Associations Between Fatigue, Physical Fitness, and Physical Activity in Patients with Inflammatory Bowel Disease

Aim Fatigue is a common and debilitating symptom in patients with Inflammatory Bowel Disease (IBD) and may be linked to physical fitness and physical activity. However, their interrelationships are not fully understood. More objective knowledge is needed to guide physical interventions to reduce fatigue. This study aimed to investigate the association of physical fitness and physical activity with fatigue in patients with IBD. Additionally, the association between physical fitness and physical activity was investigated. Methods Patients with IBD in remission or with mild-to-moderate disease activity were included. Fatigue was defined as a score of ≥ 35 on the subjective fatigue subscale of the checklist individual strength. Physical fitness measurements were performed using gold standard methodologies for body composition, cardiorespiratory fitness, muscular strength, muscular endurance, and flexibility. Physical activity was quantified using accelerometry. Results In total, 53 patients were included, of whom 17 (32.1%) experienced fatigue. Fatigued patients exhibited a higher fat-mass index (p = 0.014), lower cardiorespiratory fitness (p = 0.017), and less quadriceps muscular endurance (p = 0.026, p = 0.008). No differences were observed in physical activity. Multiple linear regression showed that fat-mass index and cardiorespiratory fitness independently predicted fatigue (p = 0.029, p = 0.012). Significant correlations were found between fatigue and physical fitness, but not with physical activity. Conclusions Reduced physical fitness was associated with fatigue in patients with IBD, suggesting that enhancing physical fitness could help alleviate fatigue. Physical activity was not associated with fatigue or physical fitness, indicating that simply increasing physical activity may have limited impact on reducing fatigue or improving physical fitness in this population.