Digital Technology: Concerns that radiation from mobile phones may damage health have receded, but the new scare could be of long-term damage to fingers and hands from excessive computer game-playing and use of thumbs to send text messages, writes Muiris Houston, Medical Correspondent.

Both a mobile phone and a Gameboy have entered our household during the summer. It has been an eye-opening experience for a parent to observe how differently children and young adults use new technology.

The mobile is rarely used as a conventional telephone. Instead, text messages are typed with amazing rapidity in a series of abbreviated conversations. Thumbs fly up and down, the message is sent and within seconds a reply has come through. When asked do they not miss the spontaneity of the caller's voice, a withering look signals the teenager's view of an ageing parent who is simply not "with it".

But with some concern about the health effects of radiation from mobile phones, maybe parents should be glad that text-messaging is hip. There has been no definitive evidence to support a specific health risk, but at the same time has there been no endorsement giving mobile phones the "all-clear".

A British government inquiry found that mobile phones should be used with caution in the young until further research is carried out. It concluded there was a "risk of a risk" which needed further investigation.

Theoretical concerns revolve around the amount of electro-magnetic radiation that mobile phones emit. It has been postulated that if the device is pressed against the side of the head for long periods of time, then the radiation could enter the brain and cause a tumour.

But a study in the New England Journal of Medicine has found no evidence that mobiles increase the risk of brain tumours. Researchers from the US National Cancer Institute compared mobile phone use in cancer patients and a group of healthy individuals. They concluded that people who use mobiles for 60 minutes or more a day are at no more risk of a brain tumour than non-users.

Any research linking mobile phone emissions with cancer has been carried out in animals but it has been difficult to replicate this research and no consistent pattern has emerged.

However, recent remarks by Dr Gro Harlem Bruntland, the director general of the World Health Organisation, have refocused attention on mobile phone safety. She told journalists that she suffers from headaches when using a mobile phone, being very sensitive to electro-magnetic radiation. "I think we have reason to be cautious and not use mobile phones more than necessary," Dr Brutland said, adding that the younger you are, the more reason to take precautions.

So, from a radiation perspective, we should be glad that it is the thumbs and not the ears of our teenagers which come into contact with mobile phones, And, of course, with their Gameboys. Thumbs have become the new index finger, with one study suggesting they have replaced fingers as the hands' most muscled and dexterous digit. It also found the younger generation is using the thumb for other tasks that are traditionally the fingers' job, such as pointing at things or ringing doorbells.

The trend is particularly marked in Japan, where under 25s refer to themselves as "oya yubi sedai" - the thumb generation or thumb tribe, according to Dr Sadie Plant, an expert in the Cybernetic Culture. Older people use one or more fingers to access the keyboard of a mobile phone, while the younger generation use both thumbs, barely looking at the keys as they make rapid entries. The same movement is the key to dexterously handling a Gameboy.

But are there health risks associated with such extensive use of thumbs? We know that repetitive strain injury or, to give it its correct name, cumulative trauma disorder , is a hazard of some occupations. Jobs that involve extensive use of computer keyboards can cause the condition. The musculo skeletal system becomes overloaded by a succession of tiny "microtraumas" which, added together over time, give rise to the symptoms of CTD.

Excessive or forced repetitive movements irritate the area between a muscle tendon and its covering sheath. Normally, the tendon moves smoothly within the sheath as it contracts and relaxes. At a certain point, however the sheath thickens, causing pain and swelling (tendonitis). A particular type of tendonitis is caused by repeated movements of the thumb, leading to a thickening of the thumb muscle sheaths. A person with the syndrome will notice a pain in the thumb which often spreads up the forearm, and there will be tenderness at the back of the wrist where the base of the thumb joins it. In theory, excessive use and even forceful compression of a Gameboy or other computer games with the thumbs could lead to problems in children and teenagers. A case report in the Scottish Medical Journal, entitled "Nintendinitis?", described a case of CTD in a child who played a lot of computer games. And in February of this year, doctors at Great Ormond Street Children's Hospital, in London, wrote to the British Medical Journal suggesting that computer games with vibrating hand-held control devices should carry health warnings. They described a case of a 15-year-old who played such a game for up to seven hours a day and suffered pain and swelling in his hands.

His symptoms were similiar to another recognised occupational condition called hand-arm vibration syndrome. It is caused by using industrial tools - such as pneumatic drills - for long periods. It may well be that we are just beginning to see the tip of the iceberg as far as muscular problems and computer games are concerned. So it might be prudent for parents to limit the use of computer games and to encourage short bursts of playing rather than prolonged sessions. And if your child uses excessive force with his digits while playing, a gentle word to "ease up" might just prevent health problems.