Chronic exercise training intensity, immune cells, and cancer outcomes: a scoping review

BACKGROUND: Exercise has emerged as a potent, non-pharmacological intervention to enhance immune function in patients with cancer. The effects of exercise are likely influenced by patients' oncologic characteristics, such as cancer treatment, and intervention variables, such as exercise intensity, which can lead to heterogeneous outcomes. This scoping review aims to identify patterns, trends, and gaps in the literature regarding the relationship between chronic exercise training intensity and immune cell parameters in the context of treatment status. METHODS: Reports were retrieved from PubMed, MEDLINE, and CINAHL. Eligible reports were controlled clinical trials of an exercise training intervention with more than 1 exercise session, included an objectively defined exercise intensity, and reported cellular immune outcomes. RESULTS: Twenty-one articles (15 randomized controlled trials) were included. Results suggest a dose-response effect of intensity, where vigorous-intensity exercise (reported in 6 studies) elicited beneficial immunomodulation, such as enhanced natural killer cell cytotoxicity. Light-to-moderate and moderate-intensity exercise (reported in 8 studies) resulted in no significant immunological changes in 5 studies, particularly for patients undergoing active treatment. Comparisons across studies were difficult due to heterogeneity in patients' clinical characteristics, intervention details, and immune parameters. Few reported cancer clinical outcomes such as disease progression, and none directly examined the relationships between immune and clinical endpoints. CONCLUSIONS: While direct comparisons of exercise intensities are lacking, these results suggest that vigorous exercise training may exert greater immune modulation than low-to-moderate intensity exercise training. Rigorously designed trials are needed to confirm these findings and establish the role of exercise in oncologic care.