Interval training is the best way to increase speed—and burn more body fat! Alternate bursts of speed with slower walking, gradually lengthening the duration of speed and shortening the duration of slower walking. Pay attention to your breathing. During a burst of speed, you should have difficulty saying more than a few words. When you slow down, you should recover your ability to speak in sentences, but not slow to a crawl or stop!
Find the balance that allows you to recover from your hard effort without having to stop completely to catch your breath. For example, warm up, walk fast for 30 seconds, cut back for 2 minutes, repeat as many times as you can, then cool down to an even, sustainable pace.
Gradually, over a workout or over several workouts, increase your fast walk to 1 minute and decrease your slower walk to 30 seconds. Over time, you learn to walk at a faster pace, which short or no recovery periods. Once you feel comfortable at a new speed, you can interval train again to get faster. Getting beyond 12-minute miles, (5 miles an hour) may mean learning specialized fitness walking techniques to break through to a faster time.