Doggie farlek

I began my most recent run with a "doggie fartlek." (Fartlek means "speed play" in Swedish, and refers to periods of higher intensity broken up by slower recovery, though I assume you know that) I usually run with two dogs. Molly, the labrador, runs off-leash and the doggie farlek involves letting her run ahead and running faster after her until she stops to sniff something/chase a butterfly/etc. then I jog slowly until she tears past me again. This doesn't last too long, though, because she tires herself out and then just runs next to me. I don't know what kind of mileage I'm doing these days, but I'm doing runs that are about 45 minutes long or so. I'm definately not pushing the pace, though. Running is starting to feel "normal" again and I'm itching to enter a race. I've looked though, and races are definately fewer and farther between in this area than they were in Virginia.