Scientists claim regular strenuous exercise could increase a person's risk of developing motor neurone disease.
While a team of experts from the University of Sheffield insist people don't need to avoid workouts, they have warned the findings from the new study could help screen for people who may be high risk.
"We have conclusively said exercise is a risk factor for motor neurone disease (MND)," said Dr Johnathan Cooper-Knock, who was involved in the study. "The numbers of high-profile athletes affected with MND is not a coincidence.
"We don't know who is at risk and we wouldn't go as far as advising who should and shouldn't exercise. If everyone stopped exercising that would do more harm than good."
Regular strenuous exercise was defined as more than 15-30 minutes two to three times a week.
It is believed that around one in 300 people will develop the disease, which sees motor neurones carrying messages from the brain to muscles fail and affects a person's ability to talk, move and even breathe. Little is known about who is more susceptible and how large a role genetics and environmental factors play.
For some time there has been a debate over the link between MND and exercise, but previous studies have shown soccer players are six times more likely to develop the disease.
For this latest study, the genetic samples of half a million people from the UK Biobank project were analysed, using a technique called Mendelian randomisation. This showed those people who had DNA that made them more predisposed to do strenuous exercise had a higher risk of developing MND.
There is a theory that low levels of oxygen in the body during vigorous exercise may result in oxidative stress in the motor neurones.
The study was published in the EBioMedicine journal.
It is hoped that similar studies could develop screening strategies to detect heart problems in soccer players.