  We study the effect of uniaxial strain on the band structure of ZrSe$_3$, a
semiconducting material with a marked in-plane structural anisotropy. By using
a modified 3-point bending test apparatus, thin ZrSe$_3$ flakes were subjected
to uniaxial strain along different crystalline orientations monitoring the
effect of strain on their optical properties through micro-reflectance
spectroscopy. The obtained spectra showed excitonic features that blueshift
upon uniaxial tension. This shift is strongly dependent on the direction along
which the strain is being applied. When the flakes are strained along the
b-axis, the exciton peak shifts at ~ 60-95 meV/%, while along the a-axis, the
shift only reaches ~ 0-15 meV/%. Ab initio calculations were conducted to study
the influence of uniaxial strain, applied along different crystal directions,
on the band structure and reflectance spectra of ZrSe$_3$, exhibiting a
remarkable agreement with the experimental results.
