  The isotropy of multiples of Pfister forms is studied. In particular, an
improved lower bound on the value of their first Witt index is obtained. This
result and certain of its corollaries are applied to the study of the weak
isotropy index (or equivalently, the sublevel) of arbitrary quadratic forms.
The relationship between this invariant and the level of the (quadratic) form
is investigated. The problem of determining the set of values of the weak
isotropy index of a form with respect to field extensions is addressed, with
both admissible and inadmissible integers being determined. The analogous
investigation with respect to the level of a form is also undertaken, with some
questions asked by Berhuy, Grenier-Boley and Mahmoudi being resolved. An
examination of the weak isotropy index and the level of round and Pfister forms
concludes this article.
