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Physical therapists and kinesiologists typically use a Jamar® dynamometer for initial and ongoing evaluation of handgrip strength in people experiencing hand dysfunction. The handheld instrument gauges hand and forearm strength when individuals apply isometric force by squeezing two hydraulic handles together. An aneroid or digital readout displays the amount of force applied. The Jamar® dynamometer adjusts to accommodate the hand size of different individuals.
The Jamar® dynamometer has two ergonomically-designed metal handles stacked on top of each other and separated by a hydraulic spring. The distance that separates the handles can be set to one of five adjustments, making the device suitable regardless of hand size. Attached to the top of the back handle is an aneroid or digital display, which measures grip strength in pounds or kilograms. The aneroid dial contains two needle indicators. One needle moves back and forth, indicating grip strength, returning immediately to zero once the handles are released. The other needle stays at the peak hold position for easy reference and returns to zero with manual adjustment.
The aneroid display shows pounds or kilograms, graduated in 5 pound or 2.5 kilogram increments. Most of the Jamar® dynamometer models show grip strength ranging from 0 to 200 pounds (90 kilograms). The digital dynamometer operates on batteries and contains a liquid crystal display, and users may adjust the read-out to display pounds or kilograms. The digital model automatically stores and calculates averages, standard deviations, and coefficient of variations.
The digital model comes with an alarm system which signals when the user has maintained his grip for a designated period of time, usually three to five seconds. Certain models of the Jamar® dynamometer are equipped with a protective rubber coating on the outer edge of the aneroid gauge that protects the instrument from breakage if accidentally dropped. Performing muscle strength and fatigue screening generally requires the subject to hold the device in one hand, with the gauge facing away, while squeezing the handles together as forcibly as possible.
For an accurate depiction of hand and forearm strength, individuals operate the Jamar® dynamometer while standing and holding the device with the testing arm extended comfortably at their side. Subjects might also use the dynamometer while seated and having the testing arm flexed at a 90 degree angle at the elbow. Therapists can employ the instrument to check grip strength on stroke victims, patients recovering from hand trauma, and individuals suffering from nerve tissue disorders.