Unit 5: Strength and Elasticity of the Body

Moving patients is a routine part of Jolene’s work as a MED floor RN, but in reality there is nothing routine about the biomechanics of lifting and transferring patients. In fact,  “disabling back injury and back pain affect 38% of nursing staff” and healthcare makes up the majority of positions in the top ten ranking for risk of back injury, primarily due to moving patients. Spinal load measurements indicated that all of the routine and familiar patient handling tasks tested placed the nurse in a high risk category, even when working with a patient that “[had a mass of] only 49.5 kg and was alert, oriented, and cooperative—not an average patient.”[1]. In this unit and the associated lab we will analyze forces within the body and examine how body tissues respond to those forces. This unit will introduce the concepts required, static equilibrium, lever classes, mechanical advantage, range of motion, stress, strain, elastic modulus, and Hooke’s Law. The learner outcomes for this unit are listed just below and below those are some key terms and concepts to look out for.

Learner Outcomes

  1. Identify classes of levers and explain advantages and disadvantages of each in terms of mechanical advantage and range of motion.[2]
  2. Apply lever and static equilibrium concepts to solve for forces and calculate mechanical advantage. [3]
  3. Identify and define the features of a stress-strain curve, including stress, strain, elastic region, elastic modulus, elastic limit, plastic region, ultimate strength, and fracture/rupture.[2]
  4. Apply Hooke’s Law along with the definitions of stress, strain, and elastic modulus to calculate the deformations of structures. [3]

Key Takeaways


Resistance (Load)



Lever Arm

Effort Arm

Resistance (Load) Arm

Lever Classes

Mechanical Advantage

Range of Motion





Elastic Modulus

Ultimate Strength

Linear Region

Elastic Region

Elastic Limit

Plastic Region

Yield Point





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