Rethinking Margin of Stability: Incorporating Step-To-Step Regulation to Resolve the Paradox

ABSTRACTMaintaining frontal-plane stability is a major objective of human walking. Derived from inverted pendulum dynamics, the mediolateral Margin of Stability (MoSML) is frequently used to measure people’s frontal-plane stability on average. However, typical MoSML-based analyses deliver paradoxical interpretations of stability status. To address mediolateral stability using MoSML, we must first resolve this paradox. Here, we developed a novel framework that unifies the well-established inverted pendulum model with Goal-Equivalent Manifold (GEM)-based analyses to assess how humans regulate step-to-step balance dynamics to maintain mediolateral stability. We quantified the extent to which people corrected fluctuations in mediolateral center-of-mass state relative to a MoSML-defined candidate stability GEM in the inverted pendulum phase plane. Participants’ variability and step-to-step correction of tangent and perpendicular deviations from the candidate stability GEM demonstrate that regulation of balance dynamics involves more than simply trying to execute a constant-MoSML balance control strategy. Participants adapted these step-to-step corrections to mediolateral sensory and mechanical perturbations. How participants regulated mediolateral foot placement strongly predicted how they regulated center-of-mass state fluctuations, suggesting that regulation of center-of-mass state occurs as a biomechanical consequence of foot placement regulation. We introduce the Probability of Instability (PoI), a convenient statistic that accounts for step-to-step variance to properly predict instability likelihood on any given future step. Participants increased lateral PoI when destabilized, as expected. These lateral PoI indicated an increased risk of lateral instability, despite larger (i.e., more stable) average MoSML. PoI thereby explicitly predicts instability risk to decisively resolve the existing paradox that arises from conventional MoSML implementations.

Balance dynamics are related to age and levels of expertise. Application in young and adult tennis players

In tennis, coaches consider balance fundamental for the acquisition of skilled motor performance. However, the potential relationship between balance and tennis expertise and performance has not been explored yet. Therefore, this study assessed the relationship between balance and tennis performance using linear and non-linear parameters through 1) the comparison of tennis players of different ages and levels of expertise, and 2) analyzing the relationship between balance and tennis serving speed and accuracy. One hundred and six recreational and expert male tennis players took part in the study (age range 10–35 years old). Temporal dynamics of postural control during a balance task on an unstable surface were analyzed through the mean velocity and the detrended fluctuation analysis (DFAV) of center of pressure (COP). Tennis serve performance was quantified by measuring accuracy and speed. Traditional variables measuring balance performance only showed differences according to age but not to sport performance. COP showed a reduction of auto-correlated variability (reflected by DFAV) with age but mainly in expert players. COP dynamics was the only balance parameter discriminating sport expertise and it was related to age. Balance dynamics exhibited by expert tennis players DFAV results support the idea that, along the years, sport experience induces balance adaptations characterized by a higher ability to perform postural adjustments. These results also reinforce the use of non-linear analysis to reveal subtle balance adaptations produced by sport practice. Finally, the lack of correlations suggests that balance, measured with scattering variables, in a non-specific task is not a main determinant of sport performance in tennis serve.

Coordination and control – limits in standard representations of multi-reservoir operations in hydrological modeling

Major multi-reservoir cascades represent a primary mechanism for dealing with hydrologic variability and extremes within institutionally complex river basins worldwide. These coordinated management processes fundamentally reshape water balance dynamics. Yet, multi-reservoir coordination processes have been largely ignored in the increasingly sophisticated representations of reservoir operations within large-scale hydrological models. The aim of this paper is twofold, namely (i) to provide evidence that the common modeling practice of parameterizing each reservoir in a cascade independently from the others is a significant approximation and (ii) to demonstrate potential unintended consequences of this independence approximation when simulating the dynamics of hydrological extremes in complex reservoir cascades. We explore these questions using the Water Balance Model, which features detailed representations of the human infrastructure coupled to the natural processes that shape water balance dynamics. It is applied to the Upper Snake River basin in the western US and its heavily regulated multi-reservoir cascade. We employ a time-varying sensitivity analysis that utilizes the method of Morris factor screening to explicitly track how the dominant release rule parameters evolve both along the cascade and in time according to seasonal high- and low-flow events. This enables us to address aim (i) by demonstrating how the progressive and cumulative dominance of upstream releases significantly dampens the ability of downstream reservoir rules' parameters to influence flow conditions. We address aim (ii) by comparing simulation results with observed reservoir operations during critical low-flow and high-flow events in the basin. Our time-varying parameter sensitivity analysis with the method of Morris clarifies how independent single-reservoir parameterizations and their tacit assumption of independence leads to reservoir release behaviors that generate artificial water shortages and flooding, whereas the observed coordinated cascade operations avoided these outcomes for the same events. To further explore the role of (non-)coordination in the large deviations from the observed operations, we use an offline multi-reservoir water balance model in which adding basic coordination mechanisms drawn from the observed emergency operations is sufficient to correct the deficiencies of the independently parameterized reservoir rules from the hydrological model. These results demonstrate the importance of understanding the state–space context in which reservoir releases occur and where operational coordination plays a crucial role in avoiding or mitigating water-related extremes. Understanding how major infrastructure is coordinated and controlled in major river basins is essential for properly assessing future flood and drought hazards in a changing world.

Time-scale dependent mechanism of atmospheric CO2 concentration drivers of watershed water-energy balance

<p>The elevated atmospheric carbon dioxide concentration (CO<sub>2</sub>), as a key variable linking human activities and climate change, seriously affects the watershed hydrological processes. However, whether and how atmospheric CO<sub>2</sub> influences the watershed water-energy balance dynamics at multiple time scales have not been revealed. Based on long-term hydrometeorological data, the variation of non-stationary parameter n series in the Choudhury's equation in the mainstream of the Wei River Basin (WRB), the Jing River Basin (JRB) and Beiluo River Basin (BLRB), three typical Loess Plateau regions in China, was examined. Subsequently, the Empirical Mode Decomposition method was applied to explore the impact of CO<sub>2</sub> on watershed water-energy balance dynamics at multiple time scales. Results indicate that (1) in the context of warming and drying condition, annual n series in the WRB displays a significantly increasing trend, while that in the JRB and BLRB presents non-significantly decreasing trends; (2) the non-stationary n series was divided into 3-, 7-, 18-, exceeding 18-year time scale oscillations and a trend residual. In the WRB and BLRB, the overall variation of n was dominated by the residual, whereas in the JRB it was dominated by the 7-year time scale oscillation; (3) the relationship between CO<sub>2 </sub>concentration and n series was significant in the WRB except for 3-year time scale. In the JRB, CO<sub>2 </sub>concentration and n series were significantly correlated on the 7- and exceeding 7-year time scales, while in the BLRB, such a significant relationship existed only on the 18- and exceeding 18-year time scales. (4) CO<sub>2</sub>-driven temperature rise and vegetation greening elevated the aridity index and evaporation ratio, thus impacting watershed water-energy balance dynamics. This study provided a deeper explanation for the possible impact of CO<sub>2</sub> concentration on the watershed hydrological processes.</p>

Energy Balance Dynamics: Exercise, Appetite, Diet, and Weight Control

Individuals seeking to achieve weight loss are encouraged to achieve a negative energy balance, essentially eat less and move more. The complex relationship between energy expenditure and intake is often overlooked, leaving individuals and practitioners underwhelmed by the results of weight loss efforts. Independently, physical activity and diet interventions can yield modest weight loss and when combined have synergistic effects that promote sustained weight loss. Although physical activity benefits appetite suppression, reduces food rewards, and can be considered a gateway to healthy eating, high levels of daily activity are needed to induce weight loss. Diet is an important component to achieving weight loss, and high-protein diets have the potential for supporting weight loss as well. This column will be focused on the benefits of physical activity in reducing body weight, more specifically, the interdependent relationship between dietary intake and physical activity in achieving weight reduction.

MODEL OF WATER CONSUMPTION RATIONING AND CALCULATING THE OPERATION REGIME OF AGRICULTURAL CROPS IRRIGATION

Purpose: development of a current model of water consumption rationing and calculation of the corresponding rates and terms for agricultural crops irrigation under various hydrometeorological parameters. Materials and methods: the basis for the developed model is a series of field experiments conducted in 2012–2014, as well as analytical studies, the scheme of the experiment, soil and hydrometeorological characteristics, water balance dynamics, precipitation and total moisture supply of the irrigated massif, water consumption according to the development stages of summer planting potatoes were determined. Results and discussion: the model under consideration includes taking into account the water-physical properties of soil, the lowest moisture capacity and moisture reserves, setting critical limit for the irrigation regime, temperature and air humidity deficit, the duration of the growing and inter-irrigation periods, on the basis of which the water consumption of the selected crop is calculated according to the growth phase. Further, the irrigation regime is calculated: the irrigation rate and the difference in moisture reserves, which comparison with the critical limit allows to conclude on irrigation necessity or its prediction for the near future (up to five days) after which irrigation will be needed. A complex for differentiating the irrigation regime with the determining deficits and standards for the parameters under consideration is provided. Conclusions: the model of water consumption rationing, performed on the use of two hydrometeorological factors, taken into account the growth and development phases of the crop under consideration, makes it possible to substantiate the actual calculation of the corresponding norms and terms of agricultural crops irrigation. The model is stable and can be used in land reclamation practice as a part of general technological complex for agricultural crops cultivation on irrigated lands.