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Another situation may occur in the muscle for
which the rate of force development declines with developed
tension while contraction time remains unchanged. A
reduction in contractile capacity would give the same
results. This possibility must be given consideration.
Some authors have tested for, and found, changes in the
contractile capacity of the muscle under study (30, 44).
These are discussed below.
Reduced Capacity of the Contractile Apparatus
Fatigue may be the result of a reduced ability of the
contractile proteins to generate tension. This could be
a result of either: i) damage to myofilaments (i.e.,
misalignment or inactivation) or ii) restricted availability
of energy. In either case, the effect would be a reduced
force generation under conditions of maximal activation.
This capacity to develop tension has been traditionally
tested with either a K+ contracture or a caffein
contracture. Both of these procedures result in maximal
activation (Ca2+ concentration high enough to saturate
the contractile apparatus). Tetanic stimulation has also
been used to evaluate the capacity of a muscle to generate
tension.
Fitts and Holloszy (30) observed that tetanic force
was reduced in the rat soleus muscle following a series
of tetanic contractions. They noted that recovery of the
force generating capacity occurred relatively quickly
(within minutes). No insight into the mechanism