HDT bed rest is used extensively in the context of space physiology to simulate microgravity exposure but it is also considered as a model of muscle disuse and physical inactivity. Physical inactivity induces insulin resistance and is an independent risk factor for multiple chronic diseases. This research is determining whether HDT bed rest alters the circulating concentrations of novel biomarkers of insulin resistance and if these changes impact whole-body insulin sensitivity. In addition to this, the project is investigating whether reactive jump training (<4 minutes/day), a countermeasure designed to preserve skeletal muscle mass, can alleviate the metabolic disturbance that occurs with prolonged inactivity.