"Everybody wants to get back out there and show the world that we're still running," said Spencer Aston, who works at Marathon Sports, on Boylston Street, where the first bomb blew out the windows.
The store became a makeshift emergency room in the chaotic early moments after the attach. People ran inside and helped the staff help the injured. They pulled clothes off the rack to treat the dazed wounded.
In the year that followed, business boomed. Non-runners stopped by to show support. Membership in the weekly running club ballooned. The store raised about $700,000 for One Fund Boston, the charity that sprang up after the bombings.
But the most jubilant moment comes Monday, as runners stream across the finish line on a jubilant Boylston Street.
Read MoreScenes From the Boston Marathon Bombing
"Anybody who has run a marathon before, this is going to be the most important one they've ever run in," said Dan Soleau, a Marathon Sports executive who was cheering runners on outside the store on April 15, 2013.
It will also be different. More than 3,500 police officers, double last year, will be along the route. More than 100 cameras have been set up in the Boston stretch alone, and authorities will watch the finish-line crowd from more than 50 "observation points."
Some of the security cameras are more sophisticated than the ones that picked up grainy images of Tamerlan and Dzhokhar Tsarnaev, the brothers accused of detonating the bombs.
Authorities have urged fans not to carry backpacks — both bombs last year were concealed in them — and warned that there will be at least 40 security checkpoints, some with metal detectors. Thirteen miles of steel barricades will line the course.
Security concerns were heightened on the anniversary itself last week, when a man was arrested walking down the street, veiled in black, carrying a backpack with a rice cooker in it. The bombs last year were set off in pressure cookers.