Association between physical exercise interventions and functional capacity in individuals with type 2 diabetes: a systematic review and meta-analysis of controlled trials

Background: The prevalence of type 2 diabetes mellitus increases with age and people with type 2 diabetes are more affected by reductions in functional performance. Although exercise interventions are recommended for people with diabetes, it is relevant to assess the effects of different training modes on the available functional outcomes. Objective: To summarize the effects of distinct modes of exercise training in comparison to non-exercise on the functional capacity of adults with type 2 diabetes. Methods: A systematic review and meta-analysis of randomized (RCT) and non-randomized (NRS) controlled trials was conducted. Seven databases were searched from inception to January 2021. Eligible studies should last 8 weeks or longer, comparing structured exercise training and non-exercise control for one out of six pre-specified functional capacity outcomes (Timed Up and Go test, chair stands, walking performance, upper limb muscle strength, lower limb muscle strength, physical fitness parameter), in patients with type 2 diabetes, aged [≥]45 years or older. The risk of biases was assessed with the Checklist Downs & Black. Pooled mean differences were calculated using a random-effects model, followed by sensitivity and meta-regression analyses. Results: Of 17165 references retrieved, 29 trials (1557 patients) were included. Among these, 13 studies used aerobic training, 6 studies used combined training, 4 studies used resistance training, 3 studies had multiple intervention arms and 3 studies used other types of training. Exercise training was associated with an increase in functional capacity outcomes, as reflected by changes in 6-minute-walk test (51.6 meters; 95% CI 7.6% to 95.6%; I2 92%), one-repetition maximum leg-press (18.0 kg; 95% CI 4.0% to 31.9%; I2 0%), and peak oxygen consumption (2.41 mL/kg min; 95% CI 1.89% to 2.92%; I2 100%) compared with control groups. In sensitivity and subgroup analyses using VO2max as outcome and stratified by for the type of study (RCT or NRS), duration of diabetes diagnosis, and sex, we observed overlapping confidence intervals. Meta-regression showed no association between HbA1C levels and VO2max (p = 0.34; I2 99.6%; R2 = 2.6%). Conclusion: Structured exercise training based on aerobic training, resistance training, combination of both, or composed by other types of training (i.e. Pilates, Tai Chi and Whole-body vibration) is associated with an improvement in functional capacity in patients with type 2 diabetes, except for the upper limb muscle strength. However, we could not identify potential effect predictors associated with directional summary estimates. Registration: This systematic review was registered in the PROSPERO international prospective register of systematic reviews (CRD42020162467); date of registration: 12/15/2019. The review protocol is hosted at the Open Science Framework (OSF) (Preprint DOI: 10.31219/osf.io/kpg2m). Funding: This study was financed in part by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior - Brasil (CAPES) - Finance Code 001; National Institute of Science and Technology for Health Technology Assessment (IATS) - FAPERGS/Brasil; National Council on Technology and Scientific Development (CNPq).