Force production during eccentric contractions in skinned muscle fibres

The aim of this study was to investigate force loss in isometric contractions and during active stretch, following muscle damage, and thus gain insight into the role of the active and passive force components on muscle damage and active stretch contractions. Skinned muscle fibres were repeatedly (4 times) activated at an average sarcomere length of 2.4 µm, actively stretched to an average SL of 4.0 µm, and then deactivated. Force during isometric contraction at 2.4 µm was reduced in stretches 2-4 compared to stretch 1, while peak and steady state forces after active stretch were not affected. Force after deactivation at a SL of 4.0 µm was greater in stretches 2-4 compared to stretch 1. These results suggest an increased involvement of titin in force production after active stretch and that titin remains undamaged after eccentric contractions, and possibly even compensating for the loss in cross bridge force.