Popped Sarcomeres Regain Filament Overlap in a Stretch-shortening Cycle

INTRODUCTION The effects of stretch-induced damage, such as loss of force and appearance of localized sarcomere damage, are often explained by the popping sarcomere hypothesis [1]. This hypothesis contends that sarcomeres operating on the descending limb of the force-length relationship (FLR) are unstable. During a stretch, they are thought to undergo rapid lengthening until filament overlap is lost (‘popping’), resulting in contractile failure. However, there is no direct evidence to confirm that popped sarcomeres are functionally damaged. In fact, recent evidence suggests that sarcomeres that are stretched from optimum length to lengths well beyond filament overlap do not exhibit reductions in force or discontinuities in function [2]. These results suggested that sarcomere overstretching is not necessarily associated with functional failure. The aim of this study was to test the hypothesis that popped sarcomeres can regain filament overlap thereby retaining their structure and force capability.