  For all $p>1$ and all centrally symmetric convex bodies $K\subset
\mathbb{R}^d$ define $Mf$ as the centered maximal function associated to $K$.
We show that when $d=1$ or $d=2$, we have $||Mf||_p\ge
(1+\epsilon(p,K))||f||_p$. For $d\ge 3$, let $q_0(K)$ be the infimum value of
$p$ for which $M$ has a fixed point. We show that for generic shapes $K$, we
have $q_0(K)>q_0(B(0,1))$.
