Aging, Osteo-Sarcopenia, and Musculoskeletal Mechano-Transduction

The decline in the mass and function of bone and muscle is an inevitable consequence of healthy aging with early onset and accelerated decline in those with chronic disease. Termed osteo-sarcopenia, this condition predisposes the decreased activity, falls, low-energy fractures, and increased risk of co-morbid disease that leads to musculoskeletal frailty. The biology of osteo-sarcopenia is most understood in the context of systemic neuro-endocrine and immune/inflammatory alterations that drive inflammation, oxidative stress, reduced autophagy, and cellular senescence in the bone and muscle. Here we integrate these concepts to our growing understanding of how bone and muscle senses, responds and adapts to mechanical load. We propose that age-related alterations in cytoskeletal mechanics alter load-sensing and mechano-transduction in bone osteocytes and muscle fibers which underscores osteo-sarcopenia. Lastly, we examine the evidence for exercise as an effective countermeasure to osteo-sarcopenia.

Extended Analysis of a Valve-Controlled System with Multi-Chamber Actuator

This paper outlines an extended analysis on how multi-chamber actuators can improve the efficiency of valve-controlled systems. Resistive control is a major source of energy losses in valve-controlled systems that share the same pump to drive multiple loads. By combining different chambers, the load on multi-chamber actuators can be transformed into different pressure and flow rate levels. This allows the adaptation of its load to the loads on other actuators. This can lead to a reduction of resistive control energy losses that occur between pump and actuators when driven simultaneously. As a case study to highlight how the system efficiency can be improved, a load sensing system with a conventional and a multi-chamber actuator is analysed. The equations that describe the system steady state behaviour are presented to evaluate the effect of the load transformations on the system efficiency. A disadvantage of such architecture is the fact that load transformations result in different actuator speeds. To reduce this effect, a compensation factor for the command signal to the proportional valve is presented. The highlight from this paper is the potential for efficiency improvement enabled by the adoption of multi-chamber actuators in a valve-controlled architecture. Further research is required for the selection of number of chambers and their areas since they directly affect the system efficiency.

Influence of Novel Redirector with Bypass Damping on the Performance of Load-Sensing Steering System

Load-sensing steering systems for articulated loaders are prone to large pressure shocks and oscillations during steering operations, affecting the system stability. An optimized structure of the redirector with bypass damping is proposed to improve this phenomenon. In this structure, orifices and throttle grooves are added to the traditional redirector. To control the steering load and working conditions, the steering load of the loader is replaced by a pressure regulating valve. Simulation and experimental results reveal that the redirector with bypass damping has better load-sensing characteristics than the traditional redirector. The peak output pressure shock caused by the load unit step signal decreases from 6.50 to 5.64 MPa, which means the pressure oscillation of the hydraulic system is reduced by 13.4%. The pressure fluctuation time can be reduced from 2.09 to 1.6 s, with a decrease rate of 23.4%. The output pressure oscillation decays swiftly, and the smoothness of the steering operation is improved significantly.

Temporal Differences between Load and Movement Signal Integration in the Sensorimotor Network of an Insect Leg

Nervous systems face a torrent of sensory inputs, including proprioceptive feedback. Signal integration depends on spatially and temporally coinciding signals. It is unclear how relative time delays affect multimodal signal integration from spatially distant sense organs. We measured transmission times and latencies along all processing stages of sensorimotor pathways in the stick insect leg muscle control system using intra- and extracellular recordings. Transmission times of signals from load-sensing tibial and trochanterofemoral campaniform sensilla (tiCS, tr/fCS) to the premotor network were longer than from the movement-sensing femoral chordotonal organ (fCO). We characterized connectivity patterns from tiCS, tr/fCS, and fCO afferents to identified premotor nonspiking interneurons (NSIs) and motor neurons (MNs) by distinguishing short- and long-latency responses to sensory stimuli. Functional NSI connectivity depended on sensory context. The timeline of concurrent tiCS and fCO signals had an early phase of movement signal influences and delayed load influences. Temporal differences persisted into MN activity and muscle force development. We demonstrate a temporal difference in the processing of two distinct sensory modalities generated by the sensorimotor network and affecting motor output. The reported temporal differences in sensory processing and signal integration improve our understanding of sensory network computation and function in motor control.

Simulated and Experimental Analysis of a Log Crane With Conventional and Direct Driven Hydraulics

The present paper compares the efficiency and dynamic behavior of a log crane while using two alternative transmissions. Firstly, the conventional mobile hydraulic valves with a load-sensing pump is used, and secondly, a novel electric-hydraulic energy converter and a direct driven hydraulic actuator is used. By applying lumped parameter models and the theory of centralized pressure, the hydraulic system models are constructed in MATLAB & Simulink environment. MathWorks Simscape Multibody is used in modeling of the multi-body system of the crane. The results of the simulation models are compared with those measured in the laboratory. Based on the verification results, such modes of operation in which the agreement between simulated results is the closest are selected for further investigation. The effectiveness of the system equipped with an electro-hydraulic converter is compared with that of the conventional system with a load sensing pump. Detailed models for components are given in the paper, and the results are discussed based on what obtained through simulation and experiments. The electric-hydraulic converter used in direct driven circuit is a novel prototype developed at LUT University. It has good power stiffness, and it provides good torque properties in a wide RPM area. The prototype is used in operating the lift or tilt cylinder, which is altered by using fast switching valves. The actual test circuit does not have electric storage. The ability of the converter to recover potential energy from the lifting system inertia is approximated in the efficiency comparisons.

Analysis of the Energy Efficiency Improvement in a Load-Sensing Hydraulic System Built on the ISO Plate

The article presents a proposal to reduce energy consumption in a hydraulic system with a single pump and multiple receivers. The proposed Load-Sensing Basic (LSB) solution consists of expanding a typical hydraulic system by using additional logic valves and a dedicated differential valve. The modification is aimed at decrease in operating pressure and, thus, reduction in energy consumption. The LSB system is compact as all components are built on a single ISO plate. A detailed mathematical model of the system was formulated, then a simulation model was built and numerical tests were carried out in the Matlab/Simulink environment. The obtained results indicate that the use of the proposed LSB system for the implementation of typical working cycles with three actuators may reduce energy consumption by 4–30%, and under certain conditions even up to 70%.