Monday, Joe Mauer visited a medical specialist in Baltimore about his sore, weakened legs.

Tuesday, Mauer turned 28.

This juxtaposition -- reminders that Mauer is entering his athletic prime while confronting octogenarian ailments -- marks the latest and most important milepost in his inevitable transition to becoming a part-time or former catcher.

While many of Mauer's critics have questioned his toughness, what we are dealing with here is simple physics. He is a 6-5, 235-pound man who squats for a living. At some point in his career, squatting was bound to rob him of his ability to stay in the daily lineup and hit like a future Hall of Famer.

Questioning Mauer's desire is silly. He is known to spend up to 12 hours a day working on his leg strength, flexibility and conditioning. He has averaged 607 plate appearances over the past three years, a high number for a catcher, and he has often played while in discomfort.

The more legitimate question is whether he possesses the body type and durability to survive the rigors of his position while remaining an elite hitter. His latest ailment -- bilateral leg weakness -- provides more evidence that he will not be able to remain an everyday catcher for much longer.

Many have cast the Mauer debate thusly: He is worth $23 million only if he serves as an offensive force at a position featuring few dynamic hitters.

There are two flaws with this argument.

First, Mauer is not worth $23 million a year. Perhaps no one in the game is, in terms of sheer on-the-field production. Mauer is not being paid his objective worth as a ballplayer; he is being paid the sum of money the Twins were required to pay to retain him at a juncture in franchise history when they believed they could not afford to let him leave -- when he was coming off his MVP season and entering his prime as the local hero for a franchise entering a new ballpark.

Mauer receives about $15 million a year to play baseball, and about $8 million a year to serve as a marketing tool/public relations boon/ticket seller/symbol. A couple of years of maximum season-ticket sales and virtual sellouts make his cost reasonable, if he can stay on the field.

Second, we are witnessing an increasing number of signs that playing catcher damages Mauer's productivity. He struggled during the first half of 2010 while his legs bothered him. He underwent knee surgery in December, missing most of spring training and began poorly this season before being placed on the disabled list with his current, ominous-sounding condition.

Mauer has produced home-run power in only one big-league season -- 2009, when he missed spring training and all of April, leaving his legs fresh enough for him to be able to drive the ball.

So the proper casting of the Mauer debate is now this: Would you rather have Mauer serving as a pretty-good-hitting catcher who needs plenty of days off and occasional trips to the disabled list, or a great-hitting corner position player who plays 160 games a year?

I'll take the latter.

For the remainder of this season, the Twins will have to coax as many games at catcher as possible out of Mauer. Their current roster requires him to serve time behind the plate.

That could change as soon as this winter. Michael Cuddyer, Jason Kubel and Jim Thome all could be gone, opening right field and DH for Mauer. He could catch 80 games, which would continue to put his legs at risk, or he could catch none, and perhaps catching none would be best for him and the team.

Relieved of the physical stress and defensive concentration required of catchers, Mauer could become a latter-day Rod Carew, or he might prove to be even better.

The Twins could rotate Delmon Young, Denard Span, Ben Revere and Mauer in the outfield and at DH, and when Joe Benson is ready, they would be able to trade an outfielder for pitching or middle infield help.

With that plan, the Twins would be able to field their best lineup almost every day of the season, and Mauer could enjoy a long, productive career that might make even the great Rodney Carew envious.

Jim Souhan can be heard Sundays from 10 a.m. to noon and weekdays at 2:40 p.m. on 1500ESPN. His Twitter name is Souhanstrib. •