Unity Run participant Dave Redemske was in Galveston, Texas, for a meeting, "totally disconnected from everything", when the news "stunned" all 10 people in the room with him.
Jason Patera was also in a meeting and was "overcome" when a coworker informed him.
Emily Greenbaum was on the CTA Green Line when many on the train were simultaneously struck with "sorrow."
Greenbaum's aunt, Bonnie Grember, was in her car when a friend called. Her first thoughts were "disbelief and shock."
Greenbaum, Grember, Patera and Redemske were among the nearly 200 athletes who gathered along Lake Michigan's shoreline in a show of solidarity the best way they knew how: running.
The tragedy "sent us all reeling," said Wendy Jaehn, executive director at CARA. "We're not quitting, we're not doing anything different that would show we're afraid. That's what this run is about — support."
"I think that everyone deals with grief in different ways," said Patera, an administrator at the Chicago Academy for the Arts. "For me running is very personal. Any time I'm affected by anything, I lace up and go.
"Running for me has always been a way to deal with things."
The feeling was mutual for the runners as they took off together on the course, which most completed in about 30 minutes.
Those that arrived first cheered those that followed, and they celebrated with high-fives and handshakes.
Redemske said he ran home and jumped on his bike to make the run in time. He compared the show of unity to Chicago's "silent rides" — when cyclists travel on city streets in remembrance of riders struck by vehicles.
Said Patera: "I'd just like to think that we aren't overlooking all of the senseless deaths."
"I think a thing we don't often hear about is that people die senseless deaths every day," Patera added. "Sometimes we rally together and sometimes we don't."