A muscle fatigue monitor based on the surface electromyography signals and frequency analysis

People with lower-limb movement disorders often receive physical therapies for recovery. These procedures can cause muscle fatigue and pain without the patient noticing it. In this work the development of a system to monitor muscle fatigue is presented. It is based on the measurement of the median frequency shifting in the power spectrum density generated by surface electromyography recordings, as well as the Borg scale criteria related to pain, eventually caused by fatigue in healthy subjects. Electromyography signal processing was performed using non-parametric methods to determine the median frequency shifting, whereas the root mean square value in time domain, as indicators of muscle fatigue. Measurements were performed in rectus femoris and lateral gastrocnemius muscles of 16 healthy subjects when they were submitted to physical performance tests. Results showed fatigue in rectus femoris in 12% of cases when Welch method was applied, in contrast with 18% of cases of lateral gastrocnemius recordings when periodogram method was used.