Energetics of positive and negative work in vivo: an innovative apparatus for human muscle studies.

Here we present an innovative apparatus that provides the rigor of in vitro muscle mechanical measurements for in vivo measurement of the cost of contraction in human muscle. A simple lever linked to a pulley system 1) eliminates the release of elastic energy, 2) permits generating both positive and negative work and 3) sits in an MRI for simultaneous determination of muscle work and ATP flux.  Our measurements reject the notion that elastic recoil is responsible for the high economy of eccentric contractions.  Instead, they reveal that reduced cost underlies the greater economy of eccentric vs. concentric contractions.

Frank E. Nelson, University of Washington, Dept. of Radiology
Justus O. Ortega, University of Washington, Dept. of Radiology
Stan L. Lindstedt, University of Washington, Dept. of Radiology
Sharon A. Jubrias, University of Washington, Dept. of Radiology
Kevin E. Conley, University of Washington, Depts. of Radiology, Physiology & Biophysics, and Bioengineering