Center for Physical Activity Research (CFAS) have performed a number of trials showing that interval training can be performed as free-living interval-walking, consisting of repeating cycles of 3 minutes fast walking followed by 3 minutes slow walking with significant positive effects in cardio-metabolic health profile. Our studies show, that 16 weeks of interval-walking improved VO2peak (+4ml /kg/min) reduced bodyweight (-4 kg) and fat mass (-3 kg) in patients with type 2 diabetes. Moreover, interval-walking improved plasma lipid-profile, glucose metabolism and insulin sensitivity, in contrast to continuous walking, which was matched for training-volume and energy expenditure. In parallel with these intervention-studies, a smart-phone application, called InterWalk (www.InterWalk.dk), has been developed, which can deliver this training program of repeating cycles: 3 minutes fast walking followed by 3 minutes slow walking. The exercise-program is based on an individualized test-function with live-feedback, ensuring proper exercise-intensities (walking-speed), and can simultaneously store test- and training data (exercise-time, walking-speed, distance etc.) to an external server for research purposes. Preliminary data shows that three months home-based interval-walking using the InterWalk-application can improve fitness by ~10%. Thus, our preliminary data shows InterWalk can deliver an un-supervised, yet individualized, structured and objectively monitored exercise-program which can effectively improve cardio-metabolic health, and may be more applicable and feasible, compared to traditional hospital-based programs in stigmatized patient groups with major co-morbid complications.