27 research outputs found
Diffusion Inertial Poser: Human Motion Reconstruction from Arbitrary Sparse IMU Configurations
Motion capture from a limited number of inertial measurement units (IMUs) has
important applications in health, human performance, and virtual reality.
Real-world limitations and application-specific goals dictate different IMU
configurations (i.e., number of IMUs and chosen attachment body segments),
trading off accuracy and practicality. Although recent works were successful in
accurately reconstructing whole-body motion from six IMUs, these systems only
work with a specific IMU configuration. Here we propose a single diffusion
generative model, Diffusion Inertial Poser (DiffIP), which reconstructs human
motion in real-time from arbitrary IMU configurations. We show that DiffIP has
the benefit of flexibility with respect to the IMU configuration while being as
accurate as the state-of-the-art for the commonly used six IMU configuration.
Our system enables selecting an optimal configuration for different
applications without retraining the model. For example, when only four IMUs are
available, DiffIP found that the configuration that minimizes errors in joint
kinematics instruments the thighs and forearms. However, global translation
reconstruction is better when instrumenting the feet instead of the thighs.
Although our approach is agnostic to the underlying model, we built DiffIP
based on physiologically realistic musculoskeletal models to enable use in
biomedical research and health applications
Differences in sensorimotor noise explain age-related changes in postural strategy during perturbed standing
status: publishe
Initial posture explains variability in kinematic responses to perturbations during standing
status: Published onlin
Risk premiums in cap rates of investment property
This article reports the results of a study about the correlations and patterns over time between the composite elements of the initial yield in the prime office and retail property markets in the Netherlands, the United Kingdom (London), Belgium (Brussels), and Germany (Frankfurt). For this study, the determinant components are identified as the risk-free interest rate, inflation, and the risk premium. For the multiple regression analysis, these components are supplemented with dummy variables for property types and locations
An approximate stochastic optimal control framework to simulate nonlinear neuro-musculoskeletal models in the presence of noise.
Optimal control simulations have shown that both musculoskeletal dynamics and physiological noise are important determinants of movement. However, due to the limited efficiency of available computational tools, deterministic simulations of movement focus on accurately modelling the musculoskeletal system while neglecting physiological noise, and stochastic simulations account for noise while simplifying the dynamics. We took advantage of recent approaches where stochastic optimal control problems are approximated using deterministic optimal control problems, which can be solved efficiently using direct collocation. We were thus able to extend predictions of stochastic optimal control as a theory of motor coordination to include muscle coordination and movement patterns emerging from non-linear musculoskeletal dynamics. In stochastic optimal control simulations of human standing balance, we demonstrated that the inclusion of muscle dynamics can predict muscle co-contraction as minimal effort strategy that complements sensorimotor feedback control in the presence of sensory noise. In simulations of reaching, we demonstrated that nonlinear multi-segment musculoskeletal dynamics enables complex perturbed and unperturbed reach trajectories under a variety of task conditions to be predicted. In both behaviors, we demonstrated how interactions between task constraint, sensory noise, and the intrinsic properties of muscle influence optimal muscle coordination patterns, including muscle co-contraction, and the resulting movement trajectories. Our approach enables a true minimum effort solution to be identified as task constraints, such as movement accuracy, can be explicitly imposed, rather than being approximated using penalty terms in the cost function. Our approximate stochastic optimal control framework predicts complex features, not captured by previous simulation approaches, providing a generalizable and valuable tool to study how musculoskeletal dynamics and physiological noise may alter neural control of movement in both healthy and pathological movements
A robust optimal control method to assess the impact of sensorimotor noise on human motion
status: Published onlin
Synthesis of Biologically Realistic Human Motion Using Joint Torque Actuation
status: publishe
Adaptations in Reactive Balance Strategies in Healthy Older Adults After a 3-Week Perturbation Training Program and After a 12-Week Resistance Training Program
Both resistance training (RT) and perturbation-based training (PBT) have been proposed and applied as interventions to improve reactive balance performance in older adults. PBT is a promising approach but the adaptations in underlying balance-correcting mechanisms through which PBT improves reactive balance performance are not well-understood. Besides it is unclear whether PBT induces adaptations that generalize to movement tasks that were not part of the training and whether those potential improvements would be larger than improvements induced by RT. We performed two training interventions with two groups of healthy older adults: a traditional 12-week RT program and a 3-week PBT program consisting of support-surface perturbations of standing balance. Reactive balance performance during standing and walking as well as a set of neuro-muscular properties to quantify muscle strength, sensory and motor acuity, were assessed pre- and post-intervention. We found that both PBT and RT induced training specific improvements, i.e., standing PBT improved reactive balance during perturbed standing and RT increased strength, but neither intervention affected reactive balance performance during perturbed treadmill walking. Analysis of the reliance on different balance-correcting strategies indicated that specific improvements in the PBT group during reactive standing balance were due to adaptations in the stepping threshold. Our findings indicate that the strong specificity of PBT can present a challenge to transfer improvements to fall prevention and should be considered in the design of an intervention. Next, we found that lack of improvement in muscle strength did not limit improving reactive balance in healthy older adults. For improving our understanding of generalizability of specific PBT in future research, we suggest performing an analysis of the reliance on the different balance-correcting strategies during both the training and assessment tasks