Objective Assessment of Sedentary Behavior during and after Prolonged, Intensive Aerobic Exercise Training

Background: Observational studies have shown that individuals can be both highly sedentary and highly active, and active people sit as much as those who do not meet the physical activity guidelines. It is not known how sedentary behavior changes in response to significant exercise training, such as training for a marathon

Purpose: To determine time spent in sedentary behavior while training for, and after completion of, a marathon.

Methods: Participants included adults who self- selected to run a marathon. Sedentary behavior was assessed using an accelerometer-based motion sensor (Actigraph GT3X) for seven consecutive days during seven assessment periods (-3, -2, and -1 month prior to the marathon, within 2 weeks of the marathon, and +1, +2, and +3 months after completing the marathon). Data were summed into 60-second epochs. Body fat was assessed with dual-energy x-ray absorptiometry (GE Lunar Prodigy). Models were fitted with multiple imputation data using STATA mi module. Random intercept GLS regression models were used to predict the sedentary behavior with 7 waves of repeated measures.

Results: Twenty-three individuals, 15 females (33.3 ± 7.9y, 23.2 ± 2.4kg/m2, 26.7 ± 8.1% fat) and 8 males (35.4 ± 13.3y, 23.7 ± 2.4kg/m2, 16.2 ± 6.8% fat) completed the study. Marathon finishing times ranged from 220- 344 min (271 ± 40 min) for women and 185- 276 min (227 ± 32 min) for men. Time spent in sedentary behavior varied by only 30 min or 6.5% over the 7 month period (month -3: 653.7 ± 27.1 min, 66.9%, month -2: 634.7 ± 16.8 min, 71.6%; month -1: 622.2 ± 19.5 min, 70.2%; marathon month: 647.1 ± 21.3 min, 72.6%; month +1: 638.8 ± 18.6 min, 73.4%; month +2: 633.6 ± 18.8 min, 72.8%; month +3: 635.7 ± 16.6 min, 72.9% of daily wear time). Daily sedentary behavior did not change over the seven month training, marathon, and post-marathon period, after accounting for age, percent body fat, and wear time (t=.72, p=.47).

Conclusions: This prospective study supports the notion that physical activity and sedentary behavior are distinct behaviors, showing that sedentary behavior was not impacted while training for a marathon.