Due to a worldwide response to the COVID-19 pandemic, many changes were imposed on individuals' daily lives, including those related to the physical activity of children and adolescents. The present study aims to comprehend the impact of early COVID-19 pandemic restrictions on Portuguese adolescents' physical fitness parameters during two school years. A total of 640 students from the 5th to the 12th grades participated in the longitudinal study. Data on body composition, aerobic fitness, speed, agility, lower and upper body strength, and flexibility were collected at three moments: 1. before the COVID-19 pandemic (December 2019); 2. after the COVID-19 lockdown when the schools reopened delivering in-person classes (October 2020), and 3. two months after the in-person classes started (December 2020). To analyze the overall changes between the three moments and between two age groups, we conducted repeated measure ANOVAs. The main findings indicate that participants' body composition (i.e., waist circumference) and aerobic fitness (i.e., maximal oxygen uptake) deteriorated after the first lockdown but improved two months after the in-person classes started. However, the same did not happen to neuromuscular fitness (i.e., horizontal Jumps and Sit and Reach). These findings suggest that the COVID-19 lockdown may have negatively impacted adolescents' physical fitness, particularly older adolescents. Altogether, data reinforce the importance of in-person classes and school context in promoting adolescents' physical health.
Keywords: coronavirus disease 2019; longitudinal design; physical activity; school-aged sample.