  The decay $K^{-} \to \mu^{-} \bar{\nu} \pi^{0}$ has been studied using
in-flight decays detected with ``ISTRA+'' setup operating in the 25 GeV
negative secondary beam of the U-70 PS. About 112K events were used for the
analysis. The $\lambda_{+}$ and $\lambda_{0}$ slope parameters of the decay
formfactors $f_{+}(t)$, $f_{0}(t)$ have been measured :
  $\lambda_{+}= 0.0321 \pm 0.004$(stat) $\pm 0.002$(syst)
  $\lambda_{0}= 0.0209 \pm 0.004$(stat) $\pm 0.002$(syst); the correlation $d
\lambda_{0}/d \lambda_{+}=-0.46$ The limits on the possible tensor and scalar
couplings have been derived:
  $f_{T}/f_{+}(0)=-0.021 \pm 0.028$(stat) $\pm 0.014$(theory);
  $f_{S}/f_{+}(0)=0.004 \pm 0.005$(stat) $\pm 0.005$(theory)
