Teenagers were warned yesterday not to spend too much time texting A level grades to friends and relatives because they could injure wrists.

Physiotherapists told sixth-formers not to over-use thumbs amid predictions 100 million texts will be sent on results day tomorrow.

Texting sessions should be limited to between five and ten minutes, according to the Chartered Society of Physiotherapists.

The group advised students to make the most of predictive texting, support arms on a chair or table when texting "to take the 'load' off the neck", and swap hands.

Claire Doherty, of the Association of Chartered Physiotherapists in Occupational Health and Ergonomics, said: "Text messaging is a great way to stay in touch but it's also a lazy shortcut.

"Mobile phones are not ergonomically designed for excessive messaging and too much can result in pain and swelling of tendons at the base of thumb and wrist."