But wait there’s more! 
Those are the energy systems in the muscles and which ones adapt more to which stimulus. The heart itself is experiencing different demands …
During aerobic exercise the heart is experiencing sustained volume overload, delivering more blood to muscles against normal or even decreased vascular resistance. Over a matter of just a few months of training the heart adapts by increasing stroke volume, all chambers enlarge and specifically the left ventricle wall thickens.
Resistance training is a pressure overload rather than a volume overload state. It does not tend to increase stroke volume and the heart remodeling is modest thickening of all walls concentrically.
Combining both approaches is most effective.
In conclusion, among individuals at an increased risk for CVD, as little as 8-weeks of combined training may provide more comprehensive CVD benefits compared to time-matched aerobic or resistance training alone.
Not sure what happened to you @Spice_Weasel but I’d give yourself a good recovery day and then a lighter active recovery exercise day in any case.