"I've been doing all my things and my work and have been working out," Zambrano said. "I'm trying to throw as hard as I can, and you see the gun -- 91, 88 [mph]. Everybody goes through these, and I just have to wait for my arm strength and my arm power to come back, so I can do a good job for my team."
Zambrano is 1-1 with a 7.43 ERA in five August starts, and 13-5 with a 3.53 ERA overall. He'll have one more start this month, on Sunday in the series finale against the Phillies. In his last outing Tuesday against the Pirates, he lasted 4 1/3 innings and gave up six runs on eight hits. He threw 98 pitches, which is his average this month, and did not get a decision.
Since that game, Zambrano has lightened up his workload. Instead of throwing a bullpen session, Cubs pitching coach Larry Rothschild had the right-hander play catch. That way, Zambrano can stretch out his arm and strengthen it.
"I think this is the time, when you have close to 180 innings, you have to save your bullets, you have to do whatever it takes to rest your arm," said Zambrano, who has totaled 168 1/3 innings in his 26 starts. "I didn't throw side sessions [Friday] or the day before, I just played long catch and I think it worked for me."
"He's pitched a lot of innings in the last six, seven years," Rothschild said. "You can compare him with a lot of people, but I don't know anyone who has logged the pitches and innings that he has.
"Hopefully, it's just something he's going through and he rebounds and it becomes a dead issue. He's a big, strong guy and he expects a lot out of himself, and it all feeds into it."
The good news is that there is no pain. Zambrano was on the disabled list in June because of soreness in his right shoulder, but this is different.
"I don't feel any pain in my arm at all," Zambrano said. "If I felt pain, I'd tell them. I don't want to pitch through pain, like I did in Tampa Bay [on June 16]. They knew it, I knew it. I said [at that time] I can't throw like this and I needed a little rest, and everything worked better. It's just a dead arm now."
Cubs manager Lou Piniella said one option is to give Zambrano and the other starters another day of rest between starts. Once rosters expand Monday, the Cubs will have extra pitchers available to do that. Among the arms available are Jon Lieber and Angel Guzman, who will both be activated from the disabled list at that time.
"We'll sit down and talk about this," Piniella said. "I might even throw [Sean] Marshall in the rotation for a day so [Zambrano] can get a little more rest."
Zambrano had a similar problem last August, and he went 0-4 with a 7.06 ERA in five starts. He rebounded to finish 4-2 with a 3.44 ERA in six September games.
"This happens to a lot of pitchers, especially when you're a power pitcher," Zambrano said. "The most important thing and the thing to learn here is to know how to pitch with this. This is a new experience for me. Two years in a row, it's happened to me. Next year, if it happens, I will try to pitch with it and make an adjustment and just get through."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.