Body stability and muscle and motor cortex activity during walking with wide stance

Abstract

Farrell BJ, Bulgakova MA, Beloozerova IN, Sirota MG, Prilutsky BI. Body stability and muscle and motor cortex activity during walking with wide stance. J Neurophysiol 112: 504 -524, 2014. First published April 30, 2014 doi:10.1152/jn.00064.2014.-Biomechanical and neural mechanisms of balance control during walking are still poorly understood. In this study, we examined the body dynamic stability, activity of limb muscles, and activity of motor cortex neurons [primarily pyramidal tract neurons (PTNs)] in the cat during unconstrained walking and walking with a wide base of support (wide-stance walking). By recording three-dimensional full-body kinematics we found for the first time that during unconstrained walking the cat is dynamically unstable in the forward direction during stride phases when only two diagonal limbs support the body. In contrast to standing, an increased lateral between-paw distance during walking dramatically decreased the cat's body dynamic stability in doublesupport phases and prompted the cat to spend more time in threelegged support phases. Muscles contributing to abduction-adduction actions had higher activity during stance, while flexor muscles had higher activity during swing of wide-stance walking. The overwhelming majority of neurons in layer V of the motor cortex, 82% and 83% in the forelimb and hindlimb representation areas, respectively, were active differently during wide-stance walking compared with unconstrained condition, most often by having a different depth of striderelated frequency modulation along with a different mean discharge rate and/or preferred activity phase. Upon transition from unconstrained to wide-stance walking, proximal limb-related neuronal groups subtly but statistically significantly shifted their activity toward the swing phase, the stride phase where most of body instability occurs during this task. The data suggest that the motor cortex participates in maintenance of body dynamic stability during locomotion.body dynamic stability; motor cortex activity; pyramidal tract neurons; locomotion; cat THE ABILITY TO CONTROL body balance and stability during locomotion is essential to prevent falls and recover from perturbations. Maintenance of stable standing and locomotion is complicated by injury (Day et al. 2012;Duong et al. 2004;Holder-Powell and Rutherford 2000), aging (Schrager et al. 2008), fear of falling (Chamberlin et al. 2005;Dunlap et al. 2012), and other factors. Several motor strategies have been found to help maintain stability while walking on complex terrain. They include 1) reducing walking velocity (Chamberlin et al. 2005;Dingwell et al. 2000;Gálvez-López et al. 2011; Maki 1997), 2) reducing stride length and increasing stance width (Dunlap et al. 2012; Maki 1997;Misiaszek 2006), and 3) lowering the center of mass (Gálvez-López et al. 2011;Schmidt and Fischer 2010) and prolonging the double-support phase (Chamberlin et al. 2005; Maki 1997). While stability of the human body during locomotion has been analyzed in detail, little is known ab...

Stabilization of cat paw trajectory during locomotion

“…To recover balance in this situation, the foot must be placed in front of the extrapolated center of mass and "in order to walk stable and in a straight path, the foot ... has to be placed with an accuracy of a few millimetres" (p. 257: Hof et al 2007). A recent study on dynamic stability in walking cats (Farrell et al 2011(Farrell et al , 2014 indicates that the cat is dynamically unstable in the sagittal plane (the extrapolated center of mass is in front of the base of support) during the short phases of double support by diagonal fore-and hindlimbs. The forward fall of the cat is prevented by placement of the swing forepaw in front of the extrapolated center of mass during both regular walking and walking with a constrained stance width (Farrell et al 2011(Farrell et al , 2014.…”

“…A recent study on dynamic stability in walking cats (Farrell et al 2011(Farrell et al , 2014 indicates that the cat is dynamically unstable in the sagittal plane (the extrapolated center of mass is in front of the base of support) during the short phases of double support by diagonal fore-and hindlimbs. The forward fall of the cat is prevented by placement of the swing forepaw in front of the extrapolated center of mass during both regular walking and walking with a constrained stance width (Farrell et al 2011(Farrell et al , 2014. Hindpaw accurate placement in front of the extrapolated center of mass in the frontal plane may also be important for maintaining body lateral stability at the transition from a double support period by ipsilateral fore-and hindlimbs to a three-legged support period (Farrell et al 2014).…”

“…The forward fall of the cat is prevented by placement of the swing forepaw in front of the extrapolated center of mass during both regular walking and walking with a constrained stance width (Farrell et al 2011(Farrell et al , 2014. Hindpaw accurate placement in front of the extrapolated center of mass in the frontal plane may also be important for maintaining body lateral stability at the transition from a double support period by ipsilateral fore-and hindlimbs to a three-legged support period (Farrell et al 2014). Thus covarying limb segment angles (and possibly other elemental variables) to ensure reproducible paw position prior to paw placement seems important not only for accurate stepping, but also for regular walking.…”

“…Note that human experiments have provided evidence for increased V UCM during movements to uncertain targets and practice in conditions of instability (de Freitas et al 2007;Freitas and Scholz 2009;Wu et al 2012). The differences in patterns of V UCM and V ORT for endpoint limb position between human movements and cat walking could reflect relatively high dynamic stability of quadrupedal locomotion (Farrell et al 2011;Farrell et al 2014).…”

“…Thus in this locomotor behavior, paw position during swing can be hypothesized to be a performance variable. Recent studies on dynamic stability of regular walking in humans (Hof et al 2005(Hof et al , 2007 and cats (Farrell et al 2014) have also demonstrated the importance of accurate foot or paw placement in front of the extrapolated center of mass of the body to maintain dynamic stability in the frontal and sagittal planes. Therefore, it is reasonable to assume that paw position during cat regular walking could be a performance variable.…”