AbstractWhile the relationship between exercise and life span is well‐documented, little is known about the effects of specific exercise protocols on modern measures of biological age. Transcriptomic age (TA) predictors provide an opportunity to test the effects of high‐intensity interval training (HIIT) on biological age utilizing whole‐genome expression data. A single‐site, single‐blinded, randomized controlled clinical trial design was utilized. Thirty sedentary participants (aged 40–65) were assigned to either a HIIT group or a no‐exercise control group. After collecting baseline measures, HIIT participants performed three 10 × 1 HIIT sessions per week for 4 weeks. Each session lasted 23 min, and total exercise duration was 276 min over the course of the 1‐month exercise protocol. TA, PSS‐10 score, PSQI score, PHQ‐9 score, and various measures of body composition were all measured at baseline and again following the conclusion of exercise/control protocols. Transcriptomic age reduction of 3.59 years was observed in the exercise group while a 3.29‐years increase was observed in the control group. Also, PHQ‐9, PSQI, BMI, body fat mass, and visceral fat measures were all improved in the exercise group. A hypothesis‐generation gene expression analysis suggested exercise may modify autophagy, mTOR, AMPK, PI3K, neurotrophin signaling, insulin signaling, and other age‐related pathways. A low dose of HIIT can reduce an mRNA‐based measure of biological age in sedentary adults between the ages of 40 and 65 years old. Other changes in gene expression were relatively modest, which may indicate a focal effect of exercise on age‐related biological processes.