TEMPE, Ariz. -- It could be a nasty virus, with an aching body and the chills. It could be a stiff neck or a tight hamstring.
More often than not, it's a throbbing sensation up and down his right arm. Rarely has Los Angeles Angels pitcher Dan Haren walked on a mound in the past six years when his body felt wonderful, his arm fresh and he couldn't wait to start abusing his ligaments, tendons and muscles all over again.
But he does it. anyway.
Haren is starting to build a reputation as the game's most durable starting pitcher. No other major leaguer has made as many as Haren's 203 starts since 2005. In his career, which has spanned four teams, he has never missed his turn in the rotation.
When the Angels acquired Haren from the Arizona Diamondbacks for four young pitchers last July, they were pretty confident about one thing: They could bank on Haren taking the mound.
"When guys have track records that show they stay healthy, you feel more comfortable," Angels general manager Tony Reagins said.
Some old-timers will tell you the average major league starter leads a country club lifestyle nowadays because he typically pitches on four days' rest. Haren isn't necessarily bragging about his durability either, saying, "It's only 100 pitches every five days."
But the word "pitch" doesn't quite capture the violence of a major league pitcher's delivery or the torque placed on the elbow and shoulder or the strain of converting one's entire body into a slingshot with the sole purpose of throwing a baseball in ways that baffle the best hitters in the world.
Renowned orthopedist Lewis Yocum said it's almost as if the pitcher were trying to deliver his arm to home plate along with the ball. Here's how he describes the effects on the body: "'Hell' is an appropriate word."
"The physical demands it forces on the elbow alone are more than enough to tear apart the ligaments," Yocum said.
A pitcher can't do much about the strength of his connective tissue, Yocum explained, but he can do plenty about the muscles around it. Haren inherited good genes. He has ideal size for a pitcher, at 6-feet-5 and 215 pounds. But he has worked hard since he was a teenager to refine his mechanics and build up his muscles to support what Yocum calls the "unnatural act" of throwing a baseball overhand.
When Haren was at Pepperdine, his team played USC in an NCAA regional game. Haren remembers watching Barry Zito's puzzling pregame routine, which included playing catch from about 200 feet.
Soon, Haren was learning from the same Southern California private pitching instructor Zito used, Alan Jaeger, a leading proponent of long toss and arm-strengthening exercises. Zito and Haren pitched together on the Oakland Athletics and are close friends. Neither pitcher has ever been on the disabled list.
Haren's durability appears to be a confluence of his workouts, favorable genetics and an ability to ignore pain. It took just a few hours for them all to be tested when Haren landed in Anaheim.
On July 26 at Angel Stadium, Haren got two outs in the fifth inning of his Angels debut, before Kevin Youkilis swung at his 62nd pitch and sent it right back in Haren's face. Haren got his hands up in time and the ball deflected off his right forearm. He left the game early, the first time in his career he'd been knocked out by an injury. Had it landed an inch further up his arm, on his elbow, it might have jeopardized his career.
Five days later, Haren pitched a complete game.
Seeing Haren rebound from the injury so quickly reminded Angels manager Mike Scioscia of some of the durable pitchers he had caught with the Dodgers: Don Sutton near the end of his career, Orel Hershiser and Fernando Valenzuela. It reminded him of the stories he had heard about what Sandy Koufax did to get ready.
"They had to work to rebuild their arm between starts and still maintain a certain level," Scioscia said.
Scioscia had heard about Haren's resiliency from asking around before the Angels made the trade.
"The guy's never missed a start, and you know a guy who throws as many innings as he has is not always feeling hunky-dory," Scioscia said.
Haren has made 30 or more starts and pitched at least 215 innings in six straight seasons. It's not as if he's just an innings-eater. He finished tied for seventh in the majors in strikeouts and fifth in fewest home runs allowed last year.
He likely will be the Angels' No. 2 starter behind Jered Weaver this April. Starting pitching is the anchor around which the Angels are building their 2011 hopes.
And Haren is having the time of his life. He grew up in West Covina, Calif., and used to drive south with his dad to attend Angels games. He and his wife are just finishing the move from Arizona to a permanent residence in Southern California.
"To go to L.A. and bring my family back to where we're both from, it's pretty exciting," Haren said.
Mark Saxon covers the Angels for ESPNLosAngeles.com. Follow him on Twitter.