Body Levers: Three Classes in Strength Exercises

Students identify the three classes of levers in the human body by doing real strength exercises and use resistance bands to test how the effort changes when the resistance arm gets longer. The physics of levers is linked to safe exercise technique.

How to play

1. Sketch the fulcrum, effort and load, and show three examples: neck extension (first class), calf raise (second class) and elbow flexion (third class) (5 min).
2. In pairs, students rotate through three stations with a worksheet: at each one they do 10 reps and draw where the fulcrum, the muscle force and the load are (9 min).
3. Band experiment: lateral shoulder raise with the elbow bent and then straight; each pair rates the effort from 0 to 10 for both (6 min).
4. Repeat the experiment with a squat holding the band close to the chest and then with arms straight out in front, and compare results (5 min).
5. Group discussion: why the body mostly uses third-class levers and how we use the resistance arm to scale an exercise (5 min).

Rules

• Check bands before use and never let go of a stretched band.
• Keep a neutral spine in every exercise even though the goal is to observe.
• Effort never goes above 7 out of 10: this is an experiment, not a max test.
• Each pair keeps 6 feet away from other pairs when using bands.

Variations

Adaptations

• Limited mobility: do all upper-body stations seated and analyze the partner's calf raise.
• Visual impairment: the partner guides the student's hand to feel the fulcrum and the pulling muscle.
• Shoulder injury: replace the lateral raise with a seated banded knee extension, which also lets you change the resistance arm.

Learning goals

• Identify the three classes of levers in the body's own movements.
• Relate the length of the resistance arm to perceived effort.
• Use this knowledge to adjust the difficulty of strength exercises.

Equipment for a class of 25

• resistance bands: 14
• worksheets: 28
• cones: 6

Teacher tip

Coordinate with the physics department so you both use the same torque notation. A worksheet with blank body outlines speeds things up a lot.

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