Measures of Trunk Muscle Endurance and Neuromuscular Control Are Not Correlated

Abstract

Trunk stability influences injury and has been previously demonstrated to be dependent on neuromuscular control of the abdominal muscles. Clinical tests of muscle endurance have been used to assess trunk stability. It is not known if abdominal muscle endurance and neuromuscular control are related or measure different factors that influence trunk stability and injury risk separately. PURPOSE: The purpose of this study was to determine the association between trunk muscle endurance and changes in muscle thickness of the lateral abdominal muscles during abdominal hollowing. METHODS: Nineteen healthy, physically active subjects participated in this study. Ultrasound images of the lateral abdominal muscles were collected at rest and during performance of abdominal hollowing. All abdominal hollowing tasks were performed in a crook lying position, and subjects were provided tactile, verbal, and visual feedback. Increase in thickness of the transversus abdominis was calculated relative to the increase in the thickness of all the lateral abdominal muscles. Three trials were performed and subjects were required to hold each contraction for ten seconds each. Subjects also performed two endurance tests: human arrow and lateral side bridge. Each required the subject to hold a position for as long as possible, each was recorded for time until failure, when the subject was unable to hold the position or respond to verbal corrections. Pearson product moment correlation coefficients were calculated to assess the association within subject among the relative increase in transversus abdominis muscle thickness and the recorded times for each task. RESULTS: Changes in transversus abdominis thickness were not correlated with time to failure for the human arrow test (r=0.01, p=0.983) or the lateral bridge (r=-0.11, p=0.665). Time to failure for the human arrow and lateral bridge tasks were significantly correlated (r=0.786, p<0.001). CONCLUSION: Measures of trunk muscle endurance and abdominal neuromuscular control are not correlated within subjects. These findings indicate that endurance tests may not provide an adequate assessment of trunk stability.