Symposia Sessions

Percentage of older population (65ys old~) in Japan reached 29.1% in 2021 and those in other countries are also increasing. In preparation for “Super-Aged Society”, understanding of aged-human body and its countermeasures are more required from now on. Declines in muscle strength or motor functions had been explained mainly by muscle atrophy, that we can recognize visually. However, recent data pointing out that decreases in muscle strength following aging in older adults cannot be explained only by decreases in muscle mass. Age-related changes in central nervous system is one of major contributors to declines in muscle strength or motor functions. Unlike the muscle mass, changes in central nervous system, i.e., motor unit functions/anatomy or neural coordination, is difficult to visually recognize. Recent studies with various technique, i.e., intramuscular EMG, high-density EMG, ultrasonography, or novel motor tasks, found and quantify the invisible aspects of age-related changes in central nervous system. This symposium invites the researchers who are providing new insights into understanding central nervous system in aged-human body.

The symposium will discuss altered muscle activity during joint loading, interlimb co-ordination during dynamic tasks following fatigue, and fatigue effects on upper limb sensorimotor control. Neck fatigue is becoming ubiquitous due to our interactions with technology, and a series of studies showing how it impacts upper limb proprioception, sensory processing and motor control will be discussed. With work clearly indicating the maladaptive effects of fatigue, the symposium will conclude with a discussion of the challenges of establishing acceptable limits for ergonomic exposures that reflect the complexity of real-world tasks and how they are affected by fatigue.

Spinal motoneurons represent the final pathway of movement. The activity of the alpha motoneurons directly translates to behaviour due to the one-to-one correspondence between axonal action potentials and muscle unit force. This symposium will present recent results on the way motor neurons are controlled during natural tasks including novel methodological advances. We will first discuss on the limits and variability of motor unit decomposition across human individuals. We will evaluate the effects of volume conductor and neuromuscular properties on high-density surface EMG decomposition from experimental data. These results include the characteristics of the muscle and volume conductor (muscle fiber architecture, muscle cross-sectional area, subcutaneous fat layer) and neural and peripheral properties of the motor units. We will then show novel divergent nonlinear firing characteristics of individual motor nuclei and coupling and decoupling of motoneurons between muscles classically considered synergistic. This will lead to a discussion on novel methodologies to assess motoneuron synergies and predict functional outcomes such as muscle rate of force development and maximal force. The new methodological advances will also include the use of deep learning to predict neuromuscular functional and anatomical characteristics from high-density EMG signals. We will present new evidence for specific adaptations of motor neuron behaviour and EMG characteristics to external stimuli, such as training, neurorehabilitation, electrical stimulation. These results include high-density EMG recordings during highly dynamic motor tasks. We will then present novel results on motor unit behaviour during electrical stimulation that allow accurate assessment of inhibition and excitation within a motor pool.

Unilateral motor practice improves motor performance not only in the practice limb but, curiously, also in the opposite limb that did not perform any practice. Under certain conditions, the magnitude of such cross-education or inter-limb transfer can reach 20% and clinical significance. The mechanisms of cross-education are not fully understood. A peculiar phenomenon overlooked for some 100 years but now correcting textbooks is that the activation of the brain during unilateral muscle contraction is actually not really confined to structures in the contralateral hemisphere. Instead, when healthy humans contract muscles in one arm or leg, there is a concurrent activation of the homologous muscle pair in the ‘resting limb’ and brain areas in the hemisphere ispilateral to the contracting muscles. An understanding of the reasons and need for such ‘ipsilateral’ activation is a contentious and highly relevant issue for conceptual and clinical reasons. Examining the brain ipsilateral activation using magnetic brain stimulation paradigms, EEG, MRI, and MEG would help us to better understand hemispheric specialization of willed and unwilled motor acts. We could then exploit this improved understanding of ipsilateral brain activation for developing treatment options for patients with unilateral neurological or orthopedic conditions. Indeed, there is some preliminary evidence for the efficacy of this rehabilitation modality in patients with an acute or chronic stroke and in patients for reducing weakness after a wrist fracture or anterior cruciate ligament surgery.

This symposium will focus on the presentation of innovative approaches to assess electrical and mechanical properties of the muscle-tendon unit. The final goal is to provide an overview on the latest advancements in the field and on their potentialities in different contexts.

Sensorimotor integration (SMI) refers to the ability to process sensory information and formulate effective motor outputs. Disordered SMI may result from both acute and chronic changes in sensory input. This symposium will discuss changes in interlimb co-ordination tasks in stroke patients, the effect of chronic pain on sensorimotor conflicts and how cognitive factors influence the interaction between chronic pain and the motor system, as well as how both acute and chronic effects of altered neck inputs on limb sensorimotor control, and the effects of spinal manipulation on SMI.

Fatigue is a frequent consequence of upper extremity activities and is often considered as a precursor of musculoskeletal disorders. Developing methods to detect and manage fatigue during real life upper extremity activities is therefore crucial for motor performance and injury prevention. The effects of fatigue on the motor system in such context are, however, complex and misunderstood. This symposium will present recent fundamental and applied research on upper extremity fatigue.

Chemotherapies used in the standard treatments for many types of cancer exhibit neurotoxic adverse effects. Depending on individual compounds, chemotherapy can damage the nervous system through various mechanisms. These adverse effects are commonly referred to as chemotherapy-induced peripheral neuropathy or neurotoxicity. While the focus has often been on the peripheral nervous system, there is also evidence of central neurotoxicity. Central effects are reported most frequently for platinum compounds and taxanes. The clinical presentations of patients with chemotherapy-induced neuropathies include sensory symptoms such as numbness/tingling, neuropathic pain, increased sensibility to hot/cold temperatures and decreased vibration and pinprick sensitivity. Motor symptoms may include hyporeflexia, weakness and muscle cramps. These symptoms can present immediately or progress after several cycles of treatment and their severity usually increases with drug accumulation. While many symptoms can improve over time after treatment cessation, some persist for years in a subset of patients, limiting their quality of life across the entire cancer illness trajectory. Persistent effects include compromised movement control and contributing to functional impairments in day-to-day tasks. For this reason, there has been growing interest in the rehabilitation of cancer survivors but there is little knowledge on the mechanisms of sensorimotor impairment, aside from peripheral neuropathies, to guide rehabilitation practices. This symposium will begin with a review the scope of the problem for cancer rehabilitation targeting chemotherapy-induced neuropathy, provided by Flores. Housley will then provide evidence for the motor unit dysfunction that can arise from using platinum-based compounds to treat cancer. Wang will show how platinum-based chemotherapies can contribute to sensorimotor deficits in human cancer survivors that are separate from the commonly reported symptoms associated

This symposium will show examples of studies exploring new solutions for increasing the functionality of upper and lower limb prostheses. After major limb amputation, current prosthetic solutions do not allow the user to receive sensory information on his environment or on the position of the prosthetic limb during object manipulation or walking. This lack of sensory feedback contributes to a motor control of the prosthesis that is not intuitive and requires learning. One way of improving the functionality of prostheses is by technological adds. Another (non-exclusive) way might be via natural non-painful phantom sensations that many amputees have after their amputation, such as phantom mobility or referred sensations. This symposium will give examples of these approaches that aim to improve intuitive control of prostheses.

The interpretation and utility of correlated oscillations in conventionally recorded surface EMG signals (i.e., interference EMG) have been debated.  This symposium will explore the implications of correlated EMG oscillations by discussing recent observations on correlated EMG oscillations within or between agonist and antagonist muscles in various conditions.  The specific topics include alterations of correlated EMG oscillations with aging, a comparison between correlated oscillations in surface EMG signals and those in motor unit discharges, modulation of correlated EMG oscillations with unique practice, and the relationship between correlated EMG oscillations and steady co-contraction performance.

The symposium will show recent improvements in the analysis of motor unit discharge patterns for the decoding and interpretation of the synaptic organization of motor commands. All invited speakers will be members of the International Motoneuron Society.

This symposium will explore the clinical application of sEMG to neurological and neuromuscular disorders with the objective of illustrating how sEMG can be used to provide insight into changes within the neuromuscular system and the response to therapeutic interventions. Using a number of example applications, including age-related dysfunction in the neuromuscular system, diabetes, Parkinson?s disease, stroke and amyotrophic lateral sclerosis, the potential utility of sEMG in a clinical setting will be explored. Challenges which currently limit the clinical use of sEMG will also be discussed.

Healthy aging and clinical conditions affect the brain and motor-cognitive functions. Systematic exercise can induce favorable changes in the brain and spinal cord. It is unclear if brain responses to exercise scale with the severity of impairment and the intensity of exercise. The symposium aims to provide mechanistic evidence for the dose-dependent relationship between exercise training intensity, brain neuroplasticity, and motor-cognitive function in health and disease. The hypothesis is that brain neuroplasticity scales with exercise intensity but this relationship is weaker in patients compared with healthy adults.

Methodologies for analysis of neural codes in sensorimotor system are under intensive development. But their mutual comparisons and discussions of their joint potentials are relatively rare and currently lacking. In this symposium, we will present, compare and discuss recent progresses and research visions made by five research groups in the fields of motor unit identification from invasive and noninvasive high-density EMG in both voluntary and elicited contractions, reverse engineering of human motor unit firing patterns, assessment of functional connectivity networks of motor neurons during multi-joint tasks as well as motor unit analysis in different pathologic states.

An optimal trunk control is essential to maintain balance and perform everyday human movements. Neural networks controlling trunk muscles are dispersed across the central nervous system and can be tested using neurophysiological techniques. However, testing neural control of trunk muscles is challenging and has been overlooked in humans. The first objective of this symposium is to present the knowledge about the ‘normal’ neural control of trunk muscles. The second objective is to discuss how various clinical conditions (e.g. pain, scoliosis or spinal cord injury) alter neural control of trunk muscles and how addressing modifications of neural control may optimise treatments.