V. Monaco

Age-Related Modifications of Muscle Synergies and Spinal Cord Activity During Locomotion

Recent findings have shown that neural circuits located in the spinal cord drive muscular activations during locomotion while intermediating between descending signals and peripheral sensory information. This relationship could be modified by the natural aging process. To address this issue, the activity of 12 ipsilateral leg muscles was analyzed in young and elderly people (7 subjects per group) while walking at six different cadences (40-140 steps/min). These signals were used to extract synergies underlying muscle activation and to map the motoneuronal activity of the pools belonging to the lumbosacral enlargement (L(2)-S(2)). The comparison between the two groups showed that neither temporal patterning of motor primitives nor muscles loading synergies seemed to be significantly affected by aging. Conversely, as the cadence increased, spinal maps differ significantly between the groups, showing higher and scattered activity during the whole gait cycle in elders and well-defined bursts in young subjects. The results suggested that motor primitives lead the synchronization of muscle activation mainly depending on the biomechanical demand of the locomotion; hence they are not significantly affected by aging. Nevertheless, at the spinal cord level, biomechanical requirements, peripheral afference, and descending inputs are differently integrated between the two groups, probably reflecting age-related changes of both nervous system and motor control strategies during locomotion.

Effects of early and intensive neuro-rehabilitative treatment on muscle synergies in acute post-stroke patients: a pilot study

BackgroundAfter a stroke, patients show significant modifications of neural control of movement, such as abnormal muscle co-activation, and reduced selectivity and modulation of muscle activity. Nonetheless, results reported in literature do not allow to unequivocally explain whether and, in case, how a cerebrovascular accident affects muscle synergies underlying the control of the upper limb. These discrepancies suggest that a complete understanding of the modular re-organization of muscle activity due to a stroke is still lacking. This pilot study aimed at investigating the effects of the conjunction between the natural ongoing of the pathology and the intense robot-mediated treatment on muscle synergies of the paretic upper limb of subacute post-stroke patients.MethodsSix subacute patients, homogenous with respect to the age and the time elapsed from the trauma, and ten healthy age-matched subjects were enrolled. The protocol consisted in achieving planar movement of the upper limb while handling the end-effector of a robotic platform. Patients underwent 6 weeks long treatment while clinical scores, kinematics of the end-effector and muscle activity were recorded. Then we verified whether muscle coordination underlying the motor task was significantly affected by the cerebrovascular accident and how muscle synergies were modified along the treatment.ResultsResults show that although muscle synergies in subacute stroke patients were qualitatively comparable to those of healthy subjects, those underlying the movement of the shoulder can reflect the functional deficit induced by the pathology. Moreover, the improvement of motor performance due to the treatment was achieved in conjunction with slight modifications of muscle synergies. In this regard, modifications of muscle synergies appeared to be influenced by the different recovering mechanisms across patients presumably due to the heterogeneity of lesions, sides and location of the accident.ConclusionsThe results support the hypothesis that muscle synergies reflect the injury of the cerebrovascular accident and could document the effects of the functional recovery due to a suitable and customized treatment. Therefore, they open up new possibilities for the development of more effective neuro-rehabilitation protocols.

The effect of arm weight support on upper limb muscle synergies during reaching movements

BackgroundCompensating for the effect of gravity by providing arm-weight support (WS) is a technique often utilized in the rehabilitation of patients with neurological conditions such as stroke to facilitate the performance of arm movements during therapy. Although it has been shown that, in healthy subjects as well as in stroke survivors, the use of arm WS during the performance of reaching movements leads to a general reduction, as expected, in the level of activation of upper limb muscles, the effects of different levels of WS on the characteristics of the kinematics of motion and of the activity of upper limb muscles have not been thoroughly investigated before.MethodsIn this study, we systematically assessed the characteristics of the kinematics of motion and of the activity of 14 upper limb muscles in a group of 9 healthy subjects who performed 3-D arm reaching movements while provided with different levels of arm WS. We studied the hand trajectory and the trunk, shoulder, and elbow joint angular displacement trajectories for different levels of arm WS. Besides, we analyzed the amplitude of the surface electromyographic (EMG) data collected from upper limb muscles and investigated patterns of coordination via the analysis of muscle synergies.ResultsThe characteristics of the kinematics of motion varied across WS conditions but did not show distinct trends with the level of arm WS. The level of activation of upper limb muscles generally decreased, as expected, with the increase in arm WS. The same eight muscle synergies were identified in all WS conditions. Their level of activation depended on the provided level of arm WS.ConclusionsThe analysis of muscle synergies allowed us to identify a modular organization underlying the generation of arm reaching movements that appears to be invariant to the level of arm WS. The results of this study provide a normative dataset for the assessment of the effects of the level of arm WS on muscle synergies in stroke survivors and other patients who could benefit from upper limb rehabilitation with arm WS.

Relevance of orthostatic posturography for clinical evaluation of hip and knee joint arthroplasty patients

In order to verify whether orthostatic posturography (OP) can support clinical assessment of total hip (THA) and knee arthroplasty (TKA), 81 subjects with THA and 100 with TKA were recruited and compared with 59 healthy volunteers. All patients were tested one or two days prior to surgery; 42 subjects (20 THA and 22 TKA) were tested again after six months, and 34 (14 THA and 20 TKA) yet again after 12 months. OP was performed using a Kistler 9286A piezoelectric force plate and the following postural parameters (PPs) were adopted on account of their functional meaning: mean velocity and the root mean square of the distance of the centre of pressure (CoP), sway area, and 95% of the CoP power frequency. Eye condition and fatigue related to the test duration were also examined. The three most meaningful PPs were identified and a logarithmic transformation was then applied to these, as well as standardization. Almost all the PP values were higher preoperatively in the patients as compared with the healthy subjects and it was possible to detect many statistically significant differences between patients and healthy subjects. However, when examining the 181 subjects at the preoperative stage, the PPs did not show congruence with the clinical scores as well as they did during follow-up. Therefore, the use of the OP is not recommended to monitor patients undergoing THA or TKA.

Design and Evaluation of a new mechatronic platform for assessment and prevention of fall risks

BackgroundStudying the responses in human behaviour to external perturbations during daily motor tasks is of key importance for understanding mechanisms of balance control and for investigating the functional response of targeted subjects. Experimental platforms as far developed entail a low number of perturbations and, only in few cases, have been designed to measure variables used at run time to trigger events during a certain motor task.MethodsThis work introduces a new mechatronic device, named SENLY, that provides balance perturbations while subjects carry out daily motor tasks (e.g., walking, upright stance). SENLY mainly consists of two independently-controlled treadmills that destabilize balance by suddenly perturbing belts movements in the horizontal plane. It is also provided with force sensors, which can be used at run time to estimate the ground reaction forces and identify events along the gait cycle in order to trigger the platform perturbation. The paper also describes the customized procedures adopted to calibrate the platform and the first testing trials aimed at evaluating its performance.ResultsSENLY allows to measure both vertical ground reaction forces and their related location more precisely and more accurately than other platforms of the same size. Moreover, the platform kinematic and kinetic performance meets all required specifications, with a negligible influence of the instrumental noise.ConclusionA new perturbing platform able to reproduce different slipping paradigms while measuring GRFs at run time in order to enable the asynchronous triggering during the gait cycle was designed and developed. Calibration procedures and pilot tests show that SENLY allows to suitably estimate dynamical features of the load and to standardize experimental sessions, improving the efficacy of functional analysis.

Spatio-temporal parameters and intralimb coordination patterns describing hemiparetic locomotion at controlled speed

BackgroundComparison between healthy and hemiparetic gait is usually carried out while subjects walk overground at preferred speed. This generates bias due to the lack of uniformity across selected speeds because they reflect the great variability of the functional level of post-stroke patients. This study aimed at examining coordinative adaptations during walking in response to unilateral brain damage, while homologous participants walked at two fixed speeds.MethodsFive patients with left and five with right chronic hemiparesis, characterized by similar level of motor functioning, were enrolled. Ten non-disabled volunteers were recruited as matched control group. Spatio-temporal parameters, and intralimb thigh-leg and leg-foot coordination patterns were used to compare groups while walking on a treadmill at 0.4 and 0.6 m/s. The likelihood of Continuous Relative Phase patterns between healthy and hemiparetic subjects was evaluated by means of the root mean square of the difference and the cross correlation coefficient. The effects of the group (i.e., healthy vs. hemiparetics), side (i.e., affected vs.unaffected), and speed (e.g., slow vs. fast) were analyzed on all metrics using the Analysis of Variance.ResultsSpatio-temporal parameters of all hemiparetic subjects did not significantly differ from those of healthy subjects nor showed any asymmetry between affected and unaffected limbs. Conversely, both thigh-leg and foot-leg coordination patterns appeared to account for pathology related modifications.ConclusionComparisons between hemiparetic and healthy gait should be carried out when all participants are asked to seek the same suitable dynamic equilibrium led by the same external (i.e., the speed) and internal (i.e., severity of the pathology) conditions. In this respect, biomechanical adaptations reflecting the pathology can be better highlighted by coordinative patterns of coupled segments within each limb than by the spatio-temporal parameters. Accordingly, a deep analysis of the intralimb coordination may be helpful for clinicians while designing therapeutic treatments.

Age-related neuromuscular adaptation does not affect the mechanical efficiency of lower limbs during walking

Ageing involves modifications of the locomotor system which is believed to increase energy consumption. This study aimed at verifying whether neuromuscular adaptation due to ageing, in conjunction with age-related modifications of the muscle-tendon actuators, involves greater muscle-tendon workload. Ten young and 7 elderly healthy subjects were assessed using gait analysis while walking at comparable speed. Planar models of muscle-driven locomotion, accounting for 14 muscles grouped into 9 equivalent actuators, were developed. Muscle-tendon forces were estimated by using the inverse-dynamic based static optimization where cost functions were tuned to capture the different muscle co-activation between groups. Following this, tendon and muscle shortening/lengthening was computed, and muscle-tendon work was estimated and compared between groups. Results showed that both groups produced comparable muscle mechanical work, though shared differently among muscles. In particular, young subjects showed a greater workload of ankle plantaflexor muscles and older subjects used greater eccentric energy at the knee extensors during stance phase. Moreover, young people used more elastic energy than older people. These findings suggest that the combination adaptation due to ageing, in conjunction with age-related modifications of the muscle-tendon actuators, do not significantly increase the overall energetic output of locomotion. Moreover, the motor control system appears to be characterised by a degree of adaptation which allows older individuals to achieve biomechanical efficiency comparable to younger subjects.

The effects on biomechanics of walking and balance recovery in a novel pelvis exoskeleton during zero-torque control

Fall-related accidents are among the most serious concerns in elderly people, amputees and subjects with neurological disorders. The aim of this paper was to investigate the behaviour of healthy subjects wearing a novel light-weight pelvis exoskeleton controlled in zero-torque mode while carrying out unperturbed locomotion and managing unexpected perturbations. Results showed that the proposed exoskeleton was unobtrusive and had a minimum loading effect on the human biomechanics during unperturbed locomotion. Conversely, it affected the movement of the trailing leg while subjects managed unexpected slipping-like perturbations. These findings support further investigations on the potential use of powered exoskeletons to assist locomotion and, possibly prevent incipient falls.

Effects of the Alternate Combination of “Error-Enhancing” and “Active Assistive” Robot-Mediated Treatments on Stroke Patients

This paper aimed at investigating the effects of a novel robotic-aided rehabilitation treatment for the recovery of the upper limb related capabilities in chronic post stroke patients. Eighteen post-stroke patients were enrolled in a six-week therapy program and divided into two groups. They were all required to perform horizontal pointing movements both in the presence of a robot-generated divergent force field (DF) that pushed their hands proportional to the trajectory error and perpendicular to the direction of motion, and according to the typical active assistive (AA) approach used in robotic therapy. We used a crossover experimental paradigm where the two groups switched from one therapy treatment to the other. The hypothesis underlying this paper was that the use of the destabilizing scenario forced the patient to keep the end-point position as close as possible to the ideal path, hence requiring a more active control of the arm with respect to the AA approach. Our findings confirmed this hypothesis. In addition, when the DF treatment was provided in the first therapy cycle, patients also showed straighter and smoother paths during the subsequent AA therapy cycle, while this was not true in the opposite case. In conclusion, the results herein reported provide evidence that the use of an unstable DF field can lead to better recovery outcomes, and therefore it potentially more effective than solely active assistance therapy alone.

A new robotic platform for gait rehabilitation of bedridden stroke patients

Robotic aided therapy has been developed in the last decades in order to improve the effects of gait rehabilitation on stroke patients. Although several platforms have nowadays used in clinical practice, contrasting results have been achieved with reduced significant improvements in stroke patients when they experience robotic based therapy. In particular, an improvement of the clinical outcome may be achieved by starting the rehabilitation process almost immediately after the stroke. To address this issue a new robotic system, called “NEUROBike”, has been developed. This approach is based on the hypothesis that a better recovery of the neuro-motor control of the leg could result from an early, intensive and task-oriented rehabilitation therapy. Therefore, the leg manipulation during the acute phase, following joint trajectories comparable with the ones obtained during natural walking, could improve the outcome of the rehabilitation. In this regard, desired trajectories of the end-effector of NEUROBike have been estimated in accordance with data collected from young and elderly people when walking on treadmill in a range of speeds from 0.5 to 1.3 m/s. Moreover, tracking performance of a traditional position control algorithm has been investigated. This paper is aimed at showing the first results obtained during the test of the platform. In the next months NEUROBike will be applied for the first clinical pilot studies.