Effects of Short-Term Exercise in Overweight/Obese Adults with Insulin Resistance or Type 2 Diabetes: A Systematic Review of Randomized Controlled Trials

Background: Chronic exercise training is associated with improvements in body composition and/aerobic fitness. This presents a challenge to study effects of exercise in isolation. Metabolic effects of short-term exercise training (≤ 12 weeks) are unclear, with studies reporting improvements or no change in insulin sensitivity and/or glucose control. This review systemically examined randomized controlled trials (RCTs) to establish whether short-term exercise training improves insulin resistance and type 2 diabetes (diabetes). Methods: Following the PRISMA guidelines, a systematic review was conducted on nine electronic databases (BMC Endocrine Disorders, Clinical Key, Cochrane Library, EBSChost, PubMed, Scopus, Sabinet_SA Publications, The Lancet and Web of Science) to identify randomized controlled human trials (2005-2018) examining effects of short-term exercise training (≤ 12 weeks) in overweight/obese adults with insulin resistance or diabetes. Search terms included: insulin resistance, type 2 diabetes, short-term, exercise or energy expenditure and randomized controlled trial. Studies were only included if they provided sufficient data on: insulin sensitivity, glycemic control, body composition and aerobic fitness. Results: From 374 articles, three met the inclusion criteria. Of these, two prescribed moderate intensity training (MIT); rate of perceived exertion (RPE) 12-13 and 60% lactic threshold (LT) for four and twelve weeks, respectively while one prescribed vigorous exercise training at 70% VO2max for seven days. Duration of exercise sessions was 40-60 minutes. Twelve weeks of MIT was associated with improved glycemic control vs. no change in the 7-d and four weeks studies. Seven days of vigorous training was associated with greater improvement in insulin sensitivity, 44.4% vs. no change in the four- and twelve-weeks studies. Conclusion: Short-term exercise appears to improve insulin sensitivity and glucose control independent of body fat loss or gains in aerobic fitness. Vigorous exercise training was associated with superior improvements in insulin sensitivity. More RCTs are needed to confirm these findings.