Comparison of isometric triceps brachii force measurement in different elbow positions

Objective and reliable force measurement is necessary to monitor the rehabilitation after triceps brachii pathology, injuries, and posterior approach-based surgery. It is unclear at which amount of extension the triceps is best tested and if comparison to the uninjured sided is reliable. This study aims to identify the most reliable elbow position at which elbow extension force is measured using a dynamometer. Furthermore, it aims to compare the extension strength of the dominant arm with that of the nondominant arm.

Isometric elbow extension force of the dominant and nondominant arms of healthy subjects was measured. The measurements were taken in three sequences per arm in 0, 30, 60, 90, and 120 degrees of flexion. A subgroup repeated the measurements to analyze test-retest reliability using intraclass correlation.

We included a total of 176 volunteers. The repeated measures analysis of variance for within-subject effect showed the lowest variation coefficient at 30 degrees of flexion. Extension forces showed a mean difference of 3.2-6.9 N in advantage of the dominant arm, resulting in ratios from 1.05 to 1.09. Learning curve analysis showed that during the first session in dominant and nondominant arms, less forces were exerted.

The most reliable isometric triceps brachii muscle strength measurement was at 30 degrees of flexion of the elbow. Considering the learning curve, a first tryout session for both arms is indicated. Then, a second measurement suffices as no further learning curve is observed.