A possible mechanism of length activation in insect fibrillar flight muscle.

When insect fibrillar flight muscle is stretched it becomes more active, as indicated by an increase in oscillatory work output and ATPase activity. Using glycerol-extracted muscle it is demonstrated that this effect is periodic with a repeat of around 3% length change, independent of temperature and ionic strength. This corresponds to 38 nm per half sarcomere, the same repeat as the actin helix. Since there is also a period of 38 nm in the myosin helix the periodic change of activity with muscle length could be caused by filament sliding. This may be the basis of the mechanism of length activation.