Effects of High‐Intensity Interval Training on Subcortical and Cortical Brain Volumes in Older Adolescents: Findings From the “Burn 2 Learn” Cluster Randomized Controlled Trial

ABSTRACT The aim of our study was to examine the effects of a 6‐month school‐based high‐intensity interval training intervention (Burn 2 Learn [ B2L ]) on a priori regional brain volumes in adolescents using magnetic resonance imaging ( MRI ). Participants were older adolescents [ N = 56, 61% female, 16.1 ± 0.4 years] from four schools (10 classes) participating in a larger cluster randomized controlled trial. Participants were randomized to B2L (five classes, N = 30) or a control group (five classes, N = 26) and underwent MRI at baseline and 6‐month follow‐up. Changes in regional gray matter volumes were assessed using linear mixed models adjusted for sex, weight status, intracranial volume, and class level clustering. We observed increases in total (+105.5 mm 3 , 95% confidence interval [ CI ] 25.2 to 185.8, d = 0.79) and left (+64.7 mm 3 , 95% CI 13.8 to 115.7, d = 0.76) hippocampal volume in the B2L group compared to the control group. We also observed that the B2L group retained significantly greater left medial superior frontal gyrus gray matter volume compared to the control group (+144.8 mm 3 , 95% CI 17.1 to 272.5, d = 0.68). There was a decrease in total (−30.6 mm 3 , 95% CI −50.9 to −10.2, d = −0.90), left (−15.2 mm 3 , 95% CI −28.9 to −1.5, d = −0.67), and right (−18.6 mm 3 , 95% CI −30.8 to −6.4, d = −0.92) nucleus accumbens volume, as well as total (−78.3 mm 3 , 95% CI −146.8 to −9.9, d = −0.69) and right (−58.7 mm 3 , 95% CI −99.7 to −17.6, d = 0.86) putamen volume in the B2L group compared to the control group. This is the first experimental study to show that school‐based physical activity may play a key role in nurturing the healthy development of cortical and subcortical brain regions associated with cognitive and mental health in adolescents. Larger studies are needed to replicate our findings and confirm the effects of exercise training on brain health in this population.