-- A methodology for studying the effect of vibrations generated by a haptic interface on upper limb is introduced. In the proposed methodology, a subject presses on a horizontally vibrating, rigid, virtual object with a cheap offthe-shelf (COTS) haptic device. When the subject feels vibrations of fixed amplitude and varying frequencies the electromyographic (EMG) activity of upper limb is recorded. The relationship between the maximum force feedback and the amplitude of the EMG recordings is obtained. It suggests that EMG activities in upper limb increase significantly even for small changes in the low force feedback from the haptic device. These results can be used to develop rehabilitation programs and evaluation methods that are based on vibration force feedback produced by COTS haptic devices. Keywords--Electromyography, haptics, upper limb rehabilitation