ELLERBY, D.J.; MARSH, R.L.; CARR, J.A.; HENRY, H.; Northeastern University; Northeastern University; Northeastern University; Northeastern University: Muscle function in running guinea fowl: linked muscles spanning multiple joints

The guinea fowl hind limb contains a number of linked muscles and tendons that cross multiple joints. This complex anatomical arrangement makes inference of muscle length from limb kinematics difficult. The function of these muscles is determined by their anatomy, activation, and the shifting lines of force as limb position changes during the stride cycle. Sonomicrometry and electromyography were used to determine muscle length changes and activation patterns. The flexor cruris lateralis pars accessoria (FCLP) complex is in the position of a �hamstring� muscle. The FCLP is linked to the femur by the flexor cruris lateralis pars accessoria (FCLA) and also inserts on the distal tendon of the intermediate gastrocnemius (IG). During the late swing phase/early stance phase the FCLP primarily functions in concert with the IG as an ankle extensor. Later in the stance phase IG activity ceases and the FCLA becomes active shifting function to hip extension. The iliotibialis lateralis pars postacetabular (ILPO) is the largest guinea fowl thigh muscle, with a broad origin posterior to the hip joint. The anatomy of the muscle is such that short anterior fascicles with a long tendinous connection to the patellar tendon grade antero/posteriorly into longer fascicles with a progressively shorter tendon. This arrangement appears to allow for uniform active strain across the muscle. Calculations based on moment arm of the patellar tendon under passive conditions are poor predictors of strain in the ILPO. In vivo, activity in lower leg ankle extensors attached to this tendon influences ILPO length. Supported by NIH grant AR47337.