  We study theoretically and numerically the propagation of a displacement
field imposed at the edge of a disordered elastic material. While some modes
decay with some inverse penetration depth $\kappa$, other exponentially {\it
amplify} with rate $|\kappa|$, where $\kappa$'s are Lyapounov exponents
analogous to those governing electronic transport in a disordered conductors.
We obtain an analytical approximation for the full distribution $g(\kappa)$,
which decays exponentially for large $|\kappa|$ and is finite when
$\kappa\rightarrow0$. Our analysis shows that isostatic materials generically
act as levers with possibly very large gains, suggesting a novel principle to
design molecular machines that behave as elastic amplifiers.
