Materialism is the belief, that if something is good, then the more of it one has, the better. The relation is mostly to quantity and not to quality. Of course, it is also possible to pay attention only to quality and not quantity or affordibility--this is epicurianism. Quality relates roughly to the pleasure principle, and quantity relates roughly to the reality principle.
Materialism shifts human priorities from using a good thing, to getting more of it. Accumulation becomes an end in itself and a false sign of progress. Materialism arises from the ego--the body has a natural sense of 'enough'
Materialism is fairly well understood in regard to money. Examples are available, in literature if not personal experience, of people who have more money than they could possibly enjoy, and are unable to enjoy it, but derive a false sense of accomplishment from accumulating more. Ebeneezer Scrooge is an iconic example.
But the same thing often occurs in health or self-improvement. Rather than letting a group of practices or a method work, it is common for the seeker to check more and more avenues, or to learn more and more anecdotes and footnote-like information. Or alternately, exercises are done mechanically, just to 'rack up numbers' Accumulation is a will based practice that requires no trust and no surrender. Discovery is often missed. In the Reich and Lowen tradition this has been termed bioenergetic materialism.
Materialism also biases the observer against practices that have no absolute effect but rather are balancing. For instance breathing and stretching affects participants differently according to the amount of dysregulation. With high dysregulation the effect is small because little can be affected (at least at first). With medium dysregulation the effect is more discernable. With low dysregulation the effect is again small because the territory to be gained is smaller. Always though. the movement is toward balance. With many healthy practices it is not possible to achieve 'superiority' as popularly conceived, and unfortunately, superiority not balance is what our culture conceptualizes as well-being.