On Bergh′s Inequality for Quasi-Monotone Functions

We consider an inverse Hölder type inequality of J. Bergh [Math Z.215 (1994), 205-208] yielding for quasi-concave functions. We prove that this inequality holds in a more general class of functions endowed with two quasimonotonicity growth conditions. Some classes of quasi-monotone functions in mean are introduced and some new Bergh-type inequalities in these classes are proved. Our proofs are short and completely different from that of J. Bergh.