Predicting the Maximum Force Generating Ability of the Ankle Plantarflexor Muscles Using Submaximal Contractions

Abstract

This study attempted to find an accurate method of measuring volitional activation and predicting maximum force generating ability (MFGA) that could be used with a neurologically impaired population. Deficits in muscle strength in individuals with neurological disorders are either muscular or neurological in origin. Electrical stimulation is often superimposed over a subject’s maximal volitional contraction to determine the extent of strength deficit that can be attributed to neurological impairment. This study tested the Burst Superimposition Test, the Twitch Interpolation Technique, the Doublet Interpolation Technique, and the Twitch to Tetanus Ratio Method on the ankle plantarflexor muscles of 13 healthy subjects contracting at submaximal volitional efforts (25%, 50%, and 75% of the muscle’s maximum force generating ability, MFGA) to represent the decreased volitional activation of those with neurological impairments. The predicted MFGA’s from the tests at submaximal volitional efforts were compared to the Burst Superimposition Test at maximal effort, which is considered to be the gold standard in measuring volitional activation and MFGA. The results suggest that the Burst Superimposition Test was the most accurate method at submaximal volitional efforts when predicted MFGA was adjusted by a correction equation. The Twitch to Tetanus Ratio also showed promising results at the 25% volitional effort level.