Force exertion capacity measurements in haptic virtual environments.

An objective test for evaluating functional status of the upper limbs (ULs) in patients with muscular distrophy (MD) is presented. The method allows for quantitative assessment of the UL functional state with an emphasis on force exertion capacity. The experimental measurement setup and the methodology for the assessment of maximal exertable force utilizing the Phantom 1.5 haptic interface has been developed. The measurement setup consists of a powerful virtual reality simulator, capable of providing haptic, visual and audio feedback. The patient's task in the virtual environment is goal oriented and includes stretching a virtual spring in six different directions. The Phantom 1.5 haptic interface serves as a kinematic measuring device and as a force feedback generator. By moving the haptic interface control stick the patient exerts the force in six radial directions to the best of his or her abilities. The new test offers numerical as well as graphic results. The method has been applied to 32 MD patients. Several typical force exertion capacity characteristics, affected by neuro-muscular disorders are shown in a quantitative manner. Data mining was used to demonstrate good content validity of the proposed test. The method allows for a quick, accurate, repeatable and objective measurements of the UL force exertion capability.