For one London Marathon runner his greatest challenge was waiting for him at the end of the 26 mile route - proposing to his girlfriend.
Alex Prior, 25, managed to summon the energy to get down on one knee and ask his partner Jess Seldon to marry him after taking a detour at the end of the course.
Miss Seldon, who revealed that she had no idea what was going on, eased the runner's pain when she accepted the "incredible" proposal.
"I tried to get down on one knee, to be traditional, but it was obviously pretty difficult. It was fantastic, almost surreal - so much so that I had to text her at the end and ask if she meant to say 'yes'," the 25-year-old later said.
The Football Association project manager said the two-minute rest stop was "fantastic", but admitted "it ruined my chances of a personal best."