Relative variability in muscle activation amplitude, muscle oxygenation, and muscle thickness: Changes with dynamic low-load elbow flexion fatigue and relationships in young and older females

Development of Flexible Medical Electrodes Using Carrageenan-Based Bioplastics with the Addition of Conductive Hybrid Materials Graphite and Silver Nanoparticles

Electrodes are crucial in medical devices, specifically health monitoring devices for biopotential measurements such as electrocardiography, electromyography (EMG), and electroencephalography. The commonly used rigid electrodes have limitations in their skin-electrode contact quality since they cannot conform to the skin's surface area and body contours. Flexible electrodes have been developed to better conform to the body's surface contours, improving ion transfer and minimizing motion artifacts, thereby enhancing the signal-to-noise ratio (SNR). Bioplastic substrates based on carrageenan have been chosen for their safety, abundance, flexibility, and ease of customization. Hybrid materials of graphite and silver nanoparticles (graphite-AgNPs) exhibit high electron capacitance, low charge transfer resistance, and superior surface catalytic activity. These make them ideal as conductive fillers for bioplastics to achieve good electrical characteristics as electrodes. The effect of the graphite-AgNP filler concentration, graphite particle size, and flexible electrode thickness was evaluated to assess their impact on the electrical and mechanical properties of the fabricated flexible electrodes. The graphite-AgNP fillers were incorporated into a bioplastic matrix, resulting in flexible electrodes with improved conductivity with increasing percentages of graphite-AgNP at the expense of flexibility. The thickness of the flexible electrode was varied to evaluate its effect on the conductivity. A graphite size reduction was performed to improve the electrical properties while maintaining the mechanical properties. The most optimal variation of flexible electrodes with desirable electrical and mechanical properties was achieved by adding 25% graphite-AgNP to the carrageenan, using graphite particles of 400-700 nm, and using the thinnest electrode. The optimized electrode also exhibited an improved SNR value in EMG signal measurements compared to conventional Ag/AgCl electrodes. This research presents a novel approach to developing environmentally friendly, customizable, and flexible electrodes for medical applications.

Neuromotor variability partially explains different endurance capacities of expert pianists

During fatiguing piano tasks, muscle fatigue develops differently between expert pianists. Differences in neuromotor strategies employed could explain a slower rate of fatigue development. The objective was to compare muscle activation and kinematic variabilities between ShortDuration (i.e., pianists with less endurance) and LongDuration groups. Results from 49 pianists showed that EMG activation variability of most shoulder and upper limbs muscles was greater for the ShortDuration group with time during two piano fatiguing tasks, namely Digital and Chord tasks. Segment acceleration variability, assessed using inertial measurement units, was also greater with time for the ShortDuration group at the right arm during the Digital task, and at the thorax and head during the Chord task. Finally, thorax lateroflexion variability increased with time for the LongDuration group (but not the ShortDuration group) during the Digital task. During the Chord task, wrist flexion variability was higher for the LongDuration group compared to the ShortDuration group. These results showed a direct effect of time on the pianists' acceleration variability and EMG activation variability. In contrast, a protective effect of fatigue development could be attributed to kinematic variability. Results also suggest a higher risk of injury among pianists in the ShortDuration group.

Effect of vitamin energy drinks on relieving exercise-induced fatigue in muscle group by ultrasonic bioimaging data analysis

OBJECTIVE

This work was aimed to analyze the effect of vitamin energy drink on muscle fatigue by surface electromyography (SEMG) and ultrasonic bioimaging (USBI).

METHODS

20 healthy men were selected to do increasing load fatigue test. Surface electromyographic signals and ultrasonic biological images were collected based on wavelet threshold function with improved thresholds. Time domain and frequency domain characteristic integrated electromyography (IEMG), root mean square amplitude (RMS), average power frequency (MPF), and surface and deep muscle morphological changes were analyzed. Hemoglobin concentration (HB), red blood cell number (RBC), mean volume of red blood cell (MCV), blood lactic acid (BLA), malondialdehyde (MDA), and phosphocreatine kinase (CK) were measured.

RESULTS

1) the Accuracy (94.10%), Sensitivity (94.43%), Specificity (93.75%), and Precision (94.07%) of the long and short-term memory (LSTM) specificity for muscle fatigue recognition were higher than those of other models. 2) Compared with the control group, the levels of BLA, MDA, and CK in the experimental group were decreased and HB levels were increased after exercise (P < 0.05). 3) IEMG and RMS of the experimental group were higher than those of the control group, and increased with time (P < 0.05). 4) The mean amplitude of the response signal decreased with time. Compared with the control group, the surface muscle thickness, deep muscle thickness, total muscle thickness, contrast, and homogeneity (HOM) decreased in the experimental group; while the angular second moment (ASM) and contrast increased, showing great differences (P < 0.05).

CONCLUSION

Surface electromyographic signal and ultrasonic biological image can be used as auxiliary monitoring techniques for muscle fatigue during exercise. Drinking vitamin energy drinks before exercise can relieve physical fatigue to a certain extent and promote the maintenance of muscle microstructure.

Myoelectric activity during electromagnetic resistance alone and in combination with variable resistance or eccentric overload

The purpose of this study was to compare the effects of electromagnetic resistance alone, as well as in combination with variable resistance or accentuated eccentric methods, with traditional dynamic constant external resistance exercise on myoelectric activity during elbow flexion. The study employed a within-participant randomized, cross-over design whereby 16 young, resistance-trained male and female volunteers performed elbow flexion exercise under each of the following conditions: using a dumbbell (DB); using a commercial electromagnetic resistance device (ELECTRO); variable resistance (VR) using a setting on the device that attempts to match the level of resistance to the human strength curve, and; eccentric overload (EO) using a setting on the device that increases the load by 50% on the eccentric portion of each repetition. Surface electromyography (sEMG) was obtained for the biceps brachii, brachioradialis and anterior deltoid on each of the conditions. Participants performed the conditions at their predetermined 10 repetition maximum. " The order of performance for the conditions was counterbalanced, with trials separated by a 10-min recovery period. The sEMG was synced to a motion capture system to assess sEMG amplitude at elbow joint angles of 30°, 50°, 70°, 90°, 110°, with amplitude normalized to the maximal activation. The anterior deltoid showed the largest differences in amplitude between conditions, where median estimates indicated greater concentric sEMG amplitude (~ 7-10%) with EO, ELECTRO and VR compared with DB. Concentric biceps brachii sEMG amplitude was similar between conditions. In contrast, results indicated a greater eccentric amplitude with DB compared to ELECTRO and VR, but unlikely to exceed a 5% difference. Data indicated a greater concentric and eccentric brachioradialis sEMG amplitude with DB compared to all other conditions, but differences were unlikely to exceed 5%. The electromagnetic device tended to produce greater amplitudes in the anterior deltoid, while DB tended to produce greater amplitudes in the brachioradialis; amplitude for the biceps brachii was relatively similar between conditions. Overall, any observed differences were relatively modest, equating to magnitudes of ~ 5% and not likely greater than 10%. These differences would seem to be of minimal practical significance.

Size and structure of motor variability in young and old adults performing a rhythmic, repetitive tapping task

The size of motor variability increases with fatigue in repetitive upper limb tasks, and the structure of variability differs with old age. However, the combined influences of old age and fatigue on the size and structure of movement-to-movement variability are unclear. Eighteen young and sixteen old adults performed a fatiguing repetitive tapping task while seated using their dominant arm. Optoelectronic motion capture served to measure upper body angles via forward kinematics. Movement-to-movement variability was measured by the size at joints (standard deviation: SD) and by the structure of the uncontrolled manifold (variance: V_UCM, V_ORT; synergy index: ΔV_z) in the first and final minutes of the task for the early, middle, and late forward movement phases. Outcomes were analyzed by Age*Condition*Phase general estimating equations. Old adults had lower humerothoracic abduction/adduction and flexion/extension SD, wrist flexion/extension SD, V_UCM, and V_ORT, mainly in the early movement phase (p < 0.014). With fatigue, humerothoracic flexion/extension SD increased in young adults only and humerothoracic abduction/adduction SD, wrist pronation/supination SD, wrist flexion/extension SD, and V_UCM increased in both groups. ΔV_z was positive and did not differ with age or fatigue (p > 0.014). Results indicate that fatigue adjustments were mainly in the frontal plane, old age did not affect the ratio of good vs. bad variability, and motor synergy was preserved during fatigue despite less motor flexibility in old age.

Age-related performance fatigability: a comprehensive review of dynamic tasks

Adult ageing is associated with a myriad of changes within the neuromuscular system, leading to reductions in contractile function of old adults. One of the consequences of these age-related neuromuscular adaptations is altered performance fatigability, which can limit the ability of old adults to perform activities of daily living. Whereas age-related fatigability of isometric tasks has been well characterized, considerably less is known about fatigability of old adults during dynamic tasks involving movement about a joint, which provides a more functionally relevant task compared to static contractions. This review provides a comprehensive summary of age-related fatigability in dynamic contractions, where the importance of task specificity is highlighted with a brief discussion of the potential mechanisms responsible for differences in fatigability between young and old adults. The angular velocity of the task is critical for evaluating age-related fatigability, as tasks which constrain angular velocity (i.e., isokinetic) produce equivocal age-related differences in fatigability, whereas tasks involving unconstrained velocity (i.e., isotonic-like) consistently induce greater fatigability of old compared to young adults. These unconstrained velocity tasks, that are more closely associated with natural movements, offer an excellent model to uncover the underlying age-related mechanisms of increased fatigability. Future work evaluating the mechanisms of increased age-related fatigability of dynamic tasks should be evaluated using task-specific contractions (i.e., dynamic), particularly for assessment of spinal and supra-spinal components. Advancing our understanding of age-related fatigability is likely to yield novel insights and approaches for improving mobility limitations in old adults.