Teenage boys with low levels of fitness have been found to suffer heart disease.
A recent study by Dublin City University found that even those with moderate fitness did significantly better than those with a sedentary lifestyle.
Schools are encouraged to sign up to the Schools Fitness Challenge before Friday.
Head of the school of Health and Human Performance at DCU, Niall Moyna on catching up on a worrying trend.
A recent study led by Professor Moyna found that low fit transition year students had very poor health, with 15-year-olds showing signs of heart disease similar to 60-year-olds.
Irish Life is urging schools to sign up to their schools fitness challenge – which measures the health of secondary school students before and after a six week fitness programme.
Olympic hurdler Thomas Barr says everyone can find a sport to suit them and Cork Camogie player Ashling Thompson says it helps your head as well as your heart.