Skeletal muscle is a heterogeneous tissue comprised of diverse cell types. To date, studies investigating DNA methylation (DNAm) in human muscle at rest and after exercise have predominantly focused on the tissue-level. However, this approach limits interpretation of results due to 1) the significant role that individual cell identities and the variable cellular composition of tissue play in DNAm, and 2) the specific responses of each fibre type to exercise. Recently, distinct methylation profiles of Type I and Type IIa muscle fibres have been identified, and key fibre-specific genes shown to be differentially methylated (1). Here, we aim to further distinguish DNAm profiles for Type I and Type IIa muscle fibres and investigate the fibre-type-specific DNAm changes after high intensity interval training (HIIT). Briefly, individual skeletal muscle fibres, previously collected in the Gene SMART (Skeletal Muscle Adaptive Response to Training) study (2), will be isolated, pooled and measured for DNAm using the MethylationEPIC Kit (Infinium). Next, the two major fibre types will be assessed before and after HIIT to identify to what extent exercise differentially alters the methylomes of the skeletal muscle fibre types. This will contribute to a greater understanding of molecular adaptations to exercise in skeletal muscle.