OBJECTIVE: The purpose of this study was to correlate objective measurements of muscle fatigue in the lower back to the subject's own assessment of fatigue. DESIGN: Muscle fatigue in the lower back was assessed in healthy subjects using electromyography (EMG), endurance time and the Borg scale. BACKGROUND: Muscle fatigue, measured with EMG and endurance time, in the lower back, is significant for patients with pain in the lower back. METHODS: Fifty healthy subjects participated. EMG was detected from the lumbar extensor muscles during a modified Sørensen's test, an isometric contraction for the back extensors until exhaustion. During the test, subjects rated their subjective fatigue on a Borg CR-10 scale. RESULTS: Borg scale ratings correlated with endurance time (0.68) and EMG median- and mean power frequency slopes (0.41-0.50). At a Borg rating of 3, median- and mean power frequency and endurance time were reduced by 30%. At a Borg rating of 5, median- and mean power frequency and endurance time were reduced by 50%. At a Borg rating of 7, median- and mean power frequency and endurance time were reduced by 60-70%. CONCLUSIONS: Significant correlation between the Borg scale, EMG and endurance time suggests a close relationship between subjective and objective assessment of muscle fatigue.
OBJECTIVE: The purpose of this study was to correlate objective measurements of muscle fatigue in the lower back to the subject's own assessment of fatigue. DESIGN:Muscle fatigue in the lower back was assessed in healthy subjects using electromyography (EMG), endurance time and the Borg scale. BACKGROUND:Muscle fatigue, measured with EMG and endurance time, in the lower back, is significant for patients with pain in the lower back. METHODS: Fifty healthy subjects participated. EMG was detected from the lumbar extensor muscles during a modified Sørensen's test, an isometric contraction for the back extensors until exhaustion. During the test, subjects rated their subjective fatigue on a Borg CR-10 scale. RESULTS: Borg scale ratings correlated with endurance time (0.68) and EMG median- and mean power frequency slopes (0.41-0.50). At a Borg rating of 3, median- and mean power frequency and endurance time were reduced by 30%. At a Borg rating of 5, median- and mean power frequency and endurance time were reduced by 50%. At a Borg rating of 7, median- and mean power frequency and endurance time were reduced by 60-70%. CONCLUSIONS: Significant correlation between the Borg scale, EMG and endurance time suggests a close relationship between subjective and objective assessment of muscle fatigue.