16.423J/HST515J Aerospace Biomedical Engineering and Life Support Prof. Newman Prof. Newman Summary Muscle Performance Facts [McMahon, Muscles, Reflexes and Locomotion, 1984] 1. In shortening, the relationship between the Force and Velocity is (Hill's Curve - know this!!): (T+a)(v+b) = (T 0 +a)b Hyperbolic Form ? muscles shorten more rapidly against light loads than they do against heavy ones ? muscles which are actively shortening can produce less force than those which contract isometrically. 2. There is a discontinuity in the slope of F-V curve at zero velocity. 3. Active muscle yields when the load exceeds about 1.8 T 0 (T 0 - Tetanus tension). 4. Hill's observations of the Fenn effect give a linear relation between total rate of energy liberation and tension. Fenn = muscle produces a certain extra heat when it shortens a given distance, whether shortening velocity is fast or slow. 5. Muscle shortening should be based on the relative motion of sliding filaments because: A. A-band width stays constant during stretch and shortening B. A-band disappears when myosin is dissolved away C. Actin filaments begin at Z-line, run through I-bands into A-band, but stop before reaching H-zone (muscle at rest length) I-band is entirely actin filaments H-zone is myosin filaments 6. Muscular energy liberation should be based on the splitting of a high-energy phosphate as actomyosin attachments separate.