LIFT HEAVY THINGS.
Um...how about two sixty pound bags of sand and five eighty pound bags of gravel. Does that qualify? I will not kid you and say it was easy, but I DID IT. Sitting in my recliner right now I can feel my back muscles trembling and know exactly what muscles I used in my arms. Thank goodness for a coconut milk/banana smoothie halfway through the day. Without it I couldn't have gotten this far on that project from lack of energy.
If your body is willing, your mind can push it to do some amazing things.