The use of a manual drive in a wheelchair favors the rehabilitation process, forcing the user to be physically active. Unfortunately, in most cases, the manual drive is not adapted to the individual needs and physical capabilities of the user. The article presents the results of operational tests of a wheelchair equipped with a hybrid drive in which the muscle strength generated by the user was supported by two independent electric motors. The aim of the work carried out was to investigate the influence of the applied control algorithm and the assistance factor (k) on the value of the muscular effort (MA) while driving the wheelchair with the use of strings. The study used a modified ARmedical AR-405 wheelchair equipped with two electric motors built into the hub magic pie 5 with a power of 500 W. The tests were carried out on a wheelchair dynamometer simulating the moment of resistance to movement in the range from 8 to 11 Nm and the angle of inclination of the wheelchair from 0 to 14 °. For the measurement of MA, surface electromyography was measured with the aid of a four-channel Noraxon Mini DTS apparatus. The research was carried out on five patients from the group of C50 anthropometric dimensions. The effort was measured for four muscles: deltoid - anterior part, deltoid - posteriori part, triceps brachii, extensor carpi radialis longus. The effect of the use of the hybrid drive system was apparently observed on the extensor carpi radialis longus muscle. In his case, for the standard truck, the MA ranged from 93% to 123%. On the other hand, for a hybrid stroller at k = 70%, the MA effort was in the range from 43 - 75%.