If months of marathon training fail to deliver the time you were hoping for this year, there is no need to beat yourself up – you were not born to do it.
Scientists have discovered that to run a marathon in a good time requires the right combination of genes and that nearly a fifth of people lack this special mix.
For runners with the right genes, it means their bodies can quickly adapt to carry large amounts of oxygen to their muscles, allowing them to run faster and for longer. Those who lack these genes, however, will never improve no matter how much they train.
A new DNA test could help tell anyone hoping to achieve a decent marathon time whether their efforts will be worthwhile.
Professor Jamie Timmons, of Loughborough University, has found more than 100 genes responsible for determining how the body responds to stamina training.
Thirty of these key genes can be used to predict whether someone is capable of running a marathon well.