Dynamometer
Authors of Tool:
Regnier mid 18th century; Bechtol 1954- Jamar dynamometer
Purpose:
The purpose of the dynamometer is to objectively test the strength of muscles groups in
the body.
Target Population:
The target population is very broad. Dynamometers are used to determine strength in
patients with neurological disorders, post-operatively, post-injury, and any situation in which
monitoring muscle strength would be necessary for rehabilitation.
What it tests:
There are three types of dynamometers: isokinetic, isotonic, and isometric. Isokinetic
dynamometry measures concentric and eccentric contractions at a constant velocity with variable
resistance. Isotonic dynamometry tests concentric contractions performed with a variable
velocity and a fixed resistance also known as the one-repetition maximum (1RM). Isometric
dynamometry measures the strength applied to an immovable object without joint movement.
Variations of these dynamometers include hand grip strength dynamometers, pinch
dynamometers, biodex dynamometers, and hand held dynamometers to test specific muscle
groups.
Psychometric characteristics including reliability and validity:
Calibrated weights have been used to test instrument validity and the validity results were
.97. Isokinetic dynamometry is considered to have high internal validity because it is easily
reproducible but poor external validity because the patterns are limited in sporting activities.
Isometric contractions are limited to the range of motion in which the contraction occurs but is
highly reliable with coefficients of .85-.99. In hand grip strength dynamometry the Jamar
dynamometer is the gold standard with correlation coefficients of .954.
Administration (what you need and how to do it):
Each dynamometer should be equipped with an instruction manual. Since there is a
variety of dynamometers (digital, hydraulic, computer based, dial, etc) the manuals provided will
provide the information necessary as to how to set up the dynamometer and how to use it and
read the results properly.
Time Required:
It is dependent on the machine being used. Some dynamometers require a lengthy set up
while others require minimal set up. Depending on the setup will help determine the time
required to perform a strength test on a dynamometer. Typically the actual testing takes only a
few seconds or it can be a few minutes for multiple testing. A hand grip dynamometer takes
minimal time to get the apparatus set in the patients hand and perform the contraction. Isokinetic
dynamometers initially take more time because the clinician must set the parameters on the
machine and on the computer that are patient specific. Once parameters are noted, subsequent set
ups are much faster because the parameters are already known and the strength testing is much
faster.
Advantages:
Dynamometers standardize manual muscle testing (MMT.) It reduces the subjectivity of
MMT and offers an objective measure to muscle strength. It has a very high reliability and
validity as long as the same dynamometer is used for each re-test. It also allows for objective
measures of progression in strengthening programs.
Limitations:
There are few limitations with the dynamometer. The same dynamometer should be used
for all strength testing to eliminate error between different dynamometers. Most articles found
that there is high reliability for dynamometers, but there is a variation between different types of
dynamometers. Isokinetic dynamometers are intricate and require a good deal of training for set
up and also initially require a lengthy amount of time for the proper set up of parameters.
References:
Dunn JC, Iverson MD. Inter-rater reliability of knee muscle forces obtained by
hand-held dynamometer from elderly subjects with degenerative back pain. Journal of Geriatric
Physical Therapy. 2003;26:23-29.
Shechtman O, Gestewitz L, Kimble C. Reliability and validity of the DynEx Dynamometer.
Journal of Hand Therapy. 2005;18:339-347.
Milias GA, Antonopoulou S, Athanasopoulos S. Development, reliability and validity of a new
motorized isometric dynamometer for measuring strength characteristics of elbow flexor
muscles. Journal of Medical Engineering & Technology. 2008;23:66-72.
Pearn J. Two early dynamometers. Journal of Neurological Sciences. 1979;37:127-134.
Acquisition: Med1 Online, Sammons Preston, Rehaboutlet.com
Jamar Hand Dynamometer $379
Push Pull Gauge $329-1,200
Microfet 2 Load Cell $795
Lafayette Adult Back and Leg Dynamometer $995
Appraised by: Amber Perez
Date appraised: August 1, 2008