PERSONAL trainer Christian Fox writes a regular column on how to get in shape. This week: Things to think about in-flight this summer.

Before jetting off to your holiday destination this summer, think about the preventive measures you can take to avoid the health risks associated with plane journeys.

Dehydration, immobility, and reduced oxygen availability are only a few of the problems facing passengers on board. The amount of oxygen available in the cabin will be less than normal air.

Although for most people this will be tolerable, those with heart and lung problems may find this triggers their symptoms.

Too much alcohol or coffee can cause irregular heart rhythm or palpitations to develop. Prolonged immobility during the flight can lead to blood clots in the legs or the lungs, swollen feet, aching joints and muscles, and stomach pain from indigestion. It's very easy to feel stressed, what with the travel preparations, long delays at the airport, and customs and baggage, so make sure you allow plenty of time and keep well hydrated.

Combat poor circulation, swelling, sore joints and lethargy on cramped flights by doing a short exercise routine.

For your lower body you can do calf raises - keep the balls of your feet planted and raise your legs using your calf muscles. If this is too easy, place your carry-on bag on your knees. You can also reverse this by raising your toes as high as possible. Place your hands on your armrests and raise your knees slowly (together is harder than one at a time) toward your chin. Also, flex your gluteus muscles (bum), these are the largest in the body and need to be exercised too. For your upper body - shrug your shoulders gently.

Arch your torso gently backward and forward like a cat. Stretch your arms to the front, back and sides, and also curl and extend the elbow joint. Aim to perform these exercises for five to ten minutes every hour of your flight. When aisles are relatively empty and the seatbelt sign is off, walk around, stretch and do lunges. To lunge, take a big step (about half your height) and gently lower yourself as far as you can while keeping the torso upright and both legs bent. Return to a standing position by stepping either forward with the rear foot or backward with the front foot.