LAUSR

The smallest contractile unit in striated muscles is the sarcomere. While some of the classic features of contraction assume a uniform behavior of sarcomeres within myofibrils, the occurrence of sarcomere length non-uniformities has been well-recognized for years, but it is yet not well understood. In the past years, there has been a great advance in experiments using isolated myofibrils and sarcomeres, which has allowed scientists to directly evaluate sarcomere length non-uniformity. This review will focus on studies conducted with these preparations to develop the hypotheses that (i) force production in myofibrils is largely altered and regulated by inter-sarcomere dynamics, and that (ii) the mechanical work of one sarcomere in a myofibril is transmitted to other sarcomeres in series. We evaluated studies looking into myofibril activation, relaxation, and force changes produced during activation. We conclude that force production in myofibrils is regulated by intersarcomere dynamics, which arise from the cooperative work of the contractile and elastic elements within a myofibril.