Because grip and pinch strength are highly correlated and most literature deals with the former, this article focuses on grip strength, which is controversial because, as a functional test, it can be influenced by subjective factors that are difficult to control and include effort, pain, time of day, and fatigue. The AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) identifies additional factors that influence grip and include sex, age, sensation, comorbidities, age, nutritional status, and, perhaps, handedness. Although grip strength is considered a measure of hand function, its correlation with activities of daily living is poor. Grip strength measurements must be performed in a standard manner because altering wrist, forearm, or elbow position can change the results. Impaired hand strength is compared to that of the opposite extremity, which usually is normal; if both extremities are involved, the strength measurements are compared to the average normal strengths. The AMA Guides specifies that grip measurements are regarded as reliable if there is less than 20% variation in the readings, but subjective factors may result in higher-than-normal variance between measurements of grip. Because pain interferes with maximal effort and, if present, may invalidate grip strength measurement, the latter generally is inappropriate to rate tendonitis or other painful conditions. Generally, grip strength is not used to rate neurological deficits.

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