What Are Muscles

About this printable What Are Muscles science reading passage, NGSS-aligned (Grades 3-5)

This engaging 250-word reading passage introduces fourth-grade students to the essential concept of muscles and how they create body movement. Aligned with NGSS 4-LS1-1 and the Disciplinary Core Idea LS1.A, the passage explains that muscles are body parts attached to bones that work by contracting (getting shorter) and relaxing (getting longer) to pull bones and create movement. Students learn that the human body contains hundreds of muscles and can explore this concept by feeling their own bicep muscle while bending their arm. The passage uses simple, grade-appropriate language and includes bolded key vocabulary terms with immediate definitions. A relatable hands-on example helps students connect the science concept to their own bodies. The passage includes audio integration to support diverse learners and is accompanied by a simplified differentiated version for students reading below grade level. Both English and Spanish translations are provided. Supporting activities include multiple-choice comprehension questions, writing prompts, and graphic organizers that reinforce understanding of muscle structure and function. This foundational lesson prepares students for deeper exploration of body systems and how structures support specific functions in living organisms.

Written by Workybooks TeamPublished by Workybooks

Sample passage and quiz from What Are Muscles

Muscles are body parts that make your body move. A muscle is a special type of tissue that can pull on bones to create movement. Without muscles, you would not be able to walk, run, jump, or even smile.

Muscles work by changing their length. When a muscle contracts, it gets shorter and tighter, like when you squeeze a sponge. Contracting means becoming smaller or tighter. This pulling action moves the bone that the muscle is attached to. When a muscle relaxes, it gets longer and looser again. Relaxing means returning to a resting state. Muscles can only pull—they cannot push—so they often work in pairs to move bones in different directions.

Your body has hundreds of muscles working together. Bones are the hard structures inside your body that give it shape and support. Muscles are attached to bones, which means they are connected firmly to them. When muscles contract, they pull on the bones they are attached to, causing your body parts to move. Think of muscles like rubber bands connected to sticks. When the rubber band gets shorter, it pulls the stick and makes it move.

You can feel muscles working in your own body. Bend your arm and touch the front part of your upper arm. The bump you feel is your bicep muscle contracting. The bicep is a muscle in your upper arm that helps you bend your elbow. When you straighten your arm, your bicep relaxes and gets longer again.

Interesting Fact: The strongest muscle in your body, based on the force it can produce, is the masseter muscle in your jaw. It helps you chew your food and can produce over 200 pounds of force!