A LOW-PROFILE HUMAN TENDON FORCE TRANSDUCER - THE INFLUENCE OF TENDONTHICKNESS ON CALIBRATION

An in vitro calibration method for human tendon force transducers usin g tendon thickness to predict the calibration factor has been previous ly proposed (An et al., 1990, J. Biomechanics 23, 1269-1271). However, changes in the calibration factor due to changing tendon geometry dur ing repeated tendon loading are unknown. A new, low-profile transducer design that measures tendon thickness in the transducer, in situ, is developed. An empirical model estimating the transducer's calibration factor is developed using data from in vitro tension testing of 12 fre sh frozen human linger flexor tendons. Each tendon is preseated with t en loading cycles before data collection. Using tendon thickness, the model predicts the measured calibration factor to within 0-15% (averag e 6%). During repeated loading of an in vitro tendon, the calibration factor changes 15% over the first ten cycles (0-50 N) due to the obser ved changing tendon thickness. After the first ten loading cycles the variability of the calibration factor is reduced to less than 1% for t he next three loading cycles. Hence this new, modified in vitro calibr ation procedure with tendon preseating reduces the cycle-to-cycle vari ability caused by the associated change in the tendon thickness. (C) 1 997 Published by Elsevier Science Ltd.