Acute Effects Of Interrupting Prolonged Sitting On Vascular Function In Type 2 Diabetes

Abstract

In overweight/obese adults, frequent interruptions to sitting time by brief activity bouts can mitigate the impairment of vascular function. However, it is unknown whether the benefits extend to those with type 2 diabetes (T2D), and whether there is an optimal frequency of activity break. PURPOSE: To examine the acute effects on vascular function in those with T2D, of interrupting sitting time with simple resistance activities (SRAs): 3min every 30min; or, 6min every 60min. METHODS: In a randomised crossover trial, 20 sedentary adults with T2D and overweight/obesity (35-70 yr; 11 males; 9 females) completed three 7-hour conditions (6-14 day washout between conditions): 1) uninterrupted sitting (SIT); 2) sitting with 3-min bouts of SRA every 30 min (SRA3); and, 3) sitting with 6-min bouts of SRA every 60 min (SRA6). Shear rate, blood flow and femoral artery flow-mediated dilation (FMD) were measured at 0h, 1h, 3.5h, 4.5h, 6.5h. Mixed models examined effects of condition and condition-by-time interactions, with adjustment for age, sex, BMI, baseline measurements and treatment order. Post-hoc analyses compared vascular measurements at individual timepoints and were re-run with adjustment for multiple comparisons (Šidák correction). RESULTS: Mean (±SD) resting shear rate across timepoints was significantly lower in the SIT condition (32.2 ± 23.3 s-1) relative to SRA3 (42.2 ± 27.9 s-1, PCondition < 0.0001) and SRA6 (44.6 ± 29.1 s-1, PCondition < 0.0001). Mean (±SD) resting blood flow, was significantly lower in the SIT condition (64.7 ± 45.2 ml/min), relative to SRA3 (86.1 ± 77.5 ml/min, PCondition < 0.0001) and SRA6 (85.0 ± 61.7 ml/min, PCondition < 0.0001). There were no condition differences in the temporal change in femoral artery FMD measurements across the 7h day (Ptime x condition > 0.05 for all). However, FMD was significantly lower at the 6.5h timepoint in SIT compared with SRA3 (2.8 ± 3.5% vs 5.3 ± 2.7%, P = 0.0007). CONCLUSIONS: The results demonstrate that when the volume of activity is the same, one activity break per hour is just as effective as two activity breaks per hour for increasing lower-limb blood flow and shear rate. Interrupting sitting twice per hour was also beneficial for FMD at the final reading, however changes between sitting and activity breaks remained relatively unchanged at earlier timepoints.