A sensorimotor enhanced neuromusculoskeletal model for simulating postural control of upright standing

Abstract

The human's upright standing is a complex control process that is not yet fully understood. Postural control models can provide insights into the body's internal control processes of balance behavior. Using physiologically plausible models can also help explaining pathophysiological motion behavior. In this paper, we introduce a neuromusculoskeletal postural control model using sensor feedback consisting of somatosensory, vestibular and visual information. The sagittal plane model was restricted to effectively six degrees of freedom and consisted of nine muscles per leg. Physiologically plausible neural delays were considered for balance control. We applied forward dynamic simulations and a single shooting approach to generate healthy reactive balance behavior during quiet and perturbed upright standing. Control parameters were optimized to minimize muscle effort. We showed that our model is capable of fulfilling the applied tasks successfully. We observed joint angles and ranges of motion in physiologically plausible ranges and comparable to experimental data. This model represents the starting point for subsequent simulations of pathophysiological postural control behavior.

Keywords: biomechanics; forward dynamics; motor control; neural control; neuromusculoskeletal modeling; postural control; simulation; standing.

Figure 1

Postural control model. The neural controller generates control signals based on feedforward input (FF) as well as somatosensory (SOM), vestibular (VES) and visual (VIS) feedback. Feedback values are generated by comparing time-delayed states of the model with their corresponding reference states. Indicated delays belong to the body's afferences (τ_a) and efferences (τ_e). For calculations, we used a lumped delay τ consisting of both signal transmission and processing delays (Section 2.2.2). The reference position is an upright standing pose. Signals from the neural controller lead to muscle excitations u(t) of the musculoskeletal human model.

Figure 2

Box-plots showing median and interquartile ranges of joint angles during quiet upright standing of simulation and each participant. Simulations assumed left and right symmetry, experimental data were averaged for left and right joint angles of each participant following this assumption.

Figure 3

Box-plots showing median and interquartile ranges of joint angles during upright standing on a moving platform of simulation and each participant. During the experiments, each subject fulfilled the perturbed standing task twice. Note that these participants are not the same as in the quiet standing scenario.

Figure 4

Joint angles during upright standing on a moving platform. Joint angles of simulation (orange) and experiments (mean: black, standard deviation: shaded gray area) are shown for 60 s.

Figure 5

COP during upright standing on a moving platform. The COP of simulation (orange) and experiments (mean: black, standard deviation: shaded gray area) is shown for 60 s. Additionally, an exemplary section of 10 s (highlighted with a red frame) is represented as zoom-in below.

Figure 6

Muscle activations during upright standing on a moving platform. Muscle activations of simulation (orange) and experiments (mean: black, standard deviation: shaded gray area) are represented for 60 s. Muscle activations are shown for gluteus maximus (GLU), hamstrings (HAM), iliopsoas (IL), rectus femoris (RECT), biceps femoris short head (BFSH), vastus intermedius (VAS), gastrocnemius medialis (GAS), soleus (SOL), and tibialis anterior (TA).

Figure 7

Muscle activations during upright standing on a moving platform. Muscle activations of simulation (orange) and experiments (mean: black, standard deviation: shaded gray area) are represented as an exemplary zoom-in of 10 s. Muscle activations are shown for gluteus maximus (GLU), hamstrings (HAM), iliopsoas (IL), rectus femoris (RECT), biceps femoris short head (BFSH), vastus intermedius (VAS), gastrocnemius medialis (GAS), soleus (SOL), and tibialis anterior (TA).