Physiological tremor is suppressed and force steadiness is enhanced with increased availability of serotonin regardless of muscle fatigue

Although there is evidence that 5-HT acts as an excitatory neuromodulator to enhance maximal force generation, it is largely unknown how 5-HT activity influences the ability to sustain a constant force during steady-state contractions. A total of 22 healthy individuals participated in the study, where elbow flexion force was assessed during brief isometric contractions at 10% maximal voluntary contraction (MVC), 60% MVC, MVC, and during a sustained MVC. The selective serotonin reuptake inhibitor, paroxetine, suppressed physiological tremor and increased force steadiness when performing the isometric contractions. In particular, a main effect of drug was detected for peak power of force within the 8-12 Hz range (p = 0.004) and the coefficient of variation (CV) of force (p < 0.001). A second experiment was performed where intermittent isometric elbow flexions (20% MVC sustained for 2 min) were repeatedly performed so that serotonergic effects on physiological tremor and force steadiness could be assessed during the development of fatigue. Main effects of drug were once again detected for peak power of force in the 8-12 Hz range (p = 0.002) and CV of force (p = 0.003), where paroxetine suppressed physiological tremor and increased force steadiness when the elbow flexors were fatigued. The findings of this study suggest that enhanced availability of 5-HT in humans has a profound influence of maintaining constant force during steady state contractions. The action of 5-HT appears to suppress fluctuations in force regardless of the fatigue state of the muscle.

Prediction of Long-Term Elbow Flexion Force Intervals Based on the Informer Model and Electromyography

Accurate and long-term prediction of elbow flexion force can be used to recognize the intended movement and help wearable power-assisted robots to improve control performance. Our study aimed to find a proper relationship between electromyography and flexion force. However, the existing methods must incorporate biomechanical models to produce accurate and timely predictions of flexion force. Elbow flexion force is largely determined by the contractile properties of muscles, and the relationship between flexion force and the motor function of muscles has to be thoroughly analyzed. Therefore, based on the investigation on the contributions of different muscles to the flexion force, original electromyography signals were decomposed into non-linear and non-stationary parts. We selected the mean absolute value (MAV) of the non-linear part and the variance of the non-stationary part as inputs for an Informer prediction model that does not require detailed a priori knowledge of biomechanical models and is optimized for processing time sequences. Finally, a long-term flexion force probability interval is proposed. The proposed framework performs well in predicting long-term flexion force and outperforms other state-of-the-art models when compared to experimental results.

Force-velocity relationship profile of elbow flexors in male gymnasts

Background The theoretical maximum force (F0), velocity (V0), and power (Pmax) of athletes calculated from the relationship between force and velocity (F-V relationship) and the slope of the F-V relationship, reflect their competitive and training activity profiles. Evaluating the F-V relationship of athletes facilitates categorizing the profiles of dynamic muscle functions in relation to long-term sport-specific training. For gymnastics, however, no studies have tried to examine the profiles of F-V relation and power output for upper limb muscles in relation to the muscularity, while the use of the upper extremities in this sport is very unique as described earlier. Purpose It was hypothesized that the F-V relationship of the elbow flexion in gymnasts might be characterized by low capacity for generating explosive force, notably in terms of the force normalized to muscle size. Methods The F0, V0, and Pmax derived from the force-velocity relationship during explosive elbow flexion against six different loads (unloaded condition, 15, 30, 45, 60, and 75% of maximal voluntary isometric elbow flexion force (MVFEF)) for 16 gymnasts (GYM) and 22 judo athletes (JD). F0 and Pmax were expressed as values relative to the cross-sectional area index (CSAindex) of elbow flexors (F0/CSAindex and Pmax/CSAindex, respectively), which was calculated from muscle thickness in the anterior upper arm. The electromyogram (EMG) activities of the biceps brachii (BB) during the maximal isometric and dynamic tasks were also determined. Results There were no significant differences in CSAindex of elbow flexors between GYM and JD. MVFEF/CSAindex for GYM was significantly lower than that for JD. Force was linearly associated with velocity in the dynamic elbow flexion for all the participants (r = − 0.997 to −0.905 for GYM, r = − 0.998 to −0.840 for JD). F0, F0/ CSAindex, V0, Pmax, Pmax/CSAindex, and MVFEF were significantly lower in GYM than in JD. The activity levels of BB during the dynamic tasks tended to be lower in GYM than in JD at load of <45%MVC. Conclusion Gymnasts cannot generate explosive elbow flexion force corresponding to their muscle size. This may be due to low neuromuscular activities during the maximal dynamic tasks against relatively low loads.

Neural Correlates of Knee Extension and Flexion Force Control: A Kinetically-Instrumented Neuroimaging Study

Background: The regulation of muscle force is a vital aspect of sensorimotor control, requiring intricate neural processes. While neural activity associated with upper extremity force control has been documented, extrapolation to lower extremity force control is limited. Knowledge of how the brain regulates force control for knee extension and flexion may provide insights as to how pathology or intervention impacts central control of movement.Objectives: To develop and implement a neuroimaging-compatible force control paradigm for knee extension and flexion.Methods: A magnetic resonance imaging (MRI) safe load cell was used in a customized apparatus to quantify force (N) during neuroimaging (Philips Achieva 3T). Visual biofeedback and a target sinusoidal wave that fluctuated between 0 and 5 N was provided via an MRI-safe virtual reality display. Fifteen right leg dominant female participants (age = 20.3 ± 1.2 years, height = 1.6 ± 0.10 m, weight = 64.8 ± 6.4 kg) completed a knee extension and flexion force matching paradigm during neuroimaging. The force-matching error was calculated based on the difference between the visual target and actual performance. Brain activation patterns were calculated and associated with force-matching error and the difference between quadriceps and hamstring force-matching tasks were evaluated with a mixed-effects model (z &gt; 3.1, p &lt; 0.05, cluster corrected).Results: Knee extension and flexion force-matching tasks increased BOLD signal among cerebellar, sensorimotor, and visual-processing regions. Increased knee extension force-matching error was associated with greater right frontal cortex and left parietal cortex activity and reduced left lingual gyrus activity. Increased knee flexion force-matching error was associated with reduced left frontal and right parietal region activity. Knee flexion force control increased bilateral premotor, secondary somatosensory, and right anterior temporal activity relative to knee extension. The force-matching error was not statistically different between tasks.Conclusion: Lower extremity force control results in unique activation strategies depending on if engaging knee extension or flexion, with knee flexion requiring increased neural activity (BOLD signal) for the same level of force and no difference in relative error. These fMRI compatible force control paradigms allow precise behavioral quantification of motor performance concurrent with brain activity for lower extremity sensorimotor function and may serve as a method for future research to investigate how pathologies affect lower extremity neuromuscular function.

Refinement of High-Gamma EEG Features From TBI Patients With Hemicraniectomy Using an ICA Informed by Simulated Myoelectric Artifacts

Recent studies have shown the ability to record high-γ signals (80–160 Hz) in electroencephalogram (EEG) from traumatic brain injury (TBI) patients who have had hemicraniectomies. However, extraction of the movement-related high-γ remains challenging due to a confounding bandwidth overlap with surface electromyogram (EMG) artifacts related to facial and head movements. In our previous work, we described an augmented independent component analysis (ICA) approach for removal of EMG artifacts from EEG, and referred to as EMG Reduction by Adding Sources of EMG (ERASE). Here, we tested this algorithm on EEG recorded from six TBI patients with hemicraniectomies while they performed a thumb flexion task. ERASE removed a mean of 52 ± 12% (mean ± S.E.M) (maximum 73%) of EMG artifacts. In contrast, conventional ICA removed a mean of 27 ± 19% (mean ± S.E.M) of EMG artifacts from EEG. In particular, high-γ synchronization was significantly improved in the contralateral hand motor cortex area within the hemicraniectomy site after ERASE was applied. A more sophisticated measure of high-γ complexity is the fractal dimension (FD). Here, we computed the FD of EEG high-γ on each channel. Relative FD of high-γ was defined as that the FD in move state was subtracted by FD in idle state. We found relative FD of high-γ over hemicraniectomy after applying ERASE were strongly correlated to the amplitude of finger flexion force. Results showed that significant correlation coefficients across the electrodes related to thumb flexion averaged ~0.76, while the coefficients across the homologous electrodes in non-hemicraniectomy areas were nearly 0. After conventional ICA, a correlation between relative FD of high-γ and force remained high in both hemicraniectomy areas (up to 0.86) and non-hemicraniectomy areas (up to 0.81). Across all subjects, an average of 83% of electrodes significantly correlated with force was located in the hemicraniectomy areas after applying ERASE. After conventional ICA, only 19% of electrodes with significant correlations were located in the hemicraniectomy. These results indicated that the new approach isolated electrophysiological features during finger motor activation while selectively removing confounding EMG artifacts. This approach removed EMG artifacts that can contaminate high-gamma activity recorded over the hemicraniectomy.

Muscle activation and biceps brachii strength under manual fixation of the scapula and different loading conditions

BACKGROUND: Few studies have reported the contribution of isometric-specific exercise of the biceps brachii muscle to increased strength under manual fixation of the scapula. OBJECTIVE: To investigate the activation amplitude of the biceps brachii (BB), serratus anterior (SA), and upper trapezius (UT) in a supine lying posture based on various exercise conditions. METHODS: The EMG activity of BB, SA, and UT was measured in 25 healthy adults while performing maximal elbow flexion exercise with or without manual stabilization of the scapula in two different loading conditions. RESULTS: Muscle activation of the BB was significantly greater when performed with manual fixation of the scapula under the wrist-loading exercise condition (p< 0.05) but manual fixation of the scapula or absence thereof did not have an effect. Elbow flexion force was significantly increased when applying manual fixation to the scapula in both the hand and wrist-loading exercise conditions (p< 0.05). There were no interaction effects between exercise conditions and manual fixation (with or without) in any of the EMG activation values (p> 0.05). CONCLUSION: Manual stabilization of the scapula is a useful therapeutic technique to increase BB strength. Such an intervention may also be indicated for accurate strength measurement of this muscle.

Patients outcome after distal femur- and proximal tibia replacement

Aims and Objectives: Mega-knee-arthroplasty are rare and indications are heterogeneous after fracture, tumour and infection. The outcome after distal femur- and/or proximal tibia replacement are unclear. We therefore wanted to analyse the postoperative outcome in case of primary and revision surgery. We hypothesize that I) Implantation of distal femur- and/or proximal tibia replacement are associated with reduced range of motion and function compared to the contralateral side and II) implantation in case of primary surgery is associated with better outcome than in case of revision surgery. Materials and Methods: We retrospectively analysed all patients in our trauma department between 1998 and 2017 who underwent a MUTARS distal femur replacement or proximal tibia replacement (Implantcast GmbH, Buxtehude, Germany). We collected general patients’ data, rang of motion, determined the Toronto extremity selvage score (TESS), musculoskeletal tumour society score (MSTS), knee society score (KSS) and Western Ontario MacMaster questionnaire (WOMAC) Score. Knee extension and flexion force was measured. Results: We included 59 patients with a mean age of 65+/-20 years. Out of these we had 19 (32%) male and 40 (68%) female patients. Mean follow up (f/up) was 36+/-57 month (range: 1-218). Indication for R-TKA was periprosthetic fractures (n=14), tumour (n=16), infection (n=10), traumatic fracture (n=14), aseptic loosening (n=3) and pathologic fracture (n=2). Indication for primary implantation was given in 33 (56%) patients and for implantation in case of revision surgery in 26 (44%) patients. Mean TESS was 66+/-33, mean MSTS was 14+/-7, mean KSS was 49+/-30, mean WOMAC was 36+/-26. Mean flexion on the operated side was 83°+/-24° compared to the healthy side (115°+/-20°) (p<0.001). Mean extension force on the operated side at 60° was 20+/-12 (Nm) compared to 77+/-58 (Nm) on the not operated side (p=0.31). Mean flexion force on the operated side at 60° was 32+/-26 (Nm) compared to 53+/-42 (Nm) on the not operated side (p=0.43). In case of revision surgery significant worse function scores in the TESS and KSS could be overserved (both p<0.05). Conclusion: Implantation of a distal femur- and/or proximal tibia replacement are associated with loss of flexion, a trend to reduced extension and flexion power compared to the contralateral side. In case of primary surgery better functional results in terms of function Scores can be expected than in case of revision surgery.

TRAUMATIC DORSAL DISLOCATION OF INTERMEDIATE CUNEIFORM : A RARE MIDFOOT INJURY

Dislocation of the intermediate cuneiform is a rare injury, and only a few cases have been reported .Cuneiforms dislocations have been treated in a variety of methods, ranging from open or closed reduction, without or with fixation such as Krischner wires or screws. Methods: A 24 years old female presented with right foot pain following fall from motorbike after got hit by a car from back. She related a history that her right foot was forced into torsion and plantarflexion at impact . On examination there was a bony protuberance on the dorsal surface, at cuneiform area . Radiograph showed dorsal dislocation of intermediate cuneiform. CT scan was performed and supported the radiographical findings. Manipulation under sedation was attempted, but was unsuccessful. Results: Patient was placed supine under spinal anesthesia . A dorsal incision was made centering over the protuberance proceeded distally up to the base of the second-metatarsal. The dislocated middle cuneiform was identified. There was proximal soft tissue attachment to the middle cuneiform which was carefully preserved. It temporarily reduced with Krishner wires and a 2.7 mm variable angle locking plate was fixed dorsally to butress the bone dislocation . The foot was immobilized with a boot slab for 6 weeks and subsequently physiotherapy was instituted and gradual weight-bearing started. Postoperative follow-up was uneventful. Discussion: Intermediate cuneiform is a part of the transverse and medial longitudinal arches of the foot and the stability is achieved by the deep transverse, dorsal, and plantar ligaments. It’s shaped like a wedge, the thin end pointing downwards, situated between medial and lateral cuneiforms, and articulates with the navicular posteriorly, the second metatarsal anteriorly and with the other cuneiforms on either side. Because it is wedge shaped and positioned dorsally, it has a tendency to dislocate dorsally, particularly when a plantar flexion force is applied to the midfoot. Immediate reduction and maintaining in reduced position is needed for good ligamentous healing. Conclusion: Intermediate cuneiform dislocation is a rare injury to encounter due to stable articulation of joints and ligament. Significant trauma is required for these injuries to take place. Open reduction is the gold standard treatment for these injuries. References: Kumaravel S et al An isolated middle cuneiform dislocation with a rare violence Journal of clinical orthopaedic and trauma 5 (2014) 161-171 Name

Assessment of the Flexion Force of TMA and Elgiloy Intrusion Arches to Different Lengths of Activation. An In Vitro Study

The present study analyzed the utilitary arch of Ricketts made with TMA and Elgiloy alloys, evaluating the forces that each one presented at different activation lengths. METHODS: A total of 30 arches (15 per alloy) 17x25 caliber were assessed. An acrylic model that simulated the jaw was used with tubes welded to the bands located on the first molars where the arches were attached and brackets were bonded to the lower incisors. The Ricketts arches had a total length of 100 mm and were activated in their distal branch, obtaining the lengths of 5, 10 and 15 mm measured from the slot of the anterior brackets in the midline. A Digital Universal Testing Machine CMT-5L was used to measure the bending force and the statistical analysis was carried out with the Student's T and Mann-Whitney U test. RESULTS: The TMA alloys had a significantly lower strength in each of the activations 5, 10, 15 mm (13,53; 31,61 and 42,01grams respectively) compared to Elgiloy (31.41; 62,61 y 93,00 grams respectively). While increasing the activation length, the flexural forces increased significantly for both alloys. CONCLUSION: The suggested forces for the intrusion of lower incisors were reached by the Elgiloy arches.