  The structure functions calculated in the Chiral bag model reproduce quite
well, after appropriate perturbative evolution to large energy scales, the
experimental data. We use these results to interpret the structure of the $EMC$
data as a quenching of the pion decay constant due to the in medium behavior of
the nucleon. This explanation supports recent proposals of this phenomenon
whose origin is the scale invariance of the $QCD$ lagrangian.
