Methods to find aponeurosis and tendon stiffness and the onset of muscle contraction

A method to measure small movements of living tissues either large or small is presented. The method is based on the detection of changes in reflected infrared light. An optocoupler (coupled photodiode and photodetector) and a small (< 1 cm(2)) mirror were used. The optocoupler (OC) has a low cost and it can be calibrated easily. It can be also used as the transducer of a strain-gage. Three different uses are shown: (a) as a strain-gage transducer; (b) detection of tendon and aponeurosis movements in large muscles (cat soleus); (c) detection of the onset of muscle contraction. Movements of less than 1 mu m can be detected with the aid of automatic averaging of the signals. Concerning the second use (b), it permits the estimation of tendon stretch. Concerning the third use, the onset of muscle movement precedes by at least 2 ms that of the force recorded at the tendon. (C) 1997 Elsevier Science B.V.