A randomized control trial investigating high-intensity interval training and mental health: A novel non-responder phenotype related to anxiety in young adults

Background The present study was a non-blinded, randomized control trial examining the relationship between high-intensity interval training (HIIT) and various indicators of mental health. First, we examined the effects of HIIT on anxiety symptoms, depressive symptoms, and resting-state proinflammatory cytokines relative to placebo-exercise control. Then, we examined whether baseline anxiety status moderates the relationship between HIIT and cardiorespiratory improvements to explore a potential non-responder phenotype linked to mental health. Methods Young adults (age 18–30) were randomized to either nine weeks of HIIT (n = 28) or placebo-exercise (PLACEBO; n = 32). Randomization and allocation were conducted using a computer-generator program. Anxiety and depressive symptoms, proinflammatory cytokines, and cardiorespiratory fitness were assessed at the beginning and end of the intervention period. Results HIIT and PLACEBO groups (n = 46) experienced similar reductions in depressive and anxiety symptoms (p < .001) and no change in resting-state proinflammatory cytokines (p > .05). Anxiety severity moderated the effects of HIIT on cardiorespiratory fitness (p < .05), such that individuals with low anxiety at baseline experienced greater improvements in cardiorespiratory fitness than those with higher anxiety. Conclusions These findings suggest that nine weeks of HIIT may not alter physiological indicators of mental health. Furthermore, anxiety status may be a potential non-responder phenotype. Further research is needed to examine whether these results generalize to other HIIT protocols and how the effects of HIIT compare to the consistent and robust effects of moderate-intensity continuous training on mental health. Trial registration ClinicalTrials.gov Identifier: NCT04118309. Funding Natural Sciences and Engineering Council of Canada (NSERC) Discovery Grant [grant number 296518].