The Therapress 1600i: Accelerating Knee Rehabilitation

Abstract

Objective: To design a ‘smart’ leg press machine that improves upon current rehabilitative practices for degenerative knee disorders such as osteoarthritis as well as injury induced knee pathologies. As its design entails, the machine provides rehabilitative assistance through strength training of upper leg muscles, with focus on the vastus medialis and vastus lateralis of the quadriceps group. The Therapress is designed to further improve the rate and quality of joint rehabilitation. The TP1600i is unique to current physical therapy practices because it incorporates three documented and proven strategies to combat quadriceps weakness: strength training, electrotherapy, and biofeedback [1,2]. The machine is designed to aid the user in regaining lost quadriceps strength, a condition indicative of poor knee health [3]. The machine incorporates a novel package of biofeedback, automated continuous variable resistance, and progress assessment, while maintaining subject specificity. The Therapress system utilizes a LabVIEW interface, which acquires and processes physiological signals recorded from the subject, as well as serves as a controller for output. These signals include surface electromyography (EMG) of the quadriceps, reaction forces at the foot (an indirect measurement of exercise resistance), and knee range of motion (ROM). Additionally, the subject is outfitted with stimulatory electrodes which function to characterize muscle recruitment using the Central Activation Ratio (CAR), as well as to therapeutically excite the muscle and induce accelerated hypertrophy [4]. Automated continuous variable resistance is achieved through a resistive hydraulic cylinder, which utilizes a servo motor to change the orifice size of partially overlapping valves during and between exercise sets. The resistance is adjusted based on user input of exertion and pain levels into the LabVIEW interface. The footplate of the machine houses four force sensing units to measure the resistance offered by the cylinder. A biofeedback arm attached to the system provides the subject with real-time data of their performance, including integrated EMG activity, ROM, and force production. Inclusion of biofeedback in quadriceps exercise regimens has been shown to increase strength gain [2]. The design allows the user to be in control of the exercise intensity at all times, while the machine works to maximize the efficacy of the protocol. The TP1600i is designed as a cost effective and time efficient alternative for the rehabilitation of debilitating knee disorders in a physical therapy protocol, and its ease of operation may qualify it for home use as well.