  We analyse the rheological behaviour of the generalised Maxwell and
Kelvin-Voigt models with a power law spectrum of relaxation or retardation
times, ${\cal H}\sim 1/\tau^{\alpha}$ or ${\cal L}\sim \tau^\alpha$,
respectively. When $0<\alpha<1$, both models have the same weak power law
behaviour, which occur in a variety of soft materials, including living cells.
Beyond this region, for other values of $\alpha$, the two models have different
and distinctive rheological behaviours, converging continuously to the
1-element Maxwell and Kelvin-Voigt models, respectively, for $\alpha<-1$ or
$\alpha>2$.
