Coleman has sickle cell trait, a condition he revealed in 2015 when he was entering the NFL draft after a 2,000-yard season as a junior at Indiana. In extreme forms of the condition, low oxygen levels in the air can cause complications.
Due to the fires across Northern California, the air quality index of 152 in Santa Clara was rated as "unhealthy air quality." The 49ers' standard is to practice unless the AQI reaches 200.
Coleman serves an important role in Kyle Shanahan's offense because of his style of play. Even while Raheem Mostert emerged as the team's top back last season, Coleman remained the starter. He got the starting nod in 13 games, including Super Bowl LIV.
"I've always liked Tevin's physicality," Shanahan said this week. "He's got the speed that we love, like pretty much all of our backs do, but he's never going to turn anything down and he's going to run through people and try to get those hard yards.
"I like to watch how those linebackers react when they get up after they tackle him, as opposed to how they react after they attack some other guys. The more you can do that and mix it up with certain guys, I think it does have an effect on the linebackers throughout the game."
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Coleman has been a favorite of Shanahan's since their two seasons together with the Atlanta Falcons. In 2016, Coleman had 520 yards rushing and 421 yards receiving with Shanahan as the offensive coordinator.
Last year, Coleman gained 544 yards and six touchdowns while averaging 4.0 yards a carry. Coleman rushed for 105 yards and two touchdowns in the 49ers' playoff-opening victory over the Minnesota Vikings.
Mostert came on strong to lead the 49ers in rushing last season with 772 yards, but has never started an NFL game at running back.
Shanahan said it is more important for him to find roles that fit with each player, especially when he felt the team had more than one capable starter. That is why Coleman remained as the starter.
"Raheem had always come off the bench a little bit and I thought it was kind of comfortable for him to do that," Shanahan said. "They have a little bit different style runs. We keep working both of them in."
49ers' Tevin Coleman misses practice as precaution due to air quality originally appeared on NBC Sports Bay Area