Scientists at Loughborough University claim your genetic make-up affects how well you respond to stamina training, and one in five will struggle to improve their performance in this endurance test, no matter how hard they try.
According to Professor Jamie Timmons, head of systems biology at the University, a key group of 30 genes determines how the body responds to this particular type of training, and therefore whether marathon running will be your thing.
And the researchers discovered that those that fall into a certain genetic group are ill-suited to long distance running.
The tests were designed to find out which genes remodel muscle fibres, allowing small blood vessels to grow in between and carry oxygen to the hard-working muscles during exercise.
Speaking to the Sunday Telegraph, Prof. Timmons said: "From our work, we know that 20 per cent of people do not respond at all to training and in fact can get worse. They push themselves as hard as everyone else, but their muscles do not extract the same amount of oxygen."
He added: "These low aerobic responders would be better going to the gym to build up their strenght and muscle tissue or taking up other competitive sports like martial arts or strength related sports."
So if you've tried and tried to no avail to improve your stamina, don't beat yourself up over it - your talents may lie elsewhere. As Prof. Timmons pointed out: "What is clear is that there is no one recipe that fits all."
Do you believe marathon running success is all in the genes, or will hard work and training prevail? Leave your comments below...