In sand, the legs struggle for propulsion while the upper body fights a constant battle to maintain equilibrium on the unstable terrain. This mimics late-race fatigue. And the forced communion between the upper and lower body (rare in running training) develops strong hip flexors, calves and quadriceps, and also ingrains the ability to use the arms and torso to maintain form when you're exhausted.
Craig Hummer knows about sand running. The California lifeguard is former champ of the Waikiki King's Race, a surf-rescue competition that begins with a 2-mile soft-sand run, followed by 3 miles of kayaking, a mile of swimming and, finally, a mile on the paddleboard. Training primarily on soft sand, Hummer posted a 32:10 personal best for 10K in 1993.
Hummer has two favorite workouts, both run entirely on sand.
One is a 40- to 60-minute endurance run at around 80 percent of max. "I do this just once a week. It serves as my prime endurance-builder," he says.
The other is more involved.
"Start with a 15- or 20-minute warmup," he said. "Then run 45 seconds at 5K race pace followed by 15 seconds easy. Then do 30 seconds at quick stride pace followed by 15 seconds easy. Finally, go 15 seconds at a sprint. Rest for 2 minutes, then go again."
Hummer recommends aiming for four to six sets the first few times you do the workout but says you don't really need to do more than eight. And always cool down for around 20 minutes.
"The workout may not sound like much," he laughs knowingly, "until you get to your third or fourth set."
Hummer also says to beware of tender feet. If yours get sore easily on sand, wear running shoes.