The association between daily steps and health, and the mediating role of body composition: a pedometer-based, cross-sectional study in an employed South African population

The association between daily steps and health, and the mediating role of body composition: a pedometer-based, cross-sectional study in an employed South African population

Background: Walking is recognised as an easily accessible mode of physical activity and is therefore supported as a strategy to promote health and well-being. To complement walking, pedometers have been identified as a useful tool for monitoring ambulatory physical activity, typically measuring total steps/day. There is, however, little information concerning dose-response for health outcomes, in relation to intensity or duration of sustained steps. We aimed to examine this relationship, along with factors that mediate it, among employed adults.

Methods: A convenience sample, recruited from work-site health risk screening (N=312, 37±9yrs), wore a pedometer for at least 3 consecutive days. Steps were classified as “aerobic” (≥100 steps/minute and ≥10 consecutive minutes) or 'non-aerobic' (<100 steps/minute and/or <10 consecutive minutes). The data were sub-grouped according to intensity-based categories i.e. 'no aerobic activity', 'low aerobic activity' (1-20 minutes/day of aerobic activity) and 'high aerobic activity' (≥21 minutes/day of aerobic activity), the latter used as a proxy for current PA guidelines (150-minutes of moderate-intensity physical activity per week). Health outcomes included blood pressure, body mass index, percentage body fat, waist circumference, blood cholesterol and blood glucose. Analyses of co-variance, adjusting for age, gender and total steps/day were used to compare groups according to volume and intensity-based steps categories. A further analysis compared the mediation effect of body fat estimates (percentage body fat, body mass index and waist circumference) independently on the association between steps and health outcomes.

Results: Average steps/day were ,574±3,541; Total steps/day were inversely associated with most health outcomes in the expected direction (p<0.05). The 'no aerobic activity' group was significantly different from the 'low aerobic activity' and 'high aerobic activity' in percentage body fat and diastolic blood pressure only (P>0.05). Percentage body fat emerged as the strongest mediator of the relationship between steps and outcomes; body mass index showed the least mediation effect.

Conclusion: The study provides a presentation of cross-sectional pedometer data that relate to a combination of intensity and volume-based steps/day and its relationship to current guidelines. The integration of volume, intensity and duration of ambulatory physical activity in pedometer-based messages is of emerging relevance.