Inside ace Corey Kluber’s offseason training at Cressey Sports Performance in Hudson, Mass.

It's a cold winter morning, just days before the new year, and one of the most intimidating pitchers on the planet is humming fastballs in a near-empty gym in central Massachusetts.

Corey Kluber, two-time AL Cy Young Award winner, has driven 40 minutes from Winchester, Mass., to Cressey Sports Performance in Hudson, Mass. — his home away from offseason home.

In a couple of hours, there will be a parade of pro pitchers and prospects throwing, lifting and fraternizing amid a din of laughter, chatter and loud music. But, right now, it’s just Kluber progressing through an intense workout — including throwing, stretching, lifting and more — with a quiet determination and without much attention or any fanfare.

"The environment is awesome," Kluber said, "and obviously there are a lot of other pro guys who train here." The expansive facility is otherwise empty except for a handful of middle-agers participating in a small group workout nearby. But save for the chiseled nature of the 6-foot-4, 215-pound physical specimen — and the unmistakable "pop" of elite fastball hitting catcher’s mitt — they might not even know he’s a pro athlete, let alone the most durable and dominant pitcher in the American League.