Rapid feedback responses are flexibly coordinated across arm muscles to support goal-directed reaching

Assessment of the Impact of the Tipstim® Device Application and the Study Position on Motor Coordination and Grip Strength of the Affected Upper Limb Post-Ischemic Stroke—A Randomized Parallel Crossover Trial

In the acute phase of stroke, most patients have reduced efficiency of the upper limb and in the chronic phase more than half of these patients still have a deficit in the mobility of the upper limb. The aim of this study was to investigate the effect of using the tipstim® device and the tested position of the body and affected upper limb on parameters of motor coordination and grip strength in patients after an ischemic stroke. A randomized, parallel crossover study was conducted in the Rehabilitation Department. The study included 29 people aged 68 ± 9.2 years, 5–7 weeks after ischemic stroke. Patients were randomly assigned to two parallel groups (A/B = 15 people and B/A = 14 people). In each of them, the patient received both experimental (A = tipstim®) and control (B = placebo effect) treatment in a specific order. The HandTutor was used to measure the parameters of motor coordination (maximum range of motion and frequency of motion). We also used an electronic dynamometer to measure the handgrip strength. The patients were examined in two positions: sitting (unstable) and lying with the trunk and affected upper limb stabilized. Results: The analysis showed smaller differences between the measurements in the A/B group than in the B/A group, both without stabilization and with stabilization (wrist Hz = p ˂ 0.001; fingers 2–5 Hz = p ˂ 0.001; handgrip strength = p ˂ 0.049 and p ˂ 0.003). When comparing the influence of the tested position on the results of motor coordination and the handgrip strength, statistically significant differences were found in the placebo group in a stable position (Hz wrist p = 0.007, MaxROM wrist = 0.038, HzF5 = 0.039, MaxROM F4 = 0.035, HzF3 = 0.035, MaxROM F3 = 0.010, HzF2 = 0.049). Conclusions: Repeated use of the tipstim® device did not improve the tested parameters. A significant improvement in the results of coordination of movements and grip strength is possible in a stable position, lying down.

Motor coordination and grip strength assessed after the break and in various positions of the upper limb in patients after stroke in relation to healthy subjects. An observational study

BACKGROUND

Stroke patients often have weakness of the shoulder (scapular) stabilizers, which may contribute to motor impairment of the hand and wrist.

AIM

of the study was to analyze the effect of stabilization of the affected upper limb and the break in the examination on hand motor coordination and grip strength in patients after stroke in relation to healthy subjects.

DESIGN

An observational study.

SETTING

A hospital Rehabilitation Department.

POPULATION

Eighty post-stroke patients mean, 62 ± 17 years, and 77 healthy individuals mean, 25,7 ± 6,5 years.

METHODS

A Hand Tutor device and manual dynamometer were used to measure hand motor coordination parameters. Subjects were assessed in two positions: supine with the tested upper extremity extended perpendicularly to the vertical axis of the body (i.e., passive stabilization of the trunk; no stabilization of the shoulder), and supine with the tested upper extremity held close to the body (i.e., passive stabilization of the trunk and shoulder).

RESULTS

Stabilization of the shoulder improved the motor coordination parameters of the fingers and the wrist, and resulted in greater grip strength in post-stroke patients and healthy subjects (P ˂ .001). Local stabilization of the shoulder was particularly beneficial for improving hand motor coordination in females and non-dominant hands.

CONCLUSIONS

A stable position of the upper extremity can improve motor coordination and grip strength during stroke rehabilitation.

CLINICAL REHABILITATION IMPACT

Placing subjects in a supine position and stabilizing their affected upper limb may help restore motor coordination of the hand and wrist following stroke.

Influence of the Passive Stabilization of the Trunk and Upper Limb on Selected Parameters of the Hand Motor Coordination, Grip Strength and Muscle Tension, in Post-Stroke Patients

Objective: Assessment of the influence of a stable trunk and the affected upper limb (dominant or non-dominant) on the parameters of the wrist and hand motor coordination, grip strength and muscle tension in patients in the subacute post-stroke stage compared to healthy subjects. Design: An observational study. Setting: Stroke Rehabilitation Department. Subjects: Thirty-four subjects after ischemic cerebral stroke and control group-32 subjects without neurological deficits, age and body mass/ height matched were included. Main measures: The tone of the multifidus, transverse abdominal and supraspinatus muscles were assessed by Luna EMG device. A HandTutor device were used to measure motor coordination parameters (e.g., range of movement, frequency of movement), and a manual dynamometer for measuring the strength of a hand grip. Subjects were examined in two positions: sitting without back support (non-stabilized) and lying with stabilization of the trunk and the upper limb. Results: Passive stabilization of the trunk and the upper extremity caused a significant improvement in motor coordination of the fingers (p ˂ 0.001) and the wrist (p < 0.001) in patients after stroke. Improved motor coordination of the upper extremity was associated with an increased tone of the supraspinatus muscle. Conclusions: Passive stabilization of the trunk and the upper limb improved the hand and wrist coordination in patients following a stroke. Placing patients in a supine position with the stability of the affected upper limb during rehabilitation exercises may help them to access latent movement patterns lost due to neurological impairment after a stroke.

Predicting Perturbed Human Arm Movements in a Neuro-Musculoskeletal Model to Investigate the Muscular Force Response

Human movement is generated by a dynamic interplay between the nervous system, the biomechanical structures, and the environment. To investigate this interaction, we propose a neuro-musculoskeletal model of human goal-directed arm movements. Using this model, we simulated static perturbations of the inertia and damping properties of the arm, as well as dynamic torque perturbations for one-degree-of freedom movements around the elbow joint. The controller consists of a feed-forward motor command and feedback based on muscle fiber length and contraction velocity representing short-latency (25 ms) or long-latency (50 ms) stretch reflexes as the first neuronal responses elicited by an external perturbation. To determine the open-loop control signal, we parameterized the control signal resulting in a piecewise constant stimulation over time for each muscle. Interestingly, such an intermittent open-loop signal results in a smooth movement that is close to experimental observations. So, our model can generate the unperturbed point-to-point movement solely by the feed-forward command. The feedback only contributed to the stimulation in perturbed movements. We found that the relative contribution of this feedback is small compared to the feed-forward control and that the characteristics of the musculoskeletal system create an immediate and beneficial reaction to the investigated perturbations. The novelty of these findings is (1) the reproduction of static as well as dynamic perturbation experiments in one neuro-musculoskeletal model with only one set of basic parameters. This allows to investigate the model's neuro-muscular response to the perturbations that-at least to some degree-represent stereotypical interactions with the environment; (2) the demonstration that in feed-forward driven movements the muscle characteristics generate a mechanical response with zero-time delay which helps to compensate for the perturbations; (3) that this model provides enough biomechanical detail to allow for the prediction of internal forces, including joint loads and muscle-bone contact forces which are relevant in ergonomics and for the development of assistive devices but cannot be observed in experiments.

Influence of kinesthetic motor imagery and effector specificity on the long-latency stretch response

The long-latency "reflexive" response (LLR) following an upper limb mechanical perturbation is generated by neural circuitry shared with voluntary control. This feedback response supports many task-dependent behaviors and permits the expression of goal-directed corrections at latencies shorter than voluntary reaction time. An extensive body of literature has demonstrated that the LLR shows flexibility akin to voluntary control, but it has not yet been tested whether instruction-dependent LLR changes can also occur in the absence of an overt voluntary response. The present study used kinesthetic motor imagery (experiment 1) and instructed participants to execute movement with the unperturbed contralateral limb (experiment 2) to explore the relationship between the overt production of a voluntary response and LLR facilitation. Activity in stretched right wrist flexors were compared with standard "do not-intervene" and "compensate" conditions. Our findings revealed that on ~40% of imagery and ~50% of contralateral trials, a response occurred during the voluntary epoch in the stretched right wrist flexors. On these "leaked" trials, the early portion of the LLR (R2) was facilitated and displayed a similar increase to compensate trials. The latter half of the LLR (R3) showed further modulation, mirroring the patterns of voluntary epoch activity. By contrast, the LLR on "non-leaked" imagery and contralateral trials did not modulate. We suggest that even though a hastened voluntary response cannot account for all instruction-dependent LLR modulation, the overt execution of a response during the voluntary epoch in the same muscle(s) as the LLR is a prerequisite for instruction-dependent facilitation of this feedback response.NEW & NOTEWORTHY Using motor imagery and contralateral responses, we provide novel evidence that facilitation of the long-latency reflex (LLR) requires the execution of a response during the voluntary epoch. A high proportion of overt response "leaks" were found where the mentally simulated or mirrored response appeared in stretched muscle. The first half of the LLR was categorically sensitive to the appearance of leaks, whereas the latter half displayed characteristics closely resembling activity in the ensuing voluntary period.

Long-latency reflexes for inter-effector coordination reflect a continuous state feedback controller

Successful performance in many everyday tasks requires compensating unexpected mechanical disturbance to our limbs and body. The long-latency reflex plays an important role in this process because it is the fastest response to integrate sensory information across several effectors, like when linking the elbow and shoulder or the arm and body. Despite the dozens of studies on inter-effector long-latency reflexes, there has not been a comprehensive treatment of how these reveal the basic control organization that sets constraints on any candidate model of neural feedback control such as optimal feedback control. We considered three contrasting ways that controllers can be organized: multiple independent controllers vs. a multiple-input multiple-output (MIMO) controller, a continuous feedback controller vs. an intermittent feedback controller, and a direct MIMO controller vs. a state feedback controller. Following a primer on control theory and review of the relevant evidence, we conclude that continuous state feedback control best describes the organization of inter-effector coordination by the long-latency reflex.