1. Compete with yourself. Time yourself on an out-and-back course—walk to your halfway point, then try to beat your time on the way back.
2. Try intervals. After a 5-minute warm up, walk two minutes at a moderate pace then walk one minute at a faster pace. Alternate moderate and fast paces for 15 to 20 minutes. Cool down by walking 5 minutes at a slow pace.
3. Head for the hills. On a 30-minute walk, incorporate 2-3 hills. Keep a steady pace up the hill, then recover on the way down.