Trainer Jane McDonough, of Play Personal Renovations, points out the other advantage of drinking a lot of water: a lot of trips to the toilet - extra movement around the plane that is really valuable when you are spending hours sitting still.
She says it's important to keep moving, to reduce the risk of deep vein thrombosis. "Get up and walk around to keep the blood flowing through your body." Do toe raises even when you are sitting in your seat, and lots of stretching. "Lots of people get lower back pain which can be helped by stretching."
On the days leading up to the flight eat light, healthy meals and avoid gas-forming food such as lentils, beans, cabbage, onion and curry. While flying, gases in the body reportedly expand by one third, often causing discomfort. "Have small, regular meals on board," Liu says, "Go for the healthier low-fat options at meals and snacks."
Naturopath Angela Haldane recommends taking some of your own food on the plane - protein snacks such as boiled eggs - in case the meal is not good.
If you are in the middle of a training programme, there are ways to make sure your travel plans do not derail it.
McDonough says: "Do something when you get home, even if it's much lighter than usual. If you're training for a marathon, just go for a walk."
Put any downtime to use. If you are in an airport for a long stopover, go for a power walk around the terminal or do a series of press-ups, lunges and squats in the lounge. "You might even get everyone else doing it with you," McDonough says.
Haldane recommends calcium and magnesium supplements to help you relax in your seat and cut down tossing and turning.
She says a natural sleep aid such as melatonin can be a benefit, but try it out a couple of times before the flight so you know how your body will react. At the very least, use an eye mask and noise-cancelling headphones or ear plugs. Get the best seats you can - a window seat will give you something to lean against and mean no one has to clamber over you to get out.
Planes are notorious for spreading sickness, not so much because of the recycled air, as the urban myth suggests, but because of bacteria left on shared surfaces such as door handles, tray tables and bathroom fittings. Haldane suggests keeping a hand sanitiser nearby and applying it after toilet stops and before eating. She also recommends taking supplements of fish oil and echinacea to boost your immune system. Loading up on caffeine or other stimulants when you get close to landing might seem like a good idea at the time but Halden advises against doing anything to boost your energy. "You can get over-stimulated and burn out."
