Mental workouts can increase muscle strength, according to new research in the United States.

While regular visits to a gym can increase muscle strength by 30 per cent, thinking about those exercises can increase your muscle power by between 13 and 16 per cent, says research from the Cleveland Clinic Foundation, published in New Scientist magazine. The research could benefit people who are too weak to exercise.

Scientists used volunteers aged 20 to 35, who were put through strict "mental gymnastics" tests. After a few weeks they showed up to a 13.5 per cent increase in strength.

That concurs with a study in 1997 by Dr David Smith, now at Chester College, who found that people who trained could get 30 per cent increases in strength, while those who visualised the training achieved a 16 per cent rise in strength.