Submaximal contractions can serve as a reliable technique for shoulder electromyography normalization

There are a number of ways to normalize electromyographical data, the most common of which is using a maximal contraction as a reference. However, this technique is not always practical. The purpose of the present study was to assess the reliability of an electromyographical data normalization technique using standardized submaximal contractions. Twenty healthy subjects (ten male, ten female) were used for testing, which was performed using both surface and fine-wire electromyography over two sessions at 15, 30, 45, and 60 percent of the day 1 maximum force. There was a mean of 5.3 days between test days. Data were compared between days, and the resulting ICC and standard error of the measurement values indicate varying levels of reliability at each submaximal percent. All heads of the deltoid, the upper trapezius and the serratus anterior demonstrated good reliability for at least one submaximal condition. The latissimus dorsi and supraspinatus demonstrated moderate reliability for at least one submaximal condition. Finally, the infraspinatus demonstrated poor reliability under all conditions. For situations in which MVC is impractical or anticipated to change, EMG amplitude normalization to one of these submaximal percentages appears to be a viable technique, at least for most muscles.