title: Subject-specific tendon-aponeurosis definition in Hill-type model predicts higher muscle forces in dynamic tasks.
abstract: Neuromusculoskeletal models are a common method to estimate muscle forces. Developing accurate neuromusculoskeletal models is a challenging task due to the complexity of the system and large inter-subject variability. The estimation of muscles force is based on the mechanical properties of tendon-aponeurosis complex. Most neuromusculoskeletal models use a generic definition of the tendon-aponeurosis complex based on in vitro test, perhaps limiting their validity. Ultrasonography allows subject-specific estimates of the tendon-aponeurosis complex's mechanical properties. The aim of this study was to investigate the influence of subject-specific mechanical properties of the tendon-aponeurosis complex on a neuromusculoskeletal model of the ankle joint. Seven subjects performed isometric contractions from which the tendon-aponeurosis force-strain relationship was estimated. Hopping and running tasks were performed and muscle forces were estimated using subject-specific tendon-aponeurosis and generic tendon properties. Two ultrasound probes positioned over the muscle-tendon junction and the mid-belly were combined with motion capture to estimate the in vivo tendon and aponeurosis strain of the medial head of gastrocnemius muscle. The tendon-aponeurosis force-strain relationship was scaled for the other ankle muscles based on tendon and aponeurosis length of each muscle measured by ultrasonography. The EMG-driven model was calibrated twice - using the generic tendon definition and a subject-specific tendon-aponeurosis force-strain definition. The use of subject-specific tendon-aponeurosis definition leads to a higher muscle force estimate for the soleus muscle and the plantar-flexor group, and to a better model prediction of the ankle joint moment compared to the model estimate which used a generic definition. Furthermore, the subject-specific tendon-aponeurosis definition leads to a decoupling behaviour between the muscle fibre and muscle-tendon unit in agreement with previous experiments using ultrasonography. These results indicate the use of subject-specific tendon-aponeurosis definitions in a neuromusculoskeletal model produce better agreement with measured external loads and more physiological model behaviour.
authors.affiliation: Centre for Musculoskeletal Research, Griffith Health Institute, Griffith University, Gold Coast, Australia. pauline@gerus.fr
authors.forename: Pauline
authors.initials: P
authors.lastname: Gerus
authors.forename: Guillaume
authors.initials: G
authors.lastname: Rao
authors.forename: Eric
authors.initials: E
authors.lastname: Berton
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D002138:Calibration; D004576:Electromyography; D006801:Humans; D008297:Male; D008954:Models, Biological; D018485:Muscle Fibers, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D013647:Task Performance and Analysis; D013710:Tendons / Q000502:physiology*; D014463:Ultrasonography