Landing Forces Research Articles

A Brief Combat Simulation Analysis of Autonomous Legged Underwater Vehicles

Abstract : Autonomous Legged Underwater Vehicles (ALUVs) are inexpensive crab-like robotic prototypes which will systematically hunt and neutralize mines en masse in the very shallow water and the surf zone (VSW/SZ). With the advent of mine proliferation and the focal shift of military power to the littorals of the world, ALUVs have the potential to fill a critical need of the United States Navy and Marine Corps mine countermeasure (MCM) forces. Duplicating the MCM portion of the Kernel Blitz 95 exercise whenever feasible, this thesis uses the Janus interactive combat wargaming simulation to model and evaluate the effectiveness of the ALUV as a MCM. Three scenarios were developed: an amphibious landing through a minefield using no clearing/breaching; an amphibious landing through a minefield using current clearing(breaching techniques; and an amphibious landing through a minefield using ALUVs as the clearing(breaching method. This thesis compares the three scenarios using landing force kills, cost analysis, combat power ashore, and percentage of mines neutralized as measures of effectiveness.

Decreasing landing forces: effect of instruction

Objective—To examine the effects of instructions related to joint kinematics, auditory stimuli, and imagery on lowering the vertical ground reaction forces associated with landing from a jump. Study Design—Randomised controlled...

Lower-Extremity Compensations Following Anterior Cruciate Ligament Reconstruction

Several studies have demonstrated that patients with knee injury scored within a normal range during one-legged hop tests, yet showed quadriceps femoris muscle weakness with non-weight-bearing isokinetic testing. This study evaluated lower-extremity kinetics while subjects performed a single-leg vertical jump (VJ) and a lateral step-up (LSU) in an attempt to explain this phenomenon. Using a motion analysis and force platform system, hip, knee, and ankle extension moments of 20 subjects with anterior cruciate ligament (ACL) reconstructions and 20 matched subjects were measured while they performed an LSU and a VJ. An analysis of variance revealed that the knee extension moment of the ACL-reconstructed extremity was lower than that of the uninjured and matched extremities during the LSU, VJ take-off, and VJ landing. However, there was no difference in summated extension moment (hip + knee + ankle) among extremities during the LSU and VJ take-off. The summated extension moment of the ACL-reconstructed extremity during VJ landing was less than that of the uninvolved and matched extremities. These results suggest that the hip or ankle extensors may compensate for the knee extension moment deficit. The decrease in summated extension moment in the ACL-reconstructed extremity during VJ landing represents inadequate attenuation of landing forces, which may expose the skeleton and joint structures to injury.

Takeoff and landing forces of leaping strepsirhine primates

Knowledge of the forces animals generate and are exposed to during locomotion is an important prerequisite for understanding the musculoskeletal correlates of locomotor modes. We recorded takeoff and landing forces for 14 animals representing seven species of strepsirhine primates with a compliant force pole. Our sample included both specialized vertical clingers and leapers and more generalized species. Takeoff forces are higher than landing forces. Peak forces during acceleration for takeoff ranged from 6 to 12 times body weight, and the peak impact forces at landing are between 5 and 9 times body weight. There is a size-related trend in peak force magnitudes. Both takeoff and landing forces decrease with increasing body size in our sample of animals from 1kg to over 5kg. Peak forces increase with distance leapt. The distance effect is less clear, probably due to the narrow range of distances represented in our sample. A comparison of subadult and adult animals of two species of sifakas reveals a tendency for the young animals to exert relatively higher peak forces in comparison to their adult conspecifics. Finally, Lemur catta and Eulemur rubriventer, the “generalists” in our sample, tend to generate higher forces for equal tasks than the specialized vertical clingers and leapers (i.e., the indriids andHapalemur ).A broad-scale comparison of peak leaping forces and peak forces for quadrupedal and bipedal walking and running shows that leaping at small body size is associated with exceptionally high forces. Whereas relative forces (i.e., forces divided by body weight) decrease with increasing body mass for leaping, forces for walking and running do not change much with size. Leaping forces in our sample scale to (mass)−1/3, which is consistent with expectations derived from geometric similarity models. Forces associated with other locomotor activities do not appear to follow this pattern. The very high forces found in strepsirhine leapers do not seem to be matched by bone robusticity beyond that documented for quadrupedal species.

The design and control of a jointed-leg type of a quadrupedal robot for locomotion on irregular ground

In this paper, a study of a quadrupedal walking robot capable of walking on the irregular ground is presented. The robot has specially-designed feet with toes making soft and safe landings on uneven surfaces. Using the toe angle and landing force sensors integrated within the feet, its gait control algorithm can adapt the foot trajectory to the ground profile, while the body weight is evenly distributed on the supporting legs. After the landing of a foot, the roll and pitch angles of the body are measured and controlled to keep the body attitude parallel to the plane of support. The contents of this study are the design concept and working principle of the foot, including the gait control algorithm for walk on the irregular ground. Experimental results are reported.

Branching out in locomotion: the mechanics of perch use in birds and primates.

Many animals use thin perches, such as the branches of trees, as locomotory substrates. In this paper, I have reviewed the literature concerned with measurements of locomotory forces made by birds and primates on thin and flexible substrates. Through a knowledge of the locomotory forces exerted by animals when using different substrates, the mechanical cost of their use can be established. We are just beginning to learn about the magnitude and patterns of force production in various branch-using vertebrates, primarily as a result of the development of instrumented perches. Instrumented perches have been designed to measure the forces produced by birds and primates when leaping from rigid and flexible horizontal and flexible vertical perches, and also from instrumented handgrips during brachiation. The development of these techniques for birds and primates allows us to compare the way in which they use perches as locomotory substrates. In both birds and primates, the magnitudes of landing forces are smaller than those during take-off. Two explanations have been proposed; the difference is either a consequence of perch compliance or it is a strategic decision to be cautious of 'new' perches. Leaps from flexible perches may be somewhat inefficient because considerable energy is dissipated in bending the perch, and this energy may remain unrecovered when the animal leaves contact with the perch.

EFFECTS OF PEANUTS ON ENERGY BALANCE, BODY FAT AND EXERCISE PERFORMANCE ON FEMALE DANCERS

475 Dancers may have inadequate dietary intakes for their elite performance levels. We tested the hypothesis that adding peanuts to the diet of female dancers would improve athletic performance by improving nutrient intake. Nine screened dancers were randomly assigned, using a crossover design, to continue their habitual diet (HD) or to supplement their diet with 450 kcal/d of peanuts for one week (PN). Testing, done during mid-luteal phase, was preceded by one week of food records. Testing consisted of 5 pliés, 4 sautés and 3 fouettés on a force plate (series repeated 4 times), followed by treadmill running for 5 min. at 5 mph. This cycle was repeated until exhaustion during running, followed by dance testing. During HD, dancers ate less dietary fat (27 vs 37 %E), protein (56 vs 74 mg/d), calories (1542 vs 1987 kcal/d), dietary fiber (12 vs 18 g/d) and calcium (580 vs 725 mg/d) than PN. Body weight (58.7 vs 58.8 kg), body fat (19 vs 18%), running time (40.1 vs 42.1 min.) and heart rate after last dance testing (119 vs 128 bps) were not different (HD vs PN). After both diets, exhaustion was evidenced by an increase in the lowest to highest ground reaction forces during the plies, representing poor muscular control (383 to 518 N). After HD and not PN, exhaustion resulted in a decrease in fouetté peak landing forces, representing decreased muscle control on landing or decreased flight time (1690 to 1522 N). Sauté flight time was more consistent after exhaustion after both diets, however, this was only seen after PN during the more difficult fouetté. Peanuts are useful for increasing energy, protein and calcium intake for young female dancers while not changing body shape. Addition of peanuts to the diet may be beneficial for muscle performance at exhaustion. Supported by a research grant from Shear/Kershman Labs, Inc

Teaching Landing to Children with and Without Developmental Coordination Disorder

This study investigated landing patterns of children aged 7–9 years with either developmental coordination disorder (DCD) or without coordination problems (NC). Initially, 16 DCD and 15 NC children were videotaped performing two-foot landings from a height of 21.5 cm onto a force platform sampling at 500 Hz. Each landing was videotaped at 60 Hz. Regression modeling of the data identified that 72% of peak maximum loading force was explained by landing time, knee angle at touchdown, and hip joint range of motion. Dis-criminant function analysis using landing force, landing time and lower limb joint kinematic variables reliably separated the groups. In the second part, 12 DCD and 10 NC children participated in 6 weekly landing lessons. The only significant adjustment produced by the program was a decrease in the range of motion at the hip in response to instructions to look straight ahead and sit into the landing.

Plyometric training in female athletes. Decreased impact forces and increased hamstring torques.

The purpose of this study was to test the effect of a jump-training program on landing mechanics and lower extremity strength in female athletes involved in jumping sports. These parameters were compared before and after training with those of male athletes. The program was designed to decrease landing forces by teaching neuromuscular control of the lower limb during landing and to increase vertical jump height. After training, peak landing forces from a volleyball block jump decreased 22%, and knee adduction and abduction moments (medially and laterally directed torques) decreased approximately 50%. Multiple regression analysis revealed that these moments were significant predictors of peak landing forces. Female athletes demonstrated lower landing forces than male athletes and lower adduction and abduction moments after training. External knee extension moments (hamstring muscle-dominant) of male athletes were threefold higher than those of female athletes. Hamstring-to-quadriceps muscle peak torque ratios increased 26% on the nondominant side and 13% on the dominant side, correcting side-to-side imbalances. Hamstring muscle power increased 44% with training on the dominant side and 21% on the nondominant. Peak torque ratios of male athletes were significantly greater than those of untrained female athletes, but similar to those of trained females. Mean vertical jump height increased approximately 10%. This training may have a significant effect on knee stabilization and prevention of serious knee injury among female athletes.

FORCE PARAMETER VARIABILITY IN RESPONSE TO LOWER EXTREMITY DYNAMIC FATIGUE922

Neuromuscular fatigue has been associated both with decrements in human performance and increased incidence of musculoskeletal injury. The purpose of this study was to assess force parameter variability associated with fatigue-related decreases in continuous maximal vertical jumping performance. Limited information is available characterizing the kinetic changes associated with dynamic fatigue. Four healthy adults [mean (± sd) age: 30.4± 7.5 yrs, height: 173 ± 15 cm, weight: 711 ± 233 N] performed two bouts (with sufficient recovery time between bouts) of continuous maximal vertical jumps to self-identified fatigue. Mean number of jumps per bout was 30.8 ± 6.5. Jumps were performed on a force platform sampling force records at 1000 Hz. Data were statistically evaluated using a repeated-measures ANOVA with Scheffe test comparisons among means. Selected unfatigued jumps (UJ) at the beginning of each bout were compared to those fatigued jumps (FJ) made just prior to the end of each bout. Flight times confirmed significant (p<.01) fatigue-related decrements in performance between UJ (420 ± 51 ms) and FJ (306 ± 85 ms) trials. Significant differences (p<.05) were found between UJ and FJ trials on measures of impulse (Ft) duration, absolute and body-weight-normalized vertical impulse and average impulsive force. Force profiles showed a landing peak force (LP) and a propulsive peak force (PP), both of which were significantly (p<.03) lower in the FJ compared to the UJ trials (LP: 2014± 616 N vs. 2602 ± 983 N; PP: 1502 ± 410 N vs. 1764± 495 N). Results show force parameter variability associated with fatigue-related performance decrements and may prove to have important training implications.

Measuring leg thrust forces in the common starling

We describe the design of a force-transducing perch which measures the reaction forces of small birds taking off and landing. In common starlings, landing forces are lower than take-off forces, because the bird may decelerate prior to landing by using its wings. Both landing and take-off forces are significantly correlated with body mass; however, the angles of these reaction forces show no significant mass-dependence and are not repeatable within individuals. Diversity in take-off or landing strategy could be advantageous in confusing predators.

Kinetics of leaping primates: Influence of substrate orientation and compliance

Our current knowledge about the forces leapers generate and absorb is very limited and based exclusively on rigid force platform measurements. In their natural environments, however, leapers take off and land on branches and tree trunks, and these may be compliant. We evaluated the influence of substrate properties on leaping kinetics in prosimian leapers by using a combined field and laboratory approach. Tree sway and the timing of takeoffs relative to the movements of trees were documented for animals under natural conditions in Madagascar. Field data collected on three species (Indri indri, Propithecus diadema, Propithecus verreauxi) indicate that in the majority of takeoffs, the substrate sways and the animals takeoff before the elastic rebound of the substrate. This implies that force is "wasted" to deform supports. Takeoff and landing forces were measured in an experimental setting with a compliant force pole at the Duke University Primate Center. Forces were recorded for 2 Propithecus verreauxi and 3 Hapalemur griseus. Peak takeoff forces were 9.6 (P. verreauxi) and 10.3 (H. griseus) times body weight, whereas peak landing forces were 6.7 (P. verreauxi) and 8.4 (H. griseus) times body weight. As part of the impulse generated does not translate into leaping distance but is used to deform the pole, greater effort is required to reach a given target substrate, and, consequently, takeoff forces are high. The landing forces, on the other hand, are damped by the pole/substrate yield that increases the time available for deceleration. Our results contrast with previous studies of leaping forces recorded with rigid platform measuring systems that usually report higher landing than takeoff forces. We conclude that 1) Leapers generate and are exposed to exceptionally high locomotory forces. The takeoff forces are higher than the landing forces when using compliant supports, indicating that the takeoff rather than the landing may be critical in interpreting leaping behavior and related aspects of musculoskeletal design. 2) Large-bodied vertical clingers and leapers do not usually take advantage of the elastic energy stored in substrates. Rather, force (and energy) is wasted to deform compliant supports. 3) A compliant force pole approximates the conditions faced by large-bodied vertical clingers and leapers in the wild more closely than do rigid force platforms.

Relationships among initial body positions and implied joint stiffnesses on landing impact forces and muscular activity

Relationships among initial body positions and implied joint stiffnesses on landing impact forces and muscular activity

垂直跳および着地動作におけるパワー発揮の大きさと下肢関節の貢献度

The purposes of this study were to identify the changes in moments, powers, mechanical works, and contributions of the lower limb joints in vertical jump takeoff and landing from vertical fall, and to propose an interpretation of recruitment of the body segments in sports skills. Fifteen male track and field athletes as subjects performed vertical jumps with no arm swing in six different levels of effort: 100% (maximum effort), 90, 80, 60, 45, and 30%. Eleven subjects landed from the five different heights of 0.25, 0.4, 0.6, 0.8, and 1.0m so as to minimize the landing impact force as much as possible. Five reflective landmarkers on the lower extremity were automatically detected at 60Hz with Quick-Mag System I, and interpolated using cubic spline function to convert data equivalent to sampling rate of 100Hz. Ground reaction force data were sampled at 1000Hz with a Kistler force platform. Two-dimensional inverse dynamics were performed on a four-link segment model to obtain the moments and powers of the hip, knee, and ankle. Mechanical works and contributions of the lower limb joints were calculated from these data. The results were summarized as follows. 1. With changes in relative jumping height the maximum joint moment and power on the hip increased remarkably, while those of the knee and ankle did not show such a sharp increase. Relative contributions of the ankle, knee, and hip to the total positive mechanical work changed from 37.6, 40.4, and 22.0% for 40% jumping height to 29.4, 29.0, and 41.6% for maximum jump, respectively. 2. With increases in heights of fall, the maximum joint moments and negative powers increased in all three joints. The hip showed the maximum muscle moments, followed by the knee and ankle. The knee joint exerted the greatest negative power at every height to dissipate the energy of the fall. Relative contributions of the ankle, knee, and hip were 19.6, 51.8, and 28.6% for height of 0.25m and 14.8, 48.8, and 36.4% for height of 1.0m. Considering these results together with the inertia properties and mechanical work capacities of the lower limb muscles, it would be speculated that the smaller segments must first be recruited so that energy and load on the body can be minimized, but in the case of the maximum power output, the greater segments with large inertia and mechanical work capacities may join the preceding segments, where achieving the objectives of the skills may take priority over the principles of minimizing energy and muscle stress.

The naval air command in the 1990s

Naval air power is, although complementary to its land‐based counterpart, essential in its own right due to the fact that naval forces can reach trouble‐spots within hours and remain there for extended periods of time without the political and, military risks of landing forces or deploying aircraft. Rear Admiral Cooke‐Priest highlights the advantages of the different platforms and aircraft which operate as a specialist unit within a highly integrated and increasingly sophisticated force rising to the challenges of peace and war in future years.

Ajax Bay

SummaryAs a result of fierce aerial attacks on the fleet supporting the landing force on Friday, 21 May 1982, SS Canberra was ordered to sail from San Carlos Water. Elements of her medical organisation were hurriedly put ashore into a deserted refrigeration plant at Ajax Bay. Three weeks later they had treated over 650 battle casualties, performed 210 operations under general anaesthetic, and been bombed by Argentinian aircraft. Despite appalling circumstances, their results were a triumphant success. As Officer Commanding Medical Squadron, Commando Logistics Regiment RM, the author was in charge at Ajax Bay throughout the land phase of hostilities.

Responses of elbow extensors to landing forces during jump downs in cats.

Forces and displacements at the elbow joint have been related to EMG responses of flexor and extensor muscles during landing from jump downs at heights of 1.2 m to 0.6 m in five cats. Prelanding EMG activity consisted of two prelanding extensor bursts. Onset of both bursts was constant across all jump heights with reference to landing and not to take-off, occurring on average 73 +/- 12 ms and 17 +/- 8 ms prior to ground contact for the lateral triceps. Post-landing EMG activity was less than prelanding activity and was often packaged in three bursts, occurring on average at 18 +/- 6, 34 +/- 8 and 50 +/- 9 ms after touchdown. Other measurements from extensor EMG including burst duration and integrated activity pre- and post-landing were also invariant. Across jump heights, maximum flexion angular velocity and elbow displacement were reached on average 28 +/- 5 and 85 +/- 7 ms postlanding, respectively. Although vertical (y) and horizontal (x) ground reaction forces increased with jump height, torque values at the elbow joint were not significantly different and were small in magnitude. At landing an animal typically experienced a 20 ms flexor torque (0.3 Nm/kg b.wt.) followed by an extensor torque (0.4 Nm/kg b.wt.) that continued for the major portion of elbow flexion. The temporal constancy of the kinematic and kinetic data and EMG activity across jump heights suggests that a generalized motor program can be used to activate extensor muscles at the elbow joint during the prelanding phase of self-initiated jumps. Since the onset of extensor activity is related to landing rather than to take-off, it is hypothesized that this activity is triggered by visual cues rather than by vestibular reflexes. After impact, adjustments for slight differences in post-landing torque about the elbow may be accomplished by intrinsic properties of the activated muscle as well as through segmental reflexes.

Manipulation for low back pain.

SUMMARY Anurans use a saltatorial (jumping) mode of locomotion. A jumping cycle can be divided into four subphases: propulsion, flight, landing and recovery. We studied the landing phase during locomotion in Rana esculenta by measuring the ground reaction forces during propulsion and landing over a range of distances. Landing performance affects locomotor ability in jumping frogs. Landing and recovery together take up one third of the locomotor cycle. Peak landing forces are on average almost three times larger than propulsive forces. The forelimbs appear to be fully extended when they make contact with the substrate and absorb the first impact peak. The height of this peak varies depending on arm positioning and jumping distance. Since the stiffness of the arms stays constant over the full jumping range, it is possible that this is a limiting factor in the ability of the forelimbs to work as dampers. A spring-dashpot model is used to model the effect of arm angle at touch down. Damping during landing is performed by placing the forelimbs at an optimal angle to cancel frictional forces effectively.

Roots of Japanese Imperialism: A Memorandum of General LeGendre

T HE position of an American consul in the nineteenth century was far more influential than today. The figure of Charles William LeGendre serves as a case in point: here was an American consul who became an adviser to the Japanese government and actively supported the cause of Japanese expansion while retaining American citizenship. LeGendre was born at Ouillins, France, in 1830 and, after marrying the daughter of an American family in Brussels in 1854, emigrated to the United States. He assumed American citizenship and when the Civil War broke out helped to recruit the Fifty-first New York Volunteer Infantry. By October 1861 he had received a major's commission in that regiment and rose within the next few years to the rank of colonel. His war record was a distinguished one. Twice seriously injured, he was cited for displaying most conspicuous courage until he fell wounded during the capture of New Bern, North Carolina.' After his second injury in 1864, he was honorably discharged for physical disability and given the brevet title of brigadier general for meritorious service. LeGendre's historical importance began in 1866 when he was appointed American consul at Amoy, China. The island of Formosa happened to be part of his district, and in his first year the American bark Rover was wrecked on its southern shore. Fourteen members of the crew managed to reach land but were promptly massacred by the aborigines. Since the Chinese authorities failed to co-operate by establishing a more effective control over the island, Rear Admiral Bell of the United States Navy undertook a punitive expedition against the aborigines. The American landing force fell

The Landing Forces of Domestic Pigeons

THE force with which a bird lands on a perch may have considerable ecological and anatomical significance. This force, along with the body weight of the bird, may determine the type of perch used for roosting at night and the sequence of perches or landing areas used in approaching the nest, and it may even play an important role in habitat selection. For example, it is difficult to envision a Mallard or a Pintail Duck landing on even the larger branches of a tree, if one has ever observed the apparent force with which these ducks hit the water. Other ducks of similar body weight do land in trees. Large herons may be seen landing very lightly on the smaller twigs of trees and bushes and on soft mud; much lighter birds of similar pedal structure almost never utilize such landing places. Such differences in landing may result from differences in habit, in structure, in behavior, or in the situation encountered. The force with which a bird lands is not solely a function of its weight; action of wings, of tail, and of legs modify this force, as does the pattern of landing. For the student of functional anatomy, the landing force may be a means of studying the locomotor organs-wings, tail, and legs. In the literature we find no information relative to the forces with which any of these appendages move. Wind tunnel experiments to determine flight characteristics of airplanes are fairly successful because, compared to the avian wing, the wing of an airplane is very simple. It has been estimated that there are at least ten times as many variables in the wing of a bird. We cannot yet measure the force of the movement of the wing or the tail when these parts are in use, under natural or experimental conditions, although it is not difficult to imagine a large bird trained to fly with small transistors attached to various parts of its body to record a host of data. Fisher (in press) has described an apparatus that makes possible the actual measurement of leg thrust when a bird takes off or lands. Knowing the force of the legs at the time of the take-off and the weight and speed of the bird, it is possible to calculate the force that must have been supplied by the wings during take-off. At the time of landing there are three major groups of variables-the parts of the wing, of the tail, and of the leg. If the force of landing of a bird is constant under certain controlled conditions, any change in one of these groups may be reflected in different forces being exerted by one or both of the other groups. Unfortunately, because the force