Adaptations in muscle activity to induced, short-term hindlimb lameness in trotting dogs

Abstract

Muscle tissue has a great intrinsic adaptability to changing functional demands. Triggering more gradual responses such as tissue growth, the immediate responses to altered loading conditions involve changes in the activity. Because the reduction in a limb's function is associated with marked deviations in the gait pattern, understanding the muscular responses in laming animals will provide further insight into their compensatory mechanisms as well as help to improve treatment options to prevent musculoskeletal sequelae in chronic patients. Therefore, this study evaluated the changes in muscle activity in adaptation to a moderate, short-term, weight-bearing hindlimb lameness in two leg and one back muscle using surface electromyography (SEMG). In eight sound adult dogs that trotted on an instrumented treadmill, bilateral, bipolar recordings of the m. triceps brachii, the m. vastus lateralis and the m. longissimus dorsi were obtained before and after lameness was induced. Consistent with the unchanged vertical forces as well as temporal parameters, neither the timing nor the level of activity changed significantly in the m. triceps brachii. In the ipsilateral m. vastus lateralis, peak activity and integrated SEMG area were decreased, while they were significantly increased in the contralateral hindlimb. In both sides, the duration of the muscle activity was significantly longer due to a delayed offset. These observations are in accordance with previously described kinetic and kinematic changes as well as changes in muscle mass. Adaptations in the activity of the m. longissimus dorsi concerned primarily the unilateral activity and are discussed regarding known alterations in trunk and limb motions.

Figure 1. One of the subjects partially instrumented to illustrate the electrode positioning (for details on the skeletal landmarks, see Material & Methods).

Figure 2. Activity of the m. triceps brachii, m. vastus lateralis, and the m. longissimus dorsi shown as time-normalized SEMGs (median plus upper and lower quartiles for each of the 201 bins) across the dogs and 10 strides per dog for the sound (black) and the lame (grey) conditions.

Graphs on the left represent the recordings from the body side contralateral to the lame side; graphs on the right show the activity from the muscles ipsilateral to the lame side. Numbers in parenthesis after the muscle names indicate sample size. Each x-axis shows the stance and swing phase normalized to 50% of the stride cycle in all recordings. The x-axis for the m. triceps brachii refers to the stride cycle of the forelimbs; the x-axes of the m. vastus lateralis and the m. longissimus dorsi refer to the footfall events of the hindlimbs. Each plot has a single y-axis and is scaled to the maximum amplitude observed for that particular recording site; hence SEMG amplitudes can be compared between sound and lame conditions within a given plot. Grey and black blocks above the SEMG traces indicate bin-by-bin differences in amplitude between both conditions, with the color indicating the condition with significantly greater amplitude; no block indicates no differences. The arrows indicate significant differences in the muscle activity between sound and lame conditions: Horizontal arrows point to changes in timing of the on- or offset (bottom of the graph) and the maximum activity (top of the graph). Vertical arrows indicate significant changes in SEMG area. Stars indicate significant differences in peak activity.