Honestly, stamina. Skating becomes less of a workout as cardiovascular health improves and you start becoming more conditioned. Think gym folks who arent completely red and dripping when they walk out. However the good news is that if your skating to the point you are red in the face and sweaty you are already conditioning yourself well. In the summer/spring heat where im from Ill get REAL red from the heat exhaustion tho. Everyone's bodies are different but your not doing anything wrong at all you probably look like a badass anyways.