Functional coordination of muscles underlying changes in behavioural dynamics

Abstract

The dynamical systems approach addresses Bernstein’s degrees of freedom problem by assuming that the neuro-musculo-skeletal system transiently assembles and dismantles its components into functional units (or synergies) to meet task demands. Strikingly, little is known from a dynamical point of view about the functioning of the muscular sub-system in this process. To investigate the interaction between the dynamical organisation at muscular and behavioural levels, we searched for specific signatures of a phase transition in muscular coordination when a transition is displayed at the behavioural level. Our results provide evidence that, during Fitts’ task when behaviour switches to a different dynamical regime, muscular activation displays typical signatures of a phase transition; a reorganisation in muscular coordination patterns accompanied by a peak in the variability of muscle activation. This suggests that consistent changes occur in coordination processes across the different levels of description (i.e., behaviour and muscles). Specifically, in Fitts’ task, target size acts as a control parameter that induces a destabilisation and a reorganisation of coordination patterns at different levels of the neuro-musculo-skeletal system.

The Effect of Aging on Muscular Dynamics Underlying Movement Patterns Changes

“…All declared to be in good health and to have a full range of motion with their right upper limb. Throughout this paper, their results will be compared to previously published results of 14 right-handed younger adults [Vernooij et al, 2016; age: 23.2 ± 2.0 years (mean ± std ), 8 males]. Volunteers did not exercise or consume more than one glass of alcohol within the 12 h preceding participation (confirmed by questionnaire).…”

“…The results for the use of the W basis repertoire (Figure 4B) show that elderly subjects recruit W basis 2 most around ID 4.2 and ID 5.1, whereas W basis 4 and W basis 5 are least recruited around ID 4.2 and ID 5.1. Interestingly, the differences in recruitment are much less pronounced for elderly subjects compared to young subjects (Vernooij et al, 2016). PCA syn analyses on the temporal activation profiles H of the elderly subjects (Figure 4C) showed that the score of the first component explained most of the variance between IDs: 74.3, 71.4, 84.7, 84.9, and 90.5%, for increasing IDs respectively.…”

“…Experimental design, setup and analysis methods were identical to those reported in Vernooij et al (2016) to enable direct comparison with young subjects. In short, participants slid a stylus rhythmically over a graphical tablet placed in front and on the right side of the subject between two horizontal bar-targets.…”

“…This jump length distribution (JLD) captures the statistics of the fluctuations in muscular coordination, therefore representing a measure of variability. An extended explanation of the procedure can be found in Vernooij et al (2016). The effect of ID on the peak of the distribution was tested with a repeated measures ANOVA with ID as within-subject factor, group (young vs. old) as between-subjects factor and α = 0.05.…”

“…In the present experiment, we adopted a similar strategy to study reorganizations in muscular dynamics in parallel to (before, around, and after) transitions between dynamics regimes in Fitts' task. This strategy has been used in a previous study on the relationship between muscles and behavior in young subjects (Vernooij et al, 2016). Using Fitts' task, by increasing task difficulty via the manipulation of target width, behavior was guided through a phase transition between two dynamical regimes.…”