Stable physical activity patterns predominate in a longitudinal study of physical activity among young adults in Canada from before to during the COVID-19 pandemic.

We examined change in walking, moderate-to-vigorous physical activity (MVPA) and meeting MVPA guidelines from before to during the COVID-19 pandemic, and identified factors associated with newly meeting and no longer meeting MVPA guidelines during the pandemic. Complete data were available for 614 young adults participating in the ongoing Nicotine Dependence in Teens (NDIT) study pre-pandemically in 2010-12 and 2017-20, and during the pandemic in 2020-21. Change in physical activity was examined in four sub-groups (i.e., stable inactive , newly met MVPA guidelines , no longer met MVPA guidelines , stable active ). Factors associated with newly and no longer met MVPA guidelines were identified in multivariable logistic regression. While walking and MVPA changed little from 2010-2 to 2017-20, both declined during the pandemic (median for both = -30 min/week). 63.3% of participants reported no change in meeting MVPA guidelines during the pandemic, 11.4% newly met MVPA guidelines and 25.2% no longer met MVPA guidelines . Male sex, not university-educated, amotivated to engage in physical activity reported pre-pandemic, and endorsing physical activity as a COVID-19 coping strategy were associated with newly met MVPA guidelines . Male sex, not university-educated, higher problem-focused coping scores and endorsing physical activity as a COVID-19 coping strategy were protective of no longer met MVPA guidelines . Increased understanding of why some participants increased or decreased MVPA during the pandemic is needed to inform physical activity-related policy during pandemics.