Chronic low back pain-associated paraspinal muscle dysfunction is not the result of a constitutionally determined "adverse" fiber-type composition.
METHODS
Investigative case control study.


OBJECTIVE
To determine whether excessive paraspinal muscle fatigue in chronic low back pain results from a paucity of muscle type I fiber content.


BACKGROUND
Paraspinal muscle function is vital for spinal protection. Prospective studies suggest that excessive paraspinal muscle fatigability may increase risk of first-time low back pain. As contractile performance of the paraspinal muscles is governed by their constitutionally determined fiber composition, the question arises whether a constitutionally determined "adverse" composition could predispose to low back pain through impaired spinal protection.


METHODS
Thirty-five male patients with chronic low back pain were compared with 32 male control patients of similar age and anthropometry. During Sorensen and 60% of maximum voluntary isometric contraction fatigue tests, median frequency declines in the paraspinal muscle surface electromyograph signal were monitored and correlated with muscle histomorphometry.


RESULTS
Patients were weaker than controls during maximum voluntary isometric contractions (84.47 [28.44]vs. 98.74 [18.11] kg, respectively; P = 0.02) and more fatigable during their Sorensen tests (endurance time 105.29 [28.53]vs. 137.50 [40.38] sec, respectively; P < 0.01). There were no between-group differences in median frequency declines during the Sorensen (-0.37 [0.16]vs. -0.36 [0.12]%.sec) or 60% maximum voluntary isometric contraction (-0.42 [0.31]vs. -0.51 [0.29]%.sec) tests, for patients and controls, respectively. There were no between-group differences in the percent number of paraspinal muscle type I fibers (64 [11]vs. 64 [9]%) or the percent area occupied by type I fibers (67 [11]vs. 69 [9]%), for patients and controls, respectively. Type I and II muscle fiber narrow diameters were similar for both groups.


CONCLUSIONS
In the patients with chronic low back pain tested, their associated paraspinal muscle dysfunction was not the result of a constitutionally determined "adverse" fiber type composition.
Crossman
Kim
K
Musculoskeletal Research Group, University of Manchester, United Kingdom.
Mahon
Mike
M
Watson
Paul J
PJ
Oldham
Jacqueline A
JA
Cooper
Robert G
RG
D000328:Adult; D001706:Biopsy; D016022:Case-Control Studies; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D017116:Low Back Pain / Q000150:complications*; D008297:Male; D008875:Middle Aged; D018763:Muscle Fatigue / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000648:ultrastructure*; D018657:Muscle Fibers, Slow-Twitch / Q000648:ultrastructure*; D018482:Muscle, Skeletal / Q000473:pathology*