How do our muscles produce extension and flexion? This is especially interesting when you realize that muscles can only pull, they cannot push. Understanding that muscles come in pairs is a key concept when understanding a muscular system. 
 
Questions Answered:
How do muscles produce extension and flexion? 
Why do muscles come in pairs?
 
Topics Addressed:
Muscles can only pull, they cannot push 
Muscles come in pairs 
Tendons connect muscles to bones 
Ligaments connect bones to bones 
Contracting muscles may either flex or extend limbs
 
Materials Needed
2 rulers with holes, string, brad (paper fastener), paperclips
 
Preparation Time
none
 
Teaching Time 
About 20–30 minutes, longer with included writing assignment
 
Answer Key
Yes! Plus extensive teacher notes address the many questions that come up. You shouldn’t have to do outside research on this topic unless you want to. Specific charts and graphic organizers have keys. 
 
Target Audience
Middle School Students, Ages 11-14
 
Student Sheets
Scaffolded writing prompts & lab reporting 
Diagrams for labeling