Tevin Coleman kept pushing despite his body telling him otherwise.

During a game against No. 18 Missouri last September, the former Indiana running back and current Atlanta Falcons rookie exerted himself to the brink. Spectators at Missouri’s Memorial Stadium probably thought Coleman was injured when he was carted off during the second quarter on that 85 degree day.

He wasn’t.

Coleman’s episode was related to sickle cell disease, a blood disorder. He inherited the sickle cell trait from his father. It can cause complications if an individual is under physical stress in extremely hot weather or environments with low oxygen, such as high altitude.

Coleman never talked about his condition publicly; neither did his football coaches. The Missouri game, however, marked the one time in his three-year college career Coleman almost felt defeated by his abnormality. In spite of it, he returned in the second half and set up the game-winning score with a 44-yard, catch-and-run.

The sickle cell trait is one of several obstacles Coleman has overcome in his journey to the NFL. He was born 10 weeks premature and was given a 20 percent chance of survival. His mother, Adlevia, often reinforces with Coleman how blessed they are to be here.

Tevin Coleman rushed for an Indiana record 2,036 yards last season, second in the nation to Wisconsin's Melvin Gordon (2,587). AP Photo/Darron Cummings

"Every time I do well or do something good or accomplish something, she always tells me ... she and I could have been gone," Coleman said. "It’s always a touching moment for me. I really just think about that and say 'I’m here for a reason.' I just try to work hard and do the best that I can do."

His hard work earned him an Indiana record 2,036 rushing yards last season, second in the nation to Wisconsin’s Melvin Gordon (2,587). Gordon was a first-round draft pick by the San Diego Chargers and Coleman fell to the third round. In December, Coleman had surgery on his broken right big toe, an injury he played with the majority of the season.

"I really don’t know how I did it," said Coleman of playing despite the injury. "It was just a mental thing, and I had to go on for my team and keep playing. I didn’t want to let them down. I didn’t want to let myself down. I just went out there and fought the pain and kept on playing."

Though some teams expressed concern about his toe, Coleman believes others were scared off by the sickle cell trait.

"Teams thought I had the full-blown sickle cell anemia, but this is the trait, so it’s not as bad as sickle cell anemia," Coleman said. "If I had (sickle cell anemia), I would not even be playing. You can’t even run if you have that. I said to those teams that I just had the trait and I’ll be good. I played all throughout college. I’ll be good."

The Falcons expressed no concerns about Coleman’s condition and considered drafting him in the second round. Indiana coach Kevin Wilson, who has four or five players on the Indiana roster with the sickle cell trait, said the key with Coleman was monitoring how hard he pushed himself.

"The bottom line is in your practice, kids need recovery time," Wilson said. "A lot of guys play with the sickle cell trait. The deal is how to manage it. I think you have to credit Tevin to always being tough enough to push himself. While some folks might shy away because of it, he would push himself to the max. Because he didn’t use anything as an excuse and because he never backed away, he always strived to be great. He is, hands down, one of the best practice players I’ve ever been around. But he needed time to slow down so he wasn’t sickling."

Dr. Kevin Smith, a lead physician for the sickle cell program at Loyola University Medical Center in Maywood, Illinois, explained how the sickle cell trait is far less severe than sickle cell anemia.

"Sickle cell anemia is a mutation in one of the building blocks of a protein, so it’s one change in the protein that makes up the oxygen-carrying molecules," Smith explained. "Normally in sickle cell anemia, you get an abnormal copy from both parents.

"In sickle cell trait, you only get it from one of the parents. Then you have one abnormal copy and one normal copy. Fortunately these patients, most of the time they have no idea that they even have sickle cell trait. They act like everyone else. They don’t show signs of any illness. But the time that you see it is when people are participating in heavy exertion and high altitudes. In football, that becomes one of the concerns for patients who have sickle cell trait. ... Every person is different, so it’s hard to know exactly what their experience is going to be like."

The sickle cell trait is more common among African-Americans. Smith pointed to former NFL receiver Terrell Owens as a player who had a successful career with the sickle cell trait.

Long-time NFL defensive back Ryan Clark, now an analyst for ESPN, had a scare related to carrying the sickle cell trait. Clark had to have his spleen and gallbladder removed after playing in Denver during the 2007 season. After the incident, Steelers coach Mike Tomlin prohibited Clark from playing at Denver, including a 2011 playoff game.

"I got really sick the first time I played there and my spleen was bleeding," Clark said. "Then the second time, I lose my spleen and gall bladder. So I was relieved and understood (Tomlin’s decision).

"(Coleman) will be fine. As long as he hydrates and trains, he’ll be OK."

Coleman won’t have to worry about altitude until the 2016 season, when the Falcons are scheduled to travel to Denver. He will have to combat extreme heat on a regular basis in Atlanta. Coleman will battle second-year player Devonta Freeman for the starting role, and a two-back system would spare Coleman from shouldering the entire load, if energy becomes an issue.

"The key is just to stay hydrated and just keep on looking after how much water and fluid you take in," Coleman said. "I just have to monitor my fluids and monitor when I’m feeling it -- take two plays off and just get my breath back, and just right back out there. I’ve played in hot weather before. I know how to take care of my body. I know how to take care of myself. It will be all right."

Ironically, Falcons coach Dan Quinn said the most impressive film he saw of Coleman was the Missouri game. Coleman had 19 carries for 132 yards with a touchdown and caught three passes for 57 yards.

"I thought he played with great toughness against Missouri," Quinn said. "That's one when you just see a guy, 'Is he getting it again? Yep. Did he get yards again? Yep.' Those are the kinds of games -- when a guy continues to get it and you know he’s going to get it and still makes yards -- oftentimes that, to me, is a back that feels like he’s got something to prove."