Equations to predict female manual arm strength based on hand location relative to the shoulder

The purpose of this study was to develop regression equations to predict manual arm strength for a wide variety of hand locations within the reach envelope. Maximum voluntary manual arm strength was determined from 71 female participants in six exertion directions (superior, inferior, anterior, posterior, medial and lateral), in a total of 28 hand locations. Forces ranged from 51.3 to 164.4 N, and had a pooled coefficient of variation of 29.9%. Across all 168 combinations of hand locations and exertion directions, the multivariate regression equations explained 92.5% of the variance and had a root mean square error (RMSE) of only 6.4 N, using only the anterior, lateral and vertical location of the hand relative to the active shoulder joint as inputs. These equations provide a proof-of-principle for our novel regression approach, and represent a first step towards a more comprehensive equation to estimate maximum acceptable forces for occupational tasks.

The equations presented here demonstrate a first step towards a novel and improved method to predict manual arm strength. Although a more comprehensive equation is still needed, these equations can be confidently used in the field by ergonomists to estimate the maximum acceptable forces in the six primary force directions.