"It was a normal bullpen session for him," McCracken said. "He has a home here and resides here and is in transit to Corpus, and we wanted to get him out so he could get his bullpen in."
Appel is scheduled to make his first start for the Hooks on Wednesday. McCracken said the hurler would be in the modified tandem rotation -- two starters in one game -- being used at Corpus Christi, pitching at the front end of the piggyback and occasionally on his own day.
The struggles of Appel, who was taken with the No. 1 overall pick out of Stanford in 2013, have been well-documented. He didn't take to the tandem pitching configuration at Lancaster and wound up spending a month at extended Spring Training, battling some nagging injuries along the way.
He went 2-5 with a 9.74 ERA in 12 starts for the JetHawks, but posted his first quality start Thursday by allowing five hits and two runs and striking out seven batters in six innings. The Astros' goal for Appel was to have him pitch a bulk of the year at Corpus Christi, but that was before his missed Spring Training following an appendectomy.
"The early struggles, having to go back to Florida and going back to Lancaster and having some rough outings, that delayed the timeline," Astros general manager Jeff Luhnow said. "We were very encouraged by what we saw the last outing. The pitches were where they need to be in terms of effectiveness, and he was able to go out there and dominate for that start, and we figured it was a good opportunity to get him up to Corpus -- where we intended him to be all long -- and let him continue his development there."
More than anything, the move to Corpus gets Appel away from the hitter-friendly environment of the California League, especially in Lancaster, where the wind blows out regularly. He'll also get a chance to work with senior pitching adviser Doug Brocail, who's in Corpus Christi.
Luhnow said in at least two of Appel's starts, there were 20-mph winds blowing out, but he maintains the stuff is there. The prospect's average fastball velocity in his last start was 95 mph, and he touched 97. His final two pitches of the game were 96 mph.
"The arm strength is there," Luhnow said. "It fluctuated a little bit last year, but we haven't been concerned about arm strength. His secondary pitches, his slider and change, at times have been working and at times haven't, and they were both working the other night."
McCracken said he wasn't concerned Appel's promotion would have a negative effect on other pitchers who had pitched well at Lancaster, such as left-hander Josh Hader.
Hader, acquired in the Bud Norris trade with the Orioles a year ago, is 9-1 with a 2.46 ERA in 20 games. He's allowed only 69 hits and struck out 105 batters in 95 innings. McCracken said Hader could find himself in Double-A soon.
"All those guys are going to get their opportunity as long as they perform well," McCracken said. "They can't get caught up in the peripheral stuff, as they say. Those guys have been spoken to, they know they're going to get their opportunity. We have a plethora of pitching arms in our Minor League system. It's well-noted. You can't promote them all. You've got to do it in a systematic, pragmatic way, and that's what we're doing. Mark is one of our priority guys, and he's throwing the ball extremely well, and we're going to ride the momentum with him and hopefully get him here to Houston in upcoming future."