In the Euclidean space R(n), n greater-than-or-equal-to 2, if a functi
on f has an integrable gradient, there exists a constant A (f) such th
at f - A (f) is in L(n/(n-1)). We study this question in a rather gene
ral setting. The main result specializes to Lie groups having polynomi
al volume growth, yielding a simple proof of a recent theorem of G. Al
exopoulos and N. Lohoue.