Frequency dependence of power and its implications for contractile function of muscle fibers from the digital flexors of horses

Physiological Reports

Michael T. Butcher³  John E.A. Bertram²  Douglas A. Syme⁴  John W. Hermanson¹ 

[1] Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA;Department of Cell Biology and Anatomy, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada;Department of Biological Sciences, Youngstown State University, Youngstown, Ohio, USA;Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada

关键词: Absorption;    deep digital flexor;    skinned fiber;    superficial digital flexor;    workloop;   

DOI  :  10.14814/phy2.12174

来源: Wiley

【 摘 要 】

Abstract

The digital flexors of horses must produce high force to support the body weight during running, and a need for these muscles to generate power is likely limited during locomotion over level ground. Measurements of power output from horse muscle fibers close to physiological temperatures, and when cyclic strain is imposed, will help to better understand the in vivo performance of the muscles as power absorbers and generators. Skinned fibers from the deep (DDF) and superficial (SDF) digital flexors, and the soleus (SOL) underwent sinusoidal oscillations in length over a range of frequencies (0.5–16 Hz) and strain amplitudes (0.01–0.06) under maximum activation (pCa 5) at 30°C. Results were analyzed using both workloop and Nyquist plot analyses to determine the ability of the fibers to absorb or generate power and the frequency dependence of those abilities. Power absorption was dominant at most cycling frequencies and strain amplitudes in fibers from all three muscles. However, small amounts of power were generated (0.002–0.05 Wkg⁻¹) at 0.01 strain by all three muscles at relatively slow cycling frequencies: DDF (4–7 Hz), SDF (4–5 Hz) and SOL (0.5–1 Hz). Nyquist analysis, reflecting the influence of cross-bridge kinetics on power generation, corroborated these results. The similar capacity for power generation by DDF and SDF versus lower for SOL, and the faster frequency at which this power was realized in DDF and SDF fibers, are largely explained by the fast myosin heavy chain isoform content in each muscle. Contractile function of DDF and SDF as power absorbers and generators, respectively, during locomotion may therefore be more dependent on their fiber architectural arrangement than on the physiological properties of their muscle fibers.

【 授权许可】

CC BY   
© 2014 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.

Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.