Erector spinae and quadratus lumborum muscle endurance tests and supine leg-length alignment asymmetry: an observational study.

OBJECTIVE To determine if there is an association between supine leg-length alignment (LLA) asymmetry and the endurance of the erector spinae (ES) and quadratus lumborum (QL) muscles. METHODS Forty-seven subjects (21 women; average age, 36 years old) were tested for ES endurance using the Biering-Sorensen (B-S) test, and 69 (31 women; average age, 34.5 years) were tested for QL endurance. Subjects were examined for supine LLA and tested for ES and QL muscle endurance. The muscle endurance times were compared against those who did and did not demonstrate LLA asymmetry and the side of the "short leg." RESULTS In the B-S test, volunteers with LLA asymmetry (n = 27) had a mean endurance time of 89.7 seconds (SD, 43.3), and the no-LLA asymmetry group (n = 20) had a mean endurance time of 161.5 seconds (SD, 57.1), a significant difference (P < .001). In the QL test, after correction for the effects of sex and exercise, those with a right "short leg" (n = 22) had a right QL endurance time of 25.9 seconds (SE, 4.2) and a left QL endurance time of 34.7 seconds (SE, 4.3). The right QL endurance time was significantly different from those subjects with balanced legs (P = .001). Those with a left "short leg" (n = 20) had a left QL endurance time of 28.6 seconds (SE, 4.7) and a right QL endurance time of 38.1 seconds (SE, 4.5). Both QL endurance times were significantly different from those with balanced leg-length (P = .002 and .016, respectively). CONCLUSION This study suggests that, using the B-S test, the group of volunteers who demonstrated a commonly used sign of subluxation/joint dysfunction, supine LLA asymmetry, had a decreased endurance times over those who did not. The QL endurance tests showed that the QL muscle ipsilateral to the supine short leg had significantly decreased endurance times over the same-side QL fatigue times in the no leg-length asymmetry group.