Handheld dynamometry is a quantitative measure of grip and pinch strength using a standardized tool. Client scores may be compared to normative scores for age and sex and changes in grip and pinch strength may be tracked longitudinally over time. a brief summary of the testing procedures may be found by following this link. A table of normative measures for adults, aged 20-75+ years, may be found by following this link. A table of normative measures for children and adolescents, aged 6 to19 years, may be found by following this link.

A z-score describes a client’s raw score (X) on an assessment in relation to the population mean (μ) in terms of standard deviation units (σ). In other words, it answers the question: “How many standard deviations above or below the mean is a client’s score?” A negative z-score indicates that the client’s raw score falls below the mean; a positive z-score indicates that the client’s raw score falls above the mean. Z-scores are often used to qualify clients for therapy services. Especially in pediatric occupational therapy, clients who score more than one and a half standard deviations below the mean (z-score = -1.50) qualify for services. Often in adult services, clients who score more than two standard deviations below the mean (z-score = -2.00) qualify for services. Z-scores are always calculated to two decimal points. The equation for calculating a z-score is as follows:

z-score = (X-μ)/σ

To interpret the z-score, it is important to consider the units of measurement (such as pounds of force or time in seconds). In cases where a higher score indicates better performance (e.g., pounds of force), if a client’s score is higher than the mean, the z-score will always be positive. In cases where a higher score indicates poorer performance (e.g., time in seconds), if a client’s score is higher than the mean, the z-score will always be negative.

To calculate the client’s z-score, follow the following link.

Interestingly, 5-point grip strength dynamometry has been used to measure the effort exerted by clients in producing full and consistent grip trials. Phillips et al. (2011) demonstrated that clients with clinical depression were less likely to produce full and consistent effort during testing. It is expected that clients will demonstrate full effort when squeezing the handle of the dynamometer over multiple trials. 5-point dynamometry measures grip strength with the handle placed in each of the five positions, alternating left and right in rapid succession. Under normal testing conditions, the client’s scores may be plotted and demonstrate a bell curve, with the greatest measured strength being at handle position 2. If there is variation to this distribution (e.g., erratic distribution), it may be reasonably deduced that the client is not providing full and consistent effort in squeezing the handle. This may provide additional qualitative information to the clinician when working in industrial rehabilitation and/or with a client suspected of malingering.