Traveling can take a toll on the body—especially if it involves a lengthy flight. Jet lag, muscle stiffness, water retention, and dehydration are common complaints, says Paul H. Lilli Jr., M.D., M.P.H. (master of public health), a retired Air Force colonel and member of the Traveling Physician Association. "For a long flight, it's important to prepare your body," says Dr. Lilli. Check out these plane-ride pointers for the next time you're en route to the airport.