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purpose of this study was to determine the contribution of hamstrings
and quadriceps fatigue to quadriceps inhibition following lumbar extension
exercise. Regression models were calculated consisting of the outcome
variable: quadriceps inhibition and predictor variables: change in
EMG median frequency in the quadriceps and hamstrings during lumbar
fatiguing exercise. Twenty-five subjects with a history of low back
pain were matched by gender, height and mass to 25 healthy controls.
Subjects performed two sets of fatiguing isometric lumbar extension
exercise until mild (set 1) and moderate (set 2) fatigue of the lumbar
paraspinals. Quadriceps and hamstring EMG median frequency were measured
while subjects performed fatiguing exercise. A burst of electrical
stimuli was superimposed while subjects performed an isometric maximal
quadriceps contraction to estimate quadriceps inhibition after each
exercise set. Results indicate the change in hamstring median frequency
explained variance in quadriceps inhibition following the exercise
sets in the history of low back pain group only. Change in quadriceps
median frequency explained variance in quadriceps inhibition following
the first exercise set in the control group only. In conclusion, persons
with a history of low back pain whose quadriceps become inhibited
following lumbar paraspinal exercise may be adapting to the fatigue
by using their hamstring muscles more than controls.
KEY
WORDS: Superimposed burst technique, electromyography, spectral
median frequency, correlation and regression, low back pain.
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