Isometric knee extension force measured using a handheld dynamometer with and without belt-stabilization

Although evidence suggests that tester strength limits the magnitude of isometric force that can be measured using a handheld dynamometer (HHD), previous studies have not investigated the actual limits of force magnitude that can be measured by trained testers when a belt is or is not used to stabilize the dynamometer. Therefore, the primary aims of this study were to determine: 1) the magnitude of knee extension forces that could be measured with a HHD with and without belt-stabilization and 2) the relationship between tester characteristics and knee extension strength measured with and without belt-stabilization. The characteristics of 20 trained testers (10 men, 10 women) were determined. Thereafter, they measured isometric knee extension strength using the MicroFET HHD with and without belt-stabilization. Paired t-tests were used to compare maximal knee extension forces under two conditions. Pearson product-moment correlations were calculated to determine the relationship between tester characteristics and knee extension forces measured under the two conditions. Knee extension forces (Newtons) measured using the HHD without belt-stabilization (470.6 ± 179.8) were significantly lower (t= -7.968, p<0.001) than those measured with belt-stabilization (866.9 ± 131.7). Pearson correlations between tester characteristics and knee extension forces measured with no belt-stabilization were all statistically significant (p ≤ 0.002); however, the correlations were not statistically significant under the belt-stabilization condition. The forces that can be measured with a HHD are higher than those suggested by previous researchers. By rectifying limitations imposed by tester strength, use of a belt allows very high knee extension forces to be measured.