Abstract
Locomotion after complete spinal cord injury (spinal transection) in animal models is usually evaluated in a hindlimb-only condition with the forelimbs suspended or placed on a stationary platform and compared with quadrupedal locomotion in the intact state. However, because of the quadrupedal nature of movement in these animals, the forelimbs play an important role in modulating the hindlimb pattern. This raises the question: whether changes in the hindlimb pattern after spinal transection are due to the state of the system (intact versus spinal) or because the locomotion is hindlimb-only. We collected kinematic and electromyographic data during locomotion at seven treadmill speeds before and after spinal transection in nine adult cats during quadrupedal and hindlimb-only locomotion in the intact state and hindlimb-only locomotion in the spinal state. We attribute some changes in the hindlimb pattern to the spinal state, such as convergence in stance and swing durations at high speed, improper coordination of ankle and hip joints, a switch in the timing of knee flexor and hip flexor bursts, modulation of burst durations with speed, and incidence of bi-phasic bursts in some muscles. Alternatively, some changes relate to the hindlimb-only nature of the locomotion, such as paw placement relative to the hip at contact, magnitude of knee and ankle yield, burst durations of some muscles and their timing. Overall, we show greater similarity in spatiotemporal and EMG variables between the two hindlimb-only conditions, suggesting that the more appropriate pre-spinal control is hindlimb-only rather than quadrupedal locomotion.
Highlights
Locomotion in quadrupeds normally involves all four limbs performing coordinated movements to achieve a smooth forward progression while maintaining dynamic balance (Frigon, 2017)
The spinal transection changes the neural control of locomotion, as pathways and structures within the central nervous system normally communicate with the spinal locomotor central pattern generators (CPGs) controlling each limb during quadrupedal locomotion (Grillner, 1981; Drew et al, 1996; Frigon, 2017)
In accordance with earlier studies (Bélanger et al, 1996; de Leon et al, 1998; Frigon and Rossignol, 2008), we found that cycle and stance durations significantly decreased with increasing speed while swing duration did not change significantly
Summary
Locomotion in quadrupeds normally involves all four limbs performing coordinated movements to achieve a smooth forward progression while maintaining dynamic balance (Frigon, 2017). The spinal transection changes the neural control of locomotion, as pathways and structures within the central nervous system normally communicate with the spinal locomotor CPGs controlling each limb during quadrupedal locomotion (Grillner, 1981; Drew et al, 1996; Frigon, 2017). Placing the forelimbs on a stationary platform or suspending them in the air changes the biomechanics; for example, by shifting more weight on the hindlimbs and elevating the angle of the trunk relative to the horizontal. These biomechanical changes influence the neural control
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