TEMPE, Ariz. -- Brian Roberts is lunging and twisting his way across the floor here at the Athletes' Performance Institute, where more big leaguers can be found in January than anywhere else in North America.

Dustin Pedroia, Jed Lowrie, Jacoby Ellsbury, and Freddy Sanchez follow suit. Across the sprawling workout room, Pat Burrell is chatting with Justin Morneau.

"API" has been a popular offseason destination ever since Nomar Garciaparra won back-to-back AL batting titles training with API founder Mark Verstegen. These days, several dozen players make their way to Arizona for a minimum of six weeks of annual preseason conditioning.

Some, like Roberts, Burrell, and Carl Crawford, have purchased homes in greater Phoenix to be closer to the facility all offseason. They're part of a contingent of veteran API clients, a group that at various points since API opened in 1999 has included Curt Schilling, Kevin Youkilis, Vernon Wells, Manny Ramirez, Jason Schmidt and Jermaine Dye.

Verstegen, 39, popularized "core training" long before fitness magazines and personal trainers adopted it as a catchphrase to refer to building washboard abs.

Under Verstegen's program, core training refers to strengthening and stabilizing the many muscles around the shoulders, hips and midsection. This not only generates greater power but also prevents long-term injuries and the type of overuse ailments so common to baseball.

There's plenty of heavy iron at Athletes' Performance. After all, each January Verstegen welcomes two dozen of the top NFL draft hopefuls in preparation for the league's annual scouting combine in February. The baseball program also includes resistance training, but there's plenty of work using foam rollers, stability balls and a giant vibrating platform called a PowerPlate.

The facility, which will be replaced later this year with a bigger, even more high-tech operation elsewhere in Phoenix, includes a 50-person staff of "performance coaches," nutritionists, physical therapy staff, and massage therapists. There's a 25-yard swimming pool, a hot tub and 55-degree "cold plunge," a café for meals, and a popular Ping-Pong table for downtime.

"You have everything under one roof," says Roberts, who has trained at API since 2002. "If you did it all on your own you'd have to pay five different people to do it at five different times."

Though Verstegen's staff works with players of all sizes at all positions, they have become best known for creating power-hitting middle infielders. Garciaparra began working with Verstegen during his college days at Georgia Tech. Pedroia learned of the program while enrolled at nearby Arizona State.

Chase Utley of the Phillies spends his offseasons training at Verstegen's facility near Long Beach, Calif. (Verstegen has a third site in Pensacola, Fla., where Ramirez is training this winter as he goes through the free-agent process).

The Red Sox media guide lists Pedroia at 180 pounds, and he's weighed even more. But during the winter of 2006-07, he trained at Athletes' Performance for the first time and lost 25 pounds of fat. Last winter, he put some of it back in the form of lean mass. This winter, he's proud to say he weighs a "solid buck sixty-five."

"I've gotten wiry strong," says the reigning A.L. MVP. "Sometimes, if you have additional weight, it's bad weight."

The program places an emphasis on "regeneration," alternating high-intensity workout days with lighter days to encourage recovery. It also prepares players for the rigors of a 162-game season.

"People used to wonder if I was big and strong enough to play at a high level the whole season," says Roberts. "My first couple of years, I struggled in the second half. Now I'm able to keep it up, and that's a tribute to what they teach us here to maintain that strength and speed over the course of the season."

Perhaps the most motivating factor of the facility is the talent on hand and the results the program has produced. Garciaparra's batting titles attracted the first wave of players and created a continuous pipeline, especially from Boston to Tempe. Schilling began training at API before his 2004 "bloody sock" season. Morneau and Pedroia have MVP trophies. Burrell and Utley soon will receive World Series rings.

Pedroia says he always considered himself quick and agile, at least until he started working out alongside Crawford.

"I watch C.C. fly through agility drills, and it's like he doesn't break a sweat," Pedroia says. "You think you're pretty good and then you see someone like that and realize how much harder you have to work. That's great motivation."

Pete Williams is a freelance writer based in Tampa, Fla.