Paraspinal muscle EMG fatigue testing with two methods in healthy volunteers. Reliability in the context of clinical applications

Objective. Comparison of the accuracy of surface electromyogram for back muscle endurance assessment with two different tests. Design. Test–retest measurements in 16 healthy volunteers on two separate occasions for each test under controlled conditions. Background. Back muscle endurance is considered important in low back pain rehabilitation. Reliability of paraspinal muscle endurance assessment is a pre-requisite for accurate and meaningful clinical applications of the technique. Methods. All participants performed each test twice. A direct comparison was made between two popular fatigue testing methods, the modified Biering–Sørensen and a 60% maximum voluntary isometric contraction in the upright position during which time fatigue was assessed from the electromyogram spectral and amplitude analysis. Results. Reproducibility of initial median frequency was excellent for both tests. Normalised median frequency slope values were more reliable with the 60% maximum voluntary contraction upright test. The clinical applicability of these measures in detecting significant differences after patient rehabilitation is recommended. Root mean square had very large between-day error for both tests. Relevance This paper provides information on the accuracy level of power spectral analysis for use as an endurance outcome measure in back muscle rehabilitation studies.