Skip to Main Content

We have a new app!

Take the Access library with you wherever you go—easy access to books, videos, images, podcasts, personalized features, and more.

Download the Access App here: iOS and Android


Christopher R. Bartlett


When you finish this chapter you should be able to

  • Analyze the mechanical properties of tissue based on the stress–strain curve model.

  • Discuss the five types of tissue loads that can produce stress and strain.

  • Examine the anatomical characteristics of the musculotendinous unit, synovial joint, bone, and nerve.

  • Evaluate how mechanical loads applied to the musculotendinous unit, synovial joint, bone, and nerve produce injury in these structures.

  • Identify and differentiate various injuries to the musculotendinous unit, synovial joint, bone, and nerve tissue.


  • trauma

  • load

  • stiffness

  • stress

  • strain

  • deformation

  • elasticity

  • yield point

  • plastic

  • creep

  • mechanical failure

  • muscle strain

  • muscle cramps

  • muscle guarding

  • clonic

  • tonic

  • muscle soreness

  • tendinopathy

  • tendinitis

  • tendinosis

  • crepitus

  • tenosynovitis

  • contusion

  • ecchymosis

  • myositis ossificans

  • synovial joints

  • diastasis

  • dislocation

  • subluxation

  • osteoarthritis

  • bursitis

  • bursae

  • osteoblasts

  • osteoclasts

  • closed fracture

  • open fracture

  • neuropraxia

  • neuritis

  • referred pain


The ability to recognize a specific injury to musculoskeletal, nerve structures, and soft tissues and understand those mechanical factors that produce injuries or trauma is essential for the athletic trainer.11 Trauma is defined as a physical injury or wound that is produced by an external or internal force.9 This chapter provides the foundation for the identification, understanding, and management of injuries to be discussed throughout this text. It examines mechanical forces and tissue characteristics of injuries and the classification of these injuries.


Newtonian physics maintains that force or mechanical energy is that which changes the state of rest or uniform motion of matter. When a force applied to any part of the body results in a harmful disturbance in function and/or structure, a mechanical injury is said to have been sustained.23 Injuries are caused by external forces directed on the body that result in internal alteration in anatomical structures that are of sufficient magnitude to cause damage or destruction to that tissue.23 How the various tissues respond to the application of an external load is determined in large part by the mechanical properties of that tissue.

9–1 Clinical Application Exercise

The stress–strain curve represents the relationship between various tissue properties when a ligament is stretched.

? How does external stress lead to an ankle sprain in a patient who steps awkwardly off a curb?

Tissue Properties

Tissue properties are described according to mechanical terminology, and their relative relationship may best be illustrated by the stress–strain curve (Figure 9–1). A load is an external force acting on tissues that causes internal reactions within the tissues. Stiffness is the relative ability of a tissue to resist a particular load. The greater the stiffness, the greater the magnitude of load it can withstand. The internal resistance of the tissues to an external load ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.