Adjustment of Muscle Mechanics Model Parameters to Simulate Dynamic Contractions in Older Adults

Abstract

The generation of muscle-actuated simulations that accurately represent the movement of old adults requires a model that accounts for changes in muscle properties that occur with aging. An objective of this study was to adjust the parameters of Hill-type musculo-tendon models to reflect nominal age-related changes in muscle mechanics that have been reported in the literature. A second objective was to determine whether using the parametric adjustments resulted in simulated dynamic ankle torque behavior similar to that seen in healthy old adults. The primary parameter adjustment involved decreasing maximum isometric muscle forces to account for the loss of muscle mass and specific strength with age. A review of the literature suggested the need for other modest adjustments that account for prolonged muscular deactivation, a reduction in maximum contraction velocity, greater passive muscle stiffness and increased normalized force capacity during lengthening contractions. With age-related changes incorporated, a musculo-tendon model was used to simulate isometric and isokinetic contractions of ankle plantarflexor and dorsiflexor muscles. The model predicted that ankle plantarflexion power output during 120 deg/s shortening contractions would be over 40% lower in old adults compared to healthy young adults. These power losses with age exceed the 30% loss in isometric strength assumed in the model but are comparable to 39-44% reductions in ankle power outputs measured in healthy old adults of approximately 70 years of age. Thus, accounting for age-related changes in muscle properties, other than decreased maximum isometric force, may be particularly important when simulating movements that require substantial power development.

Stochastic modelling of muscle recruitment during activity

“…We scaled the processed EMG signal to match the peak muscle activation calculated using static optimization [23]. The EMG-driven muscle force was calculated using the calculated muscle activation, the active and passive forcelength relationships from the work of Thelen [32] and the force -velocity relationship from the work of Delp et al [27] for all seven gait repetitions. The force range, that is, the upper (F u ) to the lower (F l ) bound of muscle forces of physiologically plausible muscle forces, was assumed at the 0.68 quantile (i.e.…”

“…The peak muscle force was calculated using a Hill-type muscle model. The active and passive force-length relationships were taken from the work of Thelen [32], whereas the force-velocity relationship was taken from the work of Delp et al [27]. Muscle force vectors within the spectrum were categorized using a single parameter, or muscle co-contraction, defined as the difference between the actual muscle force and the minimal force required to generate a given joint torque.…”

Real-Time EMG Driven Lower Limb Actuated Orthosis for Assistance As Needed Movement Strategy

“…The force produced by the muscle tendon model F mt (t) is expressed by the following equation: Where a(t) represents the muscle activation [34]; c(t) is the resulting signal from filtering, full-wave rectification and normalization to EM G max that is the maximal recorded value of EMG during the muscle's maximal voluntary contraction; τ act and τ deact represent the muscle's activation time constant and the deactivation time constant respectively; B m represents the muscle damping;l m (t) andv m (t) show the instantaneous normalized muscle fiber length and normalized muscle fiber velocity with respect to l m o and v max respectively; t represents the time variable. γ in (6) represents a shape factor and is equal to 0.45 [31]. Numerical values used in (7) represent the features of the force-velocity relationship such as curvature, maximum normalized force, etc.…”

“…The muscle models used in this study are based on the modified Stiff tendon Hill type model [25]. This model consists of a force-length (f l ) and force-velocity (f v ) relationships [31] as well as a parallel viscous damping element (f d ) [27]. Both relationships are normalized respectively to the maximum isometric muscle force (F max ), the muscle optimal fiber length l m o and the maximum muscle contraction velocity (v max ) [35].…”

Relationship between Hip Flexion Contracture and Hip-Joint Contact Force in Standing Posture: A Computer Simulation Study

“…The active force-length curve was obtained via spline interpolation of the force-length curve reported by Zajac [22]. The passive force-length curve was obtained from the function reported by Thelen [23]. The specific muscle tension [24] was set to 61 N/cm 2 .…”