So why has he been out there nearly every day since August, piling up the miles? Why does he keep going when his 37-year-old body is telling him it's about time to stop?
"Ultimately, you're making yourself better, and you're doing it for a good cause," he said.
Ensberg, a former All-Star third baseman for the Astros, has been training since August to run the Houston Marathon, scheduled for Jan. 13. He's going to run with his wife, Christi, and the couple's close friends, Adam and Jennifer Everett. Everett played shortstop for the Astros from 2001-07.
Ensberg plans to run in the marathon, while his wife and the Everetts are opting for the half marathon. It's all being done in the name of charity. They're raising money for Living Water International, a Christian-based organization which helps impoverished communities in Africa create sustainable water, sanitation and hygiene.
Donations for the Ensberg-Everett team can be made through the marathon's website.
"Kevin Edelbrock, the chaplain of the Astros, approached us about it," Ensberg said. "It's a great cause."
Ensberg, who lives in Southern California, ran the 2010 New York City Marathon, willing himself to the finish line after wanting to quit about seven miles into the race. He admits he didn't train properly, but that won't be the case this time. Ensberg's regimen will put him in position to run four minutes and walk for one minute until he reaches the finish line in downtown Houston.
In his training, he runs five days a week, with a speed day, a short-distance run and a long-distance run on Saturdays. He ran 17 miles earlier this month.
"You have to understand, I am by no means a long-distance runner," he said. "It's a really slow pace, but it's forward progress, and that's what I'm about. I will not be challenging anybody for any world records, but it will be slow and steady. It's fun to do and something that's challenging."
Everett, who lives in Georgia, has been following the lead of his wife, who has run a half marathon before.
"Jennifer's got the training program she goes by, and I'm sort of piggybacking off that," he said. "I run two miles, two to three times a week, and a then a long run toward the [end of the] week. I'm not quite running as long as she is."
Ensberg played eight years in the Major Leagues, including seven with the Astros. He had a breakout season in 2005, helping the Astros reach the World Series by hitting .283 with 36 homers and 101 RBIs and finishing fourth in Most Valuable Player voting. He retired following the 2008 season, but he still thrives on athletic competition.
"I think, for me, this is much harder than baseball because it's not a strength," he said. "With baseball, at least you know you're going to feel comfortable playing the game. I don't necessarily feel comfortable in a long-distance running situation, even if I practice a lot.
"In baseball, I have more confidence. In running, I enjoy the mental challenge. It's very difficult to continue to push when every part of your body is saying stop. They're both extremely difficult games for me because baseball is a difficult game and running is difficult for me to continue to push."
Everett, who spent seven of his 11-year career with Houston, admits he's not a fan of running either, but it's worth it to raise money for charity. This will be his first half marathon.
"Ultimately, you're making yourself better, and you have to look at it this way and you're doing it for a good cause and getting the most out of everybody, making your body healthy," he said.
Running in the Houston Marathon will also give Ensberg a chance to return to Houston, a city which he grew very fond of during his playing days.
"I don't know what it is, but I just love the people of Houston," Ensberg said. "The area is great, but it's the people of Houston. I've always been a guy that understands that Texans are very proud, and the fact they would accept a guy from California, it meant something to me.
"I know there's a line in the sand; if you're from outside of Texas, it's not a good feeling. You feel like you're being judged in a sense, but the fans and the people took me in and treated me great, and I felt like I was one of their own. I like being back in Houston."