Matzek, who will get the ball on Saturday against the D-backs, has thrown 84 innings in 15 games since the Rockies called him up in June. Combined with his 66 2/3 innings with Triple-A Colorado Springs, that's 150 innings on the 23-year-old's left arm -- more than he's ever thrown in a professional season.
Although he has never thrown that many innings since the Rockies drafted him in 2009, Matzek said he isn't feeling any adverse effects.
"Arm feels fine," Matzek said. "I had a good offseason this past offseason and built my body up to feel strong, so I'm feeling pretty good right now."
Matzek has had a rocky first season with Colorado. He's 3-9 with a 5.14 ERA, and his 4.35 FIP (fielding independent pitching) would tie him for 17th worst in the Majors if he ranked among qualified pitchers.
But his numbers naturally come with the caveats that he's a rookie pitching his first Major League season in the most hitter-friendly ballpark in the Majors, which he will likely continue to do through the end of the season without restriction.
"They haven't brought anything up to me because I feel fine, [velocity] feels fine, arm feels great," Matzek said. "So I don't think there's an issue right now."
Adam Lichtenstein is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.