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The surface EMG signal detected from voluntarily activated muscles can be used as a control signal for functional neuromuscular electrical stimulation. A proper positioning of the recording electrodes in relation to the stimulation electrodes, and a proper processing of the recorded signals is required to reduce the stimulus artefact and the non-voluntary contribution (M-wave). Six orientations and six locations of the recording electrodes were investigated in the present work. A comb filter (with and without a blanking windowing) was applied to remove the signal components synchronously correlated to the stimulus. An operative definition of the signal to noise ratio and an efficiency index were implemented. It resulted that when the recording electrodes were located within the two stimulation electrodes the best orientation was perpendicular to the longitudinal line. However the best absolute indexes were obtained when the recording electrodes were located externally of the stimulation electrodes, and in that case the best orientation was longitudinal. Concerning the filtering procedure, the use of a blanking window before the application of the comb filter, gave the best performance.

The coupling between joint kinematics and kinetics during level walking was analysed by plotting joint angles vs. joint moments about the hip, knee and ankle in nine normal male subjects walking at three different velocities. The curves obtained were reproducible, and variability among subjects was relatively low. Counterclockwise loops corresponded to energy produced, and clockwise loops to energy absorbed at the joint; both loops are described in different phases of the stride cycle. At increasing walking velocity some of the loops narrowed, thus revealing the possibility of energy recovery. Analysis of individual diagrams revealed that consistent portions of the moment-angle loops can be described as a sequence of quasi-constant slope phases, separated by transition periods where quasi-isometric changes in joint moment occur. This figure, which was particularly evident of the hip and ankle joints, is reminiscent of a mechanical system with elastic components, which, in different phases of the rhythmic locomotion activity, moves along discrete status levels characterized by specific length-tension relationships. Implications of the above results in terms of the neurol control of joint properties during active movement are discussed.

The triceps surae muscle-tendon complex has been modelled by many authors seeking to estimate the change in muscle length that occurs in locomotion. The objective of the present study is to assess to what extent the commonly adopted assumptions of foot rigidity and pure sagittal motion are acceptable. A model of the triceps surae muscle-tendon complex was implemented by taking into account all possible movements between forefoot and rear foot. Length and velocity curves from a 3-dimensional gait analysis were obtained from six normal subjects. The angle between forefoot and rear foot proved to be changeable with stride (11.8 degrees +/- 4.7 SE). The effect on the length and velocity estimation was analysed by comparing the curves obtained by our model to those obtained by a model in which the foot is considered to be a rigid body. Significant differences were found for the soleus muscle length at late stance/early swing and late swing phases, and for the soleus muscle velocity at early stance phase. The length and velocity curves were also compared to curves calculated on a pure sagittal projection. No changes were observed, except for an offset of 1-3 mm caused by the general external rotation of the foot (which is also present in standing). The curves appeared superimposable when referred to the standing upright position. Care needs to be taken, however, when extending the above results to the clinical application, where foot deformity and deviation from a normal pattern of motion can occur.