The impact of age-related increase in passive muscle stiffness on simulated upper limb reaching.

Ageing changes the musculoskeletal and neural systems, potentially affecting a person's ability to perform daily living activities. One of these changes is increased passive stiffness of muscles, but its contribution to performance is difficult to separate experimentally from other ageing effects such as loss of muscle strength or cognitive function. A computational upper limb model was used to study the effects of increasing passive muscle stiffness on reaching performance across the model's workspace (all points reachable with a given model geometry).

The impact of intrinsic muscle properties on simulated reaching performance.

Musculoskeletal modelling is used widely for studying limb motion and its control, but simulation outcomes may depend heavily on the underlying muscle model used. The aim of this study was to investigate how intrinsic muscle properties affect reaching movements in a simple upper limb model. The simulations suggest that more realistic, higher-order activation dynamics requires longer prediction from a forward model and gives rise to a higher level of unplanned co-contraction than simple activation models.

Indicators of anterior-posterior phase difference in glottal opening measured from natural production of vowels.

Voiced speech is generated by the glottal flow interacting with vocal fold vibrations. However, the details of vibrations in the anterior-posterior direction (the so-called zipper-effect) and their correspondence with speech and other glottal signals are not fully understood due to challenges in direct measurements of vocal fold vibrations. In this proof-of-concept study, the potential of four parameters extracted from high-speed videoendoscopy (HSV), electroglottography, and speech signals to indicate the presence of a zipper-type glottal opening is investigated.

Skewing of the glottal flow with respect to the glottal area measured in natural production of vowels.

In the production of voiced speech, glottal flow skewing refers to the tilting of the glottal flow pulses to the right, often characterized as a delay of the peak, compared to the glottal area. In the past four decades, several studies have addressed this phenomenon using modeling of voice production with analog circuits and computer simulations. However, previous studies measuring flow skewing in natural production of speech are sparse and they contain little quantitative data about the degree of skewing between flow and area.