Many measuring devices are available:

1. Hydraulic instruments are sealed systems that measure grip strength in kilograms or pounds of force. The most widely used is the Jamar dynamometer26,30. It is inexpensive, simple to use, versatile in its applications, and has been found to be accurate6and reproducible10,22 in its measurements. It is the most widely used and reported upon device.

2. Pneumatic instruments, for example the modified sphygmomanometer, rely on compression of an air filled compartment, and thereby measure grip pressure rather than grip strength. The limitation is that varying the surface area over which pressure is applied leads to variable results (i.e. larger hand size leads to artificially lower results than smaller hand size)7.

3. Mechanical instruments, for example the Stoelting dynamometer25, measure grip strength through the tension produced in a steel spring and read in kilograms or pounds of force. Strain gauges measure in Newtons of force and include the Isometric Strength Testing Unit21. These devices have not been widely reported on in the literature and are not considered as accurate and reproducible in their measurements.

Figure 1

Figure 2

Figure 3

A standard position for testing recommended by the American Society of Hand Therapists₂₅ requires that the patient:

• Sit in a straight-backed chair

• Feet flat on the floor

• Shoulders adducted in neutral

• Arms unsupported

• Elbows flexed at 90 degrees

• Forearm rotation neutral

• Wrist 0-30 degrees dorsiflexion and 0-15 degrees ulnar deviated

Variations from this position significantly influence results.

Figure 4

Figure 5

The Jamar dynamometer is a variable hand span instrument with five different positions for measurement. Maximal grip strength most commonly occurs in the second or third position and is usually tested at the second position (3.8cm)₂₀

No significant difference was noted when measuring maximum grip strength between 1 trial, 3 trials and an average of 3 trials₁₂. We recommend the use of a single measurement as accurate and time efficient

Most normative data studies use the Jamar dynamometer. Large variations have been found in nationality based studies which have not adequately controlled for work and leisure persuits₅. Minimal normative data exists for subjects with disabilities, and the measured standard deviations have been large. Consequently currently available measurement norms are limited in their applicability₁₉.Some generalisations however may be made:

1. Male grip strength exceeds female grip strength by 35-70%

2. Grip strength increases with age to peak between 30 and 45 years after which strength decreases3

3. There is a positive correlation between grip strength, body weight and height up to 98kilograms and 190centimeters28

4. The dominant hand is usually 10% stronger than the non-dominant hand (different studies range from 0-10% difference)24. Left handed individuals show approximately the same strength in both hands4

Janeda et al₁₅ found maximal effort grip strength variation should always be less than 10%. Ashford₂ found repeat testing was not a useful way to discriminate between maximal and submaximal effort. This test is at best equivocal as a means of determining sincerity and should not be used alone.

This test measures grip strength at each of the 5 Jamar positions. When measurements are graphed a Bell curve peaking at position 2 or 3 should result. Stokes et al31 found maximal effort produces a Bell curve, and submaximal effort produces a flat line. Firrell and Crain8 agreed but added that in a small number of subjects the Bell curve peaked in other positions. Niebuhr and Marion23held that a submaximal response was not a flat line, but was significantly flatter than a maximal response. Goldman et al9 found that subjects with injury also produced a curve of decreased amplitude but not as flat as submaximal effort. The shape of the curve is important- the flatter the curve the more likely submaximal effort is occurring.

Hildreth et al₁₄determines the maximal static grip with the Jamar dynamometer (usually position 2 or 3). The dynamometer is then alternated between hands as rapidly as possible for between 5 and 10 grips. A positive test (submaximal effort) is when the maximum rapid exchange measurement is greater than the static measurement. Joughlin et al₁₆ modified this test by setting the Jamar in the 3^rd position and determining maximal static grip. 10-15 grips are performed at the rate of 80/min and only the maximal REG grip recorded. Joughlin found that rapid exchange grip strengths were greater than static measures in most subjects, and that submaximal efforts resulted in greater variation. 16% difference between rapid and static measure was a positive result. This test has also been performed with two Jamar dynamometers (bilateral simultaneous REG test)₁₆. Hamilton-Fairfax et al₁₁ averaged 10 REG measures. If the average was greater than the static grip measure the test was positive (submaximal effort). This paper quoted 85% accuracy in determining maximal versus submaximal effort.

REG testing is useful where large variations occur but the literature conflicts on the definition of a positive test.

This test analyses variation across repeated grip strength measures. It is measured by dividing the standard deviation of the grip strength measurements by the mean₂₇. A high CV indicates an inconsistent response from the patient, assumed to be due to submaximal effort. Matheson and Ogden-Niemeyer₁₈ found females had a higher variability than males, and that submaximal effort produced greater variability than genuine effort . A positive test (submaximal effort) is defined as 10% in males and 12% in females. Simonsen₂₉ found pain also led to variable results, and found the differentiation between pain and submaximal effort difficult. Robinson₂₇used 11% to define a positive test in his series and correctly classified all maximal efforts, but only 45% submaximal efforts. The literature is equivocal on the use of CV and some researchers actively discourage its use.

Patients sustain a maximal grip for 5 seconds and the force applied is plotted over time using computer software. A maximal effort records as a rapid initial rise sustained over 5 seconds. A submaximal effort manifests as a rapid initial rise that gradually declines over the last few seconds. Lechner et al₁₇ were able to accurately identify 85% of maximal efforts and 90% of submaximal efforts. This method may hold promise but requires the use of computer software and statistical knowledge. The test is time consuming and expensive and requires complex data analysis.

Authors refer to the use of a battery of tests to improve accuracy₂₆,₃₁. No single test detects with certainty a voluntary reduction in maximal effort.