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Upon completion of this chapter the student should be able to demonstrate the following competencies and proficiencies concerning isokinetics:

  • Understand the terminology associated with isokinetic training and testing

  • Define accommodating resistance

  • Understand common isokinetic devices

  • Understand the force velocity relationship with isokinetic testing

  • Have basic knowledge of how concentric and eccentric muscle action is affected with isokinetic exercise and testing

  • Design an appropriate testing protocol for the upper and lower extremity

  • Design an appropriate rehabilitation program for the upper and lower extremity

  • Understand and interpret isokinetic testing results

  • Understand proper patient positioning for testing and training

  • Understand the indications, contraindications, and precautions of isokinetic exercise and testing


Isokinetic exercise is a form of resistance exercise that is performed at a constant velocity.1 Isokinetic exercise, like isometric and isotonic exercise, holds one variable constant. That variable is velocity, as compared to muscle length for isometric and weight for isotonic. As an example, when a patient performs a quad set, no motion occurs at the knee joint so the length of the quadriceps does not change. Also, during a straight-leg raise with a 10-pound cuff weight the hip moves into flexion and extension, causing the muscle to shorten and lengthen, but the 10-pound weight remains the same. During isokinetic exercise, the muscle length changes but the velocity of the muscle contraction is controlled by a preset constant velocity. It can be thought of as muscle force varies, but the velocity of the exercise remains the same. This type of exercise is performed on isokinetic machines, which are described later in the chapter. If the patient fails to meet a preset speed of the isokinetic device, no resistance is provided. However, when the patient meets the preset speed of the isokinetic device, resistance is experienced by the patient. After the preset speed is met, the limb cannot go any faster and any force applied into the device results in an equal reaction force to the patient. The more force applied into the device, the more force is "given back" to the patient. The resistance provided is accommodating based on the patient's effort, and the resistance can be maximal throughout the range of motion.2 Because of its ability to provide accommodating resistance, isokinetics is also referred to as accommodating variable-resistance exercise.3

Clinical Pearl 10-1

The harder the patient pushes into an isokinetic device, the greater resistance they experience.


Isokinetic rehabilitation has a language all its own. An understanding and familiarity with this terminology are essential to successfully navigating the remainder of this chapter. The resistance provided by isokinetic equipment is termed accommodating resistance. Isokinetics is unique in the realm of strengthening exercises. Rather than apply a force that the patient must overcome, isokinetic exercise utilizes a speed that the patient must meet. The speed is constant throughout the ...

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