Landing Forces Research Articles

Compliant landing of a trotting quadruped robot based on hybrid motion/force robust control

A compliant landing strategy for a trotting quadruped robot on unknown rough terrains based on contact force control is presented. Firstly, in order to lower the disturbance caused by the landing impact force, a landing phase is added between the swing phase and the stance phase, where the desired contact force is set as a small positive constant. Secondly, the joint torque optimization of the stance legs is formulated as a quadratic programming (QP) problem subject to equality and inequality/bound constraints. And a primal-dual dynamical system solver based on linear variational inequalities (LVI) is applied to solve this QP problem. Furthermore, based on the optimization results, a hybrid motion/force robust controller is designed to realize the tracking of the contact force, while the constraints of the stance feet landing angles are fulfilled simultaneously. Finally, the experiments are performed to validate the proposed methods.

Rapid Control Prototyping and PIL Co-Simulation of a Quadrotor UAV Based on NI myRIO-1900 Board

In this paper, a new Computer Aided Design (CAD) methodology for the Processor-In-the-Loop (PIL) co-simulation and Rapid Control Prototyping (RCP) of a Quadrotor Vertical Take-Off and Landing (VTOL) type of Unmanned Arial Vehicle (UAV) is proposed and successfully implemented around an embedded NI myRIO-1900 target and a host PC. The developed software (SW) and hardware (HW) prototyping platform is based on the Control Design and Simulation (CDSim) module of LabVIEW environment and an established Network Streams data communication protocol. A dynamical model of the Quadrotor UAV, which incorporates the dynamics of vertical and landing flights and aerodynamic forces, is obtained using the Newton-Euler formalism. PID and Model Predictive Control (MPC) approaches are chosen as examples for experiment prototyping. These control laws, as well as the dynamical model of the Quad, are implemented and deployed as separate LabVIEW Virtual Instruments (VI) on the myRIO-1900 target and the host PC, respectively. Several demonstrative co-simulation results, obtained for a 3D LabVIEW emulator of the Quadrotor, are presented and discussed in order to improve the effectiveness of the proposed Model Based Design (MBD) prototyping methodology

Effect of different sporting heights on ballet pirouette performance

Having a focus of attention (FOA) in executing complex motor tasks can facilitate task execution. This behaviour influences subsequent movements. We studied the effect of different fixation points on the posture of ten experienced female dancers during the performance of a pirouette. Specifically, the shifting of forces between supporting and gesture legs during the preparation phase and the times of execution of the pirouette were studied. The preparation phase showed a closer placement of the feet than found in previous studies (28% vs 40% of the leg length) and preferred spotting height of 55% of the body height. Pirouettes with a lowspotting height showed a longer start and times to peak force of the supporting leg. No statistical differences were found for bending time on the pirouettes with different spotting heights. The hell landing forces for the gesture leg were different (p<0.01) between trials for the four different spotting heights. Finally, small adjustments in external FOA (<30 cm at 3.5 m of distance) did not influence the performance of the pirouettes significantly but greater gaps did.

The effect of ankle bracing on landing biomechanics in female netballers

ObjectivesInvestigate the impact of lace-up ankle braces on landing biomechanics. DesignWithin-subject repeated measures. Participants completed a drop jump, drop land, and netball-specific task in braced and unbraced conditions. SettingBiomechanical research laboratory. ParticipantsTwenty female high school netballers. Main outcome measuresLeg, knee, and ankle stiffness, knee/ankle stiffness ratio, knee and ankle sagittal excursion, peak vertical ground reaction force, time-to-peak vertical ground reaction force, and loading rate. ResultsIn the brace condition leg stiffness increased bilaterally during the drop land (ES = 0.21, 0.22), ankle stiffness increased bilaterally during the drop jump (ES = 0.37, 0.29) and drop land (ES = 0.40, 0.60), and knee/ankle stiffness ratio decreased in all three tasks (ES = −0.22 to −0.45). Ankle sagittal excursion decreased bilaterally during the drop jump (ES = −0.35, −0.53) and drop land (ES = −0.23, −0.46), and decreased in the lead limb during the netball jump (ES = −0.36). Knee excursion decreased bilaterally during the drop jump (ES = −0.36, −0.40) and in the lead limb during netball task (ES = −0.59). Lead limb TTP was greater during the netball jump (ES = 0.41). ConclusionsLace-up ankle braces may increase leg and joint stiffness and reduce joint excursion during landing but do not appear to affect landing forces. The observed effect on landing biomechanics may predispose young netballers to injury.

Comparison of impact forces, accelerations and ankle range of motion in surfing-related landing tasks

ABSTRACTThis study aimed to describe the impact forces, accelerations and ankle range of motion in five different landing tasks that are used in training and testing for competitive surfing athletes, to assist coaches in the prescription of landing task progression and monitoring training load. Eleven competitive surfing athletes aged 24 ± 7 years participated, and inertial motion sensors were fixed to the anterior aspect of the feet, mid-tibial shafts, sacrum and eighth thoracic vertebrae on these athletes. Three tasks were performed landing on force plates and two tasks in a modified gymnastics set-up used for land-based aerial training. Peak landing force, resultant peak acceleration and front and rear side ankle dorsiflexion ranges of motion during landing were determined. The peak acceleration was approximately 50% higher when performing aerial training using a mini-trampoline and landing on a soft-density foam board, compared to a similar landing off a 50 cm box. Furthermore, the ankle ranges of motion during the gymnastic type landings were significantly lower than the other landing types (P ≤ 0.05 and P ≤ 0.001), for front and rear sides, respectively. Conclusively, increased task complexity and specificity of the sport increased the tibial peak acceleration, indicating greater training load.

Effect of Reduced Stiffness Dance Flooring on Lower Extremity Joint Angular Trajectories During a Ballet Jump.

We carried out a study to investigate how low stiffness flooring may help prevent overuse injuries of the lower extremity in dancers. It was hypothesized that performing a ballet jump (sauté) on a reduced stiffness dance floor would decrease maximum joint flexion angles and negative angular velocities at the hips, knees, or ankles compared to performing the same jump on a harder floor. The participants were 15 young adult female dancers (age range 18 to 28, mean = 20.89 ± 2.93 years) with at least 5 years of continuous ballet experience and without history of serious lower body injury, surgery, or recent pain. They performed sautés on a (low stiffness) Harlequin ® WoodSpring Floor and on a vinyl-covered hardwood on concrete floor. Maximum joint flexion angles and negative velocities at bilateral hips, knees, and ankles were measured with the "Ariel Performance Analysis System" (APAS). Paired one-tailed t-tests yielded significant decreases in maximum knee angle (average decrease = 3.4° ± 4.2°, p = 0.026) and angular negative velocity of the ankles (average decrease = 18.7°/sec ± 27.9°/sec, p = 0.009) with low stiffness flooring. If the knee angle is less acute, then the length of the external knee flexion moment arm will also be shorter and result in a smaller external knee flexion moment, given an equal landing force. Also, high velocities of eccentric muscle contraction, which are necessary to control negative angular velocity of the ankle joint, are associated with higher risk of musculotendinous injury. Hence, our findings indicate that reduced floor stiffness may indeed help decrease the likelihood of lower extremity injuries.

Jump Shrug Height and Landing Forces Across Various Loads.

The purpose of this study was to examine the effect that load has on the mechanics of the jump shrug. Fifteen track and field and club/intramural athletes (age 21.7 ± 1.3 y, height 180.9 ± 6.6 cm, body mass 84.7 ± 13.2 kg, 1-repetition-maximum (1RM) hang power clean 109.1 ± 17.2 kg) performed repetitions of the jump shrug at 30%, 45%, 65%, and 80% of their 1RM hang power clean. Jump height, peak landing force, and potential energy of the system at jump-shrug apex were compared between loads using a series of 1-way repeated-measures ANOVAs. Statistical differences in jump height (P < .001), peak landing force (P = .012), and potential energy of the system (P < .001) existed; however, there were no statistically significant pairwise comparisons in peak landing force between loads (P > .05). The greatest magnitudes of jump height, peak landing force, and potential energy of the system at the apex of the jump shrug occurred at 30% 1RM hang power clean and decreased as the external load increased from 45% to 80% 1RM hang power clean. Relationships between peak landing force and potential energy of the system at jump-shrug apex indicate that the landing forces produced during the jump shrug may be due to the landing strategy used by the athletes, especially at lighter loads. Practitioners may prescribe heavier loads during the jump-shrug exercise without viewing landing force as a potential limitation.

The Effects of an Injury Prevention Program in an Aquatic Environment on Landing Forces

The Effects of an Injury Prevention Program in an Aquatic Environment on Landing Forces

Ankle Dorsiflexion Displacement During Landing is Associated With Initial Contact Kinematics but not Joint Displacement.

The ankle, knee, and hip joints work together in the sagittal plane to absorb landing forces. Reduced sagittal plane motion at the ankle may alter landing strategies at the knee and hip, potentially increasing injury risk; however, no studies have examined the kinematic relationships between the joints during jump landings. Healthy adults (N = 30; 15 male, 15 female) performed jump landings onto a force plate while three-dimensional kinematic data were collected. Joint displacement values were calculated during the loading phase as the difference between peak and initial contact angles. No relationship existed between ankle dorsiflexion displacement during landing and three-dimensional knee and hip displacements. However, less ankle dorsiflexion displacement was associated with landing at initial ground contact with larger hip flexion, hip internal rotation, knee flexion, knee varus, and smaller plantar flexion angles. Findings of the current study suggest that restrictions in ankle motion during landing may contribute to contacting the ground in a more flexed position but continuing through little additional motion to absorb the landing. Transverse plane hip and frontal plane knee positioning may also occur, which are known to increase the risk of lower extremity injury.

Greater lower limb flexion in gymnastic landings is associated with reduced landing force: a repeated measures study

High impact forces during gymnastic landings are thought to contribute to the high rate of injuries. Lower limb joint flexion is currently limited within gymnastic rules, yet might be an avenue for reduced force absorption. This study investigated whether lower limb flexion during three gymnastic landings was related to force. Differences between landings were also explored. Twenty-one elite women's artistic gymnasts performed three common gymnastic techniques: drop landing (DL), front and back somersaults. Ankle, knee, and hip angles, and vertical ground reaction force [(vGRF) magnitude and time to peak], were measured using three-dimensional motion analysis and force platform. The DL had significantly smaller peak vGRF, greater time to peak vGRF and larger lower limb flexion ranges than landing from either somersault. Peak vGRF and time to peak vGRF were inversely related. Peak vGRF was significantly reduced in gymnasts who landed with greater hip flexion, and time to peak was significantly increased with increasing ankle, knee, and hip flexion. Increased range of lower limb flexion should be encouraged during gymnastic landings to increase time to peak vGRF and reduce high impact force. For this purpose, judging criteria limitations on lower limb flexion should be reconsidered.

J2320104 走行動作における下肢の関節反力・関節モーメント及び筋活動に関する研究

In this paper, two foot strike pattern, which are the rear foot strike (RFS) and the fore foot strike (FFS), are compared from the viewpoint ofthe joint moment, joint reaction force and muscle activity using the actual measurement of running for two subjects. As the results, the landing impact force has two peaks for RFS while one peak for FFS, and the significant features can be observed in the ankle joint rather than the knee and hip joint. The joint moment of the ankle joint for RFS acts toward the dorsal flexion direction at the beginning of landing, and then toward the plantar flexion direction, while the one for FFS acts toward the plantar flexion direction during landing. The bone-on-bone force for RFS shows two peaks as similar with the landing impact force. For RFS, the Tibialis anterior much works while for FFS, the Gastrocnemius and the Soleus works much. Moreover, the differences of subject A and B are shown as the contribition of joints on the running.

Forelimb kinematics during hopping and landing in toads.

Coordinated landing in a variety of animals involves the re-positioning of limbs prior to impact to safely decelerate the body. However, limb kinematics strategies for landing vary considerably among species. For example, human legs are increasingly flexed before impact as drop height increases, while turkeys increasingly extend their legs before impact with increasing drop height. In anurans, landing typically involves the use of the forelimbs to decelerate the body after impact. Few detailed, quantitative descriptions of anuran forelimb kinematics during jumping exist and it is not known whether they prepare for larger landing forces by changing forelimb kinematics. In this study, we used high-speed video of 51 hops from five cane toads (Bufo marinus) to test the hypothesis that forelimb kinematics change predictably with distance. We measured excursions of the elbow (flexion/extension) and humerus (protraction/retraction and elevation/depression) throughout every hop. The results indicate that elbow and humeral excursions leading up to impact increase significantly with hop length, but do so without any change in the rate of movement. Instead, because the animal is in the air longer during longer hops, near-constant velocity movements lead to the larger excursions. These larger excursions in elbow extension result in animals hitting the ground with more extended forelimbs in longer hops, which in turn allows animals to decelerate over a greater distance.

Detection of jumping and landing force in laying hens using wireless wearable sensors

Increased mobility of hens in noncaged housing presents possibilities for bone breakage due to crash landings from jumps or flights between perches or housing infrastructure. Because bone breakage is a welfare and economic concern, understanding how movement from different heights affects hen landing impact is important. By tracking 3-dimensional bird movement, an automated sensor technology could facilitate understanding regarding the interaction between noncage laying hens and their housing. A method for detecting jumps and flight trajectories could help explain how jumps from different heights affect hen landing impact. In this study, a wearable sensor-based jump detection mechanism for egg-laying hens was designed and implemented. Hens were fitted with a lightweight (10 g) wireless body-mounted sensor to remotely sample accelerometer data. Postprocessed data could detect occurrence of jumps from a perch to the ground, time of jump initiation, time of landing, and force of landing. Additionally, the developed technology could estimate the approximate height of the jump. Hens jumping from heights of 41 and 61 cm were found to land with an average force of 81.0 ± 2.7 N and 106.9 ± 2.6 N, respectively, assuming zero initial velocity (P < 0.001). This paper establishes the technological feasibility of using body-mounted sensor technology for jump detection by hens in different noncage housing configurations.

Development and evaluation of a drop-and-stick method to assess landing skills in various levels of competitive surfers.

The purpose of this study was to develop and evaluate a drop-and-stick (DS) test method and to assess dynamic postural control in senior elite (SE), junior elite (JE), and junior development (JD) surfers. Nine SE, 22 JE, and 17 JD competitive surfers participated in a single testing session. The athletes completed 5 drop-and-stick trials barefoot from a predetermined box height (0.5 m). The lowest and highest time-to-stabilization (TTS) trials were discarded, and the average of the remaining trials was used for analysis. The SE group demonstrated excellent single-measures repeatability (ICC = .90) for TTS, whereas the JE and JD demonstrated good single-measures repeatability (ICC .82 and .88, respectively). In regard to relative peak landing force (rPLF), SE demonstrated poor single-measures reliability compared with JE and JD groups. Furthermore, TTS for the SE (0.69 ± 0.13 s) group was significantly (P = .04) lower than the JD (0.85 ± 0.25 s). There were no significant (P = .41) differences in the TTS between SE (0.69 ± 0.13 s) and JE (0.75 ± 0.16 s) groups or between the JE and JD groups (P = .09). rPLF for the SE (2.7 ± 0.4 body mass; BM) group was significantly lower than the JE (3.8 ± 1.3 BM) and JD (4.0 ± 1.1 BM), with no significant (P = .63) difference between the JE and JD groups. A possible benchmark approach for practitioners would be to use TTS and rPLF as a qualitative measure of dynamic postural control using a reference scale to discriminate among groups.

Biomechanical analysis of the jump shot in basketball.

Basketball players usually score points during the game using the jump shot. For this reason, the jump shot is considered to be the most important element of technique in basketball and requires a high level of performance. The aim of this study was to compare the biomechanical characteristics of the lower limbs during a jump shot without the ball and a countermovement jump without an arm swing. The differences between variables provide information about the potential that an athlete can utilise during a game when performing a jump shot. The study was conducted among 20 second-league basketball players by means of a Kistler force plate and the BTS SMART system for motion analysis. The variables measured included the take-off time, mean power, peak power, relative mean power, jump height, maximum landing force and calculated impact ratio. Surprisingly, more advantageous variables were found for the jump shot. This finding suggests a very high performance level in the jump shot in the studied group and a maximum utilisation of their motor abilities. Both types of jumps were characterised by high mean and peak power values and average heights. The high forces at landing, which result in considerable impact ratios, may have prompted the studied group to land softly. Use of the countermovement jump without an arm swing is recommended to assess and predict the progression of player’s jumping ability.

Effects of Assisted and Traditional Drop Jumps on Jumping Performance

The purpose of the present study was to evaluate the effects of assisted and traditional drop jumps on fast stretch-shortening cycle exercises in collegiate athletes. Participants were selected into one of three groups: 1) the assisted drop jump ( n=11); the traditional drop jump ( n=11); and 3) the control ( n=11). The assisted drop jump training involved drop jumps (DJs) with assistance of tubing, whereas the traditional DJ training was performed without any assistance. Prior to and at the completion of 5-week training programs, DJs from heights of both 30 (DJ30) and 60 cm (DJ60) were conducted to determine jump height, drop jump reactivity coefficient, contact time and peak ground reaction force. Both the assisted DJ and traditional DJ training programs resulted in significant ( p&lt; 0.05) improvement in jump height, DJ reactivity coefficient and decreased contact time for DJ30. Although both the assisted DJ and traditional DJ modes also increased jump height and DJ reactivity coefficient for DJ60, an enhancement of the assisted DJ training in DJ reactivity coefficient was significantly greater compared to the traditional DJ training. In addition, the assisted DJ mode allowed for a significant reduction of ground reaction force, while the traditional DJ did not change the ground reaction force. The results of this study support the inclusion of assisted DJ training into jumping sports like basketball, volleyball, and track and field jumps. Our results further suggest that incorporating assisted DJ training may be appropriate for highly trained adult athletes due to jumping performance improvement and impact landing forces reduction simultaneously.

SIX WEEKS OF CORE STABILITY TRAINING REDUCES PEAK LANDING FORCE AMONG FEMALE CAPOEIRA ATHLETES

BackgroundCore stability training (CST) has increased in popularity among athletes and the general fitness population and is promoted as a means to reduce injury risk. In female athletes, an intervention...

ARE FORCE ASYMMETRIES MEASURED IN JUMP TESTS ASSOCIATED WITH PREVIOUS INJURY IN PROFESSIONAL FOOTBALLERS?

BackgroundIn female athletes, bilateral aysmmetry in peak landing forces during the drop jump is associated with anterior cruciate ligament (ACL) injury risk and is proposed as a marker of rehabilitation...

Fred Vivian Griffiths

London GP who flew Hurricanes and Spitfires in the second world war Given the number of close shaves Fred Vivian Griffiths had as a Royal Air Force pilot in the...

The effects of line of sight on ground reaction force and pressure during landing

“Keep your eye on the ball,” is an old sports adage. This is especially true in sports like volleyball, tennis, American football, and basketball. Among these sports, basketball is one of the few sports where airborne athletes cannot visually reestablish their relationship to the ground because they are focused on the ball. This typically happens when athletes are attempting to rebound a missed shot. Basketball players are expected to sacrifice their bodies in order to secure the ball, thus grabbing the ball is a greater priority than landing safely. As a result of this game-logic, athletes are unable to utilize their Vestibulo-Ocular Reflex (VOR) for landing. Does this create a higher risk for landing-related injuries? How does this altered line of sight affect landing strategies? What types of exercises can be implemented to minimize injury risk during these types of landings? The purpose of this study was to evaluate the effects of line of sight on ground reaction force and pressure during landing. Subjects for this study were ten female university physical education majors. Subjects all jumped in bare feet to negate the effects of shoes. The independent variable for this study was line of sight during landing (forwards or upwards). Subjects focused on a vertical visual cue while jumping, and either continued to look upwards or changed their line of sight to a horizontal cue during landing. Dependent variables were ground reaction force (passive and active force via Kistler 9287BA, Switzerland) and pressure (area of center of pressure trajectory, path length, average velocity, forefoot and rear foot average force via the Zebris, Germany). Statistical analysis was performed using SPSS for the dependent t-test. Passive force variables (maximum passive force and number of passive force peaks) were significantly larger for subjects with an upward line of sight. Landing velocity for upward line of sight was also higher, although this difference was not statistically significant. In contrast there was no significant difference for active force regardless of line of sight. For forward line of sight, there were significantly higher lengths for the x axis and path length. Subjects with an upwards line of sight had a significantly higher amount of forefoot force. These results show that different landing strategies are employed according to line of sight during landing. Normally, athletes are able to adjust their line of sight while airborne in order to land safely. This mechanism was reflected in the forward line of sight. With a forward line of sight, subjects leaned forward during landing, utilizing greater hip flexion to cushion their impact. In addition, subjects made contact with both their toes and heels during landing, allowing the foot arch to flex and dissipate landing force. The greater use of the foot during landing resulted in greater x axis length and higher path length for forward line of sight. In contrast, an upwards line of sight required a more upright spinal alignment, restricting hip movement when landing. This clearly illustrates the inter-relationship between the hip and neck during landing. As a result, subjects with an upward line of sight were far more dependent on flexion in the ankles to cushion their landing. Thus, subjects with an upward line of sight tended to land almost exclusively on their forefeet. Athletes in jumping sports should practice landing with an upward line of sight in order to safely master this movement. Furthermore, in order to accommodate the forefoot landing strategy, basketball players should increase both their ankle and forefoot dorsi flexibility. This study focused on line of sight and its influence on landing variables such as ground reaction force and center of pressure. However, dynamic balance incorporates many other variables including the visual, vestibular, and proprioceptive systems in addition to muscle strength, flexibility, and mobility. Future studies should investigate all of these variables in relation to landing with an upward line of sight in order to access which variable has the greatest influence on dynamic balance under these conditions. Furthermore, future studies should incorporate kinematic variables in addition to utilizing a downward line of sight.