Force-length relation of in-vivo human rectus femoris muscles.

In this paper the force-length relation of intact, in vivo, human rectus femoris muscles were determined experimentally and compared to a corresponding theoretical force-length relation based on the cross-bridge theory. The experimental force-length relation has a much smaller peak force and a much wider range of muscle fiber lengths where non-zero forces were observed than the theoretical relation. Possible reasons for the differences between the two force-length relations are discussed.