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Zonnino, A.

Publications and source records attributed to Zonnino, A..

2 recordsLinked to original sources
bioRxiv2018

The effect of physiological and measurement noise on the estimate of individual muscle force from indirect measurements of muscle activity

Several forward dynamics estimators have been proposed to quantify individual muscle force using non-invasive measurements of muscle activity. None of them, however, addresses the inaccuracy that arises when measurements are available only from a subset of the muscles involved in the movement under analysis. We present a novel estimator that integrates a forward dynamics estimation approach with knowledge of the optimal contraction strategy to obtain accurate estimates of individual muscle force when measurements of muscle activity are not available for all muscles. A following in-silico characterization showed that when trying to estimate forces form the forearm muscles acting around the wrist joint, our novel estimator is able to decrease the mean estimation bias by about 25% of the true value of muscle force. With a sensitivity analysis, we show that the model-based estimator is robust against physiological variability in muscle co-contraction strategy.

bioengineering↗
bioRxiv2018

Model-based analysis of the stiffness of the wrist joint in active and passive conditions

The control of joint stiffness is a fundamental mechanism used to control human movements. While many studies have observed how stiffness is controlled for tasks involving shoulder and elbow motion, a limited amount of knowledge is available for wrist movements, though the wrist plays a crucial role in fine manipulation.\n\nWe have developed a computational framework based on a realistic musculoskeletal model, which allows to calculate the passive and active components of the wrist joint stiffness. We first used the framework to validate the musculoskeletal model against experimental measurements of the passive wrist joint stiffness, and then to study the contribution of different muscle groups on the passive joint stiffness. We finally used the framework to study the effect of muscle co - contraction on the active joint stiffness.\n\nThe results show that thumb and finger muscles play a crucial role in determining the passive wrist joint stiff - ness: in the neutral posture, the direction of maximum stiffness aligns with the experimental measurements, and the magnitude increases by 113% when they are included. Moreover, the analysis of the controllability of joint stiffness showed that muscle co - contraction positively correlates with the stiffness magnitude and negatively correlates with the variability of the stiffness orientation (p < 0.01 in both cases). Finally, an exhaustive search showed that with appropriate selection of a muscle activation strategy, the joint stiffness orientation can be arbitrarily modulated. This observation suggests the absence of biomechanical constraints on the controllability of the orientation of the wrist joint stiffness.

bioengineering↗