Increasing Drop Height Research Articles

Dropping impact experiment of crisp pears and contact pressure analysis

ABSTRACT Efforts have been made to streamline the abstract as follows. If further changes are made we are concerned that the integrity of the content may be compromised. We hope you will understand. This study aimed to investigate the impact damage experienced by Pucheng crisp pears during various stages, including harvest, transportation, and processing. Drop impact tests were conducted on pears, considering drop height and collision contact material as factors influencing damage. The bruise area was used as an indicator for damage evaluation. Additionally, the pressure-sensitive film technique was employed to measure the contact stress distribution characteristics of Pucheng crisp pears after the drop impact. The relationship between contact stress distribution and damage area was examined, and the stress area range close to the damage area was determined. The results revealed that the damage area of pears increased linearly with the increasing drop height. Among the four contact materials, foam board exhibited the best cushioning properties, with a maximum safe drop height of 20 cm. The pressure distribution tended to follow a normal distribution, with a pressure range of 0.2-0.3 MPa covering the largest area, corresponding to the majority of the bruise area on the pears. Furthermore, the pressure area and average pressure were found to be related to the severity of bruising. When pears were dropped onto steel, rubber plate and corrugated board, for the former two the stress area exceeding 0.2 MPa closely approximated the damage area, with an average relative error of 7.2%. For the latter, the closest range was above 0.3 MPa, with an average relative error of 3.6%. However, when dropped onto foam board, the average relative error was 75%. This research provides valuable insights for designing packaging tools to minimize damage and serves as a theoretical basis for predicting and assessing pear bruise area using finite element analysis.

Effect of Drop Height and Impact Surface on Quality of Guava var. Piraweh Ampalu

Drop height and impact surface need to be considered during fruit postharvest handling to minimize the loss of quality and quantity. This study investigated the effect of the drop height factors (0 cm, 60 cm, 80 cm, and 100 cm) and the surface impact (cartons, plastic crates, steel plate) on guava quality var Piraweh Ampalu during temporary storage. An experimental method was conducted by treatment of drop height and impact surface with three replications. The results showed that the drop height and impact surface affected the guava’s weight loss and bruised area. In addition, the drop height also affected the TSS content. Meanwhile, the pH value of guava was not influenced by the drop height, the impact surface, or their interaction. Furthermore, absorbed impact energy increased along with the increasing drop height. It also correlated with the bruised area. A soft impact surface such as cartons and a drop height lower than 60 cm was recommended to prevent the quick deterioration of guava quality.

Effects of cushion box and closed let-down ladder usage on damage to corn during handling: physiological deterioration

BackgroundCorn seeds have a high susceptibility to mechanical damage due to their large size and mass. The main purpose of this study was to evaluate the effects of the cushion box and closed let-down ladder usage in minimizing the negative influence of the free fall on the storage potential of corn seeds. Corn seeds were evaluated for the extent of physiological damage by measuring the seed deterioration by the accelerated aging test (percentage loss in germination in the accelerated aging test), using three drop methods (free fall, with cushion box, and with closed let-down ladder) at three drop heights (5, 10, and 15 m) and five different moisture contents (10, 15, 20 and 25%).ResultsThe drop methods had a significant effect on the storage potential of corn seeds. Sample seeds dropped without a ladder (free fall) had a significantly higher average physiological quality loss of 13.87% (loss in accelerated aging germination). In the use of the cushion box, the average percentage loss in germination was calculated to be 11.38%, which was decreased by about 18% more than the free fall. Sample seeds dropped with the closed let-down ladder had a lower average percentage loss in the germination of 8.78%, which showed that the closed let-down ladder significantly helped to reduce mechanical damage to corn seeds by about 37% comparing free fall and by about 23% to the use of the cushion box. The amounts of loss in physiological quality of corn seeds increased significantly with increasing drop height and moisture content, but the use of the cushion box and closed let-down ladder systems somewhat reduced the adverse effect of the above factors. Empirical models were developed for the dependency of physiological damage to corn seeds due to the impact caused by free fall, on the drop height and moisture content at different drop methods.ConclusionsTo minimize mechanical damage to seeds as they fall into the bin, a let-down ladder should be installed in the bin so that it can receive seeds from the filling spout with minimum damage.

Optimal Drop Height in Prepubertal Boys Is Revealed by the Performance in Squat Jump.

Drop jump (DJ) performance gain with increasing drop height is well documented in adults, but there is still no clear evidence of such gain in children. This study aimed to examine the differences in DJ performance gain in male adults and prepubescent boys by comparing drop heights tailored to each individual's performance and expressed as a percentage of their squat jump (SJ) performance. Fifteen boys (9-11 y) and 15 men (19-27 y) executed DJs from drop heights that were set at 75%, 100%, 125%, and 150% of their best performance in SJ (DJ75, DJ100, DJ125, and DJ150, respectively). Vertical ground reaction force (vGRF), contact time and kinematics of the lower extremities were captured. The results showed that boys jumped significantly lower than adults in DJs, and both age groups presented jumping gain with increasing drop height, up to DJ125. Boys demonstrated longer total contact time, lower angular velocity and vGRF during the propulsive phase, as well as smaller knee flexion at touchdown and lower reactive strength index. vGRF in DJ75 and DJ100 was lower than in DJ125 and DJ150. The highest value for maximum knee flexion was also presented at DJ150. It is concluded that in prepubescent boys, the appropriate drop height for an effective DJ is linked to their performance in SJ and might be between 75% and 125% of their maximum SJ performance.

Effects of cushion box and closed let-down ladder usage on impact damage to corn kernel during handling.

The main purpose of this study was to evaluate the effects of the cushion box and closed let-down ladder usage in minimizing mechanical damage to corn kernels during free fall. Kernels from a single lot of cultivar KSC 705 were evaluated for percentage of breakage using three drop methods (free fall, with cushion box, and with closed let-down ladder) at five different moisture contents (10%, 15%, 20%, 25%, and 30%), and three drop heights (5, 10, and 15 m). The results showed that the drop methods had a significant effect on the breakage sensibility of kernels. Sample kernels dropped without a ladder (free fall) had a significantly higher average percentage breakage of 13.80%. In the use of the cushion box, the average kernel breakage was calculated to be 11.41%, which was decreased by about 17% more than the free fall. Sample kernels dropped with the closed let-down ladder had a lower average breakage of 7.26%, which showed that the closed let-down ladder significantly helped to reduce mechanical damage to corn kernels by about 47% comparing free fall and by about 37% than the use of the cushion box. The amounts of kernel damage increased significantly with increasing drop height and decreasing moisture content, but the use of the cushion box and closed let-down ladder systems somewhat reduced the adverse effect of the above factors. To minimize mechanical damage to kernels as they fall into the bin, a grain let-down ladder should be installed in the bin so that it can receive kernels from the filling spout with minimum damage. Empirical models were developed for the dependency of damage to corn kernels due to the impact caused by free fall on the drop height and moisture content at different drop methods.

Effects of cushion box and closed let-down ladder usage on mechanical damage during corn kernel handling: Cracking

Corn kernels have a high susceptibility to mechanical damage due to their large size and mass. The main purpose of this study was to evaluate the effects of the cushion box and closed let-down ladder usage in minimizing mechanical damage to corn kernels during handling. Kernels from a single lot of cultivar KSC 705 were dropped in three methods (free fall, with a cushion box and with a closed let-down ladder) at five moisture contents (10, 15, 20, 25, and 30%), and three drop heights (5, 10 and 15 m) were evaluated for the percentage of various types of cracking and cracks index (CI). The results showed that the drop method had a significant effect on the damaged kernels. Sample kernels that fell without a ladder (free-fall) had a significantly higher average CI of 144.8. In the use of the cushion box, the average cracks index was calculated to be 103.3, which was decreased by about 29% more than the free fall. Sample kernels dropped with the closed let-down ladder had a lower average CI of 51.6, which showed that the closed let-down ladder significantly helped to reduce mechanical damage to corn kernels by about 64% comparing free fall and about 50% than the use of the cushion box. The amounts of kernels damage increased significantly with increasing drop height and decreasing moisture content, but the use of the cushion box and closed let-down ladder systems somewhat reduced the adverse effect of the above factors.

Determination of Physical and Mechanical Properties of Sugarcane Single-Bud Billets

HighlightsCoefficients of restitution between billet and steel decreased with an increase in drop height and moisture content.Coefficients of restitution between billets increased with an increase in moisture content.Static friction coefficient between billet and steel, and between billets decreased with an increase in contact area.Rolling friction coefficient between billet and steel increased with an increase in angle and interval.Rolling fiction coefficient among billets first increased and then decreased with an increase in angle.Abstract. Determining the physical and mechanical properties of sugarcane single-bud billets is a critical step in the mechanical structure design of a sugarcane planter. In this study, samples of the Tai Tang F66 cultivar sugarcane billets were analyzed. The moisture content of the samples of billets ranged from 63.78% to 77.72%, and their average density was 244.67 kg/m3. The coefficient of restitution (CoR) of the samples was determined by a drop test wherein samples were dropped onto a steel plate from different heights. The static friction coefficient (SFC) of four types of samples was determined by the inclined plate method at two orientations. In addition, the rolling friction coefficient (RFC) was determined at three plate inclination angles and sample displacement. The experiment results showed that with increasing drop height and moisture content, the billet-steel CoR decreased from 0.625 to 0.458, while the billet-billet CoR increased from 0.603 to 0.698. With an increase in contact area, the billet-steel SFC decreased from 0.515 to 0.377 and the billet-billet SFC decreased from 0.498 to 0.323. With increasing angle and sample displacement, the billet-steel RFC increased from 0.0315 to 0.2175 and the billet-billet RFC increased from 0.0203 to 0.1007. These parameters can help to build a more accurate simulation model of a single-bud billet particle for the discrete element analysis of a sugarcane single-bud billet planter mechanical structure. Keywords: Coefficient of restitution, Rolling friction coefficient, Single-bud billet, Static friction coefficient.

Discrete Element Method Simulation of Wheat Bulk Density as Affected by Grain Drop Height and Kernel Size Distribution

HighlightsThe predicted bulk density of two wheat varieties varied with drop height, similar to the experiments.The percentage composition of three kernel size fractions in the wheat varieties affected the bulk density.Accurate particle shape representation simulated the heap profile better but required longer computational time.The single-sphere model is more practical to use because of its higher accuracy and lower computational cost.Abstract. Grain bulk density varies widely depending on kernel properties and handling practices. The discrete element method (DEM) can model such behavior at the particle level, including wide-ranging interactions with equipment. The objective of this study was to develop a DEM model to predict wheat bulk density as affected by grain drop height and kernel size distribution. The bulk density of two wheat varieties was measured experimentally for a range of drop heights with a modified test weight per bushel apparatus and was simulated in EDEM v2018.1 using single-sphere and five-sphere particle models that accounted for three kernel size fractions. For both particle models, simulations matched the observed behavior, showing a bulk density increase with increasing drop height and bulk density differences between varieties due to different kernel size fractions. The single-sphere particle model predicted the bulk density with higher accuracy than the five-sphere particle model, while the five-sphere model, which more accurately represented the shape of wheat kernels, allowed better simulation of the heap profile at the cost of longer computation time. These particle models can be used to simulate bulk density of wheat under compaction and to improve prediction models of grain pack factor for wheat. Keywords: Bulk density, DEM, Drop height, Size distribution, Wheat.

Biomechanical characterization of the foot-ground interaction among Service members with unilateral transtibial limb loss performing unconstrained drop-landings: Effects of drop height and added mass

There exist limited data to guide the development of methodologies for evaluating impact resilience of prosthetic ankle–foot systems, particularly regarding human-device interaction in ecologically valid scenarios. The purpose of this study was to biomechanically characterize foot–ground interactions during drop-landings among Service members with and without unilateral transtibial limb loss. Seven males with, and seven males without, unilateral transtibial limb loss completed six drop-landing conditions consisting of all combinations of three heights (20 cm, 40 cm, 60 cm) and two loads (with and without a 22.2 kg weighted vest). Peak ground reaction forces (GRF), vertical GRF loading rate and impulse, as well as ankle–foot, knee, and hip joint negative (absorption) powers and work were compared across groups (i.e., contralateral side and prosthetic side vs. uninjured controls) by height and load conditions. Loading occurred primarily in the vertical direction, and increased with increasing drop height and/or with added load. Vertical GRFs were overall ~ 15% smaller on the prosthetic side (vs. controls) with similar loading rates across limbs/groups. From the most challenging condition (i.e., 60 cm with 22 kg load), ankle–foot absorption energies on the prosthetic side were 64.6 (7.2) J; corresponding values were 187.4 (8.9) J for the contralateral limb and 161.2 (6.7) J among uninjured controls. Better understanding biomechanical responses to drop-landings in ecological scenarios will help inform future iterations of mechanical testing methodologies for evaluating impact resilience of prosthetic ankle–foot systems (enhancing prescription criteria and return-to-activity considerations) as well as identifying and mitigating risk factors for long-term secondary complications within the contralateral limb (e.g., joint degeneration).

Bruise Susceptibility and Impact on Quality Parameters of Pears During Storage

Bruise damage is one of the mechanical injury problems that could appear in fresh produce during the post-harvest supply chain. The study investigated three main effects (drop impact level, storage temperature, and storage duration), which can expand the level of bruising and cause some quality changes that contribute to the damage of pear. Pear fruit samples were purchased from the market and delivered to the post-harvest laboratory. Each pear was impacted by a ball with a known mass at three different drop heights (20, 40, and 60 cm), stored at 22°C with 45 ± 5% RH and 10°C with 85 ± 5% RH for 14 days storage period. Bruise area (BA), bruise volume (BV), and bruise susceptibility (BS) were calculated. Different quality analyses were done like color, firmness, and total soluble solids (TSS). Analysis of variance (ANOVA), regression analysis, and pearson correlation coefficient were performed. With increasing drop height and temperature for 14 days storage, BA, BV, BS, lightness (L*), yellowness (b*), color saturation (Chroma), and total color difference increased. However, firmness was highly reduced (92.82%) due to the increase in drop height (60 cm), storage temperature (22°C), and storage duration (14 days). Color purity (Hue), redness (a*), and TSS were not affected by drop height (impact level). A strong relationship with a strong linear regression (R2) was found between BS and CIEL*,a*, andb*color coordinates. A positive and strong correlation was also found between BS and CIEL*a*b*color parameters with a strong and negative correlation with firmness. Overall, this study can be considered as guideline for horticulture researchers and in fresh produce supply chain during post-harvest operations.

An Approach to Characterize the Impact Absorption Performance of Construction Helmets in Top Impact

The helmets used by construction site workers are mainly designed for head protection when objects are dropped from heights. Construction helmets are also casually called "hard hats" in industries. Common construction helmets are mostly categorized as type 1 according to different standards. All type 1 helmets have to pass type 1 standard impact tests, which are top impact tests-the helmet is fixed and is impacted by a free falling impactor on the top crown of the helmet shell. The purpose of this study was to develop an approach that can determine the performance characterization of a helmet. A total of 31 drop impact tests using a representative type 1 helmet model were performed at drop heights from 0.30 to 2.23 m, which were estimated to result in impact speeds from 2.4 to 6.6 m/s. Based on our results, we identified a critical drop height that was used to evaluate the performance of helmets. The peak impact forces and peak accelerations varied nonproportionally with the drop height. When the drop height is less than the critical height, the peak force and peak acceleration increase gradually and slowly with increasing drop height. When the drop height is greater than the critical height, the peak force and peak acceleration increase steeply with even a slight increase in drop height. Based on the critical drop height, we proposed an approach to determine the safety margin of a helmet. The proposed approach would make it possible to determine the performance characteristics of a helmet and to estimate the safety margin afforded by the helmet, if the helmet first passes the existing standardized tests. The proposed test approach would provide supplementary information for consumers to make knowledgeable decisions when selecting construction helmets.

Investigating the Feasibility of a Cushion Selection Method on Polyethylene Based on a Predictive Model

Cushion materials are very popular and widely used in various applications. Cellular solid has been used for cushioning for many years due to its low weight and high energy absorption capacity. Cushioning selection is the process of selecting a cushioning material to sufficiently cushion an object. There are a few cushion selection methods available in literature. The objective of this report is to investigate the feasibility of a cushion selection method based on predicting the impact absorption capacity from static compressive stress-strain data. This is achieved by comparing the predicted dimensionless deceleration (G) and the measured G. Polyethylene (foam) samples were used to conduct the compression test and drop test. For polyethylene, the predicted G shown higher accuracy at low drop height and became lower accuracy with increasing drop height. A dynamic factor C was introduced to account for the difference. From this report, researchers may explore the feasibility of this cushion selection method on polyethylene or even conduct experiments on other cellular solid specimens in the future.

Risk of injury analysis in depth jump and squat jump

Introduction: The depth jump (DJ) and squat jump (SJ) are accepted ways to assess and train power producing ability but are not without risk of injury. Methods: Sixteen male participants (age = 21.7 ± 1.54 yrs., height = 177.7 ± 11.4 cm, mass = 77.7 ± 13.6 kg) were evaluated for power exertion capabilities while being assessed for risk of injury in the knee and low back through a range of resistances based on a percentage of participants’ heights in the DJ (0% through 50%) and bodyweights for the SJ (0% through 100%). Two variables were used to assess the risk of injury in the knee: valgus angle and internal abduction moment (IAM). Four variables were used in the low back: compression and shear force at the L5/S1 vertebrae, intra-abdominal pressure (IAP), and erector muscle tension. Results: With increasing DJ drop height, participants showed increased risk of injury in the knee through the valgus angle and IAM. In the low back, significant correlation occurred between increasing drop height and the shear force and IAP while compression force and erector muscle tension were more correlated with the power exertion of the participants than the drop height. With increasing SJ resistance, no significant increased risk of knee injury was detected. However, all low back variables except the IAP were significantly influenced by the increased resistance. Conclusion: Risk of injury in the knee and low back can be strongly dependent not only on the type of jump, but also the amount of resistance. The resulting power exerted by the athlete can also influence the risk of injury.

Impact Injury at Harvest Promotes Body Rots in ‘Hass’ Avocado Fruit upon Ripening

Global demand for avocados has risen rapidly in recent years, yet supplying fruit that consistently meets consumer expectations for quality remains a challenge in the industry. Body rots in avocado fruit are a leading cause of consumer dissatisfaction. Anecdotal evidence suggests that body rot development may be promoted by mechanical injury at harvest and packing, despite the fruit being hard, green and mature (i.e., unripe) at these stages. Here, ‘Hass’ avocado fruit, harvested across multiple fruiting seasons from commercial orchards, were subjected to controlled impact from drop heights of 15–60 cm at the time of harvest or packing. With increasing drop height, body rot development at eating ripe stage generally occurred more frequently and produced larger lesions at the impact site and, in some experiments, elsewhere on the fruit. These findings refute a general belief that green mature avocado fruit can tolerate a degree of rough physical handling without ripe fruit quality being compromised. Ideally, best avocado harvesting and packing practice should recognize that unripe fruit must not experience drop heights of 30 cm or higher.

Bruise Patterns of Fresh Market Apples Caused by Fruit-to-Fruit Impact

Comprehensive understanding of bruise damage caused by apple-to-apple impacts is beneficial to design a low-impact fruit capturing mechanism for mass (shake-and-catch) harvesting, as well as to design other fruit handling devices. This study quantified the bruising severity in ‘Jazz’ apples induced by different levels of impact upon various fruit surface locations. Impact experiments were carried out to analyze bruising patterns in three zones in a fruit surface, i.e., middle/cheek-to-top/stem, middle-to-middle and middle-to-bottom/calyx. Moving fruit and stationary fruit were impacted using a pendulum-type test device, and an equivalent drop height of fruit was calculated to provide a more practical measure for designing a catching surface. In each impact zone, seven different levels of impacts were applied respectively at seven different locations on the fruit surface. Those locations were evenly distributed along the circumferential direction in each of the three zones, and moving fruit was replaced after each impact test. The United States Department of Agriculture (USDA) standard was then used to estimate percentages of fruit in the Extra Fancy Class 1 (no bruising), Extra Fancy (a bruising area diameter ≤ 12.7 mm) and Fresh Market (a bruising area diameter ≤ 19 mm) grades. Results showed that fruit bruising severity increased in a non-linear manner with increasing drop height. It was also found that there existed significant differences in fruit bruising severity between stationary and moving fruit under different fruit-to-fruit impact zones. The bottom zone showed the least bruising sensitivity, followed by the middle zone which was statistically similar to the same in the top zone. The results suggested that the free drop height need to be <3 cm to keep from fruit bruising caused by apple-to-apple impact at a negligible level for ‘Jazz’ apples.

Analytical Study of Reinforced Concrete Beams Tested under Quasi-Static and Impact Loadings

During dynamic events (such as impact forces), structures fail to absorb the incoming energy and catastrophic collapse may occur. Impact and quasi-static tests were carried out on reinforced concrete beams with and without externally bounded sprayed and fabric glass fiber-reinforced polymers. For impact loading, a fully instrumented drop-weight impact machine with a capacity of 14.5 kJ was used. The drop height and loading rate were varied. The load-carrying capacity of reinforced concrete beams under impact loading was obtained using instrumented anvil supports (by summing the support reactions). In quasi-static loading conditions, the beams were tested in three-point loading using a Baldwin Universal Testing Machine. ABAQUS FEA software was used to model some of the tested reinforced concrete beams. It was shown that the stiffness of reinforced concrete beams decreases with increasing drop height. It was also shown that applying sprayed glass fiber-reinforced polymers (with and without mechanical stiffeners) and fabric glass fiber-reinforced polymers on the surface of reinforced concrete beams increased the stiffness. Results obtained from the software analyses were in good agreement with the laboratory test results.

Modeling and Analysis of Cushioning Performance for Multi-layered Corrugated Structures

The objective of this study was to develop cushion curves models and analyze the cushioning performance of multi-layered corrugated structures (MLCS) using a method based on dynamic stress-energy relationship. Methods: Cushion tests were performed for developing cushion curve models under 12 combinations of test conditions: three different combinations of drop height, material thickness, and static stress for each of four levels of energy densities between 15 and 60 kJ/m 3 . Results: Dynamic stress and energy density for MLCS followed an exponential relationship. Cushion curve models were developed as a function of drop height, material thickness, and static stress for different paperboards and flute types. Generally, the differences between the shock pulse (transmitted peak acceleration) and cushion curve (position and width of belly portion) for the first drop and the averaged second to fifth drop were greater than those for polymer-based cushioning materials. Accordingly, the loss of cushioning performance of MLCS was estimated to be greater than that of polymer-based cushioning materials with the increasing number of drops. The position of the belly of the cushion curve of MLCS tends to shift upward to the left with increasing drop height, and the belly portion became narrower. However, depending on material thickness, under identical conditions, the cushion curve of MLCS showed an opposite tendency. Conclusions: The results of this study can be useful for environment-friendly and optimal packaging design as shock and vibrations are the key factors in cushioning packaging design.

Do Not Drop: Mechanical Shock in Vials Causes Cavitation, Protein Aggregation, and Particle Formation

Industry experience suggests that g-forces sustained when vials containing protein formulations are accidentally dropped can cause aggregation and particle formation. To study this phenomenon, a shock tower was used to apply controlled g-forces to glass vials containing formulations of two monoclonal antibodies and recombinant human growth hormone (rhGH). High-speed video analysis showed cavitation bubbles forming within 30 μs and subsequently collapsing in the formulations. As a result of echoing shock waves, bubbles collapsed and reappeared periodically over a millisecond time course. Fluid mechanics simulations showed low-pressure regions within the fluid where cavitation would be favored. A hydroxyphenylfluorescein assay determined that cavitation produced hydroxyl radicals. When mechanical shock was applied to vials containing protein formulations, gelatinous particles appeared on the vial walls. Size-exclusion chromatographic analysis of the formulations after shock did not detect changes in monomer or soluble aggregate concentrations. However, subvisible particle counts determined by microflow image analysis increased. The mass of protein attached to the vial walls increased with increasing drop height. Both protein in bulk solution and protein that became attached to the vial walls after shock were analyzed by mass spectrometry. rhGH recovered from the vial walls in some samples revealed oxidation of Met and/or Trp residues.

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.

Does performing drop jumps with additional eccentric loading improve jump performance?

Previous investigators have speculated that applying additional external load throughout the eccentric phase of the jumping movement could amplify the stretch-shortening cycle mechanism and modulate jumping performance and jump exercise intensity. The aims of this study, therefore, were to determine the effect of increased eccentric phase loading, as delivered using an elastic device, on drop jumps (DJs) performed from different drop heights. Of specific interest were changes in (a) the kinetics; eccentric and concentric impulse, rate of force development (RFD), concentric velocity and (b) the electromyographic (EMG) activity of leg muscles. In a randomized repeated-measure study, 15 highly resistance trained male subjects performed DJs from 3 heights (20, 35, and 50 cm) under 3 different conditions: body weight only (free DJ) and with elastic bands providing downward force equivalent to 20% (+20% DJ) and 30% (+30% DJ) of body mass. All DJs were recorded using video and force plate data that were synchronized with EMG data. Results demonstrated that using additional tensile load during the airborne and eccentric phases of the DJ could enhance eccentric impulse (p = 0.042) and RFD (p < 0.001) and resulted in small to moderate effect size (ES) increases in quadriceps intergrated EMG across the eccentric phase (0.23 > ES > 0.51). The observed greater eccentric loading, however, did not immediately alter concentric kinetics and jump height nor did it alter muscle activation levels during this phase. The findings indicated that, in addition to the conventional technique of increasing drop height, using a tensile load during the airborne and eccentric phases of the DJ could further improve eccentric loading of DJs. As it has been suggested that eccentric impulse and RFD are indicators of DJ exercise intensity, these findings suggest that the loaded DJs, using additional elastic load, may be an effective technique for improving DJ exercise intensity without acute effects on the jumping performance and neuromuscular activation level in highly trained athletes.