  We study a model of an active gel of cross-linked semiflexible filaments with
additional active linkers such as myosin II clusters. We show that the coupling
of the elasticity of the semiflexible filaments to the mechanical properties of
the motors leads to contractile behavior of the gel, in qualitative agreement
with experimental observations. The motors, however, soften the zero frequency
elastic constant of the gel. When the collective motor dynamics is incorporated
in the model, a stiffening of the network at high frequencies is obtained. The
frequency controlling the crossover between low and high frequency network
elasticity is estimated in terms of microscopic properties of motors and
filaments, and can be as low as 10^(-3)Hz.
