Trevor Rosenthal was big in October. FYI, he’s bigger now. A guy who seemingly has everything — youth, a craving to learn and, of course, triple-digit heat — left the National League championship series wanting more. The Cardinals’ breakthrough postseason performer, Rosenthal wanted to add to his credentials. He did so by getting big — or bigger, at least. For much of the winter the 22-year-old hung with Chris Carpenter, the Cardinals’ resident Cy Young Award winner and pitching elder. Carpenter compensated for shoulder and arm weakness the last couple of years with manic weight training designed to strengthen his lower body. Rosenthal, who has never thrown more than 131 2/3 innings in four professional seasons, saw more muscle as a way to enhance his durability, an attribute he hoped to parlay as a starting pitcher. Carpenter long ago became a workout monster trying to outrun a career end that has forever lurked around the next corner. He found a compadre in Rosenthal. “That’s my personality. That’s how I do it,” Rosenthal says. “If I’m not doing something I feel like I’m being lazy. For me, to get in there and do something each day I feel like I’m headed in the right direction.”