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What Is Isokinetic Testing?

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  • Written By: Jeany Miller
  • Edited By: O. Wallace
  • Last Modified Date: 13 October 2014
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Isokinetic testing often uses a computer-driven device to examine individual muscle groups. Both function and strength may be assessed with a dynamometer machine that likely operates hydraulically or electromagnetically. The machine usually accommodates patients with limited motion ranges and muscle weaknesses, although all participants are expected to put forth their best efforts to receive accurate results. Based on feedback from the machine, a physical therapist may prescribe a rehabilitation program to improve muscle and joint health. In general, isokinetic testing provides accurate data, although it may not be suitable for all applications.

The usual purpose of isokinetic testing is to assess muscle function during different intervals of exercise. Patients may receive this testing pre- and post-operatively to gauge surgery results, to measure the complications of joint arthritis or to quantify physical impairments from injury or disease. In turn, this testing may also be used to exercise specific muscle groups for rehabilitation or strength-building.

Isokinetic testing normally assesses a specific group of muscles, such as those in the shoulder or ankle. The patient’s movements often need to be as quick and powerful as possible to obtain accurate readings. Such readings are generally distributed by a computer and may be either auditory or visual. Visual feedback is likely to vary considerably between different machines, but many clinical professionals agree that results are generally an objective measure of strength deficits.

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During the initial assessment, a physical therapist or trained technician often operates a dynamometer machine that applies continual resistance to the muscles tested. This machine is likely to be hydraulic or electromagnetic in nature to reduce joint impact. The dynamometer, which is often located within the machine’s head assembly, controls speed by responding to patient effort. Variations in force output are thus accommodated for, allowing an individual with limited range of motion or muscle weakness to successfully complete the test.

Similarly, dynamometer machines may also be adjusted so a person can perform isolated plyometric exercises. These are generally used by athletes to train muscle groups for improved functioning. Plyometric movements often contract muscles in rapid sequences, thereby improving strength and elasticity.

Dynamometer machines often function according to the individual muscle groups undergoing assessment. Isokinetic testing for the knee, for example, is often performed in a seated position. A thigh strap is often used to secure a patient to the seat, and the technician may then set the desired range of leg motion. If the patient is being tested for endurance, the machine may be set for a specific period of time, such as 10 minutes. Conversely, a patient undergoing strength assessments may need to perform a certain number of repetitions, such as five.

Isokinetic testing for the shoulder may look at four different motions: flexion/extension, in which the arm is raised and lowered with the forearm facing up; adduction and abduction, in which the arms are lifted straight out to the sides; shoulder rotations; and diagonal movements with the elbow. The elbow, wrist, hip, patella femoral and ankle are additional joints and muscle groups that may be critically examined with isokinetic testing.

Factors that may influence a patient’s results include motivation, levels of physical activity before the test and familiarity with how the machine works. Many clinical offices give patients time to get acquainted with the dynamometer machine before testing begins. The test often starts after performing several practice repetitions. In addition, patients who do not put forth all effort during the testing may receive inaccurate results, and the overall assessment may therefore be skewed.

Dynamometer machines have been shown to provide basically accurate data when testing uniaxial joints like the knee. This data is generally considered unhelpful, however, when diagnosing orthopedic abnormalities. Isokinetic testing essentially allows patients to work on muscle function in a safe and controlled manner. Such a rehabilitation program, which is usually prescribed based on test results, can also be tailored to meet individual needs and expected outcomes. Periodic re-testing may occur to monitor patient progress and to gauge developing muscle strength.

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