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There is a lack of research in using electromyography (EMG) signals to control a continuous passive motion (CPM) machine. This study aimed to develop an interface instrument for digitalising EMG signals and controlling a CPM machine. Methods: The proposed device was designed with the following: (1) a signal processing unit which converted the EMGs from analogue to digital for the controller; (2) a personal computer which stored and displayed the EMG signals; (3) an LCD device to display the running angle of the CPM; and (4) a microcontroller unit to control the input/output signals and process the algorithm, driving the CPM. To validate the reliability of the proposed system, a total of 600 EMG trials were collected from 10 healthy subjects by using the proposed device via the Delsys® TringoTM EMG system and simultaneously using the Vicon® motion capture system. Result: This proposed device was able to digitalise and process EMG signals from eight channels of muscles, and the signals were able to drive a CPM. The validated results showed that the digitalised EMG signals by the proposed device were statistically similar to and correlated with the signals by the Vicon system with a median correlation coefficient of 0.81, with the 25% and 75% range being 0.56–0.92 with all pairs (300 pairs of EMG trials) (p < 0.001). Conclusions: This study confirmed that the developed device can digitalise EMG signals and drive a CPM as an applicable prototype that can work as an interface between EMG and CPM devices with high reliability.

Background: Tai Chi Chuan (TCC) is popular in exercise, but little research has been done on limb and joint strength after the exercise. This study aimed to investigate whether TCC players have different limb and joint strengths in the upper and lower limbs from non-Tai Chi Chuan (NTCC). Methods: Twenty TCC players who have at least one year of experience playing TCC were compared with a group of 25 NTCC participants. A force sensor was used to measure forces in the lower and upper limbs. Maximum forces produced by the lower limbs was measured during a standing position with straight legs or were measured in a seated position. The maximum forces produced by the upper limbs were measured in a standing position at elbow and shoulder levels. Results: The forces of the knee extensors in the TCC group were significantly higher (7.4%) than in the NTCC group; however, the forces of the knee flexors in the TCC group were significantly lower than the NTCC group. The heel-force in hip extension in the NTCC group was significantly higher (9.3%) than in TCC; the toe-force in the plantar flexion in the NTCC was significantly higher than in the TCC group. There were no significant differences between the two groups in the hand-forces in the upper limbs. Conclusions: TCC routine movements strengthen the muscles related to knee extension, which are mainly related to bending knee performance during TCC exercise. For the healthy people between 42 and 78 years old, TCC benefits the enhancement of the strength for knee extension but not for the knee flexion, ankle plantar flexion and hip extension. There is no significant difference between the TCC and NTCC groups on the strength of upper limbs and joints. As a whole, the effect of Tai Chi Chuan exercise on the strengths in the limbs and joints is compromised. In the future, a study with larger sample size than this study is highly recommended.