Multiple Sclerosis is a chronic, immune-mediated disease that affects the central nervous system.  Due to problems with balance, weakness or numbness in the feet or legs gait disability is one major symptom for Multiple Sclerosis. People with gait disabilities are twice as physically inactive as healthy people. The low level of physical activity among people with disabilities raise serious concerns regarding their health and well-being. Thus, the development of specific recommendations for type, volume and intensity of physical activity plays a major role in order to combat the effects of a sedentary lifestyle. Recommendations for health-enhancing physical activity are expressed e.g.  by a minimum energy expenditure caused by movement. A typical technique to compute the energy expenditure is indirect calorimetry. Indirect calorimetry is based on the fact that as foods are oxidized to produce heat in the body, oxygen is consumed and carbon dioxide is produced in proportion to the heat generated. Since the indirect calorimetry is not applicable in daily-life situations like vacuuming, ascending stairs or walking outside, an alternative assessment technique is preferred. Small and light-weight inertial sensors like accelerometers showed a high correlation against indirect calorimetry during treadmill running in persons with Multiple Sclerosis.