Longitudinal assessment of cardiorespiratory fitness and body mass of young healthy adults during COVID-19 pandemic.

Physical activity was reduced during the COVID-19 pandemic, especially when lockdowns were mandated; however, little is known about the impact of these lifestyle changes on objective measures of cardiorespiratory fitness. To address this knowledge gap, we evaluated the cardiorespiratory fitness of 14 young healthy adults (4 women, age: 27 ± 6 yr) just before the pandemic and after ∼1 yr of public health measures being in place. During fitness assessments, participants performed submaximal pseudorandom cycling exercise to assess cardiorespiratory kinetics, and a 25 W·min ramp-incremental cycling test to determine peak oxygen uptake (V̇o). Cluster analysis identified two subgroups of participants: those who had reduced peak V̇o at the 1-yr follow-up (-0.50 ± 0.17 L·min) and those whose peak V̇o was maintained (0.00 ± 0.10 L·min). Participants with reduced peak V̇o also exhibited slower heart rate kinetics (interaction: = 0.01), reduced peak O pulse (interaction: < 0.001), and lower peak work rate (interaction: < 0.001) after 1 yr of the pandemic, whereas these variables were unchanged in the group of participants who maintained peak V̇o. Regardless of changes in peak V̇o, both subgroups of participants gained body mass (main effect: = 0.002), which was negatively correlated with participants' level of self-reported physical activity level at the follow-up assessment (mass: ρ = -0.59, = 0.03) These findings suggest that some young healthy individuals lost cardiorespiratory fitness during the pandemic, whereas others gained weight, but both changes could potentially increase the risk of adverse health outcomes and disease later in life if left unaddressed. Some young healthy adults experienced cardiovascular deconditioning during the COVID-19 pandemic, with measurable reductions in cardiorespiratory fitness, whereas others experienced no change in fitness but gained body mass, which was related to self-reported physical activity during the pandemic.