The paper presents investigation of arm muscle activity by electromyography when exercising on inertial-type training facility. The aim of the research was to examine the muscle activity dependences on the resistance force and intensity of exercising. Muscle electrical activity measurements were performed for four main arm muscles: the deltoid (musculus deltoideus), the triceps brachii (musculus triceps brachii), the biceps brachii (musculus biceps brachii) and the branchioradialis (musculus brachioradiali) muscles.