Simultaneous control of natural and extra degrees of freedom by isometric force and electromyographic activity in the muscle-to-force null space

Objective. Muscle activation patterns in the muscle-to-force null space, i.e., patterns that do not generate task-relevant forces, may provide an opportunity for motor augmentation by allowing to control additional end-effectors simultaneously to natural limbs. Here we tested the feasibility of muscular null space control for augmentation by assessing simultaneous control of natural and extra degrees of freedom. Approach. We instructed eight participants to control translation and rotation of a virtual 3D end-effector by simultaneous generation of isometric force at the hand and null space activity extracted in real-time from the electromyographic signals recorded from 15 shoulder and arm muscles. First, we identified the null space components that each participant could control more naturally by voluntary co-contraction. Then, participants performed several blocks of a reaching and holding task. They displaced an ellipsoidal cursor to reach one of nine targets by generating force, and simultaneously rotated the cursor to match the target orientation by activating null space components. We developed an information-theoretic metric, an index of difficulty defined as the sum of a spatial and a temporal term, to assess individual null space control ability for both reaching and holding. Main Results. On average, participants could reach the targets in most trials already in the first block (72%) and they improved with practice (maximum 93%) but holding performance remained lower (maximum 43%). As there was a high inter-individual variability in performance, we performed a simulation with different spatial and temporal task conditions to estimate those for which each individual participants would have performed best. Significance. Muscular null space control is feasible and may be used to control additional virtual or robotics end-effectors. However, decoding of motor commands must be optimized according to individual null space control ability.

Competition, Conflict and Change of Mind: A Role of GABAergic Inhibition in the Primary Motor Cortex

Deciding between different voluntary movements implies a continuous control of the competition between potential actions. Many theories postulate a leading role of prefrontal cortices in this executive function, but strong evidence exists that a motor region like the primary motor cortex (M1) is also involved, possibly via inhibitory mechanisms. This was already shown during the pre-movement decision period, but not after movement onset. For this pilot experiment we designed a new task compatible with the dynamics of post-onset control to study the silent period (SP) duration, a pause in electromyographic activity after single-pulse transcranial magnetic stimulation that reflects inhibitory mechanisms. A careful analysis of the SP during the ongoing movement indicates a gradual increase in inhibitory mechanisms with the level of competition, consistent with an increase in mutual inhibition between alternative movement options. However, we also observed a decreased SP duration for high-competition trials associated with change-of-mind inflections in their trajectories. Our results suggest a new post-onset adaptive process that consists in a transient reduction of GABAergic inhibition within M1 for highly conflicting situations. We propose that this reduced inhibition softens the competition between concurrent motor options, thereby favoring response vacillation, an adaptive strategy that proved successful at improving behavioral performance.

Effect of neuromuscular electrical stimulation on functional exercise capacity in patients undergoing cardiac surgery: A randomized clinical trial

Objective To evaluate the effects of neuromuscular electrical stimulation on functional capacity of patients in the immediate postoperative period of cardiac surgery. Design A prospective, randomized controlled trial. Setting A cardiac surgery specialist hospital in Aracaju, Sergipe, Brazil. Subjects: Patients in the postoperative period of cardiac surgery. Intervention The control group received the conventional physiotherapy and the intervention group received neuromuscular electrical stimulation of the rectus femoris and gastrocnemius muscles bilaterally, applied for 60 min, twice a day for up to 10 sessions per patient, in the immediate postoperative period until postoperative day 5. Main measures The primary outcome was the distance walked, which was evaluated using the 6-min walk test on postoperative day 5. Secondary outcomes were gait speed, lactate levels, muscle strength, electromyographic activity of the rectus femoris and Functional Independence Measure, some of them evaluated on preoperative and postoperative period. Results Of 132 eligible patients, 88 patients were included and randomly allocated in two groups, and 45 patients were included in the analysis. No significant difference was found on the distance walked ( p = 0.650) between patients allocated in intervention group (239.06 ± 88.55) and control group (254.43 ± 116.67) as well as gait speed ( p = 0.363), lactate levels ( p = 0.302), knee extensor strength ( p = 0.117), handgrip strength ( p = 0.882), global muscle strength ( p = 0.104), electromyographic activity ( p = 0.179) and Functional Independence Measure ( p = 0.059). Conclusions Although the effects are still uncertain, the use of neuromuscular electrical stimulation carried out in five days didn't present any benefit on functional capacity of patients in the immediate postoperative period of cardiac surgery.

Possible predictors of phenoconversion in isolated REM sleep behaviour disorder: a systematic review and meta-analysis

BackgroundA number of promising biomarkers for predicting imminent α-synucleinopathies have been suggested in isolated rapid eye movement sleep behaviour disorder (iRBD). However, existing evidence is conflicting without quantitative evaluation.MethodsPubMed, Web of Science and ClinicalTrials.gov were searched through June 2021 to identify possible predictors of phenoconversion from iRBD to Parkinson’s disease (PD). The pooled HRs and standardised mean differences (SMDs) with 95% CIs were calculated using fixed-effects or random-effects model.ResultsA total of 123 studies were included in the meta-analysis. Significant motor dysfunction (HR 1.83, 95% CI 1.33 to 2.51, I2=86.8%, p<0.001), constipation (HR 1.52, 95% CI 1.26 to 1.84, I2=8.3%, p=0.365), orthostatic hypotension (HR 1.93, 95% CI 1.05 to 3.53, I2=54.9%, p=0.084), hyposmia (HR 2.78, 95% CI 1.83 to 4.23, I2=23.9%, p=0.255), mild cognitive impairment (HR 2.27, 95% CI 1.58 to 3.27, I2=0%, p=0.681) and abnormal colour vision (SMD −0.34, 95% CI −0.63 to −0.05, I2=45.6%, p=0.087) correlated with susceptibility to PD. The process can also be traced by putaminal dopamine transporter imaging (HR 2.60, 95% CI 1.94 to 3.48, I2=0%, p=0.781) and tonic electromyographic activity (HR 1.50, 95% CI 1.04 to 2.15, I2=70%, p=0.018).ConclusionsThe predictive value of each biomarker was initially highlighted with comprehensive evaluation. Combining specific predictors with high sensitivity is promising for detecting phenoconversion in the prodromal stage. Large-scale and multicentre studies are pivotal to extend our findings.

Proactive Modulation in the Spatiotemporal Structure of Muscle Synergies Minimizes Reactive Responses in Perturbed Landings

Stability training in the presence of perturbations is an effective means of increasing muscle strength, improving reactive balance performance, and reducing fall risk. We investigated the effects of perturbations induced by an unstable surface during single-leg landings on the mechanical loading and modular organization of the leg muscles. We hypothesized a modulation of neuromotor control when landing on the unstable surface, resulting in an increase of leg muscle loading. Fourteen healthy adults performed 50 single-leg landings from a 30 cm height onto two ground configurations: stable solid ground (SG) and unstable foam pads (UG). Ground reaction force, joint kinematics, and electromyographic activity of 13 muscles of the landing leg were measured. Resultant joint moments were calculated using inverse dynamics and muscle synergies with their time-dependent (motor primitives) and time-independent (motor modules) components were extracted via non-negative matrix factorization. Three synergies related to the touchdown, weight acceptance, and stabilization phase of landing were found for both SG and UG. When compared with SG, the motor primitive of the touchdown synergy was wider in UG (p &lt; 0.001). Furthermore, in UG the contribution of gluteus medius increased (p = 0.015) and of gastrocnemius lateralis decreased (p &lt; 0.001) in the touchdown synergy. Weight acceptance and stabilization did not show any statistically significant differences between the two landing conditions. The maximum ankle and hip joint moment as well as the rate of ankle, knee, and hip joint moment development were significantly lower (p &lt; 0.05) in the UG condition. The spatiotemporal modifications of the touchdown synergy in the UG condition highlight proactive adjustments in the neuromotor control of landings, which preserve reactive adjustments during the weight acceptance and stabilization synergies. Furthermore, the performed proactive control in combination with the viscoelastic properties of the soft surface resulted in a reduction of the mechanical loading in the lower leg muscles. We conclude that the use of unstable surfaces does not necessarily challenge reactive motor control nor increase muscle loading per se. Thus, the characteristics of the unstable surface and the dynamics of the target task must be considered when designing perturbation-based interventions.

A Methodological Framework to Capture Neuromuscular Fatigue Mechanisms Under Stress

Neuromuscular fatigue is exacerbated under stress and is characterized by shorter endurance time, greater perceived effort, lower force steadiness, and higher electromyographic activity. However, the underlying mechanisms of fatigue under stress are not well-understood. This review investigated existing methods of identifying central mechanisms of neuromuscular fatigue and the potential mechanisms of the influence of stress on neuromuscular fatigue. We found that the influence of stress on the activity of the prefrontal cortex, which are also involved in exercise regulation, may contribute to exacerbated fatigue under stress. We also found that the traditional methods involve the synchronized use of transcranial magnetic stimulation, peripheral nerve stimulation, and electromyography to identify the contribution of supraspinal fatigue, through measures such as voluntary activation, motor evoked potential, and silent period. However, these popular techniques are unable to provide information about neural alterations upstream of the descending drive that may contribute to supraspinal fatigue development. To address this gap, we propose that functional brain imaging techniques, which provide insights on activation and information flow between brain regions, need to be combined with the traditional measures of measuring central fatigue to fully understand the mechanisms behind the influence of stress on fatigue.

Electromyographic activity of the masseter muscle in individuals with group function and canine guidance

Background. There is no general consensus in restorative dentistry about which lateral guidance should be established. Some studies have shown that canine guidance decreases the tension of masticatory muscles. Others have reported that group function might achieve a better physiologic distribution of occlusal forces. Also, some reports have shown that both guidances are equally acceptable. Despite all discussions, clinical evidence of one guidance being superior to another is limited. Thus, this study aimed to analyze the electromyographic (EMG) activity of masseter muscles in individuals with group function and canine guidance. Methods. Twenty volunteers of both genders, aged 20-25, were divided into two groups: GF (group function guidance, n=10) and CA (canine guidance, n=10). EMG activity of masseters was captured using surface electrodes during habitual maximum intercuspation (HMI) and right and left lateral jaw movements and recorded using EMG amplitude values (RMS – root means square). Student’s t-test was used to compare mean RMS values between the groups and lateral movements in each group. Results. During HMI, there was no difference in masseter EMG activity between the groups. Both masseters showed higher activity in group GF only on the right side during lateral movements, while the left masseter exhibited higher activity on the nonworking side in both groups. The activity of both masseters distributed by tooth was higher in group CA. Conclusion. During tooth restorative procedures, any guidance is acceptable considering HMI. However, group function guidance is more favorable during lateral movements due to greater dissipation of occlusal pressures.

Assessment of a New Lateral Cushioned Casting Orthosis: Effects on Peroneus Longus Muscle Electromyographic Activity During Running

Background: Classical medial wedge (CMW) orthoses have been prescribed to treat overpronation foot pathologies in runners. The effects of a novel supination orthosis (NSO) on the surface electromyography (EMG) activity of the peroneus longus (PL) muscle during a complete cycle of running have yet to be tested. Purpose/Hypothesis: The purpose of this study was to compare the EMG activity of the PL in participants wearing CMW orthoses and NSOs versus neutral running shoes (NRS) during a full cycle of running gait. It was hypothesized that the PL muscle activity would be lower for the NSO compared with CMW or NRS. Study Design: Controlled laboratory study. Methods: Included were 31 healthy recreational runners of both sexes (14 male and 17 female; mean age, 38.58 ± 4.02 years) with a neutral Foot Posture Index and standard rearfoot-strike pattern. Participants ran on a treadmill at 9 km/h while wearing NSO (3-, 6-, and 9-mm thicknesses), CMW (3-, 6-, and 9-mm thicknesses), and NRS, for a total of 7 different conditions randomly selected, while the EMG signal activity of the PL was recorded for 30 seconds. Each trial was recorded 3 times, and the intraclass correlation coefficient (ICC) to test reliability of the measurements was calculated. The Wilcoxon pair to pair nonparametric test with Bonferroni correction was performed to analyze differences among the conditions. Results: The reliability of all assessments was almost perfect (ICC, >0.81). For both the CMW and NSO, regardless of thickness, the PL activity was statistically significantly lower compared with the NRS ( P < .05 for all). For all CMW thicknesses, the PL activity was lower compared with the respective NSO thicknesses, with the 3-mm thickness having the largest difference (CMW3mm, 18.63 ± 4.64 vs NSO3mm, 20.78 ± 4.99 mV; P < .001). Conclusion: Both CMW and NSO produced reduced EMG activity of the PL muscle; therefore, they can be prescribed to treat overpronation pathologies without associated PL strain concerns. In addition, the NSO saved the enhancement material placed on the medial-rear side of CMW, making it easier to wear sports shoes. Clinical Relevance: Knowing the safety of CMW and NSO will aid in understanding treatments for overpronation pathologies.