Adaptive behaviour of the spinal cord in the transition from quiet stance to walking

Abstract

BackgroundModulation of nociceptive withdrawal reflex (NWR) excitability was evaluated during gait initiation in 10 healthy subjects to investigate how load- and movement-related joint inputs activate lower spinal centres in the transition from quiet stance to walking. A motion analysis system integrated with a surface EMG device was used to acquire kinematic, kinetic and EMG variables. Starting from a quiet stance, subjects were asked to walk forward, at their natural speed. The sural nerve was stimulated and EMG responses were recorded from major hip, knee and ankle muscles. Gait initiation was divided into four subphases based on centre of pressure and centre of mass behaviours, while joint displacements were used to categorise joint motion as flexion or extension. The reflex parameters were measured and compared between subphases and in relation to the joint kinematics.ResultsThe NWR was found to be subphase-dependent. NWR excitability was increased in the hip and knee flexor muscles of the starting leg, just prior to the occurrence of any movement, and in the knee flexor muscles of the same leg as soon as it was unloaded. The NWR was hip joint kinematics-dependent in a crossed manner. The excitability of the reflex was enhanced in the extensor muscles of the standing leg during the hip flexion of the starting leg, and in the hip flexors of the standing leg during the hip extension of the starting leg. No notable reflex modulation was observed in the ankle muscles.ConclusionsOur findings show that the NWR is modulated during the gait initiation phase. Leg unloading and hip joint motion are the main sources of the observed modulation and work in concert to prepare and assist the starting leg in the first step while supporting the contralateral leg, thereby possibly predisposing the lower limbs to the cyclical pattern of walking.

Stimulation site and phase modulation of the withdrawal reflex during gait initiation

“…At HO, where an increase of the response was expected for BF and RF (Serrao et al, 2012a), our results showed that neither BF nor RF reflex responses seem to be posture dependent. The modulation on TA can be related to supporting the development of the displacement of the CoP towards the stance leg and the forward movement of the body.…”

“…In general, previous studies dealing with the relationship between gait and the NWR showed a modulation of the reflex amplitude depending on which moment of the gait process the stimulation was delivered (Spaich et al, 2004(Spaich et al, , 2006Emborg et al, 2009;Serrao et al, 2012a). However, the present study also revealed interactions between postures and stimulation sites in the GIP for the hip and ankle measurements but not for the EMG responses.…”

“…The next two sub-phases form the stepping phase (SP). This phase of the gait initiation process is divided in the single support sub-phase that finalizes with the heel contact of the starting foot (Serrao et al, 2012a) and is followed by the double support sub-phase.…”

“…In the GIP, as soon as the starting leg is unloaded and prior to any movement, the excitability of the NWR in hip and knee flexor muscles is also increased (Serrao et al, 2012a). Previous studies have been carried out during rhythmic walking (Spaich et al, 2004) and during symmetrical standing (Andersen et al, 2003) to characterize stimulation site dependencies for the NWR during these two stable, steady-state conditions.…”

Neuromuscular Function in Painful Knee Osteoarthritis

“…Withdrawal reflexes have been used comprehensively in pain research as an index of nociceptive responsiveness in both animal model and human studies (see [25,26] for reviews). Importantly, the reflex is known to be 'modular,' meaning that the organization of the reflex is dependent on site of stimulation [25,27] and phase of the gait cycle during ambulation [28]. The motor response to a noxious stimulus is to withdraw or pull away from the stimulus, which may involve activation of the flexor or extensor musculature, depending on the functional needs of the organism [29].…”