Among them are people with physical disabilities -- some even became disabled while fighting for our country. Being able to be part of different sporting events like the marathon has given many vets a new outlook on life. Daniel Casara, 37, is one of them. He's back competing in the Chicago Marathon for the third time.
Casara is training along the lakefront using a hand cycle.
"The type of chair I have is the Four Star, which is an actual racing version of the handcycle," Casara said. "There are about three or four models, maybe more than that, and some of them are more upright and have a wider grip etcetera, and mine is designed for less air drag so I do a lot of racing in their particular on this particular cycle."
Casara served with the U.S. Army from 1994 to 2007.
"I was stationed down in south Baghdad at Iraq, which is where I got injured back on September 23, 2005. I was in an armored personnel carrier small tank. We were rolling on a routine mission, nothing special, and we actually rolled over an antitank mine. That antitank mine flipped our tank killing two of my soldiers and injuring four others, me included," Casara said.
He continued: "I suffered bilateral fractures to my right tibia and fibula, shattered my left tibia, both of my heel and ankle bones were shattered. I've had 24 surgeries to date where they've fused my calcaneus bones in both feet."
Three years ago, he got interested in racing.
"I had only ridden the handcycle probably once or twice a very short distance, so for me to have to go 26.2 miles in somewhat of a competitive fashion, I didn't think I could do it. I did it back in October of 2009," Casara said.
Daniel has been working with trainer Stacee Seay.
'I met Dan through the Rehabilitation Institute of Chicago. He came to one of my classes that was there, and from the very first time I met Dan, I knew he had something special. He was probably a little bit over trained at the time, and we kind of dialed all that in and helped him to be what he is today," Seay said.
"We're working very hard on this initiative with World Sport Chicago, the U.S. Department of Veteran Affairs and the U.S. Paralympics to include injured, ill or wounded veterans in programs for people with disabilities in the metro area," Redding said.
This summer, World Sports Chicago hosted Valor Games.
"I think that we had over 100 athletes who were veterans or active duty service members with disabilities, and it was a fantastic experience for them to be able to compete for the first time," Redding said.
As for the upcoming Chicago Marathon, Seay says Casara has a great future.
"I think Dan has a future in doing whatever he puts his mind to do. He is one of the most determined individuals I've even met. He's dedicated; he's got integrity and just all of the attributes that it takes to become an incredible athlete," Seay said. "
Next Sunday, Casara says he hopes to finish the marathon in 1 hour and 40 minutes.
"This time I think I'm just going to just completely enjoy my city and the great support. There's no other marathon in the country that I've participated in or seen that has the support that Chicago gives to their athletes," Casara said.