1. Stand up straight and feel the normal ā€œSā€ curve of your spine. Then use rolled-up pillows or blankets to maintain that curve when you sit in your seat. Tuck a pillow behind your back and just above the beltline and lay another pillow across the gap between your neck and the headrest. If the seat is hollowed from wear, use folded blankets to raise your buttocks a little.

2. Check all bags heavier than 5 to 10 percent of your body weight. Overhead lifting of any significant amount of weight should be avoided to reduce the risk of pain in the lower back or neck. While lifting your bags, stand right in front of the overhead compartment so the spine is not rotated. Do not lift your bags over your head or turn or twist your head and neck in the process.

3. When stowing belongings under the seat, do not force the object with an awkward motion using your legs, feet or arms. This may cause muscle strain or spasms in the upper thighs and lower back muscles. Instead, sit in your seat first, and using your hands and feet, gently guide your bags under the seat directly in front of you.

4. While seated, vary your position occasionally to improve circulation and avoid leg cramps. Massage legs and calves. Bring your legs in, and move your knees up and down. Prop your legs up on a book or a bag under your seat.

5. Do not sit directly under the air controls. A draft can increase tension in neck and shoulder muscles.

Source: https://www.acatoday.org/Patients/Health-Wellness-Information/Preventing-Travel-Aches-and-Strains