(Georgia Institute of Technology, 2022-05)
Jones, Tamia M.
The accuracy of control and strength of contraction for muscles of the trunk, the muscles between our neck and groin, can vary significantly with conditions like hemiparesis, multiple sclerosis, or low back pain. Such medical conditions can contribute to an inability of our trunk muscles to perform at full capacity. A typical normalization method for applied physiologists includes finding a given muscle’s maximum voluntary isometric contraction (MVIC), and many individuals with muscle weakness or control-limiting conditions are unable to efficiently participate in this method. To properly assess the severity of muscle weakness or loss of control, there is a need for research on normalizing EMG signals produced from contractions in trunk muscles at a fraction of an individual’s MVIC. In order to contribute to this normalization, healthy participants in this study performed a muscle contraction task based on a submaximal MVIC. Participants attempted to reach and hold a contraction for a specific muscle group (i.e., deltoids, pectoralis major, external obliques, and latissimus dorsi) at a target contraction level defined as 25%, 12%, and 6% of their MVIC. The objective of this study was to characterize normalization of EMG signals from trunk muscle contractions with variability and offset error. The standardized measures supported the use of the 25% and 12% contraction levels as submaximal EMG signal normalization. In future studies, the 6% contraction level and the external obliques potentially require refinement in contraction maneuvers for a more accurate normalization. Nevertheless, future experiments may use the results of this study as a submaximal reference point within healthy populations acting as a measure of comparison for patients demonstrating muscle weakness.