Looking at the wear and tear on the Cubs' bullpen -- and closer Carlos Marmol in particular -- it's pretty easy to see how you can end up with Marmol yielding Tuesday nights' walk-off grand slam by Houston's Brian Bogusevic.

Only one Cubs starter threw more than 5 2/3 innings in a week before Ryan Dempster's seven on Tuesday night.

Marmol has pitched in six games in the last eight days, saving four and blowing one. That type of workload leads to a once dominant pitcher throwing 90 mph instead of 94 mph and having no bite at all on his once unhittable slider.

Marmol's eight blown saves out of 36 opportunities are way off his normal save percentage. In 2010, Marmol saved 38 games and blew only five opportunities. In 2009 -- when he was partially a set-up man and partially a closer -- Marmol had 27 holds and 15 saves in 19 opportunities.

The closer's ERA of 4.08 and WHIP of 1.45 are career lowpoints.

"Marmol is so mechanically unorthodox and so tough to keep in line [mechanically], whether it's his arm angle or the drive off the mound or everything that makes him good, mechanically it's difficult," manager Mike Quade said. "He's had a wonderful run here, and I think this is the first piece of adversity he's had in his career."

The Cubs' bullpen has logged 392 innings, the most in the National League.

"We've been able to get things done out there, but my only concern is I've been riding the bullpen pretty hard," Quade said. "They have answered the bell and they've been fantastic, but as we get through August and September, everybody wears down a bit. You have to try to be as careful as you can, and hope they continue to pitch as well as they have without going to them too often."

Quade has had to use the bullpen too much because the rotation has been ineffective. The only solution for Quade is a rotation of minor league relievers who will give some of his bullpen arms relief at this late stage of the season.

That philosophy may change if Quade's starters start being more consistent.

"They're conditioned pretty well," Quade said of his relievers. "But what has taken place in the industry of baseball is to have a guy available three straight days ... and not just be available, but to pitch well, is what most clubs look for if they're going to be successful."