The effects of high-intensity interval training on mental health and the acute inflammatory response

Abstract

Mental illness is on the rise in university students, with approximately one third of all students experiencing depression. One way that depression can arise is through chronic stress, a common experience for university students. Exercise has been shown to buffer the effects of chronic stress and improve depression. One hypothesis suggests that exercise improves depression by decreasing pro-inflammatory cytokines at rest; however, it is unclear what role exercise intensity plays. Prior work has shown that over 6 weeks of training, HIIT buffered the development of depressive symptoms, but increased stress, anxiety, and resting-state pro-inflammatory cytokines IL-6 and TNF-a. However, it is unknown how HIIT influenced the acute inflammatory response, and if adaptations in this response can improve mood. The aim of this study was to examine the effect of HIIT on mood and both resting state and acute inflammation over a training period of 9 weeks. Fifty-two sedentary university students (63% females), aged 18-30 (M±SD: 19.9±2.2 years) were randomized into one of two groups: 1) high-intensity interval training (HIIT), consisting of exercise three times per week, or 2) sham-exercise (controls), who were instructed to remain sedentary during the intervention. The sham-exercise group was given a cover story that they were part of an “acute” exercise group, and thus believed they were also assigned to an exercise condition. Mood was tracked weekly using surveys for depression (BDI-II), anxiety (BAI), and stress (PSS). Levels of pro-inflammatory cytokines (IL-6, TNF-α, IL-1β) were measured using serum draws at rest and immediately after the completion of a peak power output test at the beginning, middle, and end of the training period. Both groups decreased in depression and anxiety across the nine-week training period (p < 0.001), and decreased in stress during the first three weeks of training (p =0.07), suggesting that HIIT exercise does not improve mood to a greater extent than a sham-exercise condition. Interestingly, at the end of training, HIIT had higher levels of IL-6 compared to controls (p = 0.03), and this may be why one reason why the HIIT group did not improve mood over controls. Despite an increase in overall IL-6 levels at rest, nine weeks of HIIT attenuated the acute pro-inflammatory response to exercise compared to controls, who experienced an elevated IL-6 response (p = 0.04) and TNF-α response (p = 0.003). Taken together, these results suggest that HIIT exercise impacts the inflammatory response both at rest and in response to maximal exercise, but it may not be an effective intensity of exercise for improving mental health outcomes in sedentary individuals.