Several properties of muscle defy explanation solely based on the sliding filament-swinging cross-bridge theory. Indeed, muscle behaves as though there is a dynamic “spring” within the sarcomeres. We propose a new “winding filament” mechanism for how titin acts, in conjunction with the cross-bridges, as a force-dependent spring. The addition of titin into active sarcomeres resolves many puzzling muscle characteristics.
This paper summarizes a novel hypothesis for activation- and force-dependent increases in titin stiffness and implications for understanding muscle contraction.
1Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ; and 2Department of Biology, Valdosta State University, Valdosta, GA
Address for correspondence: Jenna A. Monroy, Ph.D., Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011-5640 (E-mail: Jenna.Monroy@nau.edu).
Accepted for publication: October 28 2011.
Associate Editor: Walter Herzog, Ph.D.