Center of mass velocity-based predictions in balance recovery following pelvis perturbations during human walking

In many simple walking models foot placement dictates the center of pressure location and ground reaction force components, whereas humans can modulate these aspects after foot contact. Because of the differences, it is unclear to what extend predictions made by models are valid for human walking. Yet, both model simulations and human experimental data have previously indicated that the center of mass (COM) velocity plays an important role in regulating stable walking.\ud \ud Here, perturbed human walking was studied for the relation of the horizontal COM velocity at heel strike and toe-off with the foot placement location relative to the COM, the forthcoming center of pressure location relative to the COM, and the ground reaction forces. Ten healthy subjects received various magnitude mediolateral and anteroposterior pelvis perturbations at toe-off, during 0.63 and 1.25 m s−1 treadmill walking.\ud \ud At heel strike after the perturbation, recovery from mediolateral perturbations involved mediolateral foot placement adjustments proportional to the mediolateral COM velocity. In contrast, for anteroposterior perturbations no significant anteroposterior foot placement adjustment occurred at this heel strike. However, in both directions the COM velocity at heel strike related linearly to the center of pressure location at the subsequent toe-off. This relation was affected by the walking speed and was, for the slow speed, in line with a COM velocity based control strategy previously applied by others in a linear inverted pendulum model. Finally, changes in gait phase durations suggest that the timing of actions could play an important role during the perturbation recovery

Risk and ambiguity aversion behavior in index-based insurance uptake decisions:Experimental evidence from Ethiopia

Index-based insurance (IBI) is an innovative pro-poor climate risk management strategy that suffers from low uptake. Evidence on the role of behavioral impediments in adoption of IBI is scant. We conducted lab-in-the-field experiments with 1139 smallholders out of whom 596 have adopted IBI in Ethiopia to elicit their risk and ambiguity aversion behavior, and examine whether risk and/or ambiguity aversion can explain actual IBI uptake decisions. Our study suggests that an increase in risk-aversion increases uptake, but an increase in ambiguity-aversion lowers uptake of IBI. We also find evidence that an increase in risk aversion speeds-up the uptake of IBI, while an increase in ambiguity aversion delays the adoption of IBI

Estimation of sagittal-plane whole-body angular momentum during perturbed and unperturbed gait using simplified body models

Human whole-body angular momentum (WBAM) during walking typically follows a consistent pattern, making it a valuable indicator of the state of balance. However, calculating WBAM is labor-intensive, where the kinematic data for all body segments is needed, that is, based on a full-body model. In this study, we focused on selecting appropriate segments for estimating sagittal-plane WBAM during both unperturbed and perturbed gaits, which were segments with significant angular momentum contributions. Those major segments were constructed as a simplified model, and the sagittal-plane WBAM based on a simplified model was calculated by combining the angular momenta of the selected segments. We found that the WBAM estimated by seven-segment models, incorporating the head & torso (HT) and all lower limb segments, provided an average correlation coefficient of 0.99 and relative angular momentum percentage of 96.8% and exhibited the most similar sensitivity to external perturbations compared to the full-body model-based WBAM. Additionally, our findings revealed that the rotational angular momenta (RAM) of lower limb segments were much smaller than their translational angular momenta (TAM). The pair-wise comparisons between simplified models with and without RAMs of lower body segments were observed with no significant difference, indicating that RAMs of lower body segments are neglectable. This may further simplify the WBAM estimation based on the seven-segment model, eliminating the need to estimate the angular velocities of lower limb segments. These findings have practical implications for future studies of using inertial measurement units (IMUs) for estimating WBAM, as our results can help reduce the number of required sensors and simplify kinematics measurement

Mestscheiding onder de roosters

Op het Proefstation voor de Varkenshouderij is gedurende een jaar het scheiden van mest onder de roosters bestudeerd. De mest werd gescheiden in een dikke en dunne fractie en dagelijks, met behulp van een mestschuif, uit de afdeling verwijderd

Ammoniakemissie bij guste en drachtige zeugen in groepshuisvesting

Het Praktijkonderzoek Varkenshouderij heeft emissiemetingen uitgevoerd bij drachtige zeugen in groepshuisvesting. Met eenvoudige bouwkundige maatregelen is een reductie van de ammoniakemissie tot onder de Groen-Labelnorm mogelijk

Ammoniakemissiemetingen bij guste en drachtige zeugen in groepshuisvesting

Op het Varkensproefbedrijf in Sterksel is in juli 1999 onderzoek gestart naar emissie-arme stalsystemen voor guste en drachtige zeugen in groepshuisvesting. Daarvoor is een afdeling voorzien van ligboxen met uitloop. Het emitterend mestkelderoppervlakwordt verkleind door middel van schuine kelderwanden

Does bundling crop insurance with certified seeds crowd-in investments? Experimental evidence from Kenya

We use a randomised experiment in Kenya to analyse how smallholder farmers respond to receiving a free hybrid crop insurance product, conditional on purchasing certified seeds. We find that farmers increase effort—increasing total investments and taking more land in production. In addition to adopting more certified seeds, they also invest more in complementary inputs such as fertilizer and hired-in farm-machinery and non-farm labour. We find limited evidence of a change in farming intensity. For example, there is no evidence of ‘crowding-out’ of effort or inputs on a per-hectare basis, even if the indemnity-based component of the insurance product potentially gives rise to asymmetric information problems (moral hazard). We also document that ex post willingness to pay for the insurance product has increased for the treatment group. This suggests that learning about the benefits of (subsidized) insurance outweighs any anchoring effects on the zero price during the pilot study

Assisting walking balance using a bio-inspired exoskeleton controller

Background: Balance control is important for mobility, yet exoskeleton research has mainly focused on improving metabolic energy efficiency. Here we present a biomimetic exoskeleton controller that supports walking balance and reduces muscle activity. Methods: Humans restore balance after a perturbation by adjusting activity of the muscles actuating the ankle in proportion to deviations from steady-state center of mass kinematics. We designed a controller that mimics the neural control of steady-state walking and the balance recovery responses to perturbations. This controller uses both feedback from ankle kinematics in accordance with an existing model and feedback from the center of mass velocity. Control parameters were estimated by fitting the experimental relation between kinematics and ankle moments observed in humans that were walking while being perturbed by push and pull perturbations. This identified model was implemented on a bilateral ankle exoskeleton. Results: Across twelve subjects, exoskeleton support reduced calf muscle activity in steady-state walking by 19% with respect to a minimal impedance controller (p < 0.001). Proportional feedback of the center of mass velocity improved balance support after perturbation. Muscle activity is reduced in response to push and pull perturbations by 10% (p = 0.006) and 16% (p < 0.001) and center of mass deviations by 9% (p = 0.026) and 18% (p = 0.002) with respect to the same controller without center of mass feedback. Conclusion: Our control approach implemented on bilateral ankle exoskeletons can thus effectively support steady-state walking and balance control and therefore has the potential to improve mobility in balance-impaired individuals.Support Biomechanical Engineerin