Isaiah 40:29-31
“He gives power to the faint, abundant strength to the weak. Though young men faint and grow weary, and youths stagger and fall, they that hope in the LORD will renew their strength, they will soar on eagles’ wings; They will run and not grow weary, walk and not grow faint.”
God will help you and reward your fitness efforts, if they are done in His service and not out of vanity or selfishness. Put your trust in God, and He will guide you.