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Effects of visual feedback and strength of contraction on electromyographic reliability
Abstract
The reliability of the surface electromyogram (EMG) for isometric maximum voluntary contractions has not been well established. The purpose of this study was to determine the effect of providing visual feedback of force on the reliability of both maximum and submaximum isometric voluntary contractions of the triceps brachii muscle. Twenty-four female subjects participated in the study. Surface EMG data were collected for both the biceps brachii muscle and the triceps brachii muscle. Data were collected over seven testing sessions, including a single baseline session, three sessions which included only trials of the maximum voluntary contraction (MVC) for the triceps brachii muscle, and three sessions that consisted of testing 9 conditions. The 9 conditions included: MVC-no feedback, MVC with feedback, 50% conditions with and without feedback, and a standard weight condition (with and without feedback). Three of the conditions were also replicated, using a daily force value in determining the target level. The feedback conditions included visual feedback of the force, provided concurrently on a computer screen. All conditions were repeated for three five second trials on each testing day. Intraclass correlation coefficients (ICC) were calculated for RMS-EMG, force, and median frequency of the last three seconds of each trial. The ICC values for RMS-EMG were high (0.94 to 0.97), and significantly greater than a critical value of 0.80. The ICC values for the force ranged from 0.71 to 0.99 depending upon the condition. All but two of conditions for force were significantly greater than the critical level (0.80). The ICC values for the median frequency were also high (0.91-0.96), and significantly greater than 0.80. The level of co-contraction (estimated by a ratio of biceps brachii RMS-EMG/triceps brachii RMS-EMG) ranged from 23 to 26 percent over all conditions. The findings of high levels of reliability for the submaximal conditions are consistent with previous works. However, the report of high level of reliability for the MVC-NF conflicts with past studies. Differences between this study and the previous works include muscle tested, reliability statistic chosen and sample size. If this finding is verified in a more general population (including males) and in other muscle groups, it suggests that the MVC without feedback is an appropriate choice for a reference contraction. Additional work is recommended to determine guidelines for reference contractions for non-isometric tasks.
Subject Area
Physical therapy|Medicine|Physiology
Recommended Citation
Miller, David John, "Effects of visual feedback and strength of contraction on electromyographic reliability" (1993). Doctoral Dissertations Available from Proquest. AAI9329645.
https://scholarworks.umass.edu/dissertations/AAI9329645