Trunk extensor EMG-torque relationship

The integrated surface electromyogram (IEMG) of the lumbar erectores spinae and the torque generated were simultaneously recorded from 27 healthy subjects in the standing posture while they pulled isometrically against resistance provided by a harness around the shoulders. The IEMG-torque ratio (eff...

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Bibliographic Details
Published in:Spine (Philadelphia, Pa. 1976) Pa. 1976), 1987-10, Vol.12 (8), p.770-776
Main Authors: STOKES, I. A. F, RUSH, S, MOFFROID, M, JOHNSON, G. B, HAUGH, L. D
Format: Article
Language:English
Subjects:
Adult
Biological and medical sciences
Biomechanical Phenomena
Body Height
Body Weight
Electromyography - methods
Female
Fundamental and applied biological sciences. Psychology
Humans
Isometric Contraction
Lumbosacral Region - physiology
Male
Muscles - physiology
Posture
Striated muscle. Tendons
Vertebrates: osteoarticular system, musculoskeletal system
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Summary:The integrated surface electromyogram (IEMG) of the lumbar erectores spinae and the torque generated were simultaneously recorded from 27 healthy subjects in the standing posture while they pulled isometrically against resistance provided by a harness around the shoulders. The IEMG-torque ratio (efficiency of electrical activity, or EEA) was used to characterize each subject. Individual recordings showed evidence of nonlinearity of the IEMG-torque relationship in that a statistically better fit to experimental recordings was obtained by using two straight lines with a breakpoint between them. However, with repeated testing, the gradients of these two lines were more variable than the slope of the single straight line fitted to the entire recording. The slope of the best fit line (EEA) was less for recordings made during torque decrease than for increasing-torque recordings. This also showed as a "hysteresis" pattern in the recordings. The coefficient of variability (within subjects) of the EEA was greater in day-to-day testing (24%) than with repeated pulls at the same testing session (14%). This was similar to variability of the maximum generated torque. About 25% of the variability between subjects was found to be due to anthropometric differences. The residual variability of the relationship would limit the accuracy of IEMG as a measure of muscular effort under changing torque conditions. However, the EEA may be useful for characterizing muscle performance, especially when maximum effort cannot be achieved.
ISSN:0362-2436
1528-1159
DOI:10.1097/00007632-198710000-00011