  Recent experiments in La$_{1-x}$Ba$_x$MnO$_3$ thin films by Zhang {\it et
al.} {[Phys. Rev. B {\bf 64}, 184404 (2001)]} showed that the ferromagnetic
Curie temperature $T_c$ is enhanced (reduced) by tensile (compressive) strain.
The results are regarded to be anomalous because it is generally understood by
the authors that the tensile strain should lead to a reduction of the electron
hopping $t$ (and thus also $T_c$) due to an elongation of the (in-plane) Mn-O
bond length. In this comment such a general understanding of the strain effects
is disapproved. It is argued that the tensile strain leads primarily to a
larger Mn-O-Mn bond angle (with the Mn-O bond length nearly unchanged), thus
the pure geometric consideration on $t$ is already in the correct direction
towards the experimental findings by Zhang {\it et al.} At the same time, an
indirect strain effect under consideration of the dynamic electron-phonon
coupling is proposed, which may improve the quantitative explanation.
