Load-Regulating Mechanisms in Gait and Posture: Comparative Aspects

Abstract

How is load sensed by receptors, and how is this sensory information used to guide locomotion? Many insights in this domain have evolved from comparative studies since it has been realized that basic principles concerning load sensing and regulation can be found in a wide variety of animals, both vertebrate and invertebrate. Feedback about load is not only derived from specific load receptors but also from other types of receptors that previously were thought to have other functions. In the central nervous system of many species, a convergence is found between specific and nonspecific load receptors. Furthermore, feedback from load receptors onto central circuits involved in the generation of rhythmic locomotor output is commonly found. During the stance phase, afferent activity from various load detectors can activate the extensor part in such circuits, thereby providing reinforcing force feedback. At the same time, the flexion is suppressed. The functional role of this arrangement is that activity in antigravity muscles is promoted while the onset of the next flexion is delayed as long as the limb is loaded. This type of reinforcing force feedback is present during gait but absent in the immoble resting animal.

Postural performance in decerebrated rabbit

“…Normally, operation of the closed-loop postural mechanisms is based mainly on the somatosensory information coming from limb mechanoreceptors rather than on vestibular and visual inputs [2,6,12,32]. The corresponding limb afferents give rise to two postural reflex loops, spinal and spino-supraspinal [5,9,11,13,17].…”

Modulation of ankle muscle postural reflexes in stroke: influence of weight-bearing load

“…Ib afferents from GTOs have been shown to be responsible for increasing muscle activity in response to increased limb load in cats (Duysens and Pearson, 1980;Pearson, 1995;Pearson and Collins, 1993). Subsequently, Dietz et al (1992) and Duysens et al (2000) have argued that GTOs signal load in humans as well. In addition, cutaneous afferents from plantar mechanoreceptors in the foot have been shown to be important for postural control (Kavounoudias et al 2001) and compensatory postural reflexes elicited in response to a forward fall while standing (Do et al, 1990).…”

“…Reactive postural control entails a response, mediated by postural muscle reflexes, to a sudden unexpected perturbation applied to the body and relies on the central nervous system's (CNS) ability to interpret afferent information to ensure that the centre of mass (COM) stays within the base of support. Proprioceptive afferents from extensor muscles in the legs and exteroceptive afferents from mechanoreceptors in the foot are among the available inputs to the CNS to modulate standing or locomotor postural reflexes (Duysens et al, 2000). It has been suggested that these afferent inputs can provide information regarding load, and thus, have been referred to as load receptors and are particularly useful in signalling COM position (Dietz et al, 1992).…”

“…Furthermore, greater load applied to the body during standing platform translations on land was associated with an increase in the magnitude of extensor muscle postural reflexes in healthy individuals (Dietz et al, 1992). It is believed that Ib afferents from golgi tendon organs (GTOs) provide load information to the spinal cord (Dietz et al, 1992;Duysens et al, 2000). In addition to Ib afferents from GTOs, cutaneous mechanoreceptors in the sole of the foot are in an optimal location to sense limb load and have been recently shown to be important in standing balance (Kavounoudias et al, 2001).…”

Development of a kinematic coordination pattern in toddler locomotion: planar covariation

“…The second one concerns more specifically the equilibrium system related to the body configuration and posture control. The third one is comprised of phasic feedback mechanisms activating, modulating, and further developing central pattern generators (CPGs) and other neural networks, using reflexive (neural; Duysens et al 2000) and preflexive (mechanical; Zehr and Stein 1999) factors.…”