Recent animal experiments have shown that up to 37% of muscle force may be transmitted to adjacent structures rather than reach the insertion of the muscle's tendon, and that the extent of such force transmis-sion depends on the length and relative position of these structures. We tested whether the force-length characteristics of the distally tenotomized human flexor carpi ulnaris muscle (FCU) of nine patients with cerebral palsy varied with the change of relative length of adjacent structures induced by a change of wrist position. In four patients, the FCU exerted up to 40% more active force in a flexed wrist position at short FCU length, whereas the active force was not significantly higher in the other five. In the same manner, passive force-length characteristics of the spastic FCU changed upon changes in wrist position. Variability in myofascial force transmission may partly explain the variability in success of the FCU-transfer. © 2005 Wiley Periodicals, Inc.