In our previous column (ADVANCE, Sept. 17, 2012), we wrote that Dr. Lewis would be undergoing intensive training on how to properly use the instruments in the new NIH Toolbox. Well, the wait is over! As promised, we will begin to review the instruments within the toolbox for feasibility, ease of use and functionality.
The NIH has established a comprehensive listing of functional tools for our use in a broad range of ages (3-85 years) that measure the domains of motor, cognitive, sensory and emotional performance. Each instrument has a video component where you can preview how to correctly perform the test or use the instrument.
When you access the NIH toolbox online, the first tool featured is one that measures grip strength, so let's start there.1 As early as 1992, the Jamar dynamometer has been found to be a reliable and valid instrument to measure grip strength in a variety of patient populations.2 In the elderly, hand grip strength along with tandem standing has been found to be just as successful in predicting recurrent falls as sophisticated measures assessing postural sway and balance.3 In addition, a study assessing grip strength as a measure of limb strength suggests that for healthy adults, isometric measures of grip, in combination with strength as demonstrated via isometric knee extension, share a common construct: limb muscle strength.4 We aren't downplaying the value of using more complex equipment and testing, but if you had to choose one or more measures to ascertain falls or the likelihood of having a recurrent fall, grip strength is a cost-effective (outside of the initial expense of buying the dynamometer), easy to administer, and time-sensitive alternative.
The NIH toolbox website supplies a written description of testing protocol and patient positioning as well as a "video protocol" that shows exactly how the test should be administered. For the grip strength test, the protocol was adopted from the American Society of Hand Therapists.5 The patient is seated in a chair with feet flat on the ground, elbow flexed to 90 degrees, and arm held firm against the trunk. The patient's wrist is in the neutral position, and when given the command, the patient is directed to squeeze, in this case a digital dynamometer, as hard as possible for three seconds. One practice trial during which they do not exert full force is followed by one test at full force with each hand. The test takes about three minutes, with resultant force recorded in pounds.
A score for each hand is recorded, with the individual's dominant hand the primary score taken into consideration. The dominant hand score is converted to the Toolbox normative scale scores and the non-dominant hand score reported as a raw score, in pounds of force. The non-dominant hand information is recorded in the "Computed Score Non-Dominant column of the Toolbox Assessment Scores output file."1
Typically within the literature where grip strength is tested, the raw score (amount of force measured in pounds) is used for interpretation, with greater force attributed to greater strength. Using the raw score allows for comparisons between dominant and non-dominant hand performance. The NIH Toolbox provides fully adjusted normative scale scores that account for gender, age, ethnicity and educational differences that can be used to evaluate performance in the dominant hand.6 The developers of the Toolbox state that a fully adjusted scale score that is two standard deviations below the mean-in other words, a scale score of 70 or below-is indicative of motor dysfunction that would benefit from further evaluation.
What do you think? Is grip strength worth doing? Based on the fact that muscle strength declines with age, and is associated with an increased risk of falls, potential hip fractures, loss of bone mineral density, functional dependence in people age 75 years and older, and loss of function in hospitalized patients,7 our answer would be a resounding yes.
1. NIH Toolbox: Assessment of neurological and behavioral function. http://www.nihtoolbox.org/Pages/default.aspx
2. Hamilton, G., McDonald, C., & Chenier, T. (1992). Measurement of grip strength: Validity and reliability of the syphygmomanometer and the Jamar grip dynamometer. JOSPT, 16(5), 215-219.
3. Stel, V., Smit, J., Pluijm, S., & Lips, P. (2003). Balance and mobility performance as treatable risk factors for recurrent falling in older persons. Journal of Clinical Epidemiology, 56, 659-668.
4. Bohannon, R., Magasi, S., Bubela, D., Want, Y., & Gershon, R. (2012). Grip and knee extension muscle strength reflect a common construct among adults. Muscle Nerve, 46(4), 555-558.
5. Fess, E. (1992). Grip strength. In Clinical assessment recommendations. 2nd edition. Edited by: Casanova, J. Chicago: American Society of Hand Therapists.
6. NIH Toolbox. Scoring and interpretation guide. September, 2012.
7. Xue, Q., Walston, J., Fried, L., & Beamer, B. (2011). Prediction of risk of falling, physical disability, and frailty by rate of decline in grip strength: The women's health and aging study. Archives of Internal Medicine, 171(12), 1119-1121.
Carole Lewis lectures exclusively on geriatric rehabilitation for Great Seminars and Books and Great Seminars Online. She is co-owner of Center of Evidence and consultant to Professional Sportscare & Rehabilitation. She is also editor-in-chief of Topics in Geriatric Rehabilitation and an adjunct professor at George Washington University Department of Geriatrics. Keiba L. Shaw is associate professor at Nova Southeastern University's College of Health Care Sciences Physical Therapy Department Hybrid Entry Level DPT Program, Tampa, FL.