Depending on the time spent in a space station, weightlessness causes varying changes to various organs and regulatory mechanisms of the human organism, among them the structures of the active and passive locomotor system. Experience has shown that regular physical activity using varying forms of training is necessary to keep astronauts and cosmonauts healthy, efficient and fit for work and to prepare them for a safe return to terrestrial conditions. One of the main tasks of physical activity is therefore to counteract the changes in the neuromuscular function, muscle strength, endurance and fatigability under conditions of weightlessness. So far, the diagnostics of these changes was limited to dynamometric measurements before and after space flights as no dynamometric method had been devised which was precise enough under conditions of weightlessness. The development and the introduction of the dynamoergometer Motomir is described against the background of previous results obtained by dynamometric, ergometric, morphometric, biochemical, histochemical and neuromuscular examinations before and after missions of varying duration under conditions of weightlessness. This device was used for the first valid and reproducible examinations of muscle strength and endurance aboard the space station Mir during the Austro-Russian space mission Austromir. The results of the examinations with this speed-controlled dynamometer and training device obtained during a short-term flight of 10 days and a long-term flight of 6 months are described and compared to previous results in the literature. Based on the existing training devices, training methods and training plans and the results of the Motomir Study, plans for devices and methodologies for future long-term space flights of up to 3 years' duration will be discussed. Finally, the possible use of a speed-controlled dynamometer and training device for rehabilitation on earth after injuries, surgery and immobilization of the active and passive locomotor system as well as in the bed-rest syndrome is being presented.