I generally take superstimuli to be things that command attention with reduced or no pay off relative to other activities. This as opposed to things that require attention and/or meet some need or goal. Obviously it's a continuum rather than a hard distinction. Porn is an obvious example of a superstimuli. As is television, nutritionally suspect yet delicious food, etc. I don't think either exercise or meditation are superstimuli. I feel bad on days I don't exercise and exercise can be addictive in that sense but it still takes sustained effort to keep to an exercise routine.