Like circuit training, sand training keeps a workout interesting and builds core strength. No sand dunes handy? Any beach or sandy riverbank will do. Use it once a week as a diversion from your usual cardio workouts. Start by sprinting through each exercise at 20 to 30 second intervals. Rest for 60 seconds before moving to the next. Start the regimen by repeating the circuit for 20 minutes, working up to 40 minutes max.
1) Crab Walk
Squat slightly, then shuffle sideways up a hill and back down again with your torso as near to a 90-degree angle from the slope as you can manage. If your glutes and abs burn, you're doing it properly.
2) Resistance Sprints
Backpedal up a hill, pulling a partner with a short rope in a tug-of-war (he should be offering some resistance). On the way back down, you should be facing downhill, still engaged in a tug-of-war with your partner. Next, push your partner up the hill with your hands on the back of his waist. Switch roles with your partner and repeat.
3) Reflex Training
Sprint up a 30-to-50-foot hill (the steeper the better), or run for 100 feet on a flat beach, drop for 10 push-ups, then sprint back down and drop for 10 more. Repeat until your arms reach muscle failure.