A Bio-mechanical Model for Elbow Isokinetic and Isotonic Flexions

Integrated Wearable System for Monitoring Skeletal Muscle Force of Lower Extremities

Continuous monitoring of lower extremity muscles is necessary, as the muscles support many human daily activities, such as maintaining balance, standing, walking, running, and jumping. However, conventional electromyography and physiological cross-sectional area methods inherently encounter obstacles when acquiring precise and real-time data pertaining to human bodies, with a notable lack of consideration for user comfort. Benefitting from the fast development of various fabric-based sensors, this paper addresses these current issues by designing an integrated smart compression stocking system, which includes compression garments, fabric-embedded capacitive pressure sensors, an edge control unit, a user mobile application, and cloud backend. The pipeline architecture design and component selection are discussed in detail to illustrate a comprehensive user-centered STIMES design. Twelve healthy young individuals were recruited for clinical experiments to perform maximum voluntary isometric ankle plantarflexion contractions. All data were simultaneously collected through the integrated smart compression stocking system and a muscle force measurement system (Humac NORM, software version HUMAC2015). The obtained correlation coefficients above 0.92 indicated high linear relationships between the muscle torque and the proposed system readout. Two-way ANOVA analysis further stressed that different ankle angles (p = 0.055) had more important effects on the results than different subjects (p = 0.290). Hence, the integrated smart compression stocking system can be used to monitor the muscle force of the lower extremities in isometric mode.

Retentive capacity of power output and linear versus non-linear mapping of power loss in the isotonic muscular endurance test

The limit of dynamic endurance during repetitive contractions has been referred to as the point of muscle fatigue, which can be measured by mechanical and electrophysiological parameters combined with subjective estimates of load tolerance for revealing the human real-world capacity required to work continuously. In this study, an isotonic muscular endurance (IME) testing protocol under a psychophysiological fatigue criterion was developed for measuring the retentive capacity of the power output of lower limb muscles. Additionally, to guide the development of electrophysiological evaluation methods, linear and non-linear techniques for creating surface electromyography (sEMG) models were compared in terms of their ability to estimate muscle fatigue. Forty healthy college-aged males performed three trials of an isometric peak torque test and one trial of an IME test for the plantar flexors and knee and hip extensors. Meanwhile, sEMG activity was recorded from the medial gastrocnemius, lateral gastrocnemius, vastus medialis, rectus femoris, vastus lateralis, gluteus maximus, and biceps femoris of the right leg muscles. Linear techniques (amplitude-based parameters, spectral parameters, and instantaneous frequency parameters) and non-linear techniques (a multi-layer perception neural network) were used to predict the time-dependent power output during dynamic contractions. Two mechanical manifestations of muscle fatigue were observed in the IME tests, including power output reduction between the beginning and end of the test and time-dependent progressive power loss. Compared with linear mapping (linear regression) alone or a combination of sEMG variables, non-linear mapping of power loss during dynamic contractions showed significantly higher signal-to-noise ratios and correlation coefficients between the actual and estimated power output. Muscular endurance required in real-world activities can be measured by considering the amount of work produced or the activity duration via the recommended IME testing protocol under a psychophysiological termination criterion. Non-linear mapping techniques provide more powerful mapping of power loss compared with linear mapping in the IME testing protocol.

The Influence of Active Hamstring Stiffness on Markers of Isotonic Muscle Performance

Background: Previous research demonstrates hamstring muscle-tendon stiffness (HMTS) influences isometric strength, landing biomechanics and architectural tissue properties. However, the influence on kinetics & kinematics during other modes of strength testing (isotonic dynamometry) has yet to be established. Purpose: Investigate how HMTS influences kinetics and kinematics during a novel isotonic muscle performance test which has never been done for the hamstrings. Previous work using dynamometry has been limited to isometric or isokinetic contractions, so the novelty arises from our custom isotonic protocol which allows quantitative assessment of the stretch-shortening cycle. Methods: Twenty-six recreationally active individuals (15 males, 11 females, 23.8 ± 2.5 years) completed baseline testing for anthropometry and maximum isometric hamstring strength (MVIC). At least 48 h later, subjects completed a measure of HMTS (damped oscillation technique) followed by an isotonic knee flexion test (eccentric velocity 180°/s; concentric torque 25% of MVIC). Separate linear regression models with examination of residuals were conducted between HMTS and each muscle performance variable. Standardized coefficients determined the magnitude of the relationships. Results: Significance was found for all outcome variables tested. HMTS and rate of torque development demonstrated the strongest relationship followed by isotonic concentric peak torque. The weakest relationship observed was with isometric peak torque. Conclusions: These findings build off previous work quantifying HMTS by showing HMTS more strongly relates to dynamic versus static muscle testing and identifies the potential clinical utility of isotonic dynamometry.

Fabrication and Characterization of Wrapped Metal Yarns-based Fabric Temperature Sensors

Textile temperature sensors are highly in demanded keep a real-time and accurate track of human body temperature for identification of healthy conditions or clinical diagnosis. Among various materials for textile temperature sensors, temperature-sensitive metal fibers have highest precision. However, those metal fibers are mechanically too weak, and break constantly during the weaving process. To enhance the mechanical strength of the metal fibers, this paper proposes to make wrapped metal fibers using wrapping technology, and characterize the effect of wrapped metal yarns on both mechanical properties and sensing behaviors. The wrapped yarns were woven into fabrics, forming the fabric temperature sensors. Results show that strength and maximum strain of the wrapped yarns are 2.69 and 1.82 times of pure Pt fibers. The response time of fabric temperature sensors using wrapped yarns was observed as 0.78 s and 1.1 s longer compared to that using Pt fibers when front and back sides contacted heat source, respectively. It is recommended that the wrapping method should be implemented for the protection of Pt fibers in fabric temperature sensors.

Fabric Circuit Board Connecting to Flexible Sensors or Rigid Components for Wearable Applications

Electronic textiles demand a new family of flexible circuit boards in the construction of fiber or fiber assemblies. This paper presents a stretchable woven fabric circuit board (FCB) with permanent as well as detachable electrical connections to sensors or other wearable electronics components. The woven FCB was created by integrating conductive yarns into an elastic woven fabric. Permanent connection was designed between the conductive tracks and flexible sensors; detachable connection was achieved by the helical structure of conductive yarns wrapping around the rigid component electrode encapsulated within elastomeric layer. The developed FCB, with its connections to flexible sensors or rigid components, is porous, flexible, and capable of stretching to 30% strain. The woven FCB with permanent connection to temperature sensors has a large fatigue life of more than 10,000 cycles while maintaining constant electrical resistance due to crimped configurations of the conductive track in the elastic fabric substrate and stable contact resistance. A prototype of the FCB assembly, with independent light-emitting diodes electrically linked and mechanically supported by the woven FCB, is also demonstrated for wearable applications.

Study of Fiber-Based Wearable Energy Systems

Fiber-based electronic and photonic devices have the most desired human-friendly features, such as being soft, ubiquitous, flexible, stretchable, light, and permeable, and thus are ideal to be employed as the interface platform between humans, the environment, and machines. Today, these smart wearable devices are normally powered by rechargeable batteries. It is extremely desirable to have an undisrupted power supply for us to go anywhere at any time. Harvesting energy from the ambient environment or our body can potentially fulfill such a goal. Explorations of high performance, flexible functional materials and energy conversion devices have led many exiting discoveries. In order to realize their applications, equally important are fundamental studies of the physical phenomena and mechanisms that will provide scientific guidance for the direction of exploration and development of devices and systems. Hence, this Account provides a brief review of our recent progress in this topic area. Based upon materials science, mechanics and device physics, we have succeeded in establishment of several new theoretical models for fiber-based piezoelectric, triboelectric, and hybrid generators. These models have been verified experimentally. Excellent results were obtained for fiber-based triboelectric generators without any adjustable parameters. Reasonable agreement was demonstrated for the piezoelectric generators because of some uncertainty in the material properties and deformation modes. From both simulated and experimental results, we did not detect any synergic effect in the hybrid generator consisting of cascaded piezoelectric and triboelectric units. The verified models can be used to predict the output voltage, current, and power of the devices in terms of material properties, parameters of device structure, harvesting circuits, and operating conditions. Furthermore, by considering the electric breakdown due to field-induced-emission and gas-ionization, we have identified the theoretical upper limits of charge density and output power from contact-mode fiber-based triboelectric nanogenerators. The analysis sheds new light on the scope and focus for further exploration and provides guidance on engineering design of such devices. In addition, we have setup an experimental platform for reliable triboelectric charge measurement of highly deformable and porous materials like fabrics. An extended triboelectric series has been reported by us including 21 types of commercial and new fibers. Based upon the findings, we have made significant improvements of the performance of these energy harvesting devices. Finally, we have explored a class of new flexible thermoelectric materials exhibiting high performance for fiber-based thermoelectric generators, which can be fabricated by low-temperature and cost-effective processes, such as in situ reduction coating and three-dimensional printing. The resultant large-area, flexible, and wearable fiber-base thermoelectric generators are key devices for great potential applications such as powering wearable microelectronic systems, active microclimate regulating systems, and waste thermal energy harvesting.