  The interaction dependent part of the $x^2$-moment of the twist-3 polarized
parton distribution $g_2(x)$ is related to the transverse force acting on the
active quark in deep-inelastic scattering off a transversely polarized nucleon
immediately after it has absorbed the virtual photon. Similarly, the
$x^2$-moment of the chirally odd twist-3 unpolarized parton distribution $e(x)$
can be related to the transverse force experienced by a transversely polarized
quark ejected from a transversely polarized nucleon.
