A cheer erupted as the horn sounded for the start of the race.
The scene at Kempton Park in Surrey would once have seemed so normal... hundreds of runners crammed beside one another ready for the off.
But for recent times this was far from usual and the joy at being together was clear.
"It's amazingly exciting," said event director Hugh Brasher from London Marathon Events.
"It's been 16 months since we last put on an event and getting the nation back together, getting them healthy physically and mentally is an amazing feeling."
There were two races, both very different, and both vital opportunities to gather evidence of the impact mass participation events have when comes to coronavirus.
The first saw runners set off two by two at three-second intervals.
But simply being at a big event doing what they love to do was excitement enough.
"It's good to be back!" said Janet Conde at the finish line.
"I do half marathons normally but not to be able to that for over a year, it's challenging."
For the second race, social distancing was nowhere to be seen and when the horn went, the runners surged forward.
Across the racecourse, 30 cameras were set up to monitor crowd movement and individuals' interactions as part of the research.
Trevor Michaels, who ran the first race, was delighted to be involved, saying "the sooner we get back to normal, the better".
"The data is really important for the government... so to be able to contribute to that and give something back - it's very important."
Every person on site had to have a lateral flow test the day before being let in.
All runners then had a PCR test at home this morning before the race and will have a second one on Thursday.
It's the data from those two lab tests that will be used for the research.
This time it was running races, but similar experiments have been held at other events including a nightclub, at the World Snooker Championship, in the FA Cup and at the BRIT Awards.
And the name of the two races was apt - The Reunion 5K.
Runners, spectators and organisers alike will hope it will help fire the starting gun on many more before too long.