High External Loads Research Articles

Force-velocity profiling in elite luge athletes during the simulated luge start

Introduction & Purpose The idea of some athletes having high strength levels but being too slow for a particular movement while others are fast but not strong enough for the demands of their sport exists among many coaches. Therefore, planning decisions are often based on the measurement results of speed and force capabilities and the interest in the relationships between additional load, force, velocity and power during the required movement is high. The luge start is a ballistic movement that requires both high forces and velocities to reach maximal performance (i.e. fast starting times). Examining the load, force, velocity and power capabilities of elite luge athletes during the luge start could deliver insights for training prescription to improve individual weak points and improve performance. This study investigated the relationship between the calculated maxima of force-velocity (FV), load-velocity (LV) and power-velocity (PV) profiles during a simulated luge start and on-ice start times in elite luge athletes. Methods Eleven Austrian national luge team athletes (1 female, 10 male, 25 [4.4] y, 182.4 [7.3] cm, 86.65 [10.4] kg) participated in this study. Measurements were conducted during a single testing session on a specially designed start simulator. Each athlete performed starts against 5 increasing resistances relative to their bodyweight (0%, 25%, 50%, 75%, 100%). For each pull, relative maximum force (Fmax), maximum power (Pmax) and maximum velocity (Vmax) were calculated using the measurements of a linear position transducer (GymAware PowerTool). An experimental approach was used to create the FV-, LV- and PV-profiles showing the highest R2. On-ice start times [s] were measured by photoelectric sensors (ALGE). A correlation matrix (p < 0.05) was used to analyze the relationships between the theoretical Pmax, Fmax (i.e. theoretical isometric maximum force), theoretically unloaded Vmax (Vmax(F0)), theoretical relative maximum loads (Lmax(V0)) and starting times obtained from the profiles. Results Ten linear FV profiles and 11 exponential LV were created (Figure 1; FV: R2mean = 0.9532 ± 0.06; LV: R2mean = 0.9918 ± 0.01). There were significant negative relationships between Vmax(F0) and on-ice starting times (r(9) = -.74, p < .05; r(9) = -.71, p < .05; r(9) = -.74, p < .05) and significant positive correlations between Lmax(V0) and ice start times (r(9) = .71, p < .05; r(9) = .71, p < .05; r(9) = .72, p < .05). Discussion The FV relationship during a simulated luge start can be represented mostly through a linear regression line, supporting the findings of former studies which showed a quasilinear relationship between force and velocity in multi-joint movements (Bobbert, 2012; Jaric, 2015). In line with earlier approaches, PV relationships could be represented quite accurately by use of second-degree polynomial regressions (Allison et al., 2013; Padulo et al., 2017). Contradictory to the linear LV relationships found in other movements (García-Ramos et al., 2018), the luge start LV profile can be better represented by exponential regression curves which could be due to the minimized friction in the luge start setup. Conclusion The abilities of accelerating high external loads and producing high velocities both affect luge start time.

Space and players' number constrains the external and internal load demands in youth futsal.

The aim of this study was to analyze the effects of space and number of players manipulation on the external and internal load demands of youth futsal athletes. Forty-two male U17 players (age = 15.62 ± 0.58 years) from three futsal teams participated in the study. In this cross-sectional study that lasted 8-week, the player's sample practiced six futsal tasks (T1-T6) and a futsal game played under the official rules (T7). From T1-T6, two task constraints were manipulated: (i) the number of players and, (ii) the space of play. The WIMU PRO™ Ultra-Wideband (UWB) tracking system was used to measure the external and internal load during the futsal tasks. External load was quantified using kinematic and mechanical variables extracted from positional data and, the internal load was quantified using Heart rate (HR) and rating of perceived exertion (RPE). Repeated measures ANOVA was used for comparison purposes. In general, the results showed high external (total distance, distance 18.1-21, above 21 Km/h, and high intensity acceleration and deceleration, p < 0.001) and internal load (heart rate average and rating of perceived exertion, p < 0.001) in the tasks with low number of players and high area. In relation to the match, the tasks with small relative area per player (GK + 2 vs. 2 + GK and GK + 3 vs. 3 + GK in 20 × 20 m) promoted low external load. It was concluded that increasing the relative area by reducing the number of players involved in the tasks in the form of small-sided games (GK + 2 vs. 2 + GK and GK + 3 vs. 3 + GK), in relation to the futsal game (GK + 4 vs. 4 + GK), can be considered a pedagogical strategy to increase the external and internal load demands of young futsal players.

A bone remodeling approach encoding the effect of damage and a diffusive bio-mechanical stimulus

The paper focuses on the effect of damage on the bone remodeling process. This is a crucial, although complex, aspect. A one-dimensional continuous deformable body is employed to model living bone tissue. The model incorporates the bone functional adaptation through an evolution law for an effective elastic modulus driven by mechanical feedback via a mechano-transduction diffusive signal. This type of information transduction, i.e., diffusion, is essential for the model to take into account remodeling in the case of minor injury or pathology-affected regions where there is no signal production. In addition, the model is able to also take into account potential tissue damage that may evolve over time according to a suitable evolution law. To illustrate the capability of the model to describe the mentioned complex coupled phenomena, numerical tests have been performed encompassing high external loads causing the onset of damage and cyclic loading for healing. The numerical simulations carried out via finite-element analyses yield insights into the mechanisms of bone remodeling, with the final goal of aiding clinical decisions and implant designs for bone health and repair. Overall, a key aspect of the paper is to highlight the feasibility of modeling the evolution in bone elasticity arising from the combined effect of damage and remodeling.

Effect of hydrodynamic aeration on bioelectricity generation from photoautotrophic Spirulina platensis in biophotovoltaic devices

A biophotovoltaic (BPV) device is a type of bioelectrochemical cell that shows potential for renewable energy production using photosynthetic exoelectrogenic microorganisms. However, the technology currently has limitations due to its relatively low power output and high dependence on biofilm attachment. Thus, this paper examines the effect of hydrodynamic aeration on the bioelectricity generation of BPV devices. Aeration is widely applied in microalgae cultivation to improve the mixing effect between microalgae cells, culture medium, and air bubbles. The methodology involves the cultivation of Spirulina platensis, device fabrication, voltage measurement in both non-aeration and aeration modes, and the use of polarization curves to determine the device performance under a gradually rising external load. The BPV devices are affected by abnormal voltage drop under high external loads, which is called power overshoot. The use of aeration successfully solved the power overshoot issues over time, but it also resulted in a gradual reduction in the voltage output and power density of the BPV devices. During aeration, the BPV devices produced a peak power density of 0.121 ± 0.056 mWm−2 on Day 1, which declined to 0.048 ± 0.025 mWm−2 on Day 13. The blowing of air bubbles had some side effects on BPV devices, including causing the attachment of Spirulina cells to the container walls and accelerating the evaporation of the culture medium. This study emphasizes the role of hydrodynamic aeration in the bioelectricity generation process and opens up possibilities for wider application of BPV devices in renewable energy production.

Reduced running performance and greater perceived exertion, but similar post-exercise neuromuscular fatigue in tropical natives subjected to a 10 km self-paced run in a hot compared to a temperate environment.

Environmental heat stress impairs endurance performance by enhancing exercise-induced physiological and perceptual responses. However, the time course of these responses during self-paced running, particularly when comparing hot and temperate conditions, still needs further clarification. Moreover, monitoring fatigue induced by exercise is paramount to prescribing training and recovery adequately, but investigations on the effects of a hot environment on post-exercise neuromuscular fatigue are scarce. This study compared the time course of physiological and perceptual responses during a 10 km self-paced treadmill run (as fast as possible) between temperate (25°C) and hot (35°C) conditions. We also investigated the changes in countermovement jump (CMJ) performance following exercise in these two ambient temperatures. Thirteen recreational long-distance runners (11 men and 2 women), inhabitants of a tropical region, completed the two experimental trials in a randomized order. Compared to 25°C, participants had transiently higher body core temperature (TCORE) and consistently greater perceived exertion while running at 35°C (p < 0.05). These changes were associated with a slower pace, evidenced by an additional 14 ± 5 min (mean ± SD) to complete the 10 km at 35°C than at 25°C (p < 0.05). Before, immediately after, and 1 h after the self-paced run, the participants performed CMJs to evaluate lower limb neuromuscular fatigue. CMJ height was reduced by 7.0% (2.3 ± 2.4 cm) at 1 h after the race (p < 0.05) compared to pre-exercise values; environmental conditions did not influence this reduction. In conclusion, despite the reduced endurance performance, higher perceived exertion, and transiently augmented TCORE caused by environmental heat stress, post-exercise neuromuscular fatigue is similar between temperate and hot conditions. This finding suggests that the higher external load (faster speed) at 25°C compensates for the effects of more significant perceptual responses at 35°C in inducing neuromuscular fatigue.

Numerical Modelling of Tunnel-Ground Interaction with Building Existence

Tunnel is complex and risky construction. When excavation of tunnel take place, the original ground equilibrium will affected thus lead to the stress redistribution and ground movement. Tunnel construction in the urban city is in concerned as tunnel will passes under a lot of existing building. Therefore, in this study, a series of simulation of tunnel construction with and without external building was conducted. Numerical model by means ABAQUS Software was conducted based on tunnel-soil-load model was developed. From the result, it can be concluded that soil stress redistributed when excavation of soil occurs especially near to the tunnel periphery. The ground settlement trough depicts a significant maximum settlement for the model with high external load and producing flat u-shape in the middle of settlement trough pattern.

Evolution Laws of Stress–Energy and Progressive Damage Mechanisms of Surrounding Rock Induced by Mining Disturbance

The rock burst induced by the mutual disturbance of mining and excavation is significantly influenced by high static load stress and external dynamic load disturbance. In this paper, the evolution characteristics and progressive damage mechanism of surrounding rock in the process of mutual disturbance of mining and excavation are systematically studied. The results show that the evolution of surrounding rock stress can be roughly divided into three stages: rapid rise in the early stage, continuous rise and step-like decline in the middle stage, and slow rise in the late stage. In the process of parallel mining, the overlying rock movement above the goaf shows the sequence of horizontal penetration of tiny fissures—fracture intensification transition to stratification—non-coordinated caving of middle–low overlying rock—obvious horizontal cracks in the upper key layer. Only under the quasi-static loading mining action does the upper key layer not reach the breaking condition. The wave side of the heading face which is close to the focal point is affected by the dynamic load disturbance, the acceleration duration is short, and the attenuation is relatively fast, so it is the area prone to the earliest impact failure in the face of mining disturbance. The conclusion is helpful to deepen the understanding of the coal burst mechanism of mutual disturbance of mining and excavation.

Prediction on onset conditions of alpha, beta, and gamma type free piston Stirling generators

AbstractThe study of the onset characteristics of the free piston Stirling generator (FPSG) is essential for its development. In this study, the onset characteristics of the FPSG were discussed based on a thermodynamic model using the Routh stability criterion. First, the onset conditions of three types of FPSG, alpha, beta, and gamma, were analyzed. Then an experimental and numerical study of a 100 W beta‐type FPSG prototype was conducted. The impacts on the onset temperatures of spring stiffness, charging pressure, and external load were further explored. The results demonstrate that no matter how the parameters are altered, alpha‐type FPSG cannot start up. Whether beta and gamma type FPSG can start up depends on the design and operating parameters. For the prototype, as the displacer spring stiffness increases, the onset temperature rises first and then drops. When the displacer spring stiffness is 19.2 N/mm, the corresponding onset temperature is the lowest of 489 K. The FPSG is easier to start up at a higher external load and higher charging pressure. The experimental results of the impacts of the spring stiffness, charging pressure, and external load on the onset temperature agree well with the calculated results, with errors ranging from 1.7% to 9.12%. The proposed approach can play a guiding significance in studying FPSG onset conditions.

Interface damage driven electrical degradation dynamics of glass fiber-reinforced epoxy composites

The damage of glass fiber-reinforced epoxy composites (GFRP) caused by mechanical loads is an important reason for the related electrical breakdown. In this paper, the L-shaped needle-wire electrode is used to simulate the coupling direction of mechanical stress and electric field, and the influences of equivalent tension and compression load on the electrical tree degradation of GFRP are obtained. It is found that both tensile and compressive loads will aggravate the electrical tree degradation in GFRP and reduce the average breakdown time. Under tensile load, the damage area of electrical tree increases, and even the sample breaks at the moment of electrical breakdown. However, the color of electrical tree channels is light and the number of branches is small under compression load. The narrow carbonization channels after breakdown will be accompanied by spherical damage areas. The simulation results of GFRP interface damage confirm that the increase of tension and compression load will lead to different degrees of damage at the fiber-matrix interface, and then cause local electric field distortion. At the same time, the combined action of high temperature and high pressure and external mechanical load will aggravate the electrical tree degradation process of GFRP.

Exploring long-term trends in microcystin toxin values associated with persistent harmful algal blooms in Grand Lake St Marys

High external nutrient loads from agricultural runoff have led to persistent and highly toxic algal blooms in Grand Lake St Marys (GLSM) for decades. These pervasive blooms are concurrent with long-term (2009 – 2021) toxin and environmental monitoring, providing a robust weekly dataset for modeling microcystins. Median weekly microcystin concentrations (23.2 µg/L) routinely exceeded World Health Organization recreational limits (20 µg/L) for the study period (ranged 0.03 - 185.0 µg/L). Here, we used a Bayesian hierarchical dynamic linear model to hindcast weekly microcystin toxins using external nutrient loads from tributary data as well as internal lake nutrient and physicochemical concentrations. Overall, lake TN was the biggest driver of microcystin concentration in GLSM. Likewise, TN:TP was a strong negative driver of microcystin (i.e. low N:P ratios align with lower total microcystins), suggesting that N availability directly impacts toxins. External nutrient loading was positively related to microcystin during winter and spring; however, there was no relationship detected between toxin and external loading during summer or fall (particulate phosphorus exhibited the strongest signal but all external nutrients were unsurprisingly correlated). This lack of direct correlation on a weekly timescale between external loads and cyanobacterial toxins during the summer months likely results from nutrient saturation and reflects the importance of internal loading for bloom maintenance as supported by the correlation between in-lake TN and microcystin. Thus, management goals to reduce the highest biomass and toxins in the summer should focus on reduction of winter and spring external nutrient loads. Supporting this, both 2010 and 2021 had lower rain in the first half of the year (winter/spring), resulting in less loading, and experienced smaller/later low toxicity blooms. This suggests that, although internal nutrient loads are important for bloom maintenance, reduced external loads are an effective management strategy even in nutrient saturated systems such as GLSM.

Relationships between external loads, sRPE-load, and self-reported soreness across a men's collegiate soccer season.

The purpose was to examine relationships between external loads (ELs), perceived exertion, and soreness. Collegiate men soccer players (n = 19) were monitored for 72 sessions (training: n = 53; matches: n = 19). Likert scale assessments (0-6) of lower body soreness were collected prior to each session, and ELs were collected using positional monitoring technology. Session rate of perceived exertion (sRPE-load) was calculated by multiplying perceived exertion values (Borg CR-10 Scale) by respective session duration to determine internal load. Multiple analyses of variance were used to determine differences in ELs across seasons (pre-season, in-season, post-season) and sessions (training, match). Bivariate Pearson correlation coefficients and linear regression analyses were used to evaluate relationships among soreness, ELs, and sRPE-load. Greatest ELs were observed during pre-season and post-season phases (p < 0.001). Sessions with high perceived exertion and low soreness were associated with higher ELs (p < 0.05). Duration (t = 16.13), total distance (t = 9.17), sprint distance (t = 7.54), player load (t = 4.22), top speed (t = 4.69), and acceleration (t = 2.02) positively predicted sRPE-load (F = 412.9, p < 0.001, R2 = 0.75). Soreness was weakly and trivially correlated with ELs (p < 0.05). The very strong relationship between ELs and sRPE-load highlights the utility of sRPE-load as a practical means to estimate workload; however, more research into the relationship between soreness and workload is warranted.

STUDY OF THE WELDABILITY OF MOLYBDENUM TUBULAR FITTINGS OF THERMAL CONVERTERS

The purpose of the work is to optimize the technological solution for the production of molybdenum tubular fittings of heat exchangers (TСs) that work at high temperatures and external mechanical load on calculated and practical modes of electron beam welding. The results of welding largely depend on the degree of contamination of the material, and the combined calculation of EBW parameters according to a set of existing methods does not give an unambiguous solution, but allows to outline the range of their acceptable values for further experimental clarification. The proposed methods of testing welded fittings according to mechanical parameters and resistance to crack formation with simultaneous simulated application of operating temperature load (500...12000С) initiate the detection of cracks and provide information on the actual strength and plasticity of the metal of the welding zone in real conditions of operation of the fittings.

Aluminium matrix hybrid composite materials reinforced with carbides and intermetallics

Composite materials based on aluminum, reinforced withparticles of titanium carbide and intermetallic compounds of titanium aluminide, are made by casting technology. Investigations of the structure, mechanical and tribotechnical characteristics of the manufactured composite materials have been carried out. It is shown that the reinforcement of an aluminum matrix with TiC particles, or intermetallic phases of Al3Ti, formed by introducing reactive titanium powders into the melt, is an effective way to increase the tribotechnical characteristics. It has been established that the reinforcement of the aluminum matrix with TiC particles has a greater effect on the reduction of the friction coefficient and the wear rate, in comparison with the reinforcement with intermetallic phases Al3Ti, despite the higher volume fraction of the latter. It has been determined that the greatest wear resistance is provided by hybrid reinforcing of an aluminum matrix with TiC particles and intermetallic phases. The additional introduction of stronger TiC particles leads to a decrease in the load on the Al3Ti intermetallics, thereby preventing their destruction under the action of high external loads. In addition, the presence of a larger number of reinforcing phases in hybrid composite materials than in other composite materials samples provides not only a decrease in the load on each reinforcing particle separately, but also a decrease in the fraction of the matrix in the friction surface, thereby expanding the range of triboloading.

Study of microbial desalination cell performance with different saline streams: Analysis of current efficiency and freshwater production

Microbial desalination cell (MDC) is a sustainable and energy-self-sufficient technology that simultaneously treats wastewater, produces electric energy, and desalinates water in a single device. The optimal desalination process depends on the potential generated in the system, which is mainly limited by cathode reaction, high external load values used, initial salinity of saline stream, or other conditions such as anolyte buffer concentration. As transport processes (i.e., migration and diffusion) in the device overlap under such conditions, it is difficult to identify the factors that affect desalination performance. Most of the existing MDC studies have used oxygen reduction (at neutral pH) as a cathode reaction limiting the performance. The removal of the cathode reaction limitation could help to clarify the operation of the MDC and identify different transport phenomena and their influence on the performance (current efficiency, freshwater production, and salt removal rate). This study presents a systematic analysis of a laboratory-scale MDC (cross-section 100 cm2, batch mode) behaviour under different initial saline concentrations from slightly brackish water (1.3 g L−1 NaCl) to seawater (40 g L−1 NaCl) without limitation in the desalination process (i.e., using a low value of external resistance and potassium ferricyanide as a liquid catholyte). For each initial salinity, the parameters of wastewater treatment capacity, energy and freshwater production are discussed and compared with the literature. The values of freshwater production between 0.5 and 10.6 L m−2 h−1 for each initial saline concentration in the saline compartment are achieved with optimal current efficiency values (80–100%). Additionally, the influence of anolyte buffer capacity on current density in the MDC system (from 0.8 to 1.2 mA cm−2) is analysed. Furthermore, the behaviour of the system during a seawater desalination process is discussed in terms of treatment capacity and Coulombic efficiency. This study could help understand the performance of these systems in possible natural saline scenarios where MDC technology can be implemented in the future.

Atomistic insights into migration mechanism of graphene-based membranes on soil mineral phases

Graphene-based membranes (GBM) will migrate in the soil and enter the groundwater system or plant roots, which will eventually pose potential risks to human beings. The migration mechanism of GBM depends on the interface behavior of complex soil components. Herein, we use molecular dynamics (MD) simulations to probe the interface behavior between GBM and three type minerals (quartz, calcite and kaolinite). Based on the investigation of binding energy, maximum pulling force and barrier energy, the order of the difficulty of GBM adsorption and desorption on the three minerals from small to large is roughly: quartz, calcite and kaolinite respectively. The graphene-oxide (GO), improves the binding energy and energy barrier, making GBM difficult to migrate in soil. Remarkably, a larger GBM sheet and high velocity external load improve GBM migration in soil to a certain extent. These investigations give the dynamic information on the GBM/mineral interaction and provide nanoscale insights into the migration mechanisms of GBM in soil.

The Effect of the Weight and Type of Equipment on Shoulder and Back Muscle Activity in Surface Electromyography during the Overhead Press-Preliminary Report.

The overhead press is a multi-joint exercise that has the potential to use a high external load due to the cooperation of many muscle groups. The purpose of this study was to compare the activity of shoulder and back muscles during the overhead press with a kettlebell and a dumbbell. Surface electromyography (EMG) for the anterior and posterior deltoid, upper and lower trapezius, serratus anterior, and spinal erectors was analysed for 20 subjects. Participants performed the four trials of pressing kettlebell and dumbbell, weighted at 6 kg, and 70% of one maximum repetition (1RM) in the sitting position. Statistical analysis was performed using a non-parametric Friedman test and a post-hoc test of Dunn Bonferroni. No significant differences were found in the activation of assessed muscles when comparing dumbbell to kettlebell press trials with the same load (6 kg and 70% of 1RM). However, muscle activity of all muscles except the upper trapezius was always higher for kettlebell pressing. Different center of gravity locations in the kettlebell versus the dumbbell can increase shoulder muscle activity during the overhead press. However, more studies are required to confirm these results.

External loading of common training drills: Ranking drills to design progressive return-to-run programs

Return-to-run protocols following lower extremity injuries commonly include a gradual training and loading progression to allow positive adaptation of musculoskeletal tissue. Before full return to running, training drills designed to provide a low to high external loading progression (i.e., vertical forces) may therefore minimize the risks of re-injury. However, the magnitude of external loading among various training drills has not yet been quantified. ObjectivesThe purpose of this study was to quantify peak vertical forces of multiple common training drills and rank each of them in order from lowest to highest peak vertical force. Design/Participants: 11 experienced runners completed five trials of 46 training drills while in-shoe vertical reaction force (vRF) was measured with wireless force insoles. Main outcome measuresAverage peak vRF was calculated for each drill across all participants. Drills were also grouped by vRF into four categories intended for use by clinicians as stages of rehabilitation. Results46 training drills were ranked in order from least to greatest vRF. The drill with the highest average peak vRF was “Ladder Single Leg Hop Forward”, at 2.80 BW. The drill with the lowest average peak vRF was “Squat Mini Jump”, at 1.02 BW. ConclusionsThese data provide valuable information for clinicians, coaches and pelvic floor practitioners when programming rehabilitation and return-to-run training progressions for runners coming back from lower extremity or pelvic injuries.

Experimental study on freezing point of deep clay under high external load conditions

A rational evaluation of freezing point of deep clay under high pressure is required for artificial freezing construction of deep mining works. The freezing point of deep clay under high external load was measured via a self-designed apparatus with soil temperature monitored by high-precision temperature transducer and external load applied by servo-hydraulic system. The feasibility of the apparatus was verified by comparing the test result to that of the common cooling curve method under no external load. Cooling curves for deep clay sampled from a coal mine at 510–515 m were acquired at six load levels (0.0, 2.0, 4.0, 6.0, 8.0 and 10.0 MPa) and four water contents (25.0%, 30.0%, 34.0% and 38.0%). Results show that the greater the water content, the more pronounced the equilibrium freezing stage. In the absence of external load, equilibrium freezing was observed, whereas temperature jump becomes more noticeable with increasing load. Freezing point and initial nucleation temperature both rise with greater water content, while depress approximately linearly with higher load. A simple model for evaluating the freezing point of deep clay was developed based on the Mizoguchi model, incorporating both matric and pressure potential. The results will provide theoretical evidence for determining the thickness and location of frozen wall during artificial freezing construction in deep strata.

A mechanochemical model of the forward/backward movement of motor protein kinesin-1

Kinesin-1 is an ATP-driven, two-headed motor protein that transports intracellular cargoes (loads) along microtubules. The movement of kinesin-1 has generally been modeled according to its correlation with ATP cleavage (forward movement), synthesis (backward movement), or unproductive cleavage (futile consumption). Based on recent experimental observations, we formulate a mechanochemical model for this movement in which the forward/backward/futile cycle can be realized through multiple biochemical pathways. Our results show that the backward motion of kinesin-1 occurs mainly through backward sliding along the microtubule and is usually also coupled with ATP hydrolysis. We also found that with a low external load, about 80% of ATP is wasted (futile consumption) by kinesin-1. Furthermore, at high ATP concentrations or under high external loads, both heads of kinesin-1 are always in the ATP- or ADP Pi-binding state and tightly bound to the microtubule, while at low ATP concentrations and low loads, kinesin-1 is mainly in the one-head-bound state. Unless the external load is near the stall force, the motion of kinesin-1 is almost deterministic.

An Examination of Loading Profiles for Youth Athletes Performing the Hang Power Clean

Weightlifting derivatives have become an increasingly popular form of resistance training among youth athletes over the past decade. This study aimed to examine the loading profiles of youth athletes during the hang power clean to determine optimal loading parameters for force, power, rate of force development, and barbell velocity. Sixteen male youth athletes (Age: 16.94 ± 0.97 years; Height: 180.08 ± 8.14 cm; Body mass: 81.06 ± 15.04 kg; Hang Clean 1RM 70.17 ± 14.41 kg) performed three repetitions of the hang power clean at 10% intervals ranging from 30-90% of their one-repetition maximum (1RM). One-way repeated measures ANONAs revealed that external load had a significant effect on the peak and average of all variables examined (p &lt; 0.05). Most notably, peak power was maximized at 70% 1RM which was not significantly different 60-90% 1RM. Peak rate of force development was maximized at 90% 1RM, though it was not significantly greater than 50-90%1RM. Conversely peak barbell velocity was maximized at 30% 1RM which was significantly greater than 50-90% 1RM. While the results for power are similar to that of older, stronger athletes, the youth population in this study maximized barbell velocity and rate of force development at different external loads compared to more developed athletes. These results seem to suggest that youth athletes need to achieve a higher level of strength before they are capable of training with high relative external loads while maintaining high barbell velocities.