Portrait drawing & painting constitute a better exercise regimen.

The history of art making includes the footnote about how beginning artists acquire skills & practicing artists maintain skills by drawing & painting the figure.  There is something a bit better.  Most accomplished figure limners or modelers reach an acceptable level of satisfaction with their work, with one exception – the accurate rendering of the head is often not quite up to par.  This is usually the point where the figure student looks for that portrait class.  The converse is usually not the case.  The accomplished portraitist rarely has any problem transferring those skills to the figure.  The only appropriate conclusion is that practice with the head (portrait) is superior to practice with the figure for acquiring or maintaining compositional, color & rendering skills.  Take a portrait class to see if this theory holds true for you.