Velocity controlled dynamometry and gait analysis : Development of methods and applications

Abstract: The isokinetic systems developed in the present study can measure torque in maximal voluntary and passive movements. The torque recordings may be combined with surface EMG recordings from pairs of antagonistic muscles involved in the movement. Healthy subjects and patients with spastic paresis have been examined. The recordings have been performed on the knee joint. In Paper I, a previously improved Cybex II dynamometer (Knutsson and Mårtensson, 1980) is used to enable concentric recordings of maximal voluntary movements and passive movements. A report is given of additional improvements of the dynamometer and the EMG systems. The paper describes the computer programmed examination procedure, the signal characteristics and some clinical applications. The Cybex II dynamometer allows the limb attached to the instrument to move freely at velocities below the pre-set speed. When the speed is reached, artefacts will be induced which may disturb the torque record over a large part of the movement range. In Paper II, a computer-controlled dynamometer is developed that reduces or eliminates the artefacts described in Paper I. It allows the muscles to reach a high level of tension prior to the start of movement and to put load on the dynamometer's lever arm during acceleration. The amount of pre-load and the acceleration rate are set to give the individual subject optimum condition to reach the pre-set speed at shortest possible movement range. In Paper III, the concept of pre-load and resisted acceleration is used when a new computerised control system is developed for the Kin-Com isokinetic dynamometer; a dynamometer that enables concentric as well as eccentric actions. Different rates of acceleration are tested in both types of actions in knee extension in moderately trained subjects and in athletes. It is shown that the measurements are affected by the selected acceleration rate, and when it is too high, the records of torque will fluctuate and distort the assessment of muscle force. In Paper IV, muscle force and activation pattems in voluntary concentric and eccentric knee actions in patients with spastic paraparesis and in healthy subjects are studied using the system developed in Paper III. Force-velocity relationships as well as prime mover and antagonist activations are compared between the two groups. Isokinetic dynamometry is an instrument well-fitted to the study of muscle force and activation pattems in single joint actions. To study joint movements and muscle activation pattems in more complex actions, computerised systems for gait analysis, with registration of concomitant EMG, are developed. In Papers V and VI, specific interest is focused on the development of the motion analysis. In previous systems for gait analysis, it had been difficult to determine when a muscle lengthens or shortens during the stride, since some movements - particularly rotational movements - were missing or lacked accuracy. Paper V describes a computerised system for three-dimensional gait analysis based on three potentiometers orthogonally connected and optimally centred at the joints, interconnected by a modified exoskeleton. The system automatically identifies individual strides in a gait record. Identified strides are then normalised and averaged. The reliability and validity of the system is determined, comparing it with other quantitative methods and using test-retest. In Paper VI, a system for gait analysis based on electromagnetic tracking is developed. This gait analysis system can measure, in addition to leg movements, pelvis and trunk movements. It can also measure the positions of the different body segments. Miniature sensors are placed on appropriate body segments without bulky fixation apparatus. This allows the system to be used with small children as well as adults. The sensors track the movements to give position and orientation relative to a transmitter by means of the magnetic fields generated by the transmitter. The vulnerability to interference from external magnetic fields is a specific problem associated with electromagnetic tracking. Thus, methods for automatic error correction are included with the analysis of the signals. After correction, the instrument gives records of three-dimensional joint movements and body positions with high accuracy.