Ty MacArthur has no memory of his final two quarters of football, but he does remember an impulse to stay quiet about the injury that cut his career short.

The Air Force receiver was trying to block a linebacker at Boise State on Sept. 13, just the third game in his senior year, when he suffered his fourth concussion while with the Falcons.

He "blacked out" from there, though he continued to play. Concussions, unlike an injury to a knee or ankle, are often difficult to diagnose if the player doesn't first give an indication that something is wrong.

MacArthur knew if he brought it up, he might be finished. Finally, a teammate stepped up with the information. What followed were weeks of testing that showed MacArthur's memory and attention remained impaired. He was shut down for good.

"They go so in-depth that with that medical stuff," said MacArthur, who has seen a "ton of doctors" and was subjected to a four-hour exam at Fort Carson. "I would like to have played, but it wasn't my decision. I fought it for a long time, but I guess it was kind of inevitable."

MacArthur entered the season as Air Force's leading active receiver and the team's most reliable playmaker. Rather than expanding on those exploits, he became the most high-profile player lost to an injury.

Last week in a 41-21 loss to UNLV, Air Force defensive end Nick Fitzgerald, linebacker Connor Healy and wide receiver Alex Ludowig each left with head injuries.

That continues a season-long trend that has seen, among others, fullback Broam Hart, cornerback Chris Miller, quarterback Karson Roberts and receiver Sam Gagliano each miss time with concussions.

It's the most concussions coach Troy Calhoun has seen in his seven seasons with the Falcons. He attributes at least part of it to bad luck - Fitzgerald's injury, for example, occurred when he flew over a defender and rammed headfirst into the turf - but also to the growing size disparity between Air Force players and their opponents.

"If a Volkswagen runs into a big truck or if two big trucks collide, there's a little bit difference in terms of impact," Calhoun said.

MacArthur said his injury hasn't brought on headaches and light sensitivity, but he has had difficulty sleeping and there are times he can feel he's "just kind of out of it."

With doctors, coaches and his family telling him he should not play, plus with his own study of concussions, MacArthur has finally accepted his fate.

"I never would have thought that would be my last game," he said. "Senior year you never want this to happen."

Calhoun has raved about MacArthur and Miller, both of whom saw their seasons end with head injuries. He said both were ideal workers who gave all they had to the sport.

Doctors have told MacArthur the symptoms should subside with time, but as a senior on a team that sees its season end Saturday in Fort Collins, time was the one thing MacArthur no longer had to give.