Stefano Piazza

Shared muscle synergies in human walking and cycling

The motor system may rely on a modular organization (muscle synergies activated in time) to execute different tasks. We investigated the common control features of walking and cycling in healthy humans from the perspective of muscle synergies. Three hypotheses were tested: 1) muscle synergies extracted from walking trials are similar to those extracted during cycling; 2) muscle synergies extracted from one of these motor tasks can be used to mathematically reconstruct the electromyographic (EMG) patterns of the other task; 3) muscle synergies of cycling can result from merging synergies of walking. A secondary objective was to identify the speed (and cadence) at which higher similarities emerged. EMG activity from eight muscles of the dominant leg was recorded in eight healthy subjects during walking and cycling at four matched cadences. A factorization technique [nonnegative matrix factorization (NNMF)] was applied to extract individual muscle synergy vectors and the respective activation coefficients behind the global muscular activity of each condition. Results corroborated hypotheses 2 and 3, showing that 1) four synergies from walking and cycling can successfully explain most of the EMG variability of cycling and walking, respectively, and 2) two of four synergies from walking appear to merge together to reconstruct one individual synergy of cycling, with best reconstruction values found for higher speeds. Direct comparison of the muscle synergy vectors of walking and the muscle synergy vectors of cycling (hypothesis 1) produced moderated values of similarity. This study provides supporting evidence for the hypothesis that cycling and walking share common neuromuscular mechanisms.

A novel FES control paradigm based on muscle synergies for postural rehabilitation therapy with hybrid exoskeletons

Hybrid exoskeletons combine robotic orthoses and motor neuroprosthetic devices to compensate for motor disabilities and assist rehabilitation. The basic idea is to take benefits from the strength of each technology, primarily the power of robotic actuators and the clinical advantages of using patients muscles, while compensating for the respective weaknesses: weight and autonomy for the former, fatigue and stability for the latter. While a wide repertory of solutions have been proposed in literature for the control of robotic orthoses and simple motor neuroprosthesis, the same problem on a complex hybrid architecture, involving a wide number of muscles distributed on multiple articulations, still waits for a practical solution. In this article we present a general algorithm for the control of the neuroprosthesis in the execution of functional coordinated movements. The method extracts muscle synergies as a mean to diagnose residual neuromotor capabilities, and adapts the rehabilitation exercise to patient requirements in a dynamic way. Fatigue effects and unexpected perturbations are compensated by monitoring functional state variables estimated from sensors in the robot. The proposed concept is applied to a case-study scenario, in which a postural balance rehabilitation therapy is presented.

A tool for balance control training using muscle synergies and multimodal interfaces.

Balance control plays a key role in neuromotor rehabilitation after stroke or spinal cord injuries. Computerized dynamic posturography (CDP) is a classic technological tool to assess the status of balance control and to identify potential disorders. Despite the more accurate diagnosis generated by these tools, the current strategies to promote rehabilitation are still limited and do not take full advantage of the technologies available. This paper presents a novel balance training platform which combines a CDP device made from low-cost interfaces, such as the Nintendo Wii Balance Board and the Microsoft Kinect. In addition, it integrates a custom electrical stimulator that uses the concept of muscle synergies to promote natural interaction. The aim of the platform is to support the exploration of innovative multimodal therapies. Results include the technical validation of the platform using mediolateral and anteroposterior sways as basic balance training therapies.

Modular control of mediolateral postural sway

Is voluntary motor control of mediolateral rhythmic sway ruled by modular organization? Answering this question has potential implications in diagnosis and rehabilitation of neurologically impairments. Superficial EMG and computerized dynamic posturography has been used in this study to investigate modular control of six healthy subjects. Postural movements have been performed at three different frequencies to also test the influence of speed on the composition of synergies and activations. Results showed that two synergies account for more than 75% of EMG variance and are shared by all subjects across all frequency conditions. These evidences, together with a functional interpretation of computed muscle synergies, support the existence of consistent modular control across healthy subjects during mediolateral voluntary movements.

Afferent electrical stimulation during cycling improves spinal processing of sensorimotor function after incomplete spinal cord injury

OBJECTIVE Appropriate afferent feedback delivery during the execution of motor tasks is important for rehabilitation after incomplete spinal cord injury (iSCI). However, during leg-cycling therapy, the plantar afferent feedback is minimal. We hypothesize that the augmentation of sensory input by combining cycling with a locomotor-like stimulation of plantar cutaneous innervations (ES-cycling), might help to restore proper spinal processing of sensorimotor function. METHODS Thirteen non-injured subjects and 10 subjects with iSCI performed 10 minutes of cycling and, on another session, of ES-cycling. To assess spinal processing of sensorimotor function, soleus H-reflex response was tested following a conditioning plantar electrical stimulation applied at 25-100 ms inter-stimulus intervals (ISIs), measured before and after the execution of the tasks. RESULTS Before tasks execution, the conditioned H-reflex response was modulated in non-injured subjects, and absent in subjects with iSCI; after cycling, modulation profiles were unchanged. However, after ES-cycling a significant increase in H-reflex excitability was observed in the non-injured group at 100 ms ISI (p < 0.05), and in the iSCI group between 50-75 ms ISI (p < 0.001). CONCLUSION The loss of reflex modulation in subjects with iSCI suggests reduced spinal processing of sensorimotor function. Reflex modulation recovery after ES-cycling may indicate the partial reactivation of these mechanisms.

Assessing sensorimotor excitability after spinal cord injury: a reflex testing method based on cycling with afferent stimulation

AbstractSeveral studies have examined spinal reflex modulation during leg cycling in healthy and spinal cord injury (SCI) subjects. However, the effect of cutaneous plantar afferent input on spinal excitability during leg cycling after SCI has not been characterised. The aim of the study was to test the feasibility of using controlled leg cycling in combination with plantar cutaneous electrical stimulation (ES) cycling to assess lower limb spinal sensorimotor excitability in subjects with motor complete or incomplete SCI. Spinal sensorimotor excitability was estimated by measuring cutaneomuscular-conditioned soleus H-reflex activity. Reflex excitability was tested before and after a 10-min ES cycling session in 13 non-injured subjects, 6 subjects with motor incomplete SCI (iSCI) who had moderately impaired gait function, 4 subjects with motor iSCI who had severely impaired gait function, and 5 subjects with motor complete SCI (cSCI). No modulation of soleus H-reflex with plantar cutaneous stimuli was observed after either iSCI or cSCI when compared to non-injured subjects. However, after ES cycling, reflex excitability significantly increased in subjects with iSCI and moderately impaired gait function. ES cycling facilitated spinal sensorimotor excitability only in subjects with motor iSCI with residual gait function. Increased spinal excitability induced with a combination of exercise and afferent stimulation could be adopted with diagnostic and prognostic purposes to reveal the activity-based neurorehabilitation profile of individual subjects with motor iSCI.Trial registration: ISRCTN26172500; retrospectively registered on 15 July 2016 Graphical abstractᅟ

Cycling with Plantar Stimulation Increases Cutaneomuscular-Conditioned Spinal Excitability in Subjects with Incomplete Spinal Cord Injury

The aim of this study was to investigate the effects of a rehabilitation exercise for people with incomplete Spinal Cord Injury (iSCI), based on cycling and combined afferent electrical stimulation (ES-cycling), to normalize spinal activity in response to a plantar cutaneous stimulation. We studied Soleus H-reflex excitability following ipsilateral plantar electrical stimulation applied at 25–100 ms inter-stimulus intervals (ISI’s), on 13 non-injured subjects and 10 subjects with iSCI. Reflexes were tested before and after a 10 min session of ES-cycling to evaluate the effects of the exercise. Plantar-conditioned H-reflex modulation increased in the iSCI group after ES-cycling, compared to the limited modulation observed before the exercise. Conversely, the non-injured group presented pronounced modulation both before and after the exercise. We conclude that ES-cycling improved plantar-conditioned spinal neuronal excitability in subjects with iSCI. Results could be used in the design of more effective leg-cycling therapies, to promote central neuroplasticity and rehabilitation in lower limb muscle activity following iSCI.

Cutaneomuscular Spinal Reflex Activity as a Biomarker of Motor Dysfunction and Neurorehabilitation After Incomplete Spinal Cord Injury

Cutaneomuscular afferent information is essential for voluntary motor tasks such as gait and balance. After spinal cord injury (SCI) changes in sensorimotor activity are involved in recovery of limited motor function. Here we present a review of clinical neurophysiological measures that quantify sensorimotor dysfunction and which have the potential to benchmark the therapeutic effect of cutaneous stimulation during SCI neurorehabilitation. Specifically we will show that long-latency cutaneous reflex and cutaneomuscular conditioned H-reflex techniques can quantify spinal neuronal activity and the presence of either adaptive or maladaptive motor control mechanisms after incomplete SCI. In conclusion, the development of neurorehabilitation programs in combination with cutaneomuscular stimulation protocols is a viable strategy not only to promote motor recovery but to prevent maladaptive neuroplasticity such as spasticity after SCI.

Spinal Cord Plasticity and Neuromodulation After SCI

Over the past several decades, it has been shown that the spinal cord exhibits significant adaptive plasticity during development and throughout life. This is normally a positive phenomenon, allowing the spinal cord to develop fundamental functions and learn novel behaviours. However, after a spinal cord injury, the pathways controlling the behaviours mediated by the spinal cord are interrupted and maladaptive plasticity can take place. The traditional approach to rehabilitation after spinal cord injury is to apply physical training exercises improving the overall condition and functioning of the patient, and thus to indirectly promote neural recovery. Emerging neuromodulation therapies that complement physical therapy have been proposed to directly stimulate and modify specific impaired neural pathways and thereby produce a more satisfactory functional state. This chapter presents an overview of these new treatment approaches.

Posturography Platform and Balance Control Training and Research System Based on FES and Muscle Synergies

Balance control plays a key role in neuromotor rehabilitation after stroke or spinal cord injuries. Computerized Dynamic Posturography (CDP) is a classic tool to assess the status of balance control and to identify potential disorders. In this paper, we present the development of a low cost system and tool for the assessment and training of balance based on static posturography and functional electrical stimulation (FES). The assessment features are built upon a classic a CDP basis, while for training routines, the system uses bioinspired FES patterns and algorithms based on muscle synergies. This system includes low cost technology like the Wii Fit Balance Board and the Kinect. The work described is this paper includes the implementation of the system and first results as a CDP tool.