Force Generation Research Articles

Hydrodynamic Characteristics of Offshore Wind Turbine Pile Foundations Under Combined Focusing Wave-Current Conditions

In extreme marine environments, the interaction between offshore wind turbine pile foundations (OWTPFs) is critical, and the associated hydrodynamic loads are complex. This study focused on fixed OWTPFs and used computational fluid dynamics (CFD) to numerically simulate the flow field around pile foundations under the combined action of focusing waves and current. The objective was to investigate the influence of different focusing wave and current parameters on the hydrodynamic properties of the pile foundations. The findings indicate the following: (1) When the wave and current directions are opposite, the maximum wave force on the pile foundations is greater than when they are aligned. (2) Large-amplitude focusing waves around pile foundations generate secondary loads, which are nonlinear and lead to a rapid increase in the wave force. These secondary loads are short-lived and particularly prominent near the front row of pile foundations. (3) The influence of the group pile effect diminishes under high-amplitude waves, where the wave component dominates the generation of the dimensionless wave force, and the impact of the current on this force decreases.

Force-transducing molecular ensembles at growing microtubule tips control mitotic spindle size.

Correct mitotic spindle size is required for accurate chromosome segregation during cell division. It is controlled by mechanical forces generated by molecular motors and non-motor proteins acting on spindle microtubules. However, how forces generated by individual proteins enable bipolar spindle organization is not well understood. Here, we develop tools to measure contributions of individual molecules to this force balance. We show that microtubule plus-end binding proteins act at microtubule tips synergistically with minus-end directed motors to produce a system that can generate both pushing and pulling forces. To generate pushing force, the system harnesses forces generated by the growing tips of microtubules providing unique contribution to the force balance distinct from all other motors that act in the mitotic spindle. Our results reveal that microtubules are essential force generators for establishing spindle size and pave the way for understanding how mechanical forces can be fine-tuned to control the fidelity of chromosome segregation.

Initiation of epithelial wound closure by an active instability at the purse string.

The ability of biological systems to withstand and recover from various disruptions, such as spontaneous genetic mutations and environmental damage, largely relies on intricate feedback mechanisms. We theoretically study a mechanical response of an epithelial tissue facing damage in the form of a circular wound. Our model describes a feedback loop between the generation of active forces in the actomyosin and tissue mechanics, described by the vertex model. While the exact dynamics of wound closure may be influenced by several biophysical mechanisms that interplay in a non-trivial way, our findings suggest that the closure may initiate as an active instability, triggered by a reduced myosin-turnover rate at the wound's perimeter. We explore the interplay between myosin dynamics and the elastic properties of the tissue, elucidating their collective role in determining wound's loss of stability, leading to the initiation of the closure process.

Identifying mechanisms and therapeutic targets in muscle using Bayesian parameter estimation with conditional variational autoencoders.

Machine learning techniques have potential to accelerate discoveries in biologically complex systems. However, they require large data sets and can be challenging in high dimensional systems such as cardiac muscle. In this study, we combined experimental measures of cardiac muscle twitch forces with mechanistic simulations and a newly developed mixture of Bayesian inference with neural networks (in autoencoders) to solve the inverse problem of determining the underlying kinetics for observed force generation by cardiac muscle. The autoencoders are trained on millions of simulations spanning parameter spaces that correspond to the mechanochemistry of cardiac sarcomeres. We apply the trained model to experimental data in order to infer parameters that can explain a diseased twitch and ways to recover it.

Spontaneous breathing-induced lung injury in mechanically ventilated patients.

Recent experimental and clinical studies have suggested that spontaneous effort can potentially injure the lungs. This review summarizes the harmful effects of spontaneous breathing on the lungs during mechanical ventilation in ARDS and suggests potential strategies to minimize spontaneous breathing-induced lung injury. Recent clinical and experimental studies have shown that vigorous spontaneous breathing during mechanical ventilation can potentially injure the lungs due to high transpulmonary pressure, the Pendelluft phenomenon, increased pulmonary perfusion, and patient-ventilator asynchrony. A definitive approach to minimize spontaneous breathing-induced lung injury is the systemic use of neuromuscular blocking agents; however, there is a risk of muscle atrophy. Alternatively, partial paralysis, bilateral phrenic nerve blockade, and sedatives may be useful for decreasing force generation from the diaphragm while maintaining muscle function. A higher positive end-expiratory pressure (PEEP) and prone positioning may reduce force generation from the diaphragm by decreasing neuromechanical efficiency. Several potential strategies, including neuromuscular blockade, partial paralysis, phrenic nerve blockade, sedatives, PEEP, and prone positioning, could be useful to minimize spontaneous breathing-induced lung injury.

Biomechanical validation of the field-expedient pelvic splint

IntroductionMorbidity and mortality from pelvic ring injuries can be mitigated by early and effective external pelvic stabilisation. The field-expedient pelvic splint (FEPS) is a recently described technique to improvise an...

A Novel Ungrounded Haptic Device for Generation and Orientation of Force and Torque Feedbacks.

To provide deeper immersion for the user in the virtual environments, both force and torque feedbacks are required rather than the mere use of visual and auditory ones. In this paper, we develop a novel propeller-based Ungrounded Handheld Haptic Device (UHHD) that delivers both force and torque feedbacks in one device to help the user experience a realistic sensation of immersion in a three-dimensional (3D) space. The proposed UHHD uses only a pair of propellers and a set of sliders to continuously generate the desired force and torque feedbacks up to 15N and 1N.m in magnitude in less than 370ms, respectively. The produced force and torque feedbacks are oriented in a desired direction using a gimbal mechanism where the propellers are mounted inside in such a way that a simple structure is obtained. These features facilitate the control of the proposed UHHD and enhance its practicality in various applications. To prove the capability of the system, we model it and elaborate on the force and torque analyses. Next, we develop a robust parallel force/position controller to tackle the structured and unstructured uncertainties. Finally, a measurement setup is manufactured to experimentally evaluate the performance of the UHHD and the controller. The implementation of the controller on the developed UHHD prototype shows that a satisfactory control performance is achievable in terms of offering the desired force and torque feedbacks.

Effect of an AC-DC composite longitudinal magnetic field on the microstructure and mechanical properties of WAAM Al-5 %Mg alloy

To address issues of poor forming accuracy, high porosity, and inadequate mechanical properties in wire arc additive manufacturing of aluminum alloys, this study applied external direct current (DC) and alternating current (AC) composite magnetic fields (ECMF) (AC+DC) in cold metal transition wire arc additive manufacturing (CMT-WAAM) of Al-5 % Mg alloys. The aim was to enhance the quality of forming and overall mechanical properties of the deposited specimens. Optimal ECMF (AC+DC) parameters-DC 3 A, AC 1 A, and alternating frequency 100 Hz-were determined through orthogonal experiments. Results showed that ECMF (AC+DC) facilitated arc expansion and stirred the molten pool via Lorentz force generation, thereby accelerating molten flow and improving forming precision. Compared to specimens without ECMF (AC+DC), those with ECMF (AC+DC) exhibited reduced porosity (1.07 % to 0.31 %, a decrease of 71.03 %) and finer grain size in the deposited layer (84.80 ±30.5μm to 69.10±25.1μm, an 18.51 % decrease). Additionally, average microhardness increased (83.83 HV to 96.70 HV, a 15.35 % increase), transverse tensile strength improved (239.66±1.6 MPa to 263.00± 1 MPa, a 9.86 % increase), and elongation at break enhanced from 25.50±3.8 % to 27.17±0.33 %. Longitudinal tensile strength also rose (232.33±14.33 MPa to 248.33±8.33 MPa, a 6.88 % increase), with elongation at break increasing from 19.00±7.5 % to 19.40±4.2 %. Moreover, the mechanical properties' anisotropy decreased. Consequently, ECMF (AC+DC) significantly enhanced the overall properties of CMT-WAAM Al-5 % Mg alloy deposition, providing valuable insights for extending engineering applications of Al-5 % Mg alloy WAAM.

Multi-objective optimal design of Tuned Mass Damper Inerter for base isolated structures

The BIS-TMDI is a hybrid control strategy that significantly reduces the seismic response of structures compared to conventional BIS through proper tuning, albeit with the trade-off of increased control forces exerted by the TMDI on the host building structure. However, these potentially significant forces are generally not considered in current TMDI tuning approaches. In this paper, a multi-objective optimization design method is herein developed to determine the compromise between the competing objectives of suppressing earthquake-induced vibrations in buildings and avoiding the generation of excessive control forces of TMDI. The study shows that under non-stationary excitations, the average control force of the TMDI system can be reduced by 16% compared to single optimization constraint, with a maximum reduction of up to 25%. Finally, the optimization design methods of this paper are applied to an 8-story frame as a validation case.

How Seam Inclination Influences Cricket Ball Swing

Abstract. Cricket, a sport with origins in 16th century England, involves players attempting to manipulate the lateral motion of the ball to outwit the batsman. This is often achieved by adjusting the seam inclination or altering the ball's surface roughness. This paper specifically investigates how seam inclination affects cricket ball swing through computational fluid dynamics (CFD) simulations. The focus of the study is on conventional swing for both non-rotational and rotational cricket balls. The results indicate that seam inclination significantly influences swing, with an optimal angle between 58 to 60 degrees for the maximum lateral force of non-rotational cricket. This finding provides valuable insights into the mechanics of conventional swing and offers guidelines for bowlers to enhance their performance. The research explores the complex interplay between the ball's aerodynamics, seam inclination, and the resulting swing. By utilizing CFD simulations, the study delves into the underlying fluid dynamics that govern the ball's trajectory and the generation of lateral forces.

Enhanced Attractive Force via Torsion Spring as Rotatable Tip Structure in Beam-Structure Electrostatic Chucks

This research aims to replace ball joints of beam-structure electrostatic chucks (BSESC), which are limited by issues such as structural friction and inconsistent operation, thus enhancing the applicability in industrial settings. Torsion springs are used as rotational degree-of-freedom (RDOF) mechanisms at the tip of BSESCs to reduce friction and improve repeatability, while also highlighting the positive relationship between tip rotatability and the attractive force generated. Following the law of conservation of energy, an analytical calculation was performed using a beam-spring-capacitor model to establish the correlation between tip rotatability and the maximum attractive force generated through energy system analysis. An analytical solution was derived, explicitly defining the relationship between tip rotatability and the achievable attractive force. The results were plotted using MATLAB. Experimental validations were carried out by fabricating devices that differed only in tip rotatability, and measurements of the attractive force were taken. Both analytical and experimental results clearly demonstrate a positive relationship between tip rotatability and attractive force generation in BSESCs. The use of torsion springs effectively reduces the energy concentration at the tip, delaying detachment while simultaneously increasing the attractive force, significantly improving the overall performance of BSESCs. These findings provide a foundation for future industrial applications, particularly for automated large-area manipulation of irregularly shaped targets in industries such as screen production and semiconductors.

Identification of CD44 as a key engager to hyaluronic acid-rich extracellular matrices for cell traction force generation and tumor invasion in 3D

Mechanical properties of the extracellular matrix (ECM) critically regulate a number of important cell functions including growth, differentiation and migration. Type I collagen and glycosaminoglycans (GAGs) are two primary components of ECMs that contribute to mammalian tissue mechanics, with the collagen fiber network sustaining tension, and GAGs withstanding compression. The architecture and stiffness of the collagen network are known to be important for cell-ECM mechanical interactions via integrin cell surface adhesion receptors. In contrast, studies of GAGs in modulating cell-ECM interactions are limited. Here, we present experimental studies on the roles of hyaluronic acid (HA) in single tumor cell traction force generation using a recently developed 3D cell traction force microscopy method. Our work reveals that CD44, a cell surface receptor to HA, is engaged in cell traction force generation in conjunction with β1-integrin. We find that HA significantly modifies the architecture and mechanics of the collagen fiber network, decreasing tumor cells’ propensity to remodel the collagen network, attenuating traction force generation, transmission distance, and tumor invasion. Our findings point to a novel role for CD44 in traction force generation, which can be a potential therapeutic target for diseases involving HA rich ECMs such as breast cancer and glioblastoma.

Design and Applications of High Force Generation in 3D-Printed Pneumatic Artificial Muscles

Increasing the force generation and scalability of soft pneumatic actuators poses significant challenges in robotics applications, especially where high load capacities and precise control are required. This paper presents UniBPAM, a novel, scalable soft pneumatic actuator optimized through 3D printing to enhance force generation. By analyzing design parameters, such as the number of sides, height, and origami factor, UniBPAM achieved a 21.48% increase in force generation. Scalable across diameters from 36 to 144 mm, the actuator demonstrated the ability to lift up to 57 kg with 84.9% strain at larger scales. Additionally, the BiBPAM variant enables bidirectional actuation in robotic joints via motion control, which is realized through PID systems, making it suitable for various robotic applications.

Modeling Backlash-like Hysteresis and Feedforward Control of Tendon-Sheath Mechanism Pair with Arbitrary Shape: Excluding Distal Sensory Input

Abstract The tendon-sheath mechanism (TSM) has garnered attention for its versatile applications in soft robotics, robotic hands, and surgical robots due to its adeptness in transmitting force through tortuous and narrow channels. However, precise control of the TSM is challenging due to its shape-dependent deformation and force generation, highlighting the need to address shape variations in dynamic environments where direct measurement is impractical. This paper introduces a novel methodology leveraging the concept of the equivalent circle in TSM to model its shape under varying conditions. The equivalent circle substitutes an arbitrarily shaped TSM with a circle, whose radius is derived from TSM's deformation and forces measured at the proximal end during calibration. This approach provides a concise and effective framework for understanding and analyzing the distinct characteristics of TSM. Additionally, a control strategy is proposed, utilizing the estimated equivalent circle to adapt to dynamic environments. Experimental results demonstrate promising performance without distal end sensory feedback, with mean percentage errors (MPE) of 0.78% and 2.33% for predicting cumulated curve angle and equivalent circle radius, respectively. Moreover, by utilizing the equivalent circle to calculate and feedforward deadband, effective control is achieved. The root mean square error (RMSE) reduced from 1.31 mm to an average of 0.19 mm in two feedforward experiments, representing an average reduction of 85.5%. These findings shed light on effective control strategies for TSM, offering valuable insights for robotics and surgical applications where TSM shape configurations are uncertain and subject to dynamic change.

Burst-like transcription of MYH7, allelic and contractile imbalance already in early stage hiPSC-cardiomyocytes indicate these as pathogenic factors in Hypertrophic Cardiomyopathy

Abstract Background Hypertrophic Cardiomyopathy (HCM) is caused by heterozygous mutations in sarcomeric proteins, which can cause hyper- or hypocontractiliy of cardiomyocytes. Previously we also observed highly variable force generation (contractile imbalance) among individual cardiomyocytes of HCM-patients with myosin (MYH7) or myosin-binding-protein-C mutations (MYBPC3), ranging from normal to highly altered values. Contractile imbalance is presumably caused by stochastic, burst-like transcription of mutant and wildtype allele, which induces unequal ratios of mutant vs. wildtype mRNA among individual cardiomyocytes. Variable force generation most likely is the result of also unequal fractions of mutated protein from cell to cell. Aim With this study we aimed to examine whether in addition to the effects of the mutation on sarcomere function, also allelic and contractile imbalance already exist at the beginning of disease development or whether both result from disease-related alterations in symptomatic HCM-patients. Methods and Results We studied this in patient-derived human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) with MYH7-mutation R723G as model for an early disease stage. These early, fetal-like cardiomyocytes developed typical HCM-related features like hypertrophy and increased myofibrillar disarray compared to WT-hiPSC-CMs. Calcium sensitivity was reduced, twitch kinetics were slowed down. To test whether MYH7 in these early-stage hiPSC-CMs also is transcribed in bursts or continuously, we performed RNA-fluorescence in situ hybridization (RNA-FISH). Nuclei without, with one and with two or more active transcription sites were observed which indicates stochastic, burst-like and independent transcription of the two MYH7-alleles. Ratios of mRNA from both alleles were quantified in individual cardiomyocytes by allele-specific single cell RT-PCR. We found highly variable ratios of mutated vs. wildtype mRNA among individual cardiomyocytes, similar to HCM-patient’s cardiac tissue, indicating unequal expression of mutant and wildtype mRNA from cell-to-cell. Furthermore, functional measurements on myofibrils from R723G-hiPSC-CMs revealed substantial variability in force generation at physiological calcium, compared to much smaller heterogeneity among WT-hiPSC-CMs. In addition, variability of twitch kinetics of intact hiPSC-CMs was also substantially increased among R723G- compared to WT-hiPSC-CMs. Altogether, this suggests that functional heterogeneity results from burst-like transcription in heterozygous HCM cardiomyocytes. Conclusions Our results in HCM-patient derived hiPSC-cardiomyocytes with a fetal-like developmental stage suggest that allelic and contractile imbalance among individual cardiomyocytes together with the mutation are present at the beginning of the disease. Thus, they most likely are exacerbating factors that contribute development of HCM hallmarks.

Exploring the effects of mavacamten through hemodynamic force analysis in patients with obstructive hypertrophic cardiomyopathy

Abstract Introduction Mavacamten is a first-in-class allosteric myosin inhibitor effective in relieving left ventricular (LV) outflow tract obstruction in patients with obstructive hypertrophic cardiomyopathy (oHCM). To date, however, its effect on cardiac mechanics is still unclear. Hemodynamic force (HDF) analysis represents the fluid dynamics correlate of deformation imaging, showing a greater sensitivity in detecting early mechanical abnormalities or response to treatment [1]. Purpose To explore the in vivo effect of mavacamten on cardiac mechanics in patients with HCM after a 3 year-treatment, using HDF analysis. Methods LV HDF analysis was performed in 6 patients with oHCM (representing a cohort of the MAVA-LTE study) at baseline and after 3 years of treatment. Apical 4-, 2-, and 3-chamber echocardiographic views were analysed using a dedicated and sofisticated software. Base-apex forces (where positive deflections represent a force directed from the apex to the base of LV, whilst negative ones are directed toward the LV apex) were assessed in terms of timing indexed to cardiac cycle duration. HDF curves from the 6 patients treated with macavamten were compared to those obtained from oHCM patients (n=20), non-obstructive HCM (noHCM) patients (n=20), and healthy controls (n=22). Results Figure 1 shows a different pattern of transition between diastole and systole in HCM patients compared to controls. Specifically, HCM patients exhibited an earlier onset of the systolic phase, expressed as a fusion of late diastolic deceleration and systolic thrust. This was numerically represented as a decrease in diastolic-systolic transition time, which is 0.22 [0.20-0.24] for oHCM, 0.23 [0.21-0.25] for noHCM and 0.26 [0.26-0.30] for controls (p ≤0.001 for control vs oHCM, p ≤0.01 for control vs noHCM). Additionally, HCM patients showed an increased rate of force generation. The time to systolic peak (i.e., time interval from the onset of systole to the maximum force) was reduced in HCM patients compared to controls, and was shorter in oHCM than in noHCM patients (0.13 [0.11-0.15] vs 0.16 [0.14-0.17], p ≤0.01), thus reflecting an increased clinotropism in HCM. After 3 years of mavacamten treatment, the diastolic-systolic transition time and the time to systolic peak returned to a level similar to that of healthy controls (0.30 [0.27-0.30] in mavacamten group vs 0.26 [0.26-0.30], p >0.05, and 0.21 [0.20-0.22] vs 0.19[0.17-0.20], p=0.04, respectively) (Figure 2). Conclusion HDF analysis reveals that mavacamten affects the duration of transition from diastole to systole and prolongs time from the onset to the peak in systole. These findings may explain the removal of the mechanical coupling substrate responsible for the systolic anterior movement of mitralic leaflets and the subsequent resolution of LV outflow tract obstruction by mavacamten.Distribution of time parameters

Differential effects of myosin activators on myocardial contractile function in non-failing and failing human hearts.

The second-generation myosin activator danicamtiv (DN) has shown improved function compared to the first generation myosin activator omecamtiv mecarbil (OM) in non-failing myocardium by enhancing cardiac force generation but attenuating slowed relaxation. However, whether the functional improvement with DN compared to OM persists in remodeled failing myocardium remain unknown. Therefore, this study aimed to investigate the differential contractile response to myosin activators in non-failing and failing myocardium. Mechanical measurements were performed in detergent-skinned myocardium isolated from donor and failing human hearts. Steady-state force, stretch activation responses, and loaded shortening velocity were analyzed at submaximal [Ca2+] in the absence or presence of 0.5 µmol/L OM or 2 µmol/L DN. The effects of DN and OM on Ca2+-sensitivity of force generation were determined by incubating myocardial preparations at various [Ca2+]. The inherent impairment in force generation and cross-bridge behavior sensitized failing myocardium to the effects of myosin activators. Specifically, increased Ca2+-sensitivity of force generation, slowed rates of cross-bridge recruitment and detachment following acute stretch, slowed loaded shortening velocity, and diminished power output were more prominent following treatment with OM or DN in failing myocardium compared to donor myocardium. Although these effects were less pronounced with DN compared to OM in failing myocardium, DN impaired contractile properties in failing myocardium that were not affected in donor myocardium. Our results indicate that similar to first-generation myosin activators, the DN-induced slowing of cross-bridge kinetics may result in a prolongation of systolic ejection and delayed diastolic relaxation in the heart failure setting.

Hindlimb kinematics, kinetics, and muscle dynamics during sit-to-stand and sit-to-walk transitions in emus (Dromaius novaehollandiae).

Terrestrial animals not only need to walk and run but also lie prone to rest and then stand up. Sit-to-stand (STS) and sit-to-walk (STW) transitions are vital behaviours little studied in species other than humans so far, but likely impose biomechanical constraints on limb design because they involve near-maximal excursions of limb joints that should require large length changes and force production from muscles. By integrating data from experiments into musculoskeletal simulations, we analysed joint motions, ground reaction forces, and muscle dynamics during STS and STW in a large terrestrial, bipedal, and cursorial bird: the emu (Dromaius novaehollandiae, ∼30 kg). Simulation results suggest that in both STS and STW, emus operate near the functional limits (∼50 % of shortening/lengthening) of some of their hindlimb muscles, particularly in distal muscles with limited capacity for length change and leverage. Both movements involved high muscle activations (> 50 %) and force generation of the major joint extensor muscles early in the transition. STW required larger net joint moments and non-sagittal motions than STS, entailing greater demands for muscle capacity. Whilst our study involves multiple assumptions, our findings lay the groundwork for future studies to understand, for example, how tendon contributions may reduce excessive muscle demands, especially in the distal hindlimb. As the first investigation into how an avian species stands up, this study provides a foundational framework for future comparative studies investigating organismal morphofunctional specialisations and evolution, offering potential robotics and animal welfare applications.

Rate of Force Development During a Handgrip Task Is Correlated with the Post-Impact Ball Speed of the Flat Serve

The aim of the present research was to test the hypothesis that rate of force development (RFD) during a handgrip task of the dominant arm in three different positions is associated with maximal post-impact ball speed of flat serve (PIBS). Altogether 23 elite junior boys (aged 14.84 ± 2.47 years; weight 59.51 ± 13.83 kg; height 170.47 ± 16.34 cm) tennis players participated in the study. To assess the maximal voluntary contraction (MVC) and RFD during the task, four handgrip tests and a serve test were applied to estimate PIBS. Spearman’s rank correlation showed a significant positive correlation between RFD of dominant arm in each three position and PIBS (r = 0.82–0.86; p < 0.001). A very large, significantly positive correlation was also found between MVC of the dominant arm and PIBS (r = 0.88; p < 0.01). The result of the present study indicated that rapid force generation of muscles in the forearm and wrist may probably play a role in the formation of a stable contact point, and it is in connection with PIBS. It is in contrast to the slow maximal force exertion that much rather characterizes the general strength state of players. Therefore, measurement of the RFD during a handgrip task is suggested in the testing session of the flat serve of junior tennis players.

Neuromuscular synergy characteristics of Tai Chi leg stirrup movements: optimal coordination patterns throughout various phases.

To investigate the neuromuscular activity characteristics of Tai Chi athletes and identify optimal muscle synergy patterns. Data were collected from 12 elite Tai Chi athletes using a Vicon motion capture system, a Kistler 3D force plate, and a Noraxon surface electromyography system. Muscle synergy patterns were extracted using Non-negative Matrix Factorization. Four muscle synergy patterns were identified in each of the three phases of the leg stirrup movement, with the optimal synergy pattern for each phase determined as follows: knee lift phase: rectus femoris and vastus lateralis of the right leg; extension phase: rectus femoris, vastus lateralis, biceps femoris, and medial gastrocnemius of the right leg; recovery phase: rectus femoris, vastus lateralis, and medial gastrocnemius of the right leg. These patterns explain the muscle coordination activities for each phase. This study identified the optimal muscle synergy patterns for each phase, supporting the fluidity and force generation of the leg stirrup movement. This provides Tai Chi athletes with a more efficient way to exert strength and maintain balance.