WEEK 3
Number of walks this week: 4 Time per workout: 30 minutes: Mix up your routine with agility and balance exercises this week. After a 10-minute warm-up, perform one of the agility moves for about 30 seconds, followed by 90 seconds of walking. Do about five of these two-minute drills (if you’re feeling up to it, add a few more). Finish your workout with a 10-minute brisk walk, gradually slowing to a cooldown at the end.
WEEK 4
Number of walks this week: 4 (2 with strengthening moves) Time per workout: 25 to 40 minutes: Sculpt your arms, back and shoulders with a resistance band this week. Add our four strengthening moves to two 30-minute walks this week, either in the middle or at the end. (Avoid doing these workouts consecutively—take at least one day off in between.) For the other two walks, choose a routine from the previous three weeks (focusing on distance, speed or agility).
Source: http://www.allyou.com/diet-fitness/walking-plans/walking-workout