Liste-13

ON CALCIUM DYNAMICS AND THE MECHANISMS RESPONSIBLE FOR NON-LINEAR SUMMATIONS IN MAMMALIAN MUSCLE

Dorgan DS

The underlying mechanisms responsible for the non-linear summation and timing effects observed in mammalian skeletal activated by N-let pulse trains are investigated. N-lets are sets of N high frequency pulses with highly variable inter-pulse intervals that have been shown to improve fatigue resistance, reduce fibre type transformation and maximise the force-time integral per pulse of skeletal muscles activated by Functional Neuromuscular Stimulation (FNS). These investigations are performed in simulation using a recently developed physiologically based mathematical model of mammalian skeletal muscle. This model enables investigations into the internal system dynamics of skeletal muscle to be conducted under both isometric and non-isometric conditions. The simulation results obtained are found to compare well with recent experimental input-output data for skeletal muscle. An analysis of the underlying system dynamics suggest that a subtle interplay between the rate of muscular contraction and non-linearities within the Ca2+ release and re-accumulation dynamics may be responsible for the non-linear summation effects observed. Similarly, it is suggested that the disappearance of the doublet effect observed when muscle is transformed from fast to slow fibre type may be due to changes in the Ca2+ dynamics of muscle. These mechanisms may be an important consideration in the design of N-let control strategies for use in applications such as cardiac assistance and the initiation of skeletal motion.