Public health initiatives promoting physical activity and exercise are important to prevent and treat chronic diseases. In order to understand the underlying mechanism, we have to realize that ‘every cell counts’ in the diversity of ways the human body adapts to exercise. This is especially true for skeletal muscle, which is the main target organ for adaptations to benefit health and performance. The current project aims to expand muscle physiology to the single fiber level, taking advantage of recent technical progress in single cell sequencing. Skeletal muscle is heterogeneous, consisting of both non-muscle (30%) and muscle (70%) cells. The latter is classified into slow- and fast-twitch fibers based on myosin heavy chain isoforms. Current practice examines genome-wide mRNA expression on the whole muscle level, ignoring the diversity in adaptations per cell type. Therefore, we are developing a new approach: TRUE SINGLE FIBER TRANSCRIPTOMICS. Its utility will be demonstrated by challenging 3 common practices in muscle physiology: - to provide a more accurate way of mapping muscle adaptation in response to exercise - to perform a more precise fiber type clustering beyond the current method of myosin heavy chain isoform expression - to introduce a liquid biopsy method for determining muscle typology replacing the traditional muscle biopsy method This endeavor will transform standard methodologies in exercise science with a broad application spectrum for health and sport.