And what he's already accomplished isn't bad. Despite dealing with a hiatal hernia that affected his eating and thus weakened him, Rasmus hit .251 with a .307 on-base percentage and a .407 slugging percentage, the vast majority of it before his 23rd birthday. He hit 16 home runs and scored 72 runs in 520 plate appearances.
"I think Colby was, overall, remarkable," manager Tony La Russa said. "He did have the expectations of the No. 1 prospect. And he had a manager and coaching staff that were not giving him a spot on the club. He had to live up to the expectations of fans. The organization has hyped him. He had to earn the job on a club that had a chance to win. And then throughout the season, against pitchers he had never seen before and in situations he hadn't seen before in the Major Leagues, he had a very solid season."
Now the task is to build on that, to have a bigger 2010 than '09. To do that, though, Rasmus isn't getting bigger. Quite the opposite.
Rasmus came to Spring Training in 2009 after a winter of hitting the weights. In theory, it seemed the strength might add some extra power to his well-rounded game. In practice, he felt it didn't do him any good. Moreover, Rasmus dealt with illness and injury and saw his numbers diminish in the second half.
That led him to take a different approach to preparing for the 2010 season. He's focusing more on endurance, going through workouts that he hopes will help him stay effective for six or seven months.
"Last year going in I tried to focus more on putting on a lot of weight and getting bulked up," he said. "This year I'm doing more conditioning, running, sleds, hills, that type of thing. Just to try to see if that will change up a little bit and be able to last a little longer instead of being big and looking for more power. Just be able to keep my body more maintained."
If Rasmus can simply take his first-half numbers from 2009 and expand them over a full season, it will make for a very nice year. He was batting .278 with a .329 OBP and slugging .478 at the All-Star break. If he can improve on that, he'll be a significant force in the Redbirds' lineup.
And they can use it, with the departure of Mark DeRosa as well as a notable dearth of left-handed power in the current lineup. The club will be counting on Rasmus more this season. He feels that his year of experience should help him live up to those expectations.
"I feel a lot more relaxed," he said. "I kind of know what to expect going in. Just going in trying to make the team and not thinking about August and September, those late months of the season."
But first, as he said, he has to make the club. It's hard to imagine Rasmus not breaking camp with the Major League team, but La Russa remains emphatic that the youngster not take anything for granted. So while Rasmus has the benefit of a year's experience, he knows he can't get complacent.
"He will go under the same kind of scrutiny in spring 2010," La Russa said. "Why? Because it's a brand new season and you want to make sure. ... You don't walk in there and feel you've got some entitlement going and there's a carryover and you can work less."
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.