Comparison of Physical Activity Guideline Compliance Estimates Among Active Youth Using Different Step-Based Definitions

Abstract

Among youth, several investigations have quantified steps/day thresholds corresponding to compliance with current physical activity guidelines (≥ 60 min/day of moderate-to-vigorous physical activity [MVPA]) while other reports have identified cadence (steps/min) cut-points consistent with MVPA. However, empirical applications of these two methods for use in estimating compliance to current physical activity guidelines are scant within the literature. PURPOSE: To compare physical activity guideline compliance estimates using steps/day thresholds and step-defined MVPA methods among a sample of active adolescents. METHODS: Step-based physical activity was assessed minute- by-minute using the waist-worn Fitbit Zip™ over a 7-day period among 291 adolescent soccer players (64.9% female, age: 15.2 ± 1.2 yrs, BMI: 22.1 ± 3.4 kg/m2) providing ≥ 4 days of valid data (≥ 10 hr/day of wear time). Compliance to current physical activity guidelines was quantified as: 1) mean steps/day ≥ 10,500 for boys or ≥ 9,500 for girls, and 2) mean step-defined MVPA (time spent at 100+ steps/min) ≥ 60 min/day. Compliance estimates were compared between methods using McNemar’s test. RESULTS: Participants accumulated 11,100 ± 3,217 steps/day (boys: 12,201 ± 3,543 steps/day; girls: 10,506 ± 2,865 steps/day) and 36.9 ± 16.8 min/day of step-defined MVPA (boys: 42.9 ± 18.7 min/day; girls: 33.7 ± 14.8 min/day). Compliance to current physical activity guidelines among the overall sample significantly varied between the steps/day thresholds and step-defined MVPA methods (63.2% and 9.6%, respectively; χ2 = 154.0, p < 0.001). Within sex compliance estimates also varied for the steps/day thresholds and step- defined MVPA methods among boys (65.7% and 15.7%, respectively; χ2 = 49.0, p < 0.001) and girls (61.9% and 6.3%, respectively; χ2 = 103.0, p < 0.001). CONCLUSION: Significant heterogeneity in physical activity guideline compliance estimates was observed between the steps/day thresholds and step-defined MVPA methods. It is possible that the sporadic nature of physical activity observed among youth is being obscured by the 1-min measurement epoch used herein, thereby lowering expected values of daily step- defined MVPA and associated physical activity guideline compliance estimates. Support: USDA-AFRI 2013-67001-20418