Aims/hypothesis: The aim of this study was to evaluate the effects of oxygen consumption-matched short-term interval walking training (IWT) vs continuous walking training (CWT) on glycaemic control, including glycaemic variability, in individuals with type 2 diabetes. We also assessed whether any training-induced improvements in glycaemic control were associated with systemic oxidative stress levels.
Methods: Participants (n = 14) with type 2 diabetes completed a crossover trial using three interventions (control intervention [CON], CWT and IWT), each lasting 2 weeks. These were performed in a randomised order (computerised generated randomisation) and separated by washout periods of 4 or 8 weeks after CON or training interventions, respectively. Training included ten supervised treadmill sessions, lasting 60 min/session, and was performed at the research facility. CWT was performed at moderate walking speed (75.6% ± 2.5% of walking peak oxygen consumption [[Formula: see text]]), while IWT was performed as alternating 3 min repetitions at slow (58.9% ± 2.0% [Formula: see text]) and fast (90.0% ± 3.6% [Formula: see text]) walking speed. Before and after each intervention, the following was assessed: 24 h continuous glucose monitoring (CGM) and urinary free 8-iso prostaglandin F2α (8-iso PGF2α; a marker for oxidative stress), physical fitness and body composition. Neither participants nor assessors were blinded to the interventions.
Results: No intervention-induced changes were seen in physical fitness or body composition. Compared with baseline, IWT reduced mean glucose levels non-significantly (-0.7 ± 0.3 mmol/l, p = 0.08) and significantly reduced maximum glucose levels (-1.8 ± 0.5 mmol/l, p = 0.04) and mean amplitude of glycaemic excursions (MAGE; -1.7 ± 0.4 mmol/l, p = 0.02), whereas no significant within-group changes were seen with CON or CWT. Although 8-iso PGF2α was associated with minimum glucose levels at baseline, no change in 8-iso PGF2α was seen with any intervention, nor were there any associations between changes in 8-iso PGF2α and changes in glycaemic control (p > 0.05 for all). No adverse effects were observed with any of the interventions.
Conclusions/interpretation: Short-term IWT, but not CWT, improves CGM-derived measures of glycaemic control independent of changes in physical fitness and body composition in individuals with type 2 diabetes. Systemic oxidative stress levels are unaffected by short-term walking and changes in oxidative stress levels are not associated with changes in glycaemic control.
Trial registration: ClinicalTrials.gov NCT02320526 FUNDING : The Centre for Physical Activity Research (CFAS) is supported by a grant from TrygFonden. During the study period, the Centre of Inflammation and Metabolism (CIM) was supported by a grant from the Danish National Research Foundation (DNRF55). The study was further supported by grants from Diabetesforeningen, Augustinusfonden and Krista og Viggo Petersens Fond. CIM/CFAS is a member of the Danish Center for Strategic Research in Type 2 Diabetes (DD2; the Danish Council for Strategic Research, grant no. 09-067009 and 09-075724). MR-L was supported by a post-doctoral grant from the Danish Diabetes Academy supported by the Novo Nordisk Foundation.
Keywords: 8-Isoprostanes; Continuous glucose monitoring; Exercise training; Glycaemic variability; Hypoglycaemia; Lifestyle intervention(s); Mean amplitude of glycaemic excursions; Physical activity intervention(s); Systemic inflammation.