New Physics Effects from $e^{+}{e}^{-}\to f\bar{f}$ at a Linear Collider: the Role of $A_{LR,\mu }$

We discuss New Physics effects in fermion pair production at LC in the framework of the ``Z-peak subtracted approach’', a theoretical scheme that exploits the experimental measurements at LEP1 and SLC as input parameters. In particular, we discuss the role of the longitudinal polarization asymmetry $A_{LR,\mu }$ which turns out to be a very sensitive probe to New Physics of universal type. The extension of the method to non universal effects is discussed and an application is given in two examples: general contact interactions and low energy gravity models with graviton exchange.