Teenagers should be encouraged to exercise more as poor muscle strength is associated with early death (flickr/OakleyOriginals)

Teens with low muscle strength are at a greater risk of dying early than those with strong physiques.

A study, by researchers at the Karolinska Institutet in Sweden and published in the BMJ, found weak teenagers are at risk of developing several major health problems, including cardiovascular disease.

BMI and high blood pressure at a young age are known risk factors for early death. Researchers now think, however, that muscular strength in adolescence can also be used to predict mortality.

The researchers followed over one million teens aged between 16 and 19, for a period of 24 years. Premature death was defined as below the age of 55.

The sample teenagers were tested for muscular strength at the start of the study, including knee extension strength, handgrip strength and elbow flexion strength.

During the study, 26,145 participants - or 2.3 per cent - died. Suicide was the most common cause, followed by cardiovascular disease and cancer.

Strong muscles were associated with a 20-35 percent lower risk of early death. Stronger teens were also 65 per cent less likely to suffer from psychiatric disorders.

The study also found teens in the lowest tenth of muscular strength had, by far, the highest risk of early mortality.

The researchers conclude that poor muscular strength is a major factor in premature death and shows there is a need for regular physical activity in childhood and adolescence.

It also concludes that "physically weaker people might also be mentally more vulnerable".

"People at increased risk of long term mortality, because of lower muscular strength, should be encouraged to engage in exercise programmes and other forms of physical activity," the authors said.

A study by Swedish researchers from earlier this year found that children are at risk of developing heart disease by not exercising.

Study leader Tina Tanha, said: "It is well known that physical inactivity in adults is associated with a wide range of diseases and all causes of death.

"We believe that our study now demonstrates a clear clinical association between physical inactivity and multiple cardiovascular disease risk factors in children."