Do Finger Flexor Exercises Effectively Activate the Dynamic Stabilizers of the Medial Elbow?

Background: The flexor carpi ulnaris (FCU) and the flexor digitorum superficialis (FDS) provide dynamic stability to the medial elbow with a lesser contribution from the pronator teres (PT). Hypothesis/Purpose: The purpose of this study was to compare FCU, FDS, and PT electromyograpic activation during finger flexor exercises using a finger flexor dynamometer versus rubber bands. It was hypothesized that middle and ring finger flexion selectively activate the FCU and FDS with no difference in level of activation between the dynamometer and rubber bands. Study Design: Observational cohort study; laboratory setting. Methods: Electromyography (EMG) was used to record activation of the FCU, FDS, and PT during isometric finger flexion while using the finger flexor dynamometer and rubber bands in healthy adults (8 men, 1 woman). Forefinger, middle finger, and ring finger flexion were tested on both the dominant and nondominant hands. The rubber bands were stretched to four times resting length and held isometrically. Finger flexion strength was tested using a handheld dynamometer. Contraction intensity for the rubber band exercise was calculated as the force required to stretch the rubber bands 400% divided by finger flexion strength. Contractions on the finger flexor dynamometer were instructed to be maximal effort. EMG activity was recorded during maximum voluntary contraction (MVC) tests for each of the three muscles. EMG amplitude (%MVC) during the finger flexor exercises was compared between devices and muscles using repeated measures analysis of variance. Results: FCU activation during ring finger flexion was higher (p=0.002) for rubber band (64±19% MVC) versus finger flexor dynamometer (43±17% MVC). No other EMG amplitudes were different between devices. FCU and FDS activations during rubber band finger flexions were higher than PT (p<0.05). FCU activation with the finger flexor dynamometer was significantly higher than FDS and PT for forefinger flexion (p<0.01) but there were no significant differences for other fingers. Rubber band flexion contraction intensity was 65±11%, 44±3%, and 39±5% for ring, middle, and forefinger flexion, respectively (intensity was considered 100% for measurements of the finger flexor dynamometer). Conclusion: A simple rubber band exercise was as effective, or more effective, at activating the FCU and FDS than a finger flexor dynamometer. Isometric finger flexion exercises with rubber bands provide an inexpensive practical means of activating the dynamic stabilizers of the medial elbow. Level of Evidence: 3.