More than 1,000 former amateur and professional rugby union and rugby league players have joined a long-running concussion lawsuit against the sports' governing bodies, the firm representing them said on Tuesday.

Rylands Garth said it now represents over 725 former union players and over 280 former league players in a case that began more than four years ago.

"The claimants are suffering with a range of life-altering neurological conditions including Parkinson’s Disease, Motor Neurone Disease (MND), Chronic Traumatic Encephalopathy and dementia," the company said in a statement.