Final answer:
Physical activity is any bodily movement produced by skeletal muscles that results in energy expenditure. Skeletal muscles are essential for movements, maintaining posture, and thermal homeostasis through the generation of heat. They contract in two main types: isotonic, leading to movement, and isometric, creating tension without movement.
Step-by-step explanation:
Any bodily movement produced by skeletal muscles that results in an expenditure of energy is known as physical activity. Skeletal muscles are responsible for a vast array of movements and functions within the human body, and they contribute significantly to overall health. Engaging skeletal muscles leads to movements such as walking, running, lifting, and even maintaining posture. The system name for these muscles is often derived from their shape, location, or attachments to the skeleton.
Skeletal muscle tissue is structured in bundles surrounded by connective tissue, and these muscles work by contracting and causing movement at joints. When muscles contract, they not only enable motion but also produce heat, contributing to thermal homeostasis. This is especially noticeable during exercise, where sustained muscle movement raises body temperature, or in situations like shivering, where involuntary muscle contractions generate heat in response to cold. There are two main types of muscle contractions - isotonic and isometric. Isotonic contractions occur when a muscle contraction results in movement, such as when you lift an object. Isometric contractions happen when muscle tension is generated without movement, such as trying to push against an immovable object.