An Interpretation of the Effects of Fiber Length and Calcium on the Mechanical Properties of Insect Flight Muscle

Abstract

Insect fibrillar flight muscle has many properties in common with vertebrate skeletal muscle. However, it is not capable of the constant velocity shortening at constant load which is the mechanical characteristic of vertebrate striated muscles, but is adapted to produce rapid oscillatory contractions of small amplitude. Consequently, the classical type of mechanical study, involving the measurement of force-velocity diagrams and the fitting of a hyperbola to them, is not suitable for investigations of the properties of insect flight muscle. Instead, periodic length changes must be used. The result of forcing a sinusoidal length change of low amplitude on insect flight muscle is that, over a certain range of frequencies, the resulting sinusoidal tension changes lag behind the length changes (Machin and Pringle, 1960; Jewell and Ruügg, 1966). It is this delay which allows the muscle to deliver work continuously to a resonant load without neural control. One possible way of...