In vivo approximations of the classic in vitro length-tension relationship: an isokinetic evaluation.

Several biarticular muscles of the human lower extremity were placed in various positions of stretch, using a hinged board to alter trunk-thigh relationships in 59 young adult volunteers of both sexes. Prior measurement, by direct x-ray of one subject on the test apparatus and by use of an articulated skeleton placed in the same pelvofemoral orientations as seen on the x-rays, supports the conclusion that the test positions of these 59 subjects were such that the biarticular extensor (rectus femoris) and flexors, (biceps femoris, semimembranosus and semitendinosus) were in fact being shortened or lengthened as desired under the prescribed positioning protocol. Isokinetic torques, total work output,; and average power production were obtained for maximal knee extensions and flexions through the full anatomical range of motion. The results support an assertion of close in vivo approximation to the classic in vitro length-tension relationship. J Orthop Sports Phys Ther 1986;7(5):222-231.