The effect of an eccentric strength training programme on the muscular series elastic component (SEC) was studied on the flexors of the human elbow. The characteristics of the SEC were determined using an in situ technique derived from methods commonly used on isolated muscles. The results were expressed in terms of compliance-force and tension-extension relationships. These relationships indicate a sharp increase in compliance when tension decreases. Furthermore, for a given value of tension, the SEC compliance of the trained muscles is found to be lower than that of the untrained muscles. These results are discussed in relation to the active and passive parts of the SEC.