A strength of the methodology of this experiment is that the
electromyography normalization procedures were done in a
prone position similar to that used during the exercises. Therefore,
the relative activity levels measured during the Swiss ball
exercises reflects the maximal activity obtained in a similar
position. A potential limitation of the normalization procedures
we used is that they were based on MVC. It is recognized that
for patients with LBP, the same exercise may lead to a greater
relative activity level as a result of a distorted MVC. This can
be dealt with in a rehabilitation setting by beginning with a
lower number of repetitions of exercises that a patient can
successfully perform and that elicit a greater relative intensity.
The utility of the MVC, as used in this study, was to allow
normalization of muscle activity levels for comparison between
surfaces and to show that the exercises studied can provide an
effective training stimulus