Abstract
BackgroundThis study aimed to identify which maximum voluntary isometric contraction (MVIC) and sub-MVIC tests produce the highest activation of the erector spinae muscles and the greatest reduction in inter-individual variability, to put them forward as reference normalization maneuvers for future studies.MethodsErector spinae EMG activity was recorded in 38 healthy women during five submaximal and three maximal exercises.ResultsNone of the three MVIC tests generated the maximal activation level in all the participants. The maximal activation level was achieved in 68.4% of cases with the test performed on the roman chair in the horizontal position (96.3 ± 7.3; p < 0.01). Of the five submaximal maneuvers, the one in the horizontal position on the roman chair produced the highest percentage of activation (61.1 ± 16.7; p < 0.01), and one of the lowest inter-individual variability values in the normalized signal of a trunk flexion-extension task.ConclusionsA modified Sorensen MVIC test in a horizontal position on a roman chair and against resistance produced the highest erector spinae activation, but not in 100% of participants, so the execution of several normalization maneuvers with the trunk at different inclinations should be considered to normalize the erector spinae EMG signal. A modified Sorensen test in a horizontal position without resistance is the submaximal maneuver that produces the highest muscle activation and the greatest reduction in inter-individual variability, and could be considered a good reference test for normalization.
Highlights
Surface electromyography (EMG) is a non-invasive method that allows the level of muscle activity to be quantified
The maximal activation level was achieved in 68.4% of cases (26 women) with the test performed with the roman chair in the horizontal position; 26.3% (10 women) achieved maximal activation at 45◦ with the trunk aligned with the lower extremities and 5.3% when at 45◦ with the hips flexed and the trunk parallel to the floor (Fig. 2)
The percentage of activation achieved in this maximal exercise did not significantly differ from the percentage of EMG activity obtained in the submaximal maneuver with the roman chair in the horizontal position
Summary
Surface electromyography (EMG) is a non-invasive method that allows the level of muscle activity to be quantified. This variability can affect the interpretation of the surface EMG (De Luca, 1997). To allow muscle activity to be compared between different muscles, patients, or varying electrode placements on the same muscle or on different days, the electromyographic signal must first be normalized (Lehman & McGill, 1999) In this procedure the absolute electrical activity values are expressed as a percentage with respect to a reference contraction. A modified Sorensen test in a horizontal position without resistance is the submaximal maneuver that produces the highest muscle activation and the greatest reduction in inter-individual variability, and could be considered a good reference test for normalization
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