Flexible Goals for Daily Step Count: Associations Between Sporadic and Bouted Steps and All-Cause Mortality

OBJECTIVES: To investigate the association of sporadic and bouted steps with all-cause mortality. Bouted steps were defined as those accumulated during walking bouts lasting at least 10 minutes. METHOD: A cohort study of 3072 participants (mean age: 48.6 y, 51.7% female) from the United States National Health and Nutrition Examination Survey 2005-2006. Baseline step counts were recorded using a waist-worn accelerometer over a 7-day period. Mortality was ascertained through December 2019. A random forest classifier, trained on "ground truth" image data from the Capture-24 study, was used to differentiate between sporadic and bouted steps. Sporadic and bouted steps were mutually adjusted in the Cox model after controlling for important confounders. RESULTS: Over a mean follow-up period of 13.1 years (2.7 y), 632 deaths were identified. Each 1000-step increase in sporadic steps was associated with a 10% (95% CI, 7%-13%) reduction in all-cause mortality. Each 1000-step increase in bouted steps was associated with a 27% (17%-35%) reduction. In the joint analysis, we observed an 80% reduction in all-cause mortality among individuals who took either 6000 steps (comprising 4000 sporadic and 2000 bouted steps) or 10,500 steps (comprising 10,000 sporadic and 500 bouted steps), compared with the reference group (2000 sporadic and 0 bouted steps). CONCLUSION: Both sporadic and bouted steps were inversely associated with all-cause mortality. More sporadic steps were better than less, but increasing bouted steps led to more rapid reductions in mortality. Health-benefiting daily step goals can be achieved through various combinations of these 2 step patterns.