The grind of a 162-game season takes its toll, and injuries can take down entire seasons -- not just for players but for their teams.
Yes, baseball is a game that is won with the contributions of nine players on the field, 25 on the roster and often many more than that over the course of a six-month haul. However, being without one key cog in the wheel can derail high hopes in a heartbeat.
A return to the field and to prominence by those who missed a good deal of last season because of injury could change everything. Here are five players whose healthy presence might very well alter the landscape of the standings.
Joe Mauer, Twins
The last time we saw a truly healthy Mauer at and behind the plate for the Twins, he finished eighth in the 2010 American League MVP voting after batting .327 and leading his team to an AL Central crown with a 94-68 record. The year before that, he was the AL MVP -- .365/.444/.587, 28 home runs, 96 RBIs -- and the Twins won the Central.
FIVE TO WATCH
MLB.com identifies and examines five players to watch in various categories this season:
Last season, Mauer appeared in just 82 games due to what doctors called bilateral leg weakness stemming from arthroscopic knee surgery in the winter of 2010. He also suffered from neck stiffness, a viral infection and an upper respiratory infection that turned into pneumonia late in the season. In all, Mauer hit .287 with three home runs and 30 RBIs, while catching in only 52 games.
Mauer wasn't the only Twins headliner to have a down year because of injuries. First baseman Justin Morneau and outfielder Denard Span, who both suffered from concussion-like symptoms, also missed plenty of action. Not surprisingly, the Twins went south last season, finishing with an American League-worst 63-99 record.
Winning baseball often starts behind the plate. Enter Mauer, who has appeared healthy this spring and is looking forward to once again being the Twins' anchor.
"He's ready to go," manager Ron Gardenhire said. "He feels good, he's had a good winter, and he wants to play baseball. That's what he's always wanted to do, and he didn't get that opportunity enough last year."
Josh Johnson, Marlins
When asked how valuable Johnson is to the Marlins, catcher John Buck made a strong comparison.
"I think he's very crucial," Buck said. "He could be the best pitcher in the league. Losing him is like the Phillies losing Halladay. Without a doubt, we need him to stay healthy and really make us contenders."
The rest of the new-look Marlins seem to agree, so it's a good thing that Johnson is back after being sidelined with a sore shoulder last May and missing the rest of the year. Johnson had established himself as one of the best starters in the game in 2010, posting a National League-best 2.30 ERA and striking out 186 batters in 183 2/3 innings, and last year he looked even better -- a 1.64 ERA and .978 WHIP -- in his nine starts before the shutdown.
The loss of those numbers might explain these numbers: After Johnson's departure, the Marlins, who were eight games above .500 and in contention in the NL East, lost 25 of their next 33 games and ultimately finished last in the division at 72-90.
With their horse back on the hill on Opening Day and beyond, the Marlins figure to begin a new season in new uniforms and a new stadium with a lot of confidence.
"I'm feeling good and hungry to pitch a full season and go to battle with the guys," Johnson said. "It's an exciting time around here."
Jose Reyes, Marlins
Johnson isn't the only vital Marlin. Miami agreed to a six-year, $106 million contract for Reyes to become the spark plug of new manager Ozzie Guillen's lineup and the captain of the defense. They even moved their hugely talented other shortstop, Hanley Ramirez, to third base to make for what they hope will be a smooth transition. That alone explains how valuable Reyes is to the team's fortunes.
Then again, so are healthy hamstrings. Reyes didn't have them for a portion of last year with the Mets, and even though he won a batting title by hitting .337 and also hit 16 triples, stole 39 bases and scored 101 runs, he only played in 126 games. He hasn't played in 150 games in a season since 2008. The Marlins need that to change.
"Jose makes everybody on this ballclub better, the way he goes about his business," Guillen said. "He's very enthusiastic. I think the Marlins were missing that in the past. I don't know how they were in the past. But Jose, his enthusiasm, his love for the game, and he enjoys the game."
Chase Utley, Phillies
Ryan Howard's blown Achilles tendon provided a difficult season-ending punctuation for the Phillies as they lost to St. Louis in the Division Series, and not having Howard around for the foreseeable future will hurt, too. But not having second baseman Utley around could hurt even more.
Utley, who until last year was a perennial MVP candidate and a key piece in the middle of the lineup, is trying to return to prominence while battling through a chronic right-knee condition. The knee issues forced him to miss the first 46 games last season, a campaign that ended with him hitting .259 with 11 home runs, 44 RBIs and a .769 on-base-plus-slugging percentage in 398 at-bats.
It's not a secret how valuable a healthy Utley would be. In his past five seasons in which he was able to compile at least 500 at-bats (2005-09), Utley hit a combined .301 and averaged 29 home runs and 101 RBIs. The Phillies are still waiting for him to get in Grapefruit League games, although he has said he feels better than he did last year.
"I think I can overcome this, without a doubt," Utley said. "I have pride in how I play and the way I play and that's not going to change."
Stephen Drew, D-backs
The D-backs were the surprise story of the NL last year. They ran away with the West after no one picked them to even contend. They eventually bowed out to Milwaukee in the Division Series, but what might have happened if one of their best players and leaders was healthy and on the diamond every night?
Arizona enters this season facing the same question. Drew hasn't played since suffering a broken ankle and ligament damage in July. That means the road to a return still might have a few bumps for the shortstop, who, when last healthy in 2010, continued to show the all-around offensive game (15 homers, 12 triples, 33 doubles, 83 runs scored) that indicated he was maturing into a bright talent.
The D-backs have capable veterans in John McDonald and Willie Bloomquist to man the position until Drew is ready to return, but Arizona is unquestionably a better team with a healthy Drew at shortstop and in the lineup. One shred of silver lining for the D-backs and their fans could be that Drew, at least, said he's on the upswing.
"Every day has gotten a little better," Drew said. "There are some days that [I] get sorer than others, but at the same time I've done a lot more than I have in the past, which is good."
Doug Miller is a reporter for MLB.com. Follow him on Twitter @DougMillerMLB and read his MLBlog, Youneverknow. This story was not subject to the approval of Major League Baseball or its clubs.