The purpose of our study was to determine the reliability of nonvolitional muscle function analysis (MFA) by determining the day-to-day and within-day reliability of conventional electrical stimulation and a newer, magneto-electrical stimulation method, using standard laboratory methodology. Methods: Ten healthy, human immunodeficiency virus-negative adult men volunteered as subjects. MFA consisted of measuring the maximal relaxation rate, for magneto-electrical stimulation at 1 Hz and conventional electrical stimulation at 20 Hz, and force-frequency ratios using conventional electrical stimulation at 10 Hz:20 Hz and 10 Hz:50 Hz. Within-day and day-to-day reliability were determined by calculating the coefficient of variation (CV) for all subjects. Results: Maximal relaxation rate using magneto-electrical stimulation had a significantly lower CV compared with the other nonvolitional MFA methods (p = .002). Conclusions: Maximal relaxation rate using magneto-electrical stimulation was more reliable and technically easier than the other muscle function parameters examined. However, the day-to-day CV of muscle function parameters is larger than traditional nutrition assessment techniques. Development within the field should strive to improve testing techniques so that the reliability of MFA will allow definition of a range of normal values against which an individual's value can be compared. Until this is available, the precision and reliability of MFA restrict its use to research and population studies.