Normative Data and Development of a Five-Grade Classification for Pinch Strength in Healthy Japanese Adults

Background: Pulp pinch is the most frequently used grasping pattern amongst two-finger pinches; however, normative data on pulp pinch strength based on a large Japanese population have not been reported. The utility of such normative data would be enhanced by presenting five-grade classifications in addition to the mean and standard deviation (SD). Therefore, the objective of this study was to present normative data and establish sex-specific five-grade classifications for pulp pinch strength in healthy Japanese adults. Methods: A total of 514 healthy Japanese adults (337 men and 177 women) participated in this study. Maximal voluntary pulp pinch strength between the thumb and index finger of both the dominant and nondominant hands, as well as between the thumb and middle finger of the dominant hand, was measured using a muscle strength tester equipped with a pinch force sensor. Based on the deviation score [= 50 + ((measured value - mean) / SD) × 10], pinch strength was classified into five grades as follows: grade 5, deviation score ≥ 65; grade 4, deviation score ≥ 55 and < 65; grade 3, deviation score ≥ 45 and < 55; grade 2, deviation score ≥ 35 and < 45 and grade 1, deviation score < 35. Results: As normative data for pinch strength in healthy Japanese adults, the mean ± SD values of pulp pinch strength for each condition were calculated separately for men and women. Five-grade classifications were established for each pinch condition in men and women. Conclusions: Normative data and sex-specific five-grade classifications for pulp pinch strength in healthy Japanese adults were successfully developed and may serve as normative reference values for assessing patients with hand pathologies and evaluating pinch strength recovery. Level of Evidence: Level III (Diagnostic).