effects of 6 weeks of resistance exercise training, comprised of 1 set of each exercise to voluntary failure, on insulin sensitivity and the time-course of adaptations in muscle strength/mass, in overweight men. Results of this chapter have demonstrated that six weeks of resistance exercise, volitional failure of nine exercises – taking 15-20 min per session – undertaken three times per week resulted in a 16% improvement in insulin sensitivity (61.6 ± 18.0 to 71.3 ± 22.9 mg.l2.mmol-2.mU-1.min-1 after the intervention (P<0.05) in healthy overweight men and increases in muscle strength, size and RTD (rate torque development) 50 and 100 were also observed.Several studies have demonstrated that people from South Asia are up to 4-6 times more likely to develop type 2 diabetes than White Europeans. Furthermore, in a recent study from the UK Biobank,grip strength in South-Asian men and women was 5–6 kg lower than in the other ethnic groups and a greater contributor to diabetes prevalence. As resistance exercise is the most effective intervention for increasing muscle mass, strength, and can improve insulin sensitivity, the aim of the Chapter 5 was tocompare the effect of resistance exercise on muscle and metabolic health between South Asians and White Europeans. This chapter has shown that there were no differences in the effect of 12 weeks of resistance exercise training on the majority of the muscle and metabolic outcomes measured, however the increase muscle thickness, 1.2 (95%CI 0.8 to 1.7) mm in South Asians and 2.3 (95%CI 1.8 to 2.9) mm in White Europeans and decrease in systolic blood pressure, 5.1 (95%CI:-7.5 to -2.7) mmHgin White Europeans and a 0.7 (95%CI:-2.4 to 1.0) mmHgin South Asians were attenuated in South Asians. There was also a trend for an attenuated effect of resistance exercise training on VO2max,decrease of 0.7 (95%CI -2.0 to 0.6) ml.kg.min-1 in South Asians. In summary, this thesis has demonstrated that whilst ultrasound measure of muscle thickness is valid at a single time point, this is not the case when evaluating changes with resistance exercise training. Following this we have demonstrated that resistance exercise training, involving a single set of exercise to muscle failure, is effective in inducing short-term improvements in muscle size and strength and also insulin sensitivity in White Europeans, with broadly similar findings in South Asians.

[发布机构] University:University of Glasgow;Department:Institute of Cardiovascular and Medical Sciences

[关键词] Resistance training, insulin sensitivity, metabolic health, South Asians.