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A method to study the lumbar back muscle activity to be used in back pain prevention:
Clinical Biomechanics 1990; 5: 51-52
Brief Report
A method to study the lumbar back muscle activity to be used in back pain prevention: THESIS SUMMARY P Vink MD University of Leiden, The Netherlands
This study was concerned with the way in which the lumbar back muscles stabilize the spine under various loading conditions. To this aim, the recruitment pattern of the lumbar back muscles was recorded by using 12 bipolar surface electrodes. Three columns, which correspond grossly to the multifidus, the longissimus and the iliocostalis muscles, respectively, were studied. It was investigated whether a specific activity of these three columns could be recorded with just 12 surface electrodes. It was shown that the level of cross-talk between two electrodes increased unacceptably when more than 12 electrodes were used due to the decreased distance between them. Muscle length is an important factor which should be controlled when interpreting the electromyogram. During walking, no activity was found at homolateral toe-off (see Figure 1); the phase in which the deliverance of a maximum force was necessary according to Cappozzo’. The length of the lumbar back muscles was found to be maximal at this stage (see Figure 1). Therefore, it is likely that these forces are produced by the passive lengthening of the back muscles and the surrounding tissue. Studies were made of walking with an artificial leg length discrepancy. It was predicted that during walking with unequal leg lengths, bilateral activity of the lumbar back muscles would increase (relative to walking with equal leg lengths) during heel strike of the longer limb. This bilateral activity is required to counteract the increased forward flexion of the trunk, because of a relatively increased deceleration of the raised limb. The verification of this prediction was complicated:
longer leg on pelvic rotation in the frontal and sagittal plane during walking. A leg length inequality is largely compensated by changes in phase lengths of a stride as well as in changed knee flexion and pelvic translation along the Z-axis. 2. The amplitude of the electromyograms did not differ significantly between normal walking and walking with a leg length inequality, but the duration of activity was changed significantly. The prediction was affirmed: activity time increased bilaterally at heel strike of the longer leg. The following muscle recruitment characteristics were found. The three columns of lumbar muscle behaved
,
I
,,R/A
I
emg.
I
0.1
0.2 Time
L;ft heel strike
(s)
I
I Ribht toe off
1. There appeared to be a minor influence from the &ctor of Medicine thesis, Leiden, 1999 Original title of thesis: Functions of the lumbar back muscles Correspondence to: P Vink, Arbouw, PO Box 8114,lOM dam. The Netherlands
AC Amster-
Figure 1. Changes in predicted force exerted by the most
lateral columnof the rightlumbarback muscles (derivedfrom the resultsof Cappouo’), the recordedactivity(WA e.m.g. rectifiedand averaged electromyogram)and the length of this muscle column calculated from data of pelvic and thoracic rotations, in one bipedal phase of the walking cycle.
52
C/in. Biomech. 1990: 5: No 1
differently, and their recruitment was strongly dependent on the plane in which the moments were required. Sagittul plane: All three columns were recruited during extension. In submaximal forces the medial column showed relatively more activity, relative to the maximal recorded activity, than both other columns. Frontal plane: The medial and caudal parts of the lumbar back muscles were recruited more during laterogexion of the lower lumbar vertebrae and the lateral parts were more involved with lateroflexion of the upper lumbar vertebrae and the torso. It is still not known how the back muscles should be used to avoid back pain. However, it should be possible
to generate a considerable
amount of information about the optimal use of these muscles by performing relatively simple experiments. Patterns of muscle recruitment could be studied in subjects free from back pain who have performed hazardous activities over many years. These patterns of muscle activity could then be taught to high risk groups, and appropriate environmental conditions created to enable such optimal use.
References 1 Cappozzo A. The forces and couples in the human trunk during level walking. J Biomech 1983; 16: 265-77
Brief Report
A method to study the lumbar back muscle activity to be used in back pain prevention: THESIS SUMMARY P Vink MD University of Leiden, The Netherlands
This study was concerned with the way in which the lumbar back muscles stabilize the spine under various loading conditions. To this aim, the recruitment pattern of the lumbar back muscles was recorded by using 12 bipolar surface electrodes. Three columns, which correspond grossly to the multifidus, the longissimus and the iliocostalis muscles, respectively, were studied. It was investigated whether a specific activity of these three columns could be recorded with just 12 surface electrodes. It was shown that the level of cross-talk between two electrodes increased unacceptably when more than 12 electrodes were used due to the decreased distance between them. Muscle length is an important factor which should be controlled when interpreting the electromyogram. During walking, no activity was found at homolateral toe-off (see Figure 1); the phase in which the deliverance of a maximum force was necessary according to Cappozzo’. The length of the lumbar back muscles was found to be maximal at this stage (see Figure 1). Therefore, it is likely that these forces are produced by the passive lengthening of the back muscles and the surrounding tissue. Studies were made of walking with an artificial leg length discrepancy. It was predicted that during walking with unequal leg lengths, bilateral activity of the lumbar back muscles would increase (relative to walking with equal leg lengths) during heel strike of the longer limb. This bilateral activity is required to counteract the increased forward flexion of the trunk, because of a relatively increased deceleration of the raised limb. The verification of this prediction was complicated:
longer leg on pelvic rotation in the frontal and sagittal plane during walking. A leg length inequality is largely compensated by changes in phase lengths of a stride as well as in changed knee flexion and pelvic translation along the Z-axis. 2. The amplitude of the electromyograms did not differ significantly between normal walking and walking with a leg length inequality, but the duration of activity was changed significantly. The prediction was affirmed: activity time increased bilaterally at heel strike of the longer leg. The following muscle recruitment characteristics were found. The three columns of lumbar muscle behaved
,
I
,,R/A
I
emg.
I
0.1
0.2 Time
L;ft heel strike
(s)
I
I Ribht toe off
1. There appeared to be a minor influence from the &ctor of Medicine thesis, Leiden, 1999 Original title of thesis: Functions of the lumbar back muscles Correspondence to: P Vink, Arbouw, PO Box 8114,lOM dam. The Netherlands
AC Amster-
Figure 1. Changes in predicted force exerted by the most
lateral columnof the rightlumbarback muscles (derivedfrom the resultsof Cappouo’), the recordedactivity(WA e.m.g. rectifiedand averaged electromyogram)and the length of this muscle column calculated from data of pelvic and thoracic rotations, in one bipedal phase of the walking cycle.
52
C/in. Biomech. 1990: 5: No 1
differently, and their recruitment was strongly dependent on the plane in which the moments were required. Sagittul plane: All three columns were recruited during extension. In submaximal forces the medial column showed relatively more activity, relative to the maximal recorded activity, than both other columns. Frontal plane: The medial and caudal parts of the lumbar back muscles were recruited more during laterogexion of the lower lumbar vertebrae and the lateral parts were more involved with lateroflexion of the upper lumbar vertebrae and the torso. It is still not known how the back muscles should be used to avoid back pain. However, it should be possible
to generate a considerable
amount of information about the optimal use of these muscles by performing relatively simple experiments. Patterns of muscle recruitment could be studied in subjects free from back pain who have performed hazardous activities over many years. These patterns of muscle activity could then be taught to high risk groups, and appropriate environmental conditions created to enable such optimal use.
References 1 Cappozzo A. The forces and couples in the human trunk during level walking. J Biomech 1983; 16: 265-77