Measuring pad–pad pinch strength in a non-human primate: Macaca fascicularis

The primary purpose of this study was to establish a methodology for determining and perhaps predicting (via regression analysis of anthropometric measures) Macaca fascicularis isometric pinch strength for a specific task. The larger purpose of this work was to properly scale a pinching task for the monkeys in order to study dose-response relationships in a non-human primate model for carpal tunnel syndrome. Three female and one male macaque (n = 4) of varying size and age were trained to perform a left-handed pad–pad pinch. The task required 60° of wrist flexion at a static pinching distance of 3 cm between the thumb and fingers. Subjects were trained for a period of 20-weeks. After that time, an analysis of performance gradients found that they had each reached a plateau in their force output. Pinch strength for the four animals ranged from 29.4 to 59.8 N. Regression analysis revealed that body mass (kg) and wrist circumference (cm) were both predictive of pinch strength, exhibiting adjusted R2 values of 0.93 (p = 0.024) and 0.96 (p = 0.015), respectively. Thus, the results suggest that maximal pinch strength could be acceptably estimated in future subjects using either the wrist circumference or the body mass measures, as both were strong predictors of pad–pad pinch strength.