Prolong exposure to weightlessness leads to loss of muscle and bone mass. Therefore, astronauts on board the International Space Station (ISS) currently perform mandatory daily exercises. ISS missions usually last 6 months, and future missions will become significantly longer when going, for example, to Mars. To that purpose, an exoskeleton-based exercise device, called ATHLETIC, was developed. The functionality and relevance of this device was evaluated in this study. Ten participants performed resistance exercises (squats) and plyometric exercises (countermovement jumps, reactive hops). Results showed that all participants were technically able to perform the intended exercises on ATHLETIC, albeit with reduced loading as compared to the reference exercises. This resulted in less mechanical performance and muscle activity. Due to the unfamiliar horizontal training axis, some participants had difficulty performing the movements correctly. Follow-up studies are required testing, whether an adequate number of practicing sessions could enable persons to approach the performances of reference measurements, and whether further improvements of the device are needed to improve the exercise performance.