The Muscle Monitor: Early Skeletal Muscle Indicators of Insulin Resistance and Cardiometabolic Risk

Insulin resistance is an early etiological factor in the development of type-2 diabetes (T2D), which constitutes a large societal health burden with an expected additional rise in the years to come. Skeletal muscle is the body's largest lean tissue mass and the major site of glucose disposal in response to insulin stimulation. Prior studies have suggested that a fast skeletal muscle phenotype, including a predominant fast muscle fiber composition, reduced capillary density, low fat oxidation and muscle oxidative capacity may be implicated in insulin resistance and TD2 development. However, key questions pertain in relation to the cause and effect of these relationships as well as the interaction with potential confounders and effect-modifiers including life-style factors (e.g. diet and physical activity levels) and general participant characteristics (e.g. body composition and training status). In the present project, we therefore aim to derive muscle fiber type and extensively map the proteomic signature of the early stages of insulin resistance in a large cross-sectional study using a young and apparently healthy cohort prior to T2D development, including a thorough participant characterization. We will recruit \~250 participants (men and women) in the age of 20-30 years and conduct extensive phenotyping and tissue sampling across one laboratory-based test day and a scan visit, as well as measurements of physical activity level and glucose handling in free-living conditions with wearable sensors. The study has a longitudinal aspect as participants will be re-invited at 5-year intervals for up to 20 years to delineate the trajectory of metabolic health in relation to muscle phenotype measures. The results of the project are expected to lead to significant advancements in our understanding of the importance of muscle phenotype for early-stage insulin resistance and metabolic health trajectories. Such understanding has potentially important clinical implications, as it can open new avenues for targeted interventions and individualized early preventive strategies to counter or delay the progression of insulin resistance and associated metabolic and cardiovascular disorders.