Jon Lester latest Red Sox casualty

BOSTON -- If we have learned anything from listening to Red Sox pitchers discuss their injuries this season, it's that they almost all tend to offer sunny forecasts that fail to hold up. In the end, inevitably, there are storm clouds.

Bobby Jenks has a little biceps strain in May that turns into an absence of 27 games. Back tightness in June that Jenks expects to last a couple of days becomes another DL stint that costs 17 games.

Daisuke Matsuzaka hurts his elbow and rules out surgery; next thing you know, he's undergoing a season-ending Tommy John procedure.

Clay Buchholz feels a little muscle issue in his lower back that he figures might cost him a few days; instead it turns into a DL stint that is now into its third week and has him flying to North Carolina on Wednesday morning for a second opinion.

John Lackey has an elbow strain he deems not serious, misses 21 games and, a few weeks later, is back to being kicked around the yard but insisting the elbow is not an issue.

Even Josh Beckett, who didn't go on the DL with what he called the stomach flu, went 13 days between starts last month, a longer stretch than you might expect for what Terry Francona calls "intestinal distress."

And now comes Jon Lester, who walked off the mound at Fenway Park on Tuesday night with a no-hitter after four innings and didn't come back, the Red Sox announcing a couple of innings later that the left-hander had a strained lat muscle.

That's shorthand for the latissimus dorsi, the largest muscle in the back and directly under the shoulder, one that plays a vital role in a pitcher's ability to hurtle a baseball through space.

Not to worry, Lester says. Not a long-term issue, he insists. DL? Not him, he declares. With the All-Star break coming up, maybe the Red Sox will have to "alter" one of his starts, he asserts, but beyond that, he can't see missing any time.

"It's not something I'm worried about long term,'' he said. "It should be fine for the rest of the season."

But let's for a moment consider a short list of pitchers who have had lat issues in recent years. We could start with Jake Peavy of the White Sox, but that would be unduly alarmist; Peavy actually tore the muscle from the bone last July, knocking him out for the rest of the season and raising questions of whether he'd ever be the same. Peavy has come back this season, but it has been a struggle.

At the other end of the spectrum? Well, maybe Sox reliever Matt Albers, who strained his lat muscle April 5, went on the DL and was back in the minimum 15 days.

But check out this sampling of pitchers with the same injury, the only difference a variation in degree (and the number of games they missed):

Francona said Lester will undergo extensive evaluation Wednesday, which almost certainly will include an MRI, although Francona said he could offer no details. This is not an injury to be trifled with, not when the lat muscle plays such an important role in what a pitcher does.

There was an article last year on BaseballProspectus.com that broke down the mechanics of a pitcher's delivery into several stages. One such stage, the authors called the "arm-cocking phase.'' Here's how they defined it:

"The arm-cocking phase is where the body gathers up all of the potential energy stored during the windup and stride phases and prepares to transform it into to kinetic energy. The hips and trunk twist to face the plate, and the arm cocks back to the point of maximal external rotation, at which point the pitcher transitions into the acceleration phase.''

This, they say, is where the lat is one of a group of muscles placed under "maximal eccentric stress.''

"They are stretched to the maximum,'' the article states, "before forcefully contracting to accelerate the ball. We have seen an increase in diagnosed latissimus dorsi strains over the last several years, likely due to improved accuracy of diagnosis. The latissimus dorsi is at risk for strains beginning at this point.''

Lester said Tuesday night the muscle was sore. He felt it in the fourth inning; he felt it after the game. He expects the soreness to go away, sooner than later.

It might not be quite that simple. It was around the same time last season that the Red Sox had a run of injuries that threw the brakes on what looked like a certain trip to October. The injuries came in multiples: Dustin Pedroia, Buchholz, Victor Martinez, Jason Varitek, Kevin Youkilis, Jacoby Ellsbury, Mike Cameron. Pedroia, Ellsbury and Youkilis were all lost for the season.

Every team must deal with injuries, but if Lester is out for any length of time -- and a club source told ESPN Boston's Joe McDonald that a lat strain typically sidelines a player from two weeks to a month -- the depth of the Sox rotation will be stretched to the limit.

Matsuzaka is already history, Lackey seems to be hanging by a thread, Buchholz is searching for answers, Tim Wakefield turns 45 in August and now Lester? GM Theo Epstein has other arms at the ready -- Andrew Miller, Alfredo Aceves, Felix Doubront, Kyle Weiland, Kevin Millwood -- but the drop-off is potentially drastic.

The weather forecast for Wednesday is plenty of sunshine. Lester and the Sox can only hope the same applies to them.

Gordon Edes covers the Red Sox for ESPNBoston.com.