| Popis: |
Extensive study of the mechanical properties of cardiac muscle over the past two decades has led to a fairly well-established view of the way in which the primary variables, force, length and velocity, are interrelated. Developed force is observed to fall rapidly with decreasing fibre length below the optimum length (L max) approaching zero in the vicinity of 80% L max (1,2,3). The relationship of force and velocity is highly dependent on the method of measurement, but is often not well described by the Hill equation since linear regions and maximum velocities at non-zero forces sometimes occur (4,5,6). The dependence of velocity on length has not been extensively studied but recent work by Brutsaert has shown unloaded shortening velocity to be independent of length above about 87% L max, falling with length below that region (7). It has also been shown that the muscle’s capability for maximal velocity is developed very early after stimulation, as contrasted to the capability for force development, which builds nearly as slowly as the twitch force (7,8). |
