Effects of physical inactivity behavior during COVID-19 pandemic on physical fitness, body composition, inflammatory cytokine, and immunocytes in older adults: A retrospective and prospective study

The prolonged period of COVID-19 has ingrained physical inactivity as a habit, leading to a reluctance to move. This has resulted in a decline in physical fitness and the loss of a healthy body composition. While this trend is particularly noticeable among the older adults, its impact on the immune cell defense system, which is crucial for minimizing viral infections, remains unclear. This study aimed to investigate the physical fitness, body composition, cytokines and immunocytes of older adults who engaged in physical activity (PA) before the COVID-19 pandemic but had to stop it due to the lockdown. A total of 172 older adults aged 61 to 85 years participated in this study: 90 in non-PA group (NPAG, 34 men and 56 women), and 82 in PA group (PAG, 29 men and 53 women). Physical inactivity was 45.13 ± 5.67 weeks in the NPAG and 1.70 ± 0.43 weeks in the PAG. Although there was no significant difference in calorie intake, PA volume showed a significant decrease in NPGA (P < 0.001). VO₂max, strength, and sit-ups decreased in NPAG, whereas they maintained or increased in PAG (Ps < 0.001). NPAG experienced an increase in fat mass (∼33.0 %), along with a decrease in muscle mass (∼10.4 %), but PAG showed slight increases (∼1.1 % vs. ∼1.5 %, Ps < 0.001). Interleukin-6 (∼38.9 %), tumor necrosis factor-α (∼38.3 %), and C-reactive protein (∼33.6 %) increased, whereas immunocytes decreased in NPAG (Ps < 0.001). In contrast, those in PAG showed the opposite phenomenon. This study indicates that even during the COVID-19 situation, maintaining active PA in the older adults helps retain beneficial physical fitness and body composition, reduces inflammatory factors, and contributes to preserving or enhancing the function of immunocytes.