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What Is the Role of Titin in Active Muscle?

Monroy, Jenna A.1; Powers, Krysta L.1; Gilmore, Leslie A.1; Uyeno, Theodore A.2; Lindstedt, Stan L.1; Nishikawa, Kiisa C.1

Exercise and Sport Sciences Reviews: April 2012 - Volume 40 - Issue 2 - p 73–78
doi: 10.1097/JES.0b013e31824580c6

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:

Accepted for publication: October 28 2011.

Associate Editor: Walter Herzog, Ph.D.

©2012 The American College of Sports Medicine