Effects of chronic low back pain on trunk coordination and back muscle activity during walking: changes in motor control

Abstract

Low back pain (LBP) is often accompanied by changes in gait, such as a decreased (preferred) walking velocity. Previous studies have shown that LBP diminishes the normal velocity-induced transverse counter-rotation between thorax and pelvis, and that it globally affects mean erector spinae (ES) activity. The exact nature and causation of these effects, however, are not well understood. The aim of the present study was to examine in detail the effect of walking velocity on global trunk coordination and ES activity as well as their variability to gain further insights into the effects of non-specific LBP on gait. The study included 19 individuals with non-specific LBP and 14 healthy controls. Gait kinematics and ES activity were recorded during treadmill walking at (1) a self-selected (comfortable) velocity, and (2) sequentially increased velocities from 1.4 up to maximally 7.0 km/h. Pain intensity, fear of movement and disability were measured before the experiment. The angular movements of thorax, lumbar and pelvis were recorded in three dimensions. ES activity was recorded with pairs of surface electrodes. Trunk-pelvis coordination and mean amplitude of ES activity were analyzed. In addition, invariant and variant properties of trunk kinematics and ES activity were studied using principal component analysis (PCA). Comfortable walking velocity was significantly lower in the LBP participants. In the transverse plane, the normal velocity-induced change in pelvis-thorax coordination from more in-phase to more antiphase was diminished in the LBP participants, while lumbar and pelvis rotations were more in-phase compared to the control group. In the frontal plane, intersegmental timing was more variable in the LBP than in the control participants, with additional irregular movements of the thorax. Rotational amplitudes were not significantly different between the LBP and control participants. In the LBP participants, the pattern of ES activity was affected in terms of increased (residual) variability, timing deficits, amplitude modifications and frequency changes. The gait of the LBP participants was characterized by a more rigid and less variable kinematic coordination in the transverse plane, and a less tight and more variable coordination in the frontal plane, accompanied by poorly coordinated activity of the lumbar ES. Pain intensity, fear of movement and disability were all unrelated to the observed changes in coordination, suggesting that the observed changes in trunk coordination and ES activity were a direct consequence of LBP per se. Clinically, the results imply that conservative therapy should consider gait training as well as exercises aimed at improving both intersegmental and muscle coordination.

Figures

Fig. 1

Average time series of the global pattern of segment rotations in the transverse (left two panels) and frontal (right two panels) planes are shown for one control and one LBP participant. The dotted lines represent the SD

Fig. 2

The variability of the global (upper panels) and residual (lower panels) patterns of segment rotations in the transverse and frontal plane quantified as the ratio between the average variance over stride cycles of each segment for each LBP participant and that of the control group (ratio). Error bars indicate SD

Fig. 3

Mean relative Fourier phase (mRP) and the coupling (WC) between thoracic–pelvic and lumbar–pelvic rotations in the transverse plane (upper panels) and frontal plane (lower panels). The left y-axis represents values of the mRP, and the right y-axis values of the coupling (WC) between the segments

Fig. 4

Individual time series of superimposed stride cycles of the left ES recorded at the level of L4 for one control and three LBP participants at walking velocities of 2.2, 3.8, 4.6 and 6.2 km/h

Fig. 5

Eigenvalue spectra (λκ) of the LBP group and control group plotted on a logarithmic scale. At walking velocities of 3.8 km/h and higher, the amount of variance explained by the first principal component is smaller in the LBP group than in the control group. Note that at velocities of 1.4 and 2.2 km/h no clear gap between successive modes is present in either group

Fig. 6

PCA of EMG data obtained at a walking velocity of 5.4 km/h. The first column shows the eigenvalue spectra (λk); note the decrease in eigenvalues after mode 3. The second column shows the time series (ξ1..ξ3) corresponding to the first three modes, which together formed the global pattern of LES activity. The eigenvector coefficients (νk) are averaged over strides of LBP and control (Con) participants and represent the contribution of each muscle per group to the pattern (column 3)

Fig. 7

Variability of the global (upper panel) and residual pattern (lower panel) of left and right LES activity quantified by calculating the average variance over stride cycles for LBP participants over that of the control group (ratio). Error bars indicate SD