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Activity 3A: Levers in the Body: They Are Not What You Might Think!



Topic: Levers in the Human Body
Part of:
Unit: Discrepant Design

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Pre/Post Test


Pre/Post Test Answer Sheet & Key




lever, system, muscle, bone, joint, flexion, extension, contract, scapula, humerus, radius, ulna, forearm, scale, elbow, bicep, tricep, percentage, fulcrum, effort, resistance


Search Curricular Keywords


Key Concepts


Levers in the human body, opposable muscle pairs, flexion & extension, using caution in the application of mechanics to human movement


Process Skills Utilized


Observing, inferring, measuring, and graphing


Intended Grade Level - 6-8



Using a model of the human arm, students will be able to:

  • Investigate lever systems in the human body
  • Observe how muscles and bones work together to move joints
  • Compare arm anatomy to model
  • Explain that muscles must pull against the weight of various
    body segments (resistance)
  • Distinguish between joint flexion and extension
  • Observe that muscles can work only by pulling (contracting)
  • Graph and analyze results

Activity Description

Students will be surprised to learn that the levers in their arm don’t behave as expected! They will use a model of the human arm, including an artistically modified scapula, humerus, radius and ulna. After measuring the weight of the forearm on their model with a spring scale, they will assemble the bones so that the elbow joint is movable. Once students have assembled the model, they will attach string “biceps and triceps muscles” to the model at origin points labeled on the model. An approximation of the actual insertion point will be labeled on the model and the other end of the string “muscle” attached to that location. The student will then investigate how the biceps muscle operates the joint as a lever system, exploring angles and the resistance and effort forces. Next, students will move the insertion point of the string muscle to examine how the lever system changes. Both the triceps and biceps will be studied in this part of the activity. Finally, using body segment weight percentages, students will relate their findings to their own bodies.


Activity Materials (per group)

  • Pattern for arm model

  • Stiff cardboard for arm model (note: more permanent models can be made with wood*)

  • 1 1 N (100g) hanging weight

  • 1 1/4” X 3/4” bolt with wing nut (if using wooden models)

  • 1” diameter plastic pulley

  • Heavy brads (if using cardboard models)

  • Rubber Cement or Craft Spray Adhesive (Liquid Nails® to attach laminated pattern to wood)

  • Ring Stand

  • 10 N Spring scale

  • Single hole punch

  • String (2 colors)

  • 6 #216 screw eyes used to attach string to wooden models (reduces friction)

  • Protractor

  • Ruler

  • Student Activity Page packet for each group

  • Student Data Page packet for each student

*1 2’ X 4’ piece of 1/4” thick wood makes about 18 models


Activity Management Suggestions

Be sure to explain to students that there is a significant amount of disagreement among experts about the classification of lever systems in the human body.


Ask the Industrial Technology class to cut the pattern pieces out of 1/4” wood for more durable models. You can glue laminated pattern pieces onto the wood for models you will be able to use year after year. A 2’ X 4’ sheet of wood makes about 18 models.


Some students may be sensitive about using their own weight for some of the calculations in this activity. These students can do the calculations using a body weight of 80 lbs.


Extension: Investigate the knee joint by identifying the forces involved in knee flexion. Determine what type of lever system is represented by knee flexion. Examine knee extension to identify the forces and type of lever system.


References Used


Broer, MR. (1973) Efficiency of human movement (Third Edition).Philadelphia: W.B. Saunders Company.


Gowitzke, BA & Milner, M. (1988). Scientific bases of human movement (Third Edition). Baltimore: Williams & Wilkins.


Gray, H. (1918). Anatomy of the human body (20th Edition). Philadelphia:Lea & Febiger.


Hamill, J. & Knutzen, KM. (2003). Biomechanical basis of human movement (Second Edition). New York: Lippincott Williams & Wilkins.


Inspiration Software™, Inc. http://www.inspiration.com


Medline Plus Medical Dictionary http://www.nlm.nih.gov/medlineplus/mplusdictionary.html


Plagenhoef S, Gaynor Evans F, and Abdelnour T. Anatomical data for analyzing human motion. Res Quart Exerc Sport 54: 169-178, 1983


Zatsiorsky. V. (2002). Kinetics of human motion. Champaign, IL: Human Kinetics.