Marathoners call it "hitting the wall" -- a point at which the body and mind fade to such a degree that it seems like you've run into an imaginary blockade of bricks. It happens when your body runs lows on glycogen, a blood sugar that fuels the brain. Since hot and humid weather stresses your body to a greater degree, you'll run out of glycogen much faster. Glucose supplements -- which come in a variety of forms, including tiny, portable packets of a flavored, pudding-like substance -- can get your body and mind back on track. It'll help you reach the finish line regardless of whether that end point is a true line or simply the completion of yard work.