Exercise Intensity and Circulating Exerkine Responses: A Narrative Review of Selected Molecules

Exerkines are bioactive molecules released in response to physical exercise and are considered important mediators of systemic adaptations. While previous research has largely focused on the effects of exercise modalities, the role of exercise intensity in regulating exerkine responses remains unclear. This narrative review summarizes findings on the effects of different exercise intensities on nine circulating exerkines with sufficient available data in healthy populations, including irisin, follistatin-like 1, myostatin, fibroblast growth factor 21, follistatin, leptin, adiponectin, apelin and brain-derived neurotrophic factor, without systematically covering all known exercise-responsive molecules. Given the narrative design of this review, the findings should be interpreted as descriptive and hypothesis-generating rather than as definitive evidence of intensity-dependent effects. The included studies show that acute exercise is associated with changes in several exerkines, with some direct within-study comparisons reporting larger responses under higher-intensity exercise conditions, whereas others exhibit increases, decreases, or no measurable changes across intensities. In contrast, studies examining chronic exercise interventions report changes in some studies and no measurable differences in others. Overall, the current evidence in this review suggests that exercise intensity may influence exerkine responses under some conditions, particularly during acute exercise, although the available findings remain limited and inconsistent across studies.