These are short pickups of no more than 20 seconds that you can easily incorporate into your training program. Short sprints can help you balance strength and flexibility and improve leg coordination.
Even if most of your training is slow, easy distance particularly during your base-training phase you should include aerobic intervals to avoid loss of biomechanical efficiency.
Do short sprints with a fast but easy effort. Think legs, not lungs. The idea is to use as big a range of motion and as rapid a turnover as possible, but for a short enough distance so that you never huff and puff.
Twenty seconds seems the perfect amount of time. Research suggests that lactic acid buildup in the muscles is insignificant for up to 20 seconds of fast running, but almost quadruples between 20 and 30 seconds. That causes eccentric contractions to begin and forces your muscles to extend while still tight. When this happens, you'll tie up.
You can do this workout at the track sprint the straightaways and jog the turns. Or you can do fartlek on the road, running hard for 20 seconds then jogging for 40 seconds.
You can even throw speed bursts into the middle of your long runs. About two-thirds through your run, start doing 15- to 20-second pickups. Cover 1 or 1 1/2 miles this way. But keep the effort easy. Don't force yourself or you'll defeat the purpose of the workout.