Electromyography and ratings of lumbar muscle fatigue using a four-level staircase protocol

Objective. The purpose of the study was to explore whether a relationship existed between subject's experience and objective measurements of back-muscle fatigue in healthy subjects. This may be used as reference material later. Design. Muscle fatigue in the lower back was measured in healthy subjects using a staircase protocol. Background. Muscle fatigue measurement in the lower back is of importance when assessing patients with low-back pain, The subject's experience of muscle fatigue needs to be explored further. Methods. Twenty healthy subjects with informed consent participated. Borg CR-10 scale responses and electromyography measurements were obtained from low-back muscles of the subjects following a staircase protocol with sustained contractions at 20%, 40%, 60%, and 80% of maximum voluntary contraction. Results. A strong correlation was found between Borg ratings and force (r = 0.83) and between slope and force (r = -0.72) but not between Borg ratings and slopes which was at best 0.43 (\r\ less than or equal to 0.43). Conclusions. Although subjective ratings and slopes showed a low correlation; increases in force with a concomitant increase in fatigue was reflected both by the subjective ratings and the slope. One cannot use subjective ratings for prediction of the slope for this type of protocol. However, a more complete description of muscle fatigue needs both the slope and the Borg ratings.