Snubbing a friend is never easy. But it's particularly hard when you have a lame excuse, as I did when I turned down my buddy Thayer's invitation to grab drinks after a long workweek. The reason, I sheepishly explained: I was too tired to go out.

Well, Thayer, I lied. The truth is, there was an e-mail in my inbox calling for an easy six-mile run, and ignoring it was harder than dissing my wingman. Never mind that it was 10 p.m. on a perfectly sociable, drizzly Friday night. I needed to run. I nixed the drinks, pounded out a lonely 50 minutes on Santa Fe's dark back roads, and hit the sack.

Call it the Randy Effect. Randy Ashley, an elite trainer with North Carolina–based ZAP Fitness, is my virtual coach. Each week he sends me a personalized slate of training runs, prepping me for 5K races this fall (long, slow miles are just part of the targeted routine he devised). With just a few brief keystrokes, this coach I never see motivates me to run more consistently, with more discipline, than ever before. It's like having a personal trainer who's always watching over my shoulder—from 1,300 miles away. It makes for a poor social life but a really fast time.