Extra/complimentary suggestion to that: when the mouse cursor hovers over a muscle group further to the 'red patch', have a pop-up small text box with name and brief description of the specific red-ed part. It would be fun/educating for the regular folk (like me, who doesn't know each muscle group and/or their names) to just 'browse' the human body and see the name of that muscle group and what it does.

Edit: on the parts that are not a muscle group (e.g. face, "love-handles", feer/hands, 'throat', etc.) maybe paint them grey so they are visibly distinguishable from the 'muscle groups'. I was veri curious to see if the 'love-handles' region has any use apart storing fat.