Lighter Loads Research Articles

Muscle Activation Patterns While Lifting Stable and Unstable Loads on Stable and Unstable Surfaces

In an attempt to mimic everyday activities that are performed in 3-dimensional environments, exercise programs have been designed to integrate training of the trunk muscles with training of the extremities. Many believe that the most effective way to recruit the core stabilizing muscles is to execute traditional exercise movements on unstable surfaces. However, physical activity is rarely performed with a stable load on an unstable surface; usually, the surface is stable, and the external resistance is not. The purpose of this study was to evaluate muscle activity of the prime movers and core stabilizers while lifting stable and unstable loads on stable and unstable surfaces during the seated overhead shoulder press exercise. Thirty resistance-trained subjects performed the shoulder press exercise for 3 sets of 3 repetitions under 2 load (barbell and dumbbell) and 2 surface (exercise bench and Swiss ball) conditions at a 10 repetition maximum relative intensity. Surface electromyography (EMG) measured muscle activity for 8 muscles (anterior deltoid, middle deltoid, trapezius, triceps brachii, rectus abdominis, external obliques, and upper and lower erector spinae). The average root mean square of the EMG signal was calculated for each condition. The results showed that as the instability of the exercise condition increased, the external load decreased. Triceps activation increased with external resistance, where the barbell/bench condition had the greatest EMG activation and the dumbbell/Swiss ball condition had the least. The upper erector spinae had greater muscle activation when performing the barbell presses on the Swiss ball vs. the bench. The findings provide little support for training with a lighter load using unstable loads or unstable surfaces.

Achieving High Efficiency Under Micro-Watt Loads with Switching Buck DC–DC Converters

The present-day and potential benefits of highly integrated miniaturized applications like wireless micro-sensors and biomedical implants in military, space, medical, and commercial markets fuel the demand for self-sustaining micro-electronic systems. Extending operational life to practical levels in such volume-constrained environments is difficult because space limits energy and power. Although switching dc-dc converters have been frequently used in power systems to supply and condition power efficiently, their quiescent and switching losses often render them inefficient at lighter loads, where micro-scale applications reside. Arbitrarily decreasing switching frequency with reductions in load, unfortunately, does not guarantee maximum efficiency because, for example, doing so in discontinuous-conduction mode also increases conduction losses. This paper therefore explores how power losses in switching dc-dc converters relate to load, switching frequency, and other design variables under extreme light loading conditions and ascertains how to manage them to achieve the highest possible efficiency across a micro-watt load. To that end, the paper discusses, analyzes, verifies, and graphically illustrates when and how each of the power-consuming mechanisms dominate efficiency performance. The results show that, after mode-hopping from continuous to discontinuous conduction when the load decreases below half the inductor ripple current, the switching frequency (and quiescent current) should decrease linearly with load at an optimal (derived) rate to balance the losses (and only use just enough quiescent current to sustain the needed bandwidth) and yield maximum efficiency results (e.g., 85-95%) across the entire micro-power range. Simulations show that a constant peak-current control converter (as would a hysteretic converter) with the optimal frequency-load ratio achieves over 86% efficiency across a 50-500 μA load range.

Evolution of wear, roughness, and friction of Alloy 600 superalloy surfaces in water-submersed sliding

Self-mated wear and friction of Alloy 600 superalloy was studied in a water-submersed ring-on-rod configuration, loading the side of a 6.35 mm diameter rod across the flat surface of a rotating annular ring of 100 mm outer diameter and 70 mm inner diameter producing two sliding contacts along the ring. Tests were conducted at sliding speeds of 0.178 and 0.330 m/s for sliding distances of 100 m. Normal loads of 51 and 204 N were applied, and initial R a surface roughnesses of the rings along the sliding direction were either smooth (∼0.2 μm) or rough (∼7.5 μm). Increased initial ring roughness caused a ∼20-fold increase in rod wear at the lighter load, whereas at the heavier load increased initial roughness only caused a ∼4-fold increase in wear. At lower initial ring roughness the 4-fold decrease in normal load caused a large (one order-of-magnitude) decrease in rod wear, whereas for rings of higher initial roughness the 4-fold decrease in normal load caused only minor (2-fold or less) decreases in rod wear. Wear during this 100 m sliding distance only experienced a minor effect from the 1.8-fold change in sliding speed, as did friction. In all cases friction coefficient rapidly settled into the range 0.6–0.7, except in the cases of lower load on rings of lower initial roughness where friction coefficient remained above 1 for most of this sliding duration. At this lower load the initial ∼0.2 μm rod roughnesses increased to nearly 0.8 μm by the 100 m sliding distance, whereas at the higher load this same sliding distance resulted in roughnesses returning near to the initial 0.2 μm. It was hypothesized more highly loaded cases also went through initial roughening prior to smoothening back to 0.2 μm roughness within the 100 m sliding distance, and given additional sliding the more lightly loaded cases would also experience subsequent smoothening. Increasing sliding distance to 400 m, roughnesses indicated a smoothening back to 0.2 μm level during those lightly loaded tests, with friction coefficient correspondingly dropping from 1 into the 0.6–0.7 range observed in all other cases. Extended sliding to 400 m at light loading against rings of lower initial roughness also allowed a rod wear rate which increased with increased sliding distance to be observed, approaching the same rate observed against initially rough rings within the 100 m sliding distance.

Analytical and Experimental Elastic-Plastic Impact Analysis of a Magnetic Storage Head-Disk Interface

As the use of hard disk drives in mobile applications increases, the susceptibility of disk damage due to high velocity slider-disk impact presents a serious challenge. The impact could result in extremely high contact stresses, leading to the failure of the head-disk interface. An elastic-plastic contact-mechanics-based impact model was developed and implemented to study the impact between a slider corner and a disk. The impact model is based on the contact of a rigid sphere on a deformable half-space. The effect of slider corner radii and impact velocities on the contact parameters was initially investigated for a homogeneous disk substrate. To examine the effects of thin-film layers on the disk, the model was extended to a realistic layered disk, where the actual layered mechanical properties were directly measured. At high impact velocities and/or small slider corner radii, the impact was found to be dominated by the substrate and the effect of layers was negligible. At low impact velocities and/or large slider corner radii, the effect of nanometer thick layers could be clearly seen, as these layers are stiffer than the substrate protecting the disk from potential damage at lighter loads. Realistic dynamic impact experiments involving a slider and a spinning thin-film disk were performed using an operational shock tester. The impact damage was characterized in terms of residual penetration depth caused by the impact force of the shock and the impact velocity of the slider. However, the results were inconclusive in correlating with the impact model. To better control the experimental parameters, quasistatic nanoindentation experiments were performed on actual thin-film media and were successfully compared with the model predictions.

Using abrasives to remove a toner-print so that office paper might be reused

If laser-print could be erased like pencil then entire sheets of office paper could be reused without the need for recycling. This article is a feasibility study on the use of an abrasive process to remove toner-print (the type of print used in laser-printers and photocopiers). The effect of varying abrasive grit size, speed, distance, load and repetition are explored. Two distinct wear regimes were visible. With larger grit sizes and at higher loads the surface layers paper were rapidly removed together with the print. At smaller grit sizes and lighter loads, the print was smeared and then slowly removed with less damage to to the paper. A reusable sheet of paper was obtained by pressing a 22 μ m grit silicon oxide abrasive with a force of 0.3 N and rubbing at a speed of 6 m/s for approximately 6 s on each character. This result must be validated on other toner and paper combinations. The potential for exploiting adhesive wear to improve performance is then discussed.

Effects of inertia correction and resistive load on fatigue during repeated sprints on a friction-loaded cycle ergometer

Seven 6 s sprints with 30 s recovery between sprints were performed against two resistive loads: 50 (L50) and 100 (L100) g · kg−1 body mass. Inertia-corrected and -uncorrected peak and mean power output were calculated. Corrected peak power output in corresponding sprints and the drop in peak power output relative to sprint 1 were not different in the two conditions, despite the fact that mean power output was 15–20% higher in L100 (P < 0.01). The effect of inertia correction on power output was more pronounced for the lighter load (L50), with uncorrected peak power output in sprint 1 being 42% lower than the corresponding corrected peak power output, while this was only 16% in L100. Fatigue assessed by the drop in uncorrected peak and mean power output in sprint 7 relative to sprint 1 was less compared with that obtained by corrected power values, especially in L50 (drop in uncorrected vs. corrected peak power output: 13.3 ± 2.2% vs. 23.1 ± 4.1%, P < 0.01). However, in L100, the difference between the drop in corrected and uncorrected mean power output in sprint 7 was much smaller (24.2 ± 3.1% and 21.2 ± 2.7%, P < 0.01), indicating that fatigue may be safely assessed even without inertia correction when a heavy load is used. In conclusion, when inertia correction is performed, fatigue during repeated sprints is unaffected by resistive load. When inertia correction is omitted, both power output and the fatigue profile are underestimated by an amount dependent on resistive load. In cases where inertia correction is not possible during a repeated sprints test, a heavy load may be preferable.

Optimal tyre inflation pressures for urban buses

The distribution of passengers using city buses suggested that buses generally carry very light loads over appreciable periods of operation. The influences of variations in tyre pressures with varying passengers load on vertical acceleration and dynamic tyre load responses are investigated. A non-linear three-dimensional model of an urban bus is employed to identify optimal tyre pressures corresponding to different passenger loads, while ensuring comparable magnitudes of static tyre deflections to minimise the risk of heat build up under lower pressures. A road test program was subsequently undertaken on selected routes and different passenger loads, to measure body acceleration as a direct measure of ride quality, and axle acceleration as indirect measures of tyre loads transmitted to the pavement. The results showed that the use of constant recommended tyre pressures causes significantly higher sprung and unsprung mass accelerations under lighter loads. Both the simulation results and the measured data revealed considerable reductions in bus body acceleration and dynamic tyre loads transmitted to the pavement with optimal tyre pressures, for the passenger loads considered. The results suggest that the implementation of a load-dependent central tyre inflation system would be beneficial for enhancement of passenger- and road-friendliness of urban buses.

Tactile Comfort Properties of Thermal Protective Clothing in Static State

To develop new products, bamboo shijira fabric is compared with conventional cotton shijira fabric. Results show that in shijira fabric : 1) Cotton has more resistance to breaking and more resistance to surface abrasion than bamboo. 2) Compressibility ratio in cotton is higher than in bamboo. 3) Cotton is thicker than bamboo under lighter load and both are similar under heavier load. 4) Warp water absorption speed in cotton is faster and higher than in bamboo. 5) Drying property in cotton is higher than in bamboo. 6) Conventional cotton is superior to bamboo in emphasizing crepe produced by the rib weave of shijira fabric.

Power Versus Strength-Power Jump Squat Training

The purpose of this investigation was to compare the impact of power training and strength-power training on the load-power relationship in the jump squat. Twenty-six recreationally trained male subjects were randomly assigned to either a power training group (P; N=10), a strength-power training group (SP; N=8), or a control group (C; N=8). The P group trained for 12 wk, performing seven sets of six jump squats with the optimal load for maximal power output (body mass only, no external load), whereas the SP group performed five sets of six jump squats with the optimal load for maximal power output (body mass only, no external load) and three sets of three squats with 90% of their one-repetition maximum (1RM). Work performed by the P and SP subjects was equivalent throughout the 12 wk of training. Peak power relative to body mass (PP), jump height (JH), peak force relative to body mass (PF), and peak velocity (PV) during the jump squat were examined across loads of body mass (BM) and 20, 40, 60, and 80 kg at week 0 (baseline) and after weeks 6 (midtest) and 12 (posttest). After training, the P group significantly increased PP at BM and 20 kg, whereas the SP group significantly increased PP output across all loading conditions. Similarly, jump height was significantly increased by the P group at the lighter loads (BM, 20 kg, and 40 kg) and by the SP group at all loads. Whereas significant improvements in maximal power output and jump height at BM were observed in both P and SP groups, no difference in maximal power output or maximal jump height existed between the training groups. Combined lower-body strength-power training is effective as power training for improving maximum jump height and maximum power output in the jump squat, and it is more effective than power training at producing all-around (i.e., from BM to 80 kg) improvements in the load-power relationship of the jump squat.

A Study of Awa Shijira Fabric Crepeusing Comparison with Plain Fabric

Awa shijira fabric was compared with plain fabric to emphasize its characteristics due to crepe. Results show: 1) Awa shijira fabric did not easily tear in a natural line of fabric in testing of warp tearing strength, but plain fabric tore in testing of warp tearing strength. 2) Thread intersection was less by rib weave in Awa shijira fabric, so warp breaking strength, warp extension percentage, and surface abrasion resistance of Awa shijira fabric was clearly less than those of plain fabric. 3) Compressibility ratio of Awa shijira fabric was more than that of plain fabric. 4) Thickness of Awa shijira fabric was more than that of plain fabric under lighter load and all fabric thickness was similar under heavier load. 5) Awa shijira fabric had bulkiness because of crepe produced by rib weave, so water absorption and drying property of Awa shijira fabric was more than that of plain fabric.

External work and peak power are reliable measures of ergometer grinding performance when tested under load, deck heel, and grinding direction conditions

The reliability of grinding performance was assessed in 18 current Emirates Team New Zealand America's Cup sailors in two test sessions separated by 5 h using a custom-built ergometer. Sixteen different grinding conditions that varied by load (Light 39 N·m, Moderate 48 N·m, Heavy 68 N·m), deck heel (Flat 0° control, Downhill 25°, Uphill 25°, Right 25°, Left 25°), and grinding direction (forwards, backwards) were assessed using peak power and external work over 5 s during maximal-effort 8-s grinds. Reliability statistics included the difference in mean (Mdiff), standard error of measurement (SEM), and intraclass correlation coefficients (ICC). External work (SEM = 1.6–6.9%; ICC = 0.91–0.99) was a more consistent performance measure than peak power (SEM = 1.3–9.6%; ICC = 0.84–0.99) across all test conditions. Testing under different load conditions resulted in external work SEMs of 1.6–3.9% with performance more reliable in lighter load conditions. Grinding performance during different heel conditions was less reliable (external work SEMs = 4.6–6.9%). Grinding direction (forward or backward) did not appear to affect performance reliability, although external work was 10–15% higher in forward grinding. Reliability is acceptable across various loads, but testing under different heel conditions may need some protocol development to allow the detection of smaller differences in performance.

A Comprehensive Analysis of Hybrid Phase-Modulated Converter With Current-Doubler Rectifier and Comparison With Its Center-Tapped Counterpart

A hybrid phase-modulated converter (HPMC) is a recent innovation in the family of soft-switching converters. It is a promising solution to most soft-switching issues. The principal bottleneck in achieving higher efficiency with this topology is the secondary side loss-mainly the losses in the transformer and the rectifier. For low-voltage high-current power supplies, the current-doubler rectification of HPMC addresses both the transformer conduction losses and the rectifier losses. The presence of an additional path for quiescent current in this scheme gives rise to a third mode of operation. There is also the possibility of magnetic integration of all the magnetic components into one, which can cause substantial reduction in magnetic requirements. These facts make the analysis of current doubler important. In this paper, all the operating modes are identified and corresponding equations and equivalent circuits that aid in filter and control design are derived. The zero-voltage-switching (ZVS) characteristics, filter requirement, small-signal transfer characteristics, device ratings, and magnetics size requirement are considered to compare this configuration with its center-tapped counterpart. The current-doubler scheme is found to have superior soft-switching characteristics in that it can achieve ZVS at lighter loads with a much lower peak magnetizing current in the transformer and leakage inductance. Also, a judicious choice of output current ripple can give an overall reduced magnetics requirement. The analyses are verified by simulation and hardware implementation. HPMC is found to be most advantageous for applications with input voltages essentially constant, but the output voltage widely varying, for example in battery chargers and converters with power factor correction front end

Brachial Plexus Lesions after Backpack Carriage in Young Adults

Carrying a heavy backpack exerts compression on shoulders, with the potential to cause brachial plexopathy. We evaluated the incidence and predisposing factors of compression plexopathy of the shoulder region in 152,095 military conscripts, hypothesizing that a low body mass index and poor physical fitness predispose to the plexus lesion. Reports of conscripts with neural lesions of the upper arm associated with load carriage were reviewed retrospectively for details associated with the condition onset, symptoms, signs, nerve conduction studies, and electromyographic examinations. Height, weight, and physical fitness scores were obtained from their military training data. The incidence of neural compression after shoulder load carriage in Finnish soldiers was 53.7 (95% confidence interval, 39.5-67.8) per 100,000 conscripts per year. The long thoracic nerve was affected in 19, the axillary nerve in 13, the suprascapular nerve in seven, and the musculocutaneous nerve in six patients. Four patients (7%) had hereditary neuropathy with susceptibility to pressure palsies (HNPP). Symptoms were induced by lighter loads in patients with HNPP. Vulnerability to brachial plexopathy was not predictable from body structure or physical fitness level. To prevent these lesions, awareness of the condition and its symptoms should be increased and backpack designs should be improved.

Work organization and technological resources in broiler production: an ergonomics approach

Ergonomic Work Analysis has made it possible to identify the main factors behind the difficulties encountered by workers in (routinely) performing their tasks. The purpose of this work was studying the relationship between the forms of work organization, the technology used in broiler production, and the impacts of both factors on this type of work from an ergonomics perspective. Both teamwork and cooperation among workers were proven to help minimizing efforts and achieving better results. If on one hand higher technological level adopted could elicit using a smaller number of workers as well as make broiler handling easier and more effective/precise, on the other hand it generated sub-tasks and made equipment operation much more dependent upon close supervision by the workers. So at the same time as the physical stress on the workers was being reduced with lighter load being carried, psychic stress was being increased with the pressure of close supervision. The analysis of production results expressed by the Production Factor (PF) indicator used in an advanced trend analysis using the Technology Utility tool, has shown that properties with a totally or partly familial workforce achieved better production results than those using a patronal workforce, possibly resulting from the fact that workers within a family-based workforce have more autonomy and, therefore, become more motivated to pursue their goals, and that facilitates achieving good results.

A least flow-time first load sharing approach for distributed server farm

The most critical property exhibited by a heavy-tailed workload distribution (found in many WWW workloads) is that a very small fraction of tasks make up a large fraction of the workload, making the load very difficult to distribute in a distributed system. Load balancing and load sharing are the two predominant load distribution strategies used in such systems. Load sharing generally has better response time than load balancing because the latter can exhibit excessive overheads in selecting servers and partitioning tasks. We therefore further explored the least-loaded-first (LLF) load sharing approach and found two important limitations: (a) LLF does not consider the order of processing, and (b) when it assigns a task, LLF does not consider the processing capacity of servers. The high task size variation that exists in heavy-tailed workloads often causes smaller tasks to be severely delayed by large tasks. This paper proposes a size-based approach, called the least flow-time first (LFF-SIZE), which reduces the delay caused by size variation while maintaining a balanced load in the system. LFF-SIZE takes the relative processing time of a task into account and dynamically assigns a task to the fittest server with a lighter load and higher processing capacity. LFF-SIZE also uses a multi-section queue to separate larger tasks from smaller ones. This arrangement effectively reduces the delay of smaller tasks by larger ones as small tasks are given a higher priority to be processed. The performance results performed on the LFF-SIZE implementation shows a substantial improvement over existing load sharing and static size-based approaches under realistic heavy-tailed workloads.

Influence of the type of load on the cervical spine: a study on Congolese bearers

Cervical spine suffers degenerative changes with age and activity. The aim is to study the cervical spine of African head bearers by analyzing clinical changes and radiographic degenerative signs in comparison with a control group. Two groups of bearers, 28 bearers of heavy loads (50 to 60 kg) over short stretches and 33 bearers who carried bundles or lighter loads (30 to 35 kg) over long distances were clinically and radiographically examined and compared with a control group of 36 building industry workers who did not bear weights on their heads. We noted the age, height, weight, body mass index (BMI), weight of load, years they had been working, width and length of the neck and any painful symptoms. We carried out a functional exploration of the cervical spine and a lateral radiograph of the cervical spine to assess degenerative changes and quantified the degenerative changes in the vertebral bodies and the discs. The angle of lordosis was measured. We found more prolapsed discs (p < .01) in the heavy-load bearing group than in the control group. The heavy-load bearers had larger neck width (p < .01) and more disc herniations (p < .05) than the bundler bearers. The frequency of prolapsed discs was higher at C5-C6 and C6-C7 levels. The listhesis was more frequent among bundle bearers than in heavy-load bearers and control group. A correlation between the number of disc herniations and age (p < .01) and years of work (p < .05) was observed. When all the bearers were compared with the control group, the differences found were the number of prolapsed discs, stiffness in the neck and reported pain (p < .01). Load bearing on the head, particularly bearers of heavy loads, produced more radiographic degenerative signs, much stiffness in the neck and more reported pain than the control group.

Smart Textiles for Soldier of the Future

The textile-based materials, equipped with nanotechnology and electronics, have a major role in the development of high-tech milltary uniforms and materials. Active intelligent textile systems, integrated to electronics, have the capacity of improving the combat soldiers performance by sensing, adopting themselves and responding to a situational combat need allowing the combat soldiers to continue their mission. Meantime, smart technologies aim to help soldiers do everyth~ng they need to do with a less number of equipment and a lighter load. In this study, recent developments on smart garments, especially designed for military usage owing to their electronic functions, and intelligent textlle-based materials that can be used in battlefield, are introduced.

Effects of resisted sled towing on sprint kinematics in field-sport athletes.

Weighted sled towing is a common resisted sprint training technique even though relatively little is known about the effects that such practice has on sprint kinematics. The purpose of this study was to explore the effects of sled towing on acceleration sprint kinematics in field-sport athletes. Twenty men completed a series of sprints without resistance and with loads equating to 12.6 and 32.2% of body mass. Stride length was significantly reduced by approximately 10 and approximately 24% for each load, respectively. Stride frequency also decreased, but not to the extent of stride length. In addition, sled towing increased ground contact time, trunk lean, and hip flexion. Upper-body results showed an increase in shoulder range of motion with added resistance. The heavier load generally resulted in a greater disruption to normal acceleration kinematics compared with the lighter load. The lighter load is likely best for use in a training program.

The revolutionary bridges of Robert Maillart

The invention of the automobile created a need for paved roads and bridges. Since highway bridges carry far lighter loads than railway bridges, new designs and materials were developed, tested and implemented in order to meet the growing need. One of the leaders, innovators, in developing new bridge designs and utilizing new building materials was Robert Maillart, 1872-1940, a Swiss structural engineer. Unconventional in his approach, he preferred to rely on his creative intuition designing and building bridges rather than build from mathematical formulas and design from accepted architectural styles. Maillart's crucial innovation was to integrate a bridge's arch and roadway into a form called the hollow-box arch. The result was that bridge loads would be carried by the three segments of the hollow-box: the deck, arch and walls. His next innovation was to develop the deck-stiffened bridge after an analysis of the effect of live loads when they are added to a dead load. Using reinforced concrete, Maillart was able to build bridges which were aesthetically very pleasing and structurally sound. After World War II, Maillart's engineering practices and design elements began to be fully appreciated and incorporated into many engineering classes. His visions and designs are still inspiring engineers today.

Analysis of Reinforced Concrete Beams Strengthened with FRP Laminates

A significant percentage of the bridges in North America were built after the Second World War. Most of them were originally designed for smaller vehicles, lighter loads, and a lower traffic volume than commonly experienced today. A study reported by Klaiber and colleagues (1987) indicates that over 50% of all bridges in the United States were built before 1940, and approximately 42% of these bridges are considered to be structurally deficient. This alarming statistic underscores the importance of developing reliable and cost-effective repair and strengthening techniques for existing bridge structures. A particularly challenging problem in this area is the rehabilitation of reinforced concrete structures. In recent years, the repair of understrengthened or damaged reinforced concrete members by the external bonding of fiber-reinforced polymer (FRP) laminates has received considerable attention. This paper investigates the flexural behavior of reinforced concrete beams strengthened with externally bonded FRP laminates. A simple and direct analytical procedure for evaluating the ultimate flexural capacity of FRP strengthened reinforced concrete flexural members is presented. The procedure is derived from equilibrium equations and compatibility of strains and is applicable to both singly and doubly reinforced concrete rectangular sections, as well as flanged sections. The procedure is validated by comparisons with results of experimental data available in the literature. Upper and lower limits of FRP that may be bonded to a reinforced concrete cross section to ensure ductile behavior are established, and design nomographs to facilitate implementation of the procedure are presented.