Relative Importance of Step Count, Intensity, and Duration on Physical Activity's Impact on Vascular Structure and Function in Previously Sedentary Older Adults

BACKGROUND: Age-related endothelial dysfunction and vascular stiffening are associated with increased cardiovascular (CV) risk. Many groups have encouraged goals of ≥10 000 steps/day or ≥30 min/day of moderate intensity physical activity (MPA) to reduce age-related CV risk. The impact of MPA on the vasculature of older adults remains unclear. METHODS AND RESULTS: We randomized 114 sedentary older adults ages ≥50 to 12 weeks of either no intervention (group 1), a pedometer-only intervention (group 2), or a pedometer with an interactive website employing strategies to increase the adoption of habitual physical activity (PA, group 3). Endothelial function by brachial flow-mediated dilation (FMD%), vascular stiffness by tonometry, step-count by pedometer, and PA intensity/distribution by accelerometer were measured. Step-count increased in groups 2 (5136±1554 to 9596±3907, P<0.001) and 3 (5474±1512 to 8167±3111, P<0.001) but not in group 1 (4931±1667 to 5410±2410). Both groups 2 and 3 increased MPA ≥30 min/day. Only group 3 increased MPA in continuous bouts of ≥10 minutes (P<0.001) and improved FMD% (P=0.001). Neither achievement of ≥10 000 steps/day nor ≥30 min/day of MPA resulted in improved FMD%. However, achieving ≥20 min/day in MPA bouts resulted in improved FMD%. No changes in vascular stiffness were observed. CONCLUSIONS: MPA reverses age-related endothelial dysfunction, but may require MPA to be performed in bouts of ≥10 minutes duration for ≥20 min/day to be effective. Commonly encouraged PA goals do not guarantee improved endothelial function and may not be as effective in reducing CV risk. CLINICAL TRIAL REGISTRATION URL: Clinicaltrials.gov. UNIQUE IDENTIFIER: NCT-01212978.