Evaluation of strength and fatigue in subjects with and without lower back pain using Sørensen prone isometric back extension

Pitcher, Mark J. (2006) Evaluation of strength and fatigue in subjects with and without lower back pain using Sørensen prone isometric back extension. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Sørensen test of low back endurance is reported to be useful in evaluating potential for developing low back pain (LBP). Sørensen test postures are also used in eliciting maximal voluntary isometric activations (MVIA), which are used as normalization values. The purpose of this study was to investigate spinal musculature fatigue during a Sørensen test and to assess reliability of force and electromyography (EMG) during maximal and sub-maximal conditions in subjects with and without LBP. Repeated measures were taken on twenty male volunteers divided into LBP and control groups. EMG activity was recorded bilaterally from lower abdominal stabilizers (LAS), upper lumbar erector spinae (ULES), lower lumbar erector spinae (LLES), and biceps femoris (BF). Force and EMG during maximal and submaximal (100-170% of head, arms and trunk mass {HAT}) efforts were collected. Spectral contents were calculated from EMG and time to failure was recorded, testing fatigue. MVIA forces were lower (p≤0.05) in LBP vs. controls. Intraclass correlation coefficients for MVIA force, ULES and LLES EMG were excellent in controls (R>0.90), but significantly less in LBP (R=0.36-0.80). BF EMG demonstrated excellent reliability for both groups (R>0.90). Control group EMG was more reliable with maximal efforts, whereas LBP EMG was more reliable with submaximal exertions. Endurance times were not significantly different at any level of HAT. Significant differences in EMG median frequency between groups primarily occurred in the BF. The data indicates that BF contributes to extension, but does not contribute to group differences. Whereas MVIA during a modified Sørensen test is reliable in healthy populations, submaximal efforts using %HAT may be more reliable for clinical populations; further, the modified Sørensen test did not demonstrate significant differences between groups.

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