DETROIT – The great part of playing first base, Joe Mauer was told all winter until he believed it himself, was that he would be healthy all season.

So why does his side ache, his back stiffen and his legs grumble so much?

"Playing first, I thought I would be more healthy," the Twins' signature star said Saturday. "But this year was a grind for me personally."

He suffered back spasms in May, and missed a month with an oblique muscle injury in his right side in July, keeping him out of the lineup for nearly six weeks. He hasn't felt completely healthy all season — and none of that is from foul tips or balls off the mask this year. Mauer, whose eight-year, $184 million contract reaches its halfway point once the season ends, will play his 120th game on Sunday — but that's about 30 games fewer than the Twins expected.

"It was a tough year," Mauer said. "It seemed like once I'd start getting going, something would come up. … But that happens, I guess. I just have to keep coming to the park, working hard and trying to give my best."

His best wasn't what it used to be this season. Mauer will close 2014 on Sunday with a batting average around .280, the lowest of his major league career. He hit only four home runs, a power drought equaled only in his injury-plagued 2011 season. He's driven in 54 runs, a paltry number for a No. 3 hitter, and he ranks only fifth on his own team in doubles.

Most notable of all, his strikeout rate keeps rising; his 96 whiffs with a game to go are a career high and mark the third straight year he's had at least 88. It clearly bugs him, too. Mauer has argued with more umpires this season about the strike zone than ever before. "Have you seen the pitches I've been annoyed at?" he said with a grin. "I don't show a whole lot of emotion, and human error is part of it, too, but it's been a year when a lot of things really didn't go my way. I've just got to keep working."

Fortunately, he said, he'll be able to this winter — unlike a year ago. Mauer's preparations for this season were delayed last year by the concussion he suffered in August, since the symptoms didn't disappear until after New Year's Day.

He couldn't work out. He couldn't lift weights. He couldn't hit, run or throw. He could barely function normally.

"This year will be a lot different for me, which is good. I'll be able to get in the work that I need to," he said. "People forget, I really couldn't do anything until January. It took me a good four months to get over the concussion."

And it led to some surprisingly disheartening results at the plate. Always a patient hitter, Mauer wasn't able to turn pitcher's counts against them the way he once could. A first-inning single off Kyle Lobstein on Saturday was just the third time all season he got a hit on an 0-2 count.

But Mauer also drew 60 walks, second-most on the team, and his .361 on-base percentage — only the second time in seven years he hasn't been above .400 — still leads the Twins.

"I need Joe Mauer in the lineup," manager Ron Gardenhire said. "I know that. When Joe Mauer is in the lineup, we're a better baseball team."