Abstract
The helical shape of the thin filaments causes their passive counterclockwise rotation during muscle stretch that increases tensile stress and torque at first by unwinding and then by winding up the four anchoring Z-filaments. This means storage of energy in the series elastic Z-filaments and a considerable decrease of the liberated energy of heat and work to (h—wap), where h is the heat energy and wap the stretch energy induced from outside by an apparatus. The steep thin filament helix with an inclination angle of 70° promotes the passive rotation during stretch, but impedes the smooth sliding of shortening by increased friction and production of frictional heat. The frictional heat may be produced by the contact with the myosin cross-bridges: (1) when they passively snap on drilling thin filaments from cleft to cleft over a distance 2 × 2.7 nm = 5.4 nm between the globular actin monomers in one groove, causing stepwise motion; or (2) when they passively cycle from one helical groove to the next (distance 36 nm). The latter causes more heat and may take place on rotating thin filaments without an effective forward drilling (“idle rotation”), e.g., when they produce “unexplained heat” at the beginning of an isometric tetanus. In an Appendix to this paper the different states of muscle are defined. The function of its most important components is described and rotation model and power-stroke model of muscular contraction is compared.
Highlights
In their basic work on the ―Energetic Aspects of Muscle Contraction‖ Woledge, Curtin and Homsher ([1], p. 209) describe the effect of stretch: ―When an active muscle is stretched, its mechanicInt
After a survey on the historical observations of the energetic differences between contracting and stretched muscles the following pages analyze the possible reasons for the differences
This small paper is a supplement to my larger one on the mechanics of muscular contraction on the basis of filament rotations [2], where these reasons so far have been briefly mentioned
Summary
In their basic work on the ―Energetic Aspects of Muscle Contraction‖ Woledge, Curtin and Homsher ([1], p. 209) describe the effect of stretch: ―When an active muscle is stretched, its mechanic. After a survey on the historical observations of the energetic differences between contracting and stretched muscles the following pages analyze the possible reasons for the differences. This small paper is a supplement to my larger one on the mechanics of muscular contraction on the basis of filament rotations [2], where these reasons so far have been briefly mentioned. A summary of these subjects is given in the Appendix to this paper with definitions of the different states of muscle, the function of its most important components, and a comparison between rotation model and power-stroke model of muscular contraction
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