A cat's stride length can be three times its body length when running. The flexible spine, strong muscles, and retractable or extensible claws that offer grip like runner's spikes all contribute to a cat's peak speed of 30 miles per hour. They use their agility and ability to change direction quickly to avoid danger at every step. Cats have two types of muscles: fast-twitch muscles that contract rapidly and produce high force levels, and slow-twitch muscles that contract more slowly but yield greater endurance capacity. This is similar to the difference between sprinting and long-distance running. Cats that need to cover a lot of ground in order to find food and shelter tend to have more fast-twitch muscle fibers, while those that need to stay alert for predators have more slow-twitch muscle fibers. All cats possess very acute senses including smell, hearing, and sight. This allows them to learn how to handle themselves in different environments by avoiding dangers that could kill or injure them. For example, a cat that lives in an apartment building will usually keep out of the way of moving furniture because it knows this means someone is about to put it through a wall or into a tree. Cats are generally lazy creatures that want nothing more than to sleep all day and eat all night. Still, they make excellent athletes because they are determined to live their lives to the fullest.