Biology subjects

Gutierrez-Farewik, E. M.

Publications and source records attributed to Gutierrez-Farewik, E. M..

2 recordsLinked to original sources

bioRxiv2025

Modeling glenohumeral stability in musculoskeletal simulations: A validation study with in vivo contact forces

Common optimization approaches to solve the muscle redundancy problem in musculoskeletal simulations can predict shoulder contact forces that violate joint stability with lines of action outside the glenohumeral joint border. Approaches with simple joint stability constraints were previously introduced imposing an upper limit on the direction of the contact force to stay within a specified stability perimeter. Such approaches predicted higher rotator cuff muscle activation than without constraints, but the estimated joint contact forces were oriented along the specified perimeter, raising questions about validity. In this study, several glenohumeral stability formulations were investigated, and tested against in vivo measurements of glenohumeral contact forces from the Orthoload dataset on one participant data in three dumbbell tasks: lateral raise, posterior raise, and and anterior raise. The investigated formulations either imposed inequality constraints on the contact force direction to remain within a stability perimeter whose shape was varied, or added a penalty term as a criterion measure to the objective function that made the objective function costly for contact force directions to deviate from the glenoid cavity center. All stability formulations predicted contact force magnitudes that agreed relatively well to the in vivo measured forces except for the strictest formulation that constrained the joint contact force to be directed at the glenoid cavity center. Models that restricted the force direction to lie within a specified shape estimated force vectors that largely lay along the perimeters. Models that instead penalized force directions that deviated from the glenoid cavity center estimated relatively more accurate contact force directions within the glenoid cavity, though still not entirely in agreement with in vivo measurements. Our findings support the proposed penalty formulations as more reasonable and accurate than other investigated existing glenohumeral stability formulations. Author summaryIn musculoskeletal models, the glenohumeral joint is often simplified as a purely rotational joint with no translation, whereas the actual joint movement involves both rotation and some translation, requiring stabilizing forces to prevent dislocation. Models that compute muscle forces based on a minimal effort strategy without specifically addressing glenohumeral stability may underestimate co-activation of the stabilizing rotator cuff muscles, and inaccurately predict that the contact force between the humerus and the glenoid is directed outside the articular surface of the joint. In this study, we compared existing stability models and proposed a new approach that penalized joint contact force whose direction deviates from the glenoid cavity center. We integrated these approaches into a muscle redundancy solver and estimated muscle and joint forces using the thoracoscapular shoulder musculoskeletal model. We compared model estimates to in vivo measurements of joint contact forces. We found that the penalty formulation reproduced the contact force direction most accurately, and promoted greater muscle co-contraction. These findings support the proposed penalty approach as a benchmark for more accurate analysis of shoulder biomechanics using musculoskeletal simulations.

bioengineering↗

bioRxiv2024

Springs vs. motors: Ideal assistance in the lower limbs during walking at different speeds

Recent years have witnessed breakthroughs in assistive exoskeletons; both passive and active devices have reduced metabolic costs near preferred walking speed by assisting muscle actions. Metabolic reductions at multiple speeds should thus also be attainable. Musculoskeletal simulation can potentially predict the interaction between assistive moments, muscle-tendon mechanics, and walking energetics. In this study, we simulated devices optimal assistive moments based on minimal muscle activations during walking with prescribed kinematics and dynamics. We used a generic musculoskeletal model with calibrated muscle-tendon parameters and computed metabolic rates from muscle actions. We then simulated walking across multiple speeds and with two ideal actuation modes - motor-based and spring-based - to assist ankle plantarflexion, knee extension, hip flexion, and hip abduction and compared computed metabolic rates. We found that both actuation modes considerably reduced physiological joint moments but did not always reduce metabolic rates. Compared to unassisted conditions, motor-based ankle plantarflexion and hip flexion assistance reduced metabolic rates, and this effect was more pronounced as walking speed increased. Spring-based hip flexion and abduction assistance increased metabolic rates at some walking speeds despite a moderate decrease in some muscle activations. Both modes of knee extension assistance reduced metabolic rates to a small extent, even though the actuation contributed with practically the entire net knee extension moment during stance. Motor-based hip abduction assistance reduced metabolic rates more than spring-based assistance, though this reduction was relatively small. Future work should experimentally validate the effects of assistive moments and refine modeling assumptions accordingly. Our computational workflow is freely available online. Author SummaryWe used simulation to identify ideal assistance at major lower limb joints that can potentially be produced by motor-based or spring-based assistive devices in slow, normal, and fast walking. We found that assistance from both actuation modes decreased muscle activations and net muscle moments to varying extents, depending on joint and walking speed, but they did not always reduce metabolic energy of muscles. Motor-based assistance was overall more effective than spring-based assistance, and spring-based assistance at times increased the metabolic energy. The largest metabolic energy reductions occurred with motor-based plantarflexion assistance, followed by motor-based hip flexion assistance, both more notably at higher speeds. Motor-based hip abduction assistance also reduced metabolic energy, somewhat inversely with walking speed. Spring-based assistance was overall less effective than motor-based assistance but did reduce metabolic energy with plantarflexion assistance in slow walking and with hip flexion assistance in fast walking. Knee extension assistance, regardless of actuation mode or walking speed, had little to no influence on metabolic energy. Our simulation findings do not support knee extension assistance at all, nor spring-based hip flexion assistance in slow walking or hip abduction assistance at any speed if a device goal is to reduce muscle activations.

bioengineering↗