Introduction: Oscillation is a type of periodic motion, whose object is called a pendulum. When the pendulum changes its equilibrium point by means of motion, it begins to oscillate. It moves from its extreme upper position toward the equilibrium point and then beyond to the other extreme upper position until it stops. It then moves in the opposite direction, and ultimately settles in its original equilibrium point. Knee joint is the largest joint in the human body. It consists of three bones, two fibrocartilage menisci and four knee ligaments. The swing test is a simple diagnostic test used to detect irregularities in the knee joint. Purpose: The purpose of this thesis is to determine the impact of the mass of the prosthesis on the Wartenberg knee pendulum test. Methods: The test was performed on two volunteers following a unilateral transtibial foot amputation. Five feet prosthesis with different mass were tested and compared to the undamaged leg. The volunteer test person was placed on the examination table in a semi-seated position. In order to detect muscle activity ECG electrodes were attached to the m. Quadriceps muscle, while infrared reflectors were attached to the thigh and lower leg. The thigh and lower leg reflectors each formed a separate line. The test person's leg was lifted into a horizontal position then released to swing freely. The computer detected the angle between the two lines. The data was compiled and used to draw a graph showing damped oscillation, and to calculate the rigidity and viscosity of the knee joint. Results: Viscosity values were lower in prosthesis than in undamaged legs. For the first volunteer, the rigidity was lower in prosthesis, while the rigidity of the prosthesis in the second volunteer was higher than the undamaged leg, which is due to diabetes. Discussion and conclusion: As expected, the viscosity and rigidity values were lower in prosthesis, excepting the rigidity in the second volunteer. Regarding the viscosity, no major differences were recorded between prosthesis and undamaged legs, while the rigidity showed discrepant results. These may be compared to other similar studies.