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Back and
hip extensor fatigability in chronic low back pain patients and
controls. Arch Phys Med Rehabil. 1998 Apr;79(4):412-7.
Kankaanpaa M, Taimela S, Laaksonen D, Hanninen O, Airaksinen O.
Department of Physical Medicine and
Rehabilitation, Kuopio Univeristy Hospital, Finland.
OBJECTIVE: To compare the lumbar paraspinal and
gluteus maximus muscle fatigability between chronic low back pain
patients and healthy controls by using electromyographic (EMG) spectral
analysis during a maximal isometric endurance task. DESIGN: A
cross-sectional comparative study between chronic low back pain
patients and healthy control subjects. SETTING: Physical medicine and
rehabilitation clinic in Finland. SUBJECTS: Twenty women with
nonspecific chronic low back pain (longer than 3 months) and 15 healthy
controls. INTERVENTION: Subjects performed maximal voluntary isometric
back extensions (MVC) at 30 degrees forward flexion in a specially
designed measurement unit. A 50% MVC load was used in isometric
endurance test. OUTCOME MEASURES: Low back pain intensity was assessed
by using the visual analogue scale and functional disability by the
Oswestry disability index. Time to endurance was measured. Bipolar
surface EMG recordings were made over the lumbar paraspinal muscles
(L3-L4, L5-S1) and over the gluteus maximus muscles. Average EMG
(aEMG%), and initial spectral median frequency (MFinit) and change over
time (MFslope) were computed. RESULTS: Pain intensity and functional
disability were higher and MVC and time to endurance were lower in the
chronic low back pain group (p < .05). Similar muscle activity
levels (aEMG%) and MFinit indicated similar muscle loading in both
groups at the beginning of the endurance test. EMG spectral decreases
(MFslope) indicated that lumbar paraspinal muscle fatigability was
similar in both groups. In the chronic low back pain group, the gluteus
maximus fatigued faster than in the control group (greater MFslope, p
< .05). However, the shorter endurance time indicated greater
fatigability in the chronic low back pain group in general (p <
.05). CONCLUSIONS: The chronic low back pain patients were weaker and
fatigued faster than the healthy controls. The EMG fatigue analysis
results suggest that the gluteus maximus muscles are more fatigable in
chronic low back pain patients than in healthy control subjects during
a sustained back extension endurance test.
PMID: 9552107 [PubMed - indexed for MEDLINE]

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