How Long Flights Affect Your Body and Mind Flying long distances involves sitting still for extended periods, often in cramped conditions. This can cause: Muscle stiffness and soreness: Limited movement tightens muscles, especially in the neck, shoulders, and lower back. Poor circulation: Sitting for hours slows blood flow, increasing the risk of swelling and discomfort in the legs. Dehydration: The dry air inside planes reduces hydration, which can cause headaches, fatigue,