Get excited, because anything goes during a fartlek workout—the name itself means “speed play” in Swedish. It’s a relaxed, slow run with faster sections (of whatever distance and pace you want) mixed in. In fact, not lowering the pace enough for the easy parts can be a problem, if you’re not letting your legs get ready to run fast again. Between fartlek intervals, Schorr suggests dropping the speed enough so you can breathe deeply and get fully rested before bringing it up again. And McGee says to simply spend the time thinking about “recovering for the next section, what your effort or pace is going to be, keeping an ease of motion—and how kick-ass you are.”
Ready to run faster or longer? Go for a tempo run: It includes at least 15 to 20 minutes at lactate-threshold pace (about 30 seconds slower than your 5K pace), with an easy jog before and after. With the focus on the harder middle section of the run, you might want to cut the warm-up or cool down short. Doing that, though, is a recipe for muscle strains or tendonitis, as you’re less limber and your joints and tendons aren’t lubricated. McGee advises “priming” during the warm-up: After some slow jogging, do a few strides, then build up to target tempo pace for about 5 minutes. The cool-down is less important, but make sure to jog slowly for at least 10 minutes to allow blood to circulate back to the heart and reduce soreness later. Just be sure not too cool down for too long and overdo it—relax, you’ve already finished the hard part!