Exoskeleton-assisted gait in chronic stroke: An EMG and functional near-infrared spectroscopy study of muscle activation patterns and prefrontal cortex activity.pptx

The study titled "Exoskeleton-assisted gait in chronic stroke: An EMG and functional near-infrared spectroscopy study of muscle activation patterns and prefrontal cortex activity" investigates how exoskeletons can assist people with chronic stroke in walking. It uses two key methods to analyze the effects:

Electromyography (EMG): This measures the electrical activity in muscles to understand how muscle activation patterns change when walking with an exoskeleton. By comparing muscle movements during exoskeleton-assisted gait to normal walking, researchers can assess how the exoskeleton influences muscle function.

Functional Near-Infrared Spectroscopy (fNIRS): This technique monitors brain activity, specifically in the prefrontal cortex, to see how cognitive load or mental effort changes while walking with the exoskeleton. The prefrontal cortex plays a role in planning and controlling movements, and the study examines whether walking with an exoskeleton increases or decreases brain activity in this region.

Main Goals of the Study:
Understanding Muscle Activation: The study aims to identify which muscles are being activated and how their patterns shift when individuals use an exoskeleton to assist in walking, compared to unaided walking.

Prefrontal Cortex Activity: Another key goal is to observe how the brain responds to using an exoskeleton, particularly focusing on the cognitive effort required to walk. This can give insights into whether using such devices reduces mental strain, making walking easier, or if it adds complexity.

Target Group:
The research focuses on people with chronic stroke, who often face long-term challenges with mobility due to muscle weakness or brain damage affecting motor control.

Relevance:
Exoskeletons are promising tools for rehabilitation, helping stroke patients regain mobility and independence. By understanding both muscle activation patterns and prefrontal brain activity, the study aims to optimize exoskeleton design for better recovery outcomes and more efficient rehabilitation processes.

This combined analysis of both physical (EMG) and cognitive (fNIRS) aspects of walking provides a holistic view of how exoskeletons can aid in stroke recovery.

Since Ekso can determine changes in muscle activity both in paretic and not paretic limb, we investigated the relationship between prefrontal metabolic profiles and lower limbs muscle pattern.
First, the regression model confirms that among stroke patients Ekso induces an increased metabolic activity in prefrontal cortex. Secondly, it shows that prefrontal cortex activity is mainly conditioned by the muscle activation pattern of the nonparetic limb, patterns associated to a greater prefrontal metabolism (increased [HbO2] and TOI and decreased [HbR].
An important finding of the regression model is the relationship between prefrontal activity and age, being prefrontal metabolism enhanced in older patients.
Findings confirm that overground walking requires an attention

1. Exoskeleton-assisted gait in chronic stroke: An EMG and functional near-infrared spectroscopy study of muscle activation patterns and prefrontal cortex activity Pietro Caliandro, Franco Molteni, Chiara Simbolotti, Eleonora Guanziroli, Chiara Iacovelli, Giuseppe Reale, Silvia Giovannini, Luca Padua Clinical Neurophysiology (Elsevier) – 2020 Neurorobotics Research Group, Air University 1

2. Introduction In the recent years, some evidence suggested that Ekso gait training might contribute to improve over-ground gait of stroke patients. Overground gait in healthy individuals is not an attention-demanding task since it does not require prefrontal cortex activation. Conversely, stroke patients with walking deficits seem to have an increased prefrontal cortex metabolism during walking task. Molteni F, Gasperini G, Gaffuri M, Colombo M, Giovanzana C, Lorenzon C, et al. Wearable robotic exoskeleton for overground gait training in sub-acute and chronic hemiparetic stroke patients: preliminary results. Eur J Phys Rehabil Med 2017;53:676–84 2

3. Objective To assess whether in stroke patients and healthy subjects the Ekso induces an attention-demanding process modifying prefrontal cortex metabolism during gait. To describe the relationship between the gait-induced muscle activation pattern and the prefrontal cortex activity in stroke patients. First hypothesis was that the use of Ekso during a gait task induces an attention-demanding process. This means an activation of prefrontal cortex among healthy subjects and an enhancement of the typical prefrontal cortex activity among stroke patients. Second hypothesis was that the muscle activation pattern during gait and the brain functioning are reciprocally interconnected in stroke patients. 3 Neurorobotics Research Group, Air University

4. Methodology Twenty-two chronic stroke patients and fifteen matched healthy subjects were enrolled. We measured variations of oxygenated ( HbO 2 ) and deoxygenated hemoglobin ( HbR ) and the tissue oxygen index (TOI) in the prefrontal cortex (PFC) during gait with and without Ekso. The measurements were achieved by the 2 channels NIRO-200 (Hamamatsu Photonics KK, Japan), a functional near-infrared spectroscopy (fNIRS) equipment which emits different wavelengths of near-infrared light (775 nm, 810 nm and 850 nm). To reduce the effect of skin blood flow on fNIRS signals, we applied on the optodes the highest pressure acceptable for the subject by a velcro fastener. Neurorobotics Research Group, Air University 4

5. Methodology Surface electromyography ( sEMG ) was evaluated by FREEEMG 1000 system (BTS Bioengineering, Milan, Italy). To describe the gait pattern, we adopted Knutsson classification, which describes three types of abnormal muscle activation: Premature activation of calf muscle EMG activity abolished or extremely low in at least two examined muscles Co-activation of several muscles during part of the gait cycle To define the gait cycles in the sEMG recordings, two pressure sensors for each foot, one under the great toe and one under the heel were utilized. Neurorobotics Research Group, Air University 5

6. Ekso and motor task Neurorobotics Research Group, Air University 6 Ekso is equipped by electric motors which power movement of the hip and knee joints and by a passive spring-loaded system for ankle joints. The gait cycle kinematic parameters of the exoskeleton were tuned using EMG of rectus femoris, hamstring muscles, tibialis anterior and triceps surae bilaterally. The motor task consisted of an overground walking along an 18 meters path with and without Ekso. EMG findings were used to assess the motor performance of patients by Knutsson classification which describes activation/co-activation patterns of the investigated muscles and to establish the distal and proximal activation-timing of both legs.

7. Results Neurorobotics Research Group, Air University 7 In stroke patients [ HbR ] was lower during gait with Ekso than during gait without Ekso while in healthy subjects [ HbR ] does not differ in the two conditions. TOI was greater in stroke patients than in healthy controls in both tasks. In stroke patients, gait with Ekso is associated to a greater TOI than gait without Ekso while in healthy controls no difference was observed between the two conditions of gait. The regression model confirms that PFC activation in stroke patients was greater during gait with Ekso than without as demonstrated by higher values of [ HbO 2 ] and TOI and lower values of [ HbR ] during Ekso gait. Moreover, muscle hypoactivation and co-activation of the non-paretic lower limb were associated to a greater PFC activation.

8. 8

9. Discussion Neurorobotics Research Group, Air University 9 Findings confirm that overground walking requires an attention effort in chronic stroke patients since prefrontal cortex metabolism of patients is enhanced during walking without Ekso as revealed by increment of [ HbO 2 ] and TOI and decrement of [ HbR ] compared to healthy subjects. Stroke patients show greater [ HbO 2 ] and TOI and lower [ HbR ] during overground walking with Ekso than during walking without Ekso. There is not a univocal interpretation in healthy subjects because, while [ HbO 2 ] is greater during walking with Ekso than without, no difference was observed in TOIc and [ HHb ]c profiles. Therefore, we can conclude that walking with Ekso does not require an attention effort in healthy people since no variation is observed. This last finding is not marginal because it might suggest that the exoskeleton does not alter the perception of body scheme and thus it does not require an attention effort.

10. Discussion Neurorobotics Research Group, Air University 10 Since Ekso can determine changes in muscle activity both in paretic and not paretic limb, we investigated the relationship between prefrontal metabolic profiles and lower limbs muscle pattern. First, the regression model confirms that among stroke patients Ekso induces an increased metabolic activity in prefrontal cortex. Secondly, it shows that prefrontal cortex activity is mainly conditioned by the muscle activation pattern of the nonparetic limb, patterns associated to a greater prefrontal metabolism (increased [ HbO 2 ] and TOI and decreased [ HbR ]. An important finding of the regression model is the relationship between prefrontal activity and age, being prefrontal metabolism enhanced in older patients.