| Studies employing modified Biering-Sørenson tests have reported
that low back endurance is related to the potential for developing
low back pain. Understanding the manner in which spinal musculature
fatigues in people with and without LBP is necessary to gain insight
into the sensitivity of the modified Biering-Sørenson test to differentiate
back health. Twenty male volunteers were divided into a LBP group
of subjects with current subacute or a history of LBP that limited
their activity (n = 10) and a control group (n = 10). The median frequency
of the fast Fourier transform was calculated from bilateral surface
electromyography (EMG) of the upper lumbar erector spinae (ULES),
lower lumbar erector spinae (LLES) and biceps femoris while maintaining
a prescribed modified Biering-Sørensen test position and exerting
isometric forces equivalent to 100, 120, 140 and 160% of the estimated
mass of the head-arms-trunk (HAT) segment. Time to failure was also
investigated across the percentages of HAT. Fatigue time decreased
with increasing load and differences between groups increased as load
increased, however these differences were not significant. Significant
differences in the EMG median frequency between groups occurred in
the right biceps femoris (p < 0.05) with significant pairwise differences
occurring at 140% for the left biceps femoris and at 160% for the
right biceps femoris. There were significant pairwise differences
at 120% for average EMG of the right biceps femoris and at 140% for
the right ULES, and right and left biceps femoris (p < 0.05). The
modified Biering-Sørensen test as usually performed at 100% HAT is
not sufficient to demonstrate significant differences between controls
and subjects with varying degrees of mild back disability based on
the Oswestry classification.
KEY
WORDS: Endurance,
electromyography, median frequency, back muscles, healthy subjects.
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