Final answer:
Sal is using his skeletal muscles, specifically slow-twitch muscle fibers, during his slow-paced walk. These fibers are designed for endurance activities. The body has three muscle types: skeletal, cardiac, and smooth, each with different roles and properties.
Step-by-step explanation:
When Sal goes for a slow walk after eating breakfast, he is primarily using his skeletal muscles. In particular, a type of skeletal muscle cell called a slow-twitch muscle fiber is being used during his slow-paced walking. These fibers are well-suited for aerobic activities such as walking, jogging, and long-distance running because they are designed for endurance and can sustain activity for extended periods without fatigue. On the other hand, fast-twitch fibers are more useful for short bursts of strength or speed, such as sprinting or lifting weights.
The human body contains three types of muscle tissue: skeletal muscle, which facilitates voluntary movements like walking; cardiac muscle, which is found only in the heart and is responsible for pumping blood throughout the body; and smooth muscle, which controls involuntary actions in various organ systems, such as digestion and blood vessel regulation. While skeletal muscles can become stronger or atrophy ('use it or lose it'), smooth muscles do not atrophy in the same way because they are continuously active without conscious effort, maintaining essential bodily functions.