Gravity-supported exercise with computer gaming improves arm function in chronic stroke.

OBJECTIVE: To investigate the effect of 4 to 6 weeks of exergaming with a computer mouse embedded within an arm skate on upper limb function in survivors of chronic stroke. DESIGN: Intervention study with a 4-week postintervention follow-up. SETTING: In home. PARTICIPANTS: Survivors (N=13) of chronic (≥6 mo) stroke with hemiparesis of the upper limb with stable baseline Fugl-Meyer assessment scores received the intervention. One participant withdrew, and 2 participants were not reassessed at the 4-week follow-up. No participants withdrew as a result of adverse effects. INTERVENTION: Four to 6 weeks of exergaming using the arm skate where participants received either 9 (n=5) or 16 (n=7) hours of game play. MAIN OUTCOME MEASURE: Upper limb component of the Fugl-Meyer assessment. RESULTS: There was an average increase in the Fugl-Meyer upper limb assessment score from the beginning to end of the intervention of 4.9 points. At the end of the 4-week period after the intervention, the increase was 4.4 points. CONCLUSIONS: A 4- to 6-week intervention using the arm skate significantly improved arm function in survivors of chronic stroke by an average of 4.9 Fugl-Meyer upper limb assessment points. This research shows that a larger-scale randomized trial of this device is warranted and highlights the potential value of using virtual reality technology (eg, computer games) in a rehabilitation setting.

Long-range correlations in motor unit discharge times at low forces are modulated by visual gain and age.

The purpose of this investigation was to examine the association between visual information and the size and temporal structure of the variability in index finger force and motor unit discharge times when young and old adults performed isometric contractions with a hand muscle. Single motor units (n = 32) in the first dorsal interosseus muscle were recorded as subjects [16 young (18-35 years old) and 16 old (≥ 70 years old)] exerted a constant abduction force with the index finger during 60 s isometric contractions. The target force was displayed on a monitor in front of the subjects, and they were asked to match the index finger force to a target force. The amount of visual feedback, or gain of the signal, was varied between 24 (low gain) and 1175 pixels N(-1) (high gain). In addition, some trials were performed in the absence of visual feedback. The dependent variables were the variability (standard deviation and coefficient of variation) and the regularity (detrended fluctuation analysis self-similarity parameter, α) of motor unit discharge times and the abduction force. Motor unit discharge times became less regular with an increase in visual feedback gain for both young and old adults, whereas motor unit discharge variability was not influenced by changes in visual gain. The regularity of motor unit discharge times was less for old adults than for young adults, but the variability was greater for old adults. However, there was a significant association between the regularity of motor unit discharge times and the regularity of force for the old adults, but not the young adults. These observations suggest that adjustments in the synaptic inputs delivered to motor neurons with changes in the visual gain differed for young and old adults.

Discharge of biceps brachii motor units is modulated by load compliance and forearm posture.

The purpose of this study was to compare the discharge characteristics of motor units in the biceps brachii during brief isometric contractions of the elbow flexors as subjects matched either a target force or a target joint angle with the forearm placed in one of two postures. One task required force control to exert a constant force against a rigid restraint (force task), whereas the other task involved position control to maintain a constant elbow angle while supporting an inertial load (position task). The left arm of right-handed subjects was rotated forward so that the upper arm was horizontal and the forearm was vertical. When the elbow flexor muscles were contracted, the wrist exerted a force in a horizontal direction. Subcutaneous electrodes were used to record the discharge of 20 motor units in neutral and supinated forearm postures during both force and position control. Motor unit recruitment thresholds ranged from 1.3 to 37.9% of maximal voluntary contraction force. Discharge rate was similar at the start of the force and position tasks in both the neutral posture (13.1 +/- 0.6 and 12.6 +/- 0.6 pps, P = 0.54) and the supinated posture (14.7 +/- 1.6 and 14.0 +/- 0.9 pps, P = 0.4) and declined during both tasks in the two forearm postures (P < 0.001). Nonetheless, the decrease in discharge rate (P < 0.001), increase in the coefficient of variation for interspike interval (P = 0.04), and increases in the standard deviation of acceleration (P = 0.02) were greatest for the position task in the supinated posture. These findings indicate that the influence of load compliance on the adjustments in motor unit activity during brief isometric contractions with the elbow flexors was modulated by changes in forearm posture.

The structure of variability in human walking and running is speed-dependent.

The variability of gait in human walking and running is not random but shows self-similarity that is dependent on the speed of locomotion. The strength of the long-range correlations for each gait pattern follows a U-shaped function that is centered on the respective preferred speed of locomotion.

Walking speed influences on gait cycle variability.

The purpose of this study was to investigate the influence of walking speed on the amount and structure of the stride-to-stride fluctuations of the gait cycle. Based on previous findings for both walking [Hausdorff JM, Purdon PL, Peng CK, Ladin Z, Wei JY, Goldberger AL. Fractal dynamics of human gait: stability of long-range correlations in stride interval fluctuations. J Appl Physiol 1996;80:1448-57], and running [Jordan K, Challis JH, Newell KM. Long range correlations in the stride interval of running. Gait Posture 2006;24:120-5] it was hypothesized that the fractal nature of human locomotion is a reflection of the attractor dynamics of human locomotion. Female participants walked for 12min trials at 80%, 90%, 100%, 110% and 120% of their preferred walking speed. Eight gait cycle variables were investigated: stride interval and length, step interval and length, and from the vertical ground reaction force profile the impulse, first and second peak forces, and the trough force. Detrended fluctuation analysis (DFA) revealed the presence of long range correlations in all gait cycle variables investigated. Speed related U-shaped functions occurred in five of the eight variables, with the minima of these curves falling between 100% and 110% of the preferred walking speed. These findings are consistent with those previously shown in running studies and support the hypothesis that reduced strength of long range correlations at preferred locomotion speeds is reflective of enhanced stability and adaptability at these speeds.

Speed influences on the scaling behavior of gait cycle fluctuations during treadmill running.

The current study examined the temporal structure of gait cycle fluctuations in running. Participants ran at 80%, 90%, 100%, 110% and 120% of preferred running speed for 8min trials. Kinematic and kinetic gait cycle variables were generated from ground reaction force data. Mean, SD and CV of the kinematic and kinetic variables changed linearly with speed, whereas U-shaped functions were found for the scaling exponent alpha in 5 of the 8 variables investigated. Our findings reveal that long range correlations are present in both kinetic and kinematic variables of the gait cycle. The dependent structure of the stride interval is reduced at preferred running speed and this is hypothesized to be related to the enhanced stability and flexibility of this gait speed.

Long range correlations in the stride interval of running.

Fluctuations in the stride interval time series of unconstrained walking are not random but exhibit long range correlations that decay as a power law [Hausdorff JM, Peng CK, Ladin Z, Wei JY, Goldberger AL. Is walking a random walk? Evidence for long range correlations in stride interval of human gait. J Appl Physiol 1995;78:349-58]. Here, we examine whether the long range correlations are present in the stride interval time series of running. Recreational female runners ran 8min trials at their preferred running speed as well as 10% and 20% slower and faster than their preferred speed. Both the average time and the amount of variability of the stride interval decreased with increasing speed. Detrended fluctuation analysis (DFA) showed that there were long range correlations present in the stride interval time series and these correlations followed a quasi U-shaped function, with the minimum at the preferred running speed. These results are consistent with the hypothesis that the preferred running speed, falling as it does between the upper and lower limits of possible running speeds, is the speed at which the most dynamical degrees of freedom are available for adaptive control of locomotion.

Visual information and multi-joint coordination patterns in one-leg stance.

This study examined the influence of visual information on the multi-joint coordination patterns in maintaining one-leg stance. 12 participants stood still on their left leg for two 1 min trials with and without visual information. The multi-joint coordination patterns in the frontal plane were examined using a frequency domain principal component analysis (PCAf) on 14 joint angular motion time series. The factor loading spectra of PC1 showed two distinct multi-joint postural coordination strategies that relate to the mechanical constraints on balance identified by Hof (2007) [7]. The more prevalent strategy was the coordination of the left ankle-left knee or the left ankle only motion that is related to the "moving the center of pressure" strategy. A 2nd multi-joint coordination strategy showed larger factor loading of the trunk and upper limbs (i.e., shoulders and elbows) in addition to the left ankle implying the role of the upper limbs to generate "counter-rotational torque against the sway of the center of mass (COM)". With eyes open, the participants predominantly utilized the 1st strategy to maintain balance but switched to the 2nd strategy when visual information was not available during the stance. The role of visual information in determining the prevalence of two dominant multi-joint coordination kinematic patterns in one-leg stance reflects the redundant and emergent properties of the postural control system that channel the biomechanical constraints on balance arising from the interaction of the task, environment and the individual.

Feasibility of using a humanoid robot for enhancing attention and social skills in adolescents with autism spectrum disorder.

This study investigated the use of robotic technology for promoting attention, communication and social skills in adolescents with autism spectrum disorder (ASD). Attention, communication and social skills were measured while participants played a memory card matching game (Face Match) using (a) a humanoid robot, (b) a Smart Board and (c) playing cards. Three participants with ASD and three with other cognitive impairments were recruited from a secondary school with a special needs unit. Participants were paired such that one of each pair had a diagnosis of ASD and Face Match was played in these pairs for ∼15 min, with a game organizer present. On 3 separate days, video recordings were made as the participants played Face Match; a different game mode (robot, Smart Board, playing cards) was used each day. A system for categorizing attention, communication and social skills was developed that described 16 subcategories of interactions and intra-actions. In general, participants with ASD showed highly individualized patterns of behaviour in the three different modes. However, repetitive behaviour was reduced in participants with ASD when using both the robot and the Smart Board compared with playing cards. We show that it is feasible to use a robot to assist teaching of social skills to adolescents with ASD, but suggest that the robot features could be further explored and utilized.

Coordination patterns of foot dynamics in the control of upright standing.

In this study, two force platforms were synchronized to investigate the coordination of the right and left foot center of pressure (COP(R) and COP(L)) and its relation to the COP(NET) in the control of 5 upright postures with and without visual information. The results revealed that the standard deviation (SD) of COP(L), COP(R), and COP(NET) progressively increased in the more challenging staggered and tandem stances, respectively, and to a lesser degree with the absence of visual information. Circular analysis of the relative phase of COP(L) and COP(R) revealed that the coupling pattern and variability were dependent on postural stances and the availability of vision. A negative correlation between the variability of the relative phase of the two feet COPs and the SD of the COP(NET) in the anterior-posterior (AP) direction was evident most strongly in the no vision conditions. Thus, the asymmetry of the mechanical constraints on the feet as a function of stance organize the coordination patterns of the feet COPs while the degree of adaptive variation between the feet COPs is dependent on both the mechanical constraints and the availability of vision.

Robotic arm skate for stroke rehabilitation.

Upper limb paresis after stroke greatly affects the performance of Activities of Daily Living (ADL). Unfortunately, rehabilitation for upper limb impairment can have poor results. The current robot-assisted devices are expensive and not readily accessible for homecare. This paper presents the development of a low-cost tabletop robotic device for upper limb rehabilitation. Conceptually, patients perform computer-based goal-directed tasks using the robotic platform. Their progress is monitored and intervention, in the form of assistance or resistance, is introduced accordingly. A prototype platform is described. Experiments demonstrate the ability of the device to provide the necessary forces during movement exercises, in relation to task completion progress, device and target location. Appropriate exercises need to be developed before clinical trials can proceed.

Heteronymous reflex responses in a hand muscle when maintaining constant finger force or position at different contraction intensities.

OBJECTIVE: This study compared heteronymous reflex responses evoked in the first dorsal interosseous muscle by electrical and mechanical stimuli during force and position tasks performed at different target torques. METHODS: Twenty-two healthy human participants contracted the first dorsal interosseus muscle either to produce a constant force against a rigid restraint (force task) or to maintain a constant position of the index finger (position task) against a constant load of 20, 40, and 60% of maximum. RESULTS: The amplitude of the short-latency reflex evoked by electrical stimulation of the median nerve was significantly greater when maintaining finger position, whereas no difference was present for the long-latency responses. In contrast, the reflex responses (short- and long-latency) did not differ between tasks when elicited by tendon-taps. CONCLUSIONS: Task difference in reflex responsiveness depended more on the type of stimulus applied than the reflex pathway and was consistent across three voluntary contraction forces. SIGNIFICANCE: The results suggest that afferent input from homonymous and heteronymous pathways is modulated similarly at the spinal level during such tasks, and implies the significance of presynaptic inhibition during motor performance.

Stability and the time-dependent structure of gait variability in walking and running.

Participants were asked to walk and run continuously (5 min trials) at speeds associated with preferred gait transition speeds. During slow running the local dynamic stability of the head was decreased compared with fast walking, with the reverse being true for the local dynamic stability of the ankle. The standard deviation of relative phase of the knee and ankle also was greater during slow running than fast walking. These findings for stability were mirrored in the detrended fluctuation analysis of the peak to peak interval of the head and ankle. Taken collectively these results support the proposition that larger long range correlations in the stride interval are associated with decreases in measures of stability.

Information and force level interact in regulating force output during two and three digit grip configurations.

The experiment examined the force fluctuations during two and three digit grip configurations to investigate the relationship between task performance and inter-digit individuation as a function of force level and visual information intermittency rate over approximately 100-fold range (0.21-20 Hz). Subjects grasped an object with either the index finger (two digit grip) or the index and middle finger (three digit grip) opposing the thumb and produced isometric force to match a low and high total force level target. Force accuracy was lower at the large visual intermittency conditions and the higher force level. The force variability was lower in the three digit grip. Inter-digit individuation increased as a function of visual intermittency rate and was greater at the low force level. There was no improvement in performance or inter-digit individuation when visual feedback intermittency was greater than approximately 6 Hz (approximately 150 ms). Linear regression between the measures of task performance and inter-digit individuation yielded a significant negative relationship that was only present in the two digit grip when visual feedback rate was 1.67 Hz or lower and in the three digit grip when the feedback rate was 10 Hz or lower. The greater biomechanical degrees of freedom in the three digit grip configuration enable the subject to use, more effectively, visual information feedback at faster timescales in maximizing task performance by increasing digit independence. The shift from visual to nonvisual dominated motor control processes is dependent on the interaction of informational and biomechanical degrees of freedom.

Motor preparation in a memorised delay task.

The effect on reaction time (RT) and movement time (MT) of remembering which one of several targets to move to was investigated in 18 participants who completed 416 trials in each task. On each trial, participants moved their index finger from a central, illuminated switch (the stimulus) to one of eight targets located on the circumference of a 6 cm radius circle. A visual cue (illumination of the target) informed the participant of the appropriate target. In the memorised delay task, the cued target was lit for 300 ms followed by a variable (450-750 ms) foreperiod during which the participant was required to remember the location of the target until the stimulus light was extinguished. In the non-memorised delay task, the target remained lit during the entire foreperiod (750-1050 ms) until the response was completed. At the "go" signal (stimulus light extinguished) participants moved as quickly and accurately as possible to the cued target. Both RT and MT were significantly (p<0.05) longer in the memorised delay task. The increase in RT shows that remembering which target imposed a greater load on motor preparation even though all the information needed for preparing the response was presented in the cue at the beginning of each trial. The increase in MT raises the possibility that movement execution was also programmed during motor preparation.

Task goal and grip force dynamics.

This study examined the effect of task goal on the structure of isometric force variability during precision grasping. In general, variability of isometric force production decreases when participants are asked to maintain a particular force output and are provided with visual feedback, although the irregularity of force output tends to increase under these conditions. In the current study we compared the tasks of holding an object using a precision grip and holding an object using a precision grip while matching a force target. Adults held an object between the index finger and thumb and force output was measured using load cells. The mass (92, 276, 460 g) and the grip aperture (5.5 and 8.5 cm) of the object were varied producing six different object conditions. The goal of the task was to either: (a) hold the object comfortably in a stable position (holding task) or (b) hold the object comfortably in a stable position while maintaining a constant target force level that matched the grip force of the holding condition (target task). The results showed that the amount of force variability in the target condition was lower than during the holding condition, while the force output was more regular in the holding condition. Increments in object mass increased force regularity in the holding condition whereas increments of force level decreased regularity in the target condition. The level of coherence between the two digits was very high (approximately 0.98) and maximum coherence occurred at a higher frequency during the target (0.94 Hz) as opposed to the holding (0.70 Hz) condition. The findings reveal that the goal of the task can qualitatively change the dynamical organization of the force output in prehension, even when the average force level produced is the same. This effect on the control strategy was mediated by visual information processes that interact with level of force output in determining the structure of variability. Theorizing about the organization of isometric force output should include the effects of task goals as well as the level of force per se.