Relative importance of step count, intensity, and duration on physical activity's impact on vascular structure and function in previously sedentary older adults

Abstract

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.

Trial registration: ClinicalTrials.gov NCT01212978.

Keywords: elderly; endothelial function; physical exercise.

Figures

Figure 1.

Study enrollment flow diagram.

Figure 2.

Brachial flow‐mediated dilation (FMD) improved in the group randomized to access to the pedometer and website, but not in either of the other groups. (P<0.001 for time, P=0.004 for time×group interaction by ANOVA). FMD% did not significantly change in group 1 (5.6±2.5% to 6.3±2.7%, P=0.10) or group 2 (6.5±3.0% to 6.7±3.9%, P=0.85), but significantly increased in group 3 (4.7±2.5% to 8.0±4.3%, *P=0.001 within the group).

Figure 3.

Step count and FMD% based on analysis by achievement of ≥10 000 steps/day (A and C) or ≥30 min/day of MPA (B and D). A, Step count increased to a greater extent in the group that achieved ≥10 000 steps/day compared to those who did not achieve this goal (4803±1531 to 5741±2111 steps vs 6069±1371 to 12486±1947, *P<0.001 between groups at week 12). B, The 46 subjects who achieved ≥30 min/day of MPA also increased their step count over the study period (4825±1604 to 5327±2671 steps vs 5570±1517 to 10196±314, *P<0.001 between groups at week 12). There was no interaction between FMD% changes over time and achieving either ≥10 000 steps/day (C), 5.5±3.1 to 7.4±3.6 for <10 000 group vs 5.7±2.6 to 6.7±3.5 for ≥10 000 step group, P=0.40 for interaction) or ≥30 min/day of MPA (d, 5.5±2.2 to 6.6±3.5 for <30 min/day vs 6.1±3.3 to 7.2±3.6 for ≥30 min/day, P=0.93 for interaction). FMD indicates flow‐mediated dilation; MPA, moderate intensity physical activity.

Figure 4.

Step count and FMD% based on those who achieved ≥20 min/day. (A) Those who achieved ≥20 min/day of in MPA in bouts significantly increase their step count to a greater extent than those who did not (4866±1599 to 6204±3172 steps vs 5785±1437 to 10439±3313 steps, *P<0.001 for both time and time×group interaction, P<0.001 between groups at week 12). (B) Those who achieved ≥20 min/day in moderate intensity in bouts significantly also increased their FMD% (5.4±3.2% to 8.1±3.7% vs 6.0±2.6% to 6.3±3.4%, *P=0.001 for time, P=0.008 for time×group interaction, P<0.001 for ≥20 min/day of MPA in bouts at week 12 vs baseline and vs both FMD measurements for those achieving ≤20 min/day of MPA). FMD indicates flow‐mediated dilation; MPA, moderate intensity physical activity.