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Key points: Activation of ankle muscles at ground contact during toe walking is unaltered when sensory feedback is blocked or the ground is suddenly dropped. Responses in the soleus muscle to transcranial magnetic stimulation, but not peripheral nerve stimulation, are facilitated at ground contact during toe walking. We argue that toe walking is supported by feedforward control at ground contact. Abstract: Toe walking requires careful control of the ankle muscles in order to absorb the impact of ground contact and maintain a stable position of the joint. The present study aimed to clarify the peripheral and central neural mechanisms involved. Fifteen healthy adults walked on a treadmill (3.0 km h−1). Tibialis anterior (TA) and soleus (Sol) EMG, knee and ankle joint angles, and gastrocnemius–soleus muscle fascicle lengths were recorded. Peripheral and central contributions to the EMG activity were assessed by afferent blockade, H‐reflex testing, transcranial magnetic brain stimulation (TMS) and sudden unloading of the planter flexor muscle–tendon complex. Sol EMG activity started prior to ground contact and remained high throughout stance. TA EMG activity, which is normally seen around ground contact during heel strike walking, was absent. Although stretch of the Achilles tendon–muscle complex was observed after ground contact, this was not associated with lengthening of the ankle plantar flexor muscle fascicles. Sol EMG around ground contact was not affected by ischaemic blockade of large‐diameter sensory afferents, or the sudden removal of ground support shortly after toe contact. Soleus motor‐evoked potentials elicited by TMS were facilitated immediately after ground contact, whereas Sol H‐reflexes were not. These findings indicate that at the crucial time of ankle stabilization following ground contact, toe walking is governed by centrally mediated motor drive rather than sensory driven reflex mechanisms. These findings have implications for our understanding of the control of human gait during voluntary toe walking. [ABSTRACT FROM AUTHOR]

Key points The early postnatal development of functional corticospinal connections in human infants is not fully clarified., Corticospinal drive to upper and lower limb muscle shows developmental changes with an increased functional coupling in infants between 9 and 25 weeks in the beta frequency band., The changes in functional coupling coincide with the developmental period where fidgety movements are present in healthy infants., Data support a possible sensitive period where functional connections between corticospinal tract fibres and spinal motoneurones undergo activity-dependent reorganization., Abstract The early postnatal development of functional corticospinal connections in human infants is not fully clarified. We used EEG and EMG to investigate the development of corticomuscular and intramuscular coherence as indicators of functional corticospinal connectivity in healthy infants aged 1-66 weeks. EEG was recorded over leg and hand area of motor cortex. EMG recordings were made from right ankle dorsiflexor and right wrist extensor muscles. Quantification of the amount of corticomuscular coherence in the 20-40 Hz frequency band showed a significantly larger coherence for infants aged 9-25 weeks compared to younger and older infants. Coherence between paired EMG recordings from tibialis anterior muscle in the 20-40 Hz frequency band was also significantly larger for the 9-25 week age group. A low-amplitude, broad-duration (40-50 ms) central peak of EMG-EMG synchronization was observed for infants younger than 9 weeks, whereas a short-lasting (10-20 ms) central peak was observed for EMG-EMG synchronization in older infants. This peak was largest for infants aged 9-25 weeks. These data suggest that the corticospinal drive to lower and upper limb muscles shows significant developmental changes with an increase in functional coupling in infants aged 9-25 weeks, a period which coincides partly with the developmental period of normal fidgety movements. We propose that these neurophysiological findings may reflect the existence of a sensitive period where the functional connections between corticospinal tract fibres and spinal motoneurones undergo activity-dependent reorganization. This may be relevant for the timing of early therapy interventions in infants with pre- and perinatal brain injury. [ABSTRACT FROM AUTHOR]

Key points Sensory input from peripheral receptors are important for the regulation of walking patterns., Cutaneous input mediates muscle responses to deal with immediate external perturbations., In this study we focused on the role of cutaneous feedback in locomotor adaptation that takes place over minutes of training., We show that interfering with cutaneous feedback reduced adaptation to ankle perturbations during walking., These results help us understand the neural mechanisms underlying walking adaptation, and have clinical implications for treating walking impairments after neurological injuries., Abstract Locomotor patterns must be adapted to external forces encountered during daily activities. The contribution of different sensory inputs to detecting perturbations and adapting movements during walking is unclear. In the present study, we examined the role of cutaneous feedback in adapting walking patterns to force perturbations. Forces were applied to the ankle joint during the early swing phase using an electrohydraulic ankle-foot orthosis. Repetitive 80 Hz electrical stimulation was applied to disrupt cutaneous feedback from the superficial peroneal nerve (foot dorsum) and medial plantar nerve (foot sole) during walking (Choi et al. 2013). Sensory tests were performed to measure the cutaneous touch threshold and perceptual threshold of force perturbations. Ankle movement were measured when the subjects walked on the treadmill over three periods: baseline (1 min), adaptation (1 min) and post-adaptation (3 min). Subjects ( n = 10) showed increased touch thresholds measured with Von Frey monofilaments and increased force perception thresholds with stimulation. Stimulation reduced the magnitude of walking adaptation to force perturbation. In addition, we compared the effects of interrupting cutaneous feedback using anaesthesia ( n = 5) instead of repetitive nerve stimulation. Foot anaesthesia reduced ankle adaptation to external force perturbations during walking. The results of the present study suggest that cutaneous input plays a role in force perception, and may contribute to the 'error' signal involved in driving walking adaptation when there is a mismatch between expected and actual force. [ABSTRACT FROM AUTHOR]

To maintain smooth and efficient gait the motor system must adjust for changes in the ground on a step-to-step basis. In the present study we investigated the role of sensory feedback as 19 able-bodied human subjects walked over a platform that mimicked an uneven supporting surface. Triceps surae muscle activation was assessed during stance as the platform was set to different inclinations (+/-3 deg, +/-2 deg and 0 deg rotation in a parasagittal plane about the ankle). Normalized triceps surae muscle activity was significantly increased when the platform was inclined (2 deg: 0.153 +/- 0.051; 3 deg: 0.156 +/- 0.053) and significantly decreased when the platform was declined (-3 deg: 0.133 +/- 0.048; -2 deg: 0.132 +/- 0.049) compared with level walking (0.141 +/- 0.048) for the able-bodied subjects. A similar experiment was performed with a subject who lacked proprioception and touch sensation from the neck down. In contrast with healthy subjects, no muscle activation changes were observed in the deafferented subject. Our results demonstrate that the ability to compensate for small irregularities in the ground surface relies on automatic within-step sensory feedback regulation rather than conscious predictive control.