For some people, nothing beats a long walk on a sandy beach. But there's no denying that it's not as easy or as fast to get around on the beach as it is on a road or a sidewalk. But why is it so hard to walk on sand?
The problem with sand is that it's soft; you "sink in" at each step. This forces you to use 2.1 to 2. 7 times more energy with every step you take. Another idea is that people walk more difficultly on soft than they do on hard surfaces（表面）, a study found. The researchers compared how people walked on foam (沫) and hard surfaces by analyzing the forces（力，力量） under their feet and how much oxygen each person consumed（消耗）. They found that walking on soft surfaces, such as sand, mud and snow, caused people to take longer steps — actions that use more energy than walking on a hard surface.
But as experienced beach walkers know, there's a way to make it easier to walk on sand: Just add water, When sand is wet, it becomes more compact (紧密), and walking on it is more similar to walking on hard surface. In other words, it's much easier to cross a beach by walking along the shoreline, where the waves roll in and out. This is a balance though; too much water could make the sand soft once again. If water isn't a choice, there is another way to make walking on sand easier — increasing your surface area. This could be completed by wearing shoes.
Although it's more difficult, there are some good reasons to exercise on sand. The impact forces are lower on sand than on hard surface. Research suggests that walking across sand is much easier on your joints (关节) and muscles, especially compared with an unforgiving(难以对付的）surface such as concrete (混凝土). This means sand is a better surface for helping athletes recover more quickly from workouts.
