It's brutal, but that's why you love it. The bear crawl utilizes all of your musculature. "It ties in your lower trunk to your upper body. That's essentially what standup is," Kalama says.
In soft sand, get down on your hands and feet so that your core is thoroughly engaged. Choose a point 50 yards in front of you, and crawl toward it as quickly as possible. When you reach your target, stand up, and take a 15-second rest. Then get down and complete another rep, crawling back the other direction. If you're fit, you might be able to finish 10 in a row without extending your rest time.