Diving for a loose ball during a summer pickup game, North Carolina center Tyler Zeller knocked heads with another player. It left him with a headache, nothing he was too worried about.

Next day, Zeller learned it was a bit more: tests revealed he had a concussion.

It was mild, enough to keep him off the court just for a couple of days. Yet it also added him to a growing list of college basketball players who have suffered concussions in a game that’s gotten bigger, faster and, as a result, much more physical.

“Now everybody looks like a sumo wrestler half the time,” North Carolina coach Roy Williams said. “Guys are so big and so strong, the collisions are going to be bigger. If a Volkswagen hits a Volkswagen, it’s a big deal. But if a dump truck hits a dump truck, there’s more damage.”

Concussions are often associated with more violent sports such as football, hockey, even soccer. But as basketball has become more brutish, the number of head injuries has increased.

A study of all divisions of NCAA sports by the National Athletic Trainers Association showed head and facial injuries in basketball increased by an annual average of 6.2 percent from 1988-2004. Concussions represented 3.6 percent of all injuries reported. Women basketball players were three times more likely to get a concussion than men.

Temple’s Juan Fernandez, Michigan State’s Delvon Roe, Louisville’s George Goode, Vanderbilt’s A.J. Ogilvy, Malcolm Lee of UCLA and Justin Hamilton of Iowa State are among the dozens players who have missed games or practices this season because of concussion-like symptoms.

Air Force has been plagued by concussions this season with at least six; center Sammy Schafer hasn’t played since the third game of the season because of lingering effects from a head injury. Boston University’s Scott Brittain, a starter last season, has been out this season after suffering a sixth concussion in preseason practice.

“Anecdotally, I would say we’ve seen an increase in that time in the number of concussions in basketball, especially in women’s basketball,” said Kevin Guskiewicz, an athletic trainer who chairs the sports science department at the University of North Carolina at Chapel Hill.

“… As I’ve talked to colleagues across the country, it appears the game has become a little more physical or the players have become more susceptible to it.”

The number of Division I players 6-foot-9 or taller increased from 649 in the 2000-01 season to 681 in 2008-09, according to STATS Inc., and they tend to be a bit more filled out than before.

The days of the frail, pipe-cleaner thin freshmen are almost over. Players today come out of high school with NBA-ready bodies: guys like Kansas’ Xavier Henry, Oklahoma’s Tiny Gallon and DeMarcus Cousins of Kentucky have more heft than players 20 years ago.

Bigger players have bigger collisions — and bigger consequences.

We’re building these players bigger, stronger, faster,” Guskiewicz said. “When you look at the physics involved — force equals mass times acceleration — you take a bigger person and they’re moving down the court more quickly and there’s a collision, the resultant forces that are applied to the head and ultimately the brain, sure, there’s going to be more concussions.”

The game has adapted to the size and strength of its players, becoming more about power than finesse.

A typical game in power conferences such as the Big 12, Big Ten and Big East can look like a wrestling match under the basket, players hitting the floor on nearly every possession, often landing in piles. These collisions offer a multitude of ways to get hit in the head: stray elbows, by the floor or an opponents’ knee, even on someone else’s head, like Zeller.

Former North Carolina power forward Tyler Hansbrough, known for his relentless play, suffered a concussion against Rutgers in 2007 and was thought to have another one — he didn’t tell anyone — against Miami last year.

Oklahoma banger Blake Griffin missed the better part of two games last season after suffering a concussion against Texas, then survived a dive over the scorer’s table in his first game back.

“I didn’t feel any effects afterward,” said Griffin, who missed his rookie season with a knee injury after being the No. 1 overall pick by the Los Angles Clippers. “I didn’t have any worries when I went back out on the court because once the dust clears, you feel normal.”

While head injuries have not received the same kind of publicity they have in football, pro leagues, the NCAA and organizations like the trainer’s association have put a priority on identifying and treating concussions, making sure coaches and athletic trainers understand the potential long-term effects.

Gone are the days of giving a player a whiff of smelling salts and a pat on the rear after a head injury.

“That’s the way it was back when we were kids: you had a headache and you went on,” Temple coach Fran Dunphy said. “Today, and I think it’s right, we need to be aware of it. It’s an acute situation.”

The NCAA added points of emphasis to the rule book for the 2009-10 season to curb excessive elbow swinging and to allow officials to stop the clock when someone gets hurt. It has concussion guidelines that apply to every sport and has asked each playing rules committee to look at ways to further decrease the number of head injuries. The basketball playing rules committee will meet next month.

The NCAA also will hold an association-wide concussion summit this spring.

This increased awareness has led to more concussions being reported, according to Guskiewicz, which could be a good thing.

As the serious nature of head injures has become understood, more players have been willing to report concussions and coaches have become more receptive to keeping players out of games until their symptoms subside. The more concussions that get reported, the better short-term treatment and long-term health for the players.

Chances are, though, the number of concussions overall isn’t going to drop. The game is too fast and physical for there not to be more collisions and concussions.

“We don’t really think about injuries,” Zeller said. “It’s just one of those things that happens. You just go out and play every day and unfortunately you have injuries once in a while. You just have to go out and do everything you can while you’re playing.”

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AP Sports Writers Dan Gelston in Philadelphia, Aaron Beard in Raleigh, N.C., and Jeff Latzke in Oklahoma City contributed to this story.