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Background: As we age, avoiding falls becomes increasingly challenging. While balance training can mitigate such challenges, the specific mechanisms through which balance control improves remains unclear. Methods: We investigated the impact of balance training in older adults on feedback control after perturbations, focusing on kinematic balance recovery strategies and muscle synergy activation. Twenty older adults aged over 65 underwent short-term (one session) and long-term (3-weeks, 10 sessions) balance training, and their recovery from unpredictable mediolateral perturbations was assessed. Perturbations consisted of 8° rotations of a robot-controlled platform on which participants were balancing on one leg. We measured full-body 3D kinematics and activation of 15 leg and trunk muscles, from which linear and rotational kinematic balance recovery responses and muscle synergies were obtained. Results: Our findings revealed improved balance performance after long-term training, characterized by reduced centre of mass acceleration and (rate of change of) angular momentum. Particularly during the later stage of balance recovery the use of angular momentum to correct centre of mass displacement was reduced after training, decreasing the overshoot in body orientation. Instead, more ankle torque was used to correct centre of mass displacement, but only for perturbations in medial direction. These situation and strategy specific changes indicate adaptations in feedback control. Activation of muscle synergies during balance recovery was also affected by training, specifically the synergies responsible for leg stiffness and ankle torques. Training effects on angular momentum and the leg stiffness synergy were already evident after short-term training. Conclusion: We conclude that balance training in older adults refines feedback control through the tuning of control strategies, ultimately enhancing the ability to recover balance. [ABSTRACT FROM AUTHOR]

Experimental and clinical studies suggest that primate species exhibit greater recovery after lateralized compared to symmetrical spinal cord injuries. Although this observation has major implications for designing clinical trials and translational therapies, advantages in recovery of nonhuman primates over other species have not been shown statistically to date, nor have the associated repair mechanisms been identified. We monitored recovery in more than 400 quadriplegic patients and found that functional gains increased with the laterality of spinal cord damage. Electrophysiological analyses suggested that corticospinal tract reorganization contributes to the greater recovery after lateralized compared with symmetrical injuries. To investigate underlying mechanisms, we modeled lateralized injuries in rats and monkeys using a lateral hemisection, and compared anatomical and functional outcomes with patients who suffered similar lesions. Standardized assessments revealed that monkeys and humans showed greater recovery of locomotion and hand function than did rats. Recovery correlated with the formation of corticospinal detour circuits below the injury, which were extensive in monkeys but nearly absent in rats. Our results uncover pronounced interspecies differences in the nature and extent of spinal cord repair mechanisms, likely resulting from fundamental differences in the anatomical and functional characteristics of the motor systems in primates versus rodents. Although rodents remain essential for advancing regenerative therapies, the unique response of the primate corticospinal tract after injury reemphasizes the importance of primate models for designing clinically relevant treatments.

Spinal cord injury (SCI) disrupts communication between supraspinal centers and spinal circuits, which leads to a range of motor disabilities. Neuromodulation strategies provide access to surviving circuits and pathways to [...], Electrical neuromodulation of lumbar segments improves motor control after spinal cord injury in animal models and humans. However, the physiological principles underlying the effect of this intervention remain poorly understood, which has limited the therapeutic approach to continuous stimulation applied to restricted spinal cord locations. Here we developed stimulation protocols that reproduce the natural dynamics of motoneuron activation during locomotion. For this, we computed the spatiotemporal activation pattern of muscle synergies during locomotion in healthy rats. Computer simulations identified optimal electrode locations to target each synergy through the recruitment of proprioceptive feedback circuits. This framework steered the design of spatially selective spinal implants and real-time control software that modulate extensor and flexor synergies with precise temporal resolution. Spatiotemporal neuromodulation therapies improved gait quality, weight-bearing capacity, endurance and skilled locomotion in several rodent models of spinal cord injury. These new concepts are directly translatable to strategies to improve motor control in humans.

Neuromotor disorders such as SCI and stroke lead to distinct impairments of motor pattern generation and balance (1), (2). Consequently, dissociating these subfunctions is essential for assessment and neurorehabilitation of [...], Central nervous system (CNS) disorders distinctly impair locomotor pattern generation and balance, but technical limitations prevent independent assessment and rehabilitation of these subfunctions. Here we introduce a versatile robotic interface to evaluate, enable and train pattern generation and balance independently during natural walking behaviors in rats. In evaluation mode, the robotic interface affords detailed assessments of pattern generation and dynamic equilibrium after spinal cord injury (SCI) and stroke. In enabling mode, the robot acts as a propulsive or postural neuroprosthesis that instantly promotes unexpected locomotor capacities including overground walking after complete SCI, stair climbing following partial SCI and precise paw placement shortly after stroke. In training mode, robot-enabled rehabilitation, epidural electrical stimulation and monoamine agonists reestablish weight-supported locomotion, coordinated steering and balance in rats with a paralyzing SCI. This new robotic technology and associated concepts have broad implications for both assessing and restoring motor functions after CNS disorders, both in animals and in humans.

Aim: To determine if muscle synergy structure (activations and weights) differs between gait patterns in children with spastic cerebral palsy (CP). Method: In this cross‐sectional study, we classified 188 children with unilateral (n=82) or bilateral (n=106) spastic CP (mean age: 9y 5mo, SD: 4y 3mo, range: 3y 9mo–17y 7mo; 75 females; Gross Motor Function Classification System [GMFCS] level I: 106, GMFCS level II: 55, GMFCS level III: 27) into a minor deviations (n=34), drop foot (n=16), genu recurvatum (n=26), apparent equinus (n=53), crouch (n=39), and jump gait pattern (n=20). Surface electromyography recordings from eight lower limb muscles of the most affected side were used to calculate synergies with weighted non‐negative matrix factorization. We compared synergy activations and weights between the patterns. Results: Synergy structure was similar between gait patterns, although weights differed in the more impaired children (crouch and jump gait) when compared to the other patterns. Variability in synergy structure between participants was high. Interpretation: The similarity in synergy structure between gait patterns suggests a generic motor control strategy to compensate for the brain lesion. However, the differences in weights and high variability between participants indicate that this generic motor control strategy might be individualized and dependent on impairment level. This original article is commented by D'Avella et al. on pages 404–405 of this issue. [ABSTRACT FROM AUTHOR]

Peripheral vision is often considered vital in (combat) sports, yet most experimental paradigms (e.g., eye tracking) ignore peripheral information or struggle to make inferences about the role of peripheral vision in an in-situ performance environment. This study aimed to determine where visual information is located in the peripheral field during an in-situ combat sports task. Eight advanced judokas competed in grip-fighting exchanges while wearing a mobile eye-tracker to locate gaze direction. Three-dimensional position data of the head and hands were tracked using a VICON motion capture system. Gaze analysis through automatic feature detection showed that participants predominantly fixated on their opponent's chest. Kinematic data were used to calculate the angles between the opponent's hands and the gaze-anchor point on the chest of the opponent. Results revealed a nonlinear relationship between visual field (VF) size and visibility of the hands, with athletes needing a VF of at least 30–40 degrees radius to simultaneously monitor both hands of the opponent most of the time. These findings hold implications for the regulation of Paralympic judo for athletes with vision impairment, suggesting that a less severe degree of impairment should be required to qualify than the current criterion of 20 degrees radius. [ABSTRACT FROM AUTHOR]