Limb and back muscle activity adaptations to tripedal locomotion in dogs.

Alterations in muscle recruitment are key to the functional plasticity of the mammalian locomotor system. One particularly challenging situation quadrupeds may face is when the functionality of a limb is reduced or lost. To better understand how mammals manage in such situations and which muscular adaptations they exhibit when locomoting on three legs, we recorded the activity patterns of two limb and one back extensor muscle in nine dogs using surface electromyography. We compared the timing and the level of recruitment before and after the loss of a hindlimb was simulated. Both the intensity and the timing of the activity changed significantly in the m. vastus lateralis of the remaining hindlimb, consistent with this limb bearing a greater proportion of the body weight as well as with previously reported kinematic changes. In accordance with the greater body weight supported by the forelimbs, the m. triceps brachii showed first and foremost an increased level of excitation. The very asymmetrical changes in the timing and the level of activity in the m. longissimus dorsi reflects the highly asymmetrical functional requirements imposed on the trunk and the pelvis when one hindlimb is no longer involved in the production of locomotor work while the other hindlimb partially compensates the loss. Integration of our electromyographical findings with kinetic and kinematic results illustrates that dogs exhibited a well-coordinated response to the functional requirements of tripedalism and underlines the importance of moment-to-moment modulation in muscular recruitment for the functional plasticity of the mammalian locomotor system.