High Intensity Interval Training (HIIT) has shown a superior effectiveness and efficiency when compared to Moderate Intensity Continuous Training (MICT) in several types of patients and in healthy subjects. There are no data on HIIT in a general geriatric population. This study is a pilot study evaluating the feasibility of using HIIT in geriatric hospitalized patients compared to the standard current rehabilitation practice without HIIT. It is our desire to perform a larger randomized comparative trial between HIIT and MICT if the pilot study proves its feasibility.