However, the national exercise recommendations are different for each group and therefore are two different variables that I am trying to use as one, if that makes sense?
No, that does not really make sense to me, two different variables generally should not be combined into one, unless you have some subject matter expertise that explains how to do this.
What makes sense to me is for each group, you predict the response based upon the appropriate x-variable for that group.
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Paige Miller