Phase synchronisation of the three leg joints in quiet human stance
Introduction
A change of paradigm has occurred in the postural research community. The simplification of a single inverted pendulum (SIP) model is not appropriate for quiet human stance. A couple of recent publications [1], [2], [3], [4], [5], [6], [7], [8], [9], [10] agreed in that quiet stance is a dynamic multi-segment phenomenon. Two of these studies [1], [4] concentrated on a quantitative description of ankle and hip joint coupling and distinguished kinematic in-phase from anti-phase relations of both joints. Few studies [2], [3], [4], [7], [8], [11], [12] ascertained contributions of the knee joint to quiet human stance. For example, high correlations of all three leg joints [2] have been found recently. In particular, these authors gave evidence that both kinematic and torque correlations between ankle and knee are prominent. On the one hand, all those studies analysing ankle and hip movement focused on fluctuations at frequencies below 4 Hz. On the other hand, there is evidence that the kinematics of ankle and knee are correlated in the frequency range 4–8 Hz [2]. Even though quiet human stance is a multi-segment phenomenon the state of all degrees of freedom involved do not necessarily evolve independently. Observing any phase synchronisation would be a strong pointer to non-linear coupling behind [13], [14], [15]. Concurrently, the dimensionality of a multi-degree-of-freedom system would be reduced for the lifetime of synchronisation. Within this study we aim at investigating whether phase synchronisations can be observed between leg joints during quiet human stance. In that, we use the “phase synchronisation index” (PSI) [16], [17], [18], [19] which enables to analyse phase synchronisation across a range of frequencies. Especially, going beyond the focus of previous studies on ankle and hip strategies, the degree of an involvement of the knee should be quantified.
Section snippets
Experimental data acquisition and digital filtering
Here, we revisited a data set of 60 trials from 10 subjects who had stood quietly on firm ground. Details about experiments and methods (e.g., inverse dynamics) can be found elsewhere [2], [3].
Digital filtering of measured input data is a crucial processing step in inverse dynamics. Inevitably, this comes along with the manipulation of the frequency content. Our data were sampled at fs = 115.5 Hz during a trial length of Ttrial = 4.43 s. In order to calculate a filtered sample value we used a
Results
Regarding phase synchronisation both of joint angular velocities (Fig. 3) and of joint torques (Fig. 4), we only find high numbers of significant PSIs when the knee is involved, i.e., between immediately adjacent joints (ankle–knee, knee–hip). In contrast, the hip does not synchronise to the ankle at any frequency, neither kinematically nor on muscular level. The joint angular velocities of knee and ankle synchronise in a broad frequency range 1.25–8 Hz. There are significant PSIs at 2–3 Hz and
Quiet human stance relies on knee function
The knee joint is synchronised to both the ankle and the hip joint, whereas there is no systematic long range synchronisation between ankle and hip joints. This applies to joint kinematics as well as joint torques. Very general, our result is in striking contradiction to literature in which coupling between ankle and hip joints was asserted (e.g., in [1], [9]). As in this research field the predominantly assumed model for human stance is currently either a single (SIP) or a double inverted
Acknowledgements
MG and SG were supported by “Deutsche Forschungsgemeinschaft” (DFG) grants during data acquisition (MG: MU1766/1-1) and manuscript preparation (MG: MU1766/1-3; SG: SE1042/2). Furthermore, the work was supported by the DFG grant WI1166/9-1. MG sends many, many thanks to Sascha at Café Lieders in Jena: a marvellous combination of coffee and music helped to pull this through at the end.
Conflict of interest statement
None of the authors is or was exposed to any conflicts of interest related to the
References (35)
- et al.
A unified view of quiet and perturbed stance: simultaneous co-existing excitable modes
Neuroscience Letters
(2005) - et al.
All leg joints contribute to quiet human stance: a mechanical analysis
Journal of Biomechanics
(2009) - et al.
Stabilization of a multi-segment model of bipedal standing by local joint control overestimates the required ankle stiffness
Gait & Posture
(2008) - et al.
Effect of the hip motion on the body kinematics in the sagittal plane during human quiet standing
Neuroscience Letters
(2009) - et al.
Handling of impact forces in inverse dynamics
Journal of Biomechanics
(2006) - et al.
Sensitivity and specifcity of coherence and phase synchronization analysis
Physics Letters A
(2006) - et al.
The handedness of postural fluctuations
Human Movement Science
(2000) - et al.
Inverse biomimetics: how robots can help to verify concepts concerning sensorimotor control of human arm and leg movements
Journal of Physiology – Paris
(2009) - M. Günther, O. Müller, R. Blickhan, Watching quiet human stance to shake off its straitjacket, Archive of Applied...
- et al.
Control and estimation of posture during quiet stance depends on multijoint coordination
Journal of Neurophysiology
(2007)
Identification of the plant for upright stance in humans: multiple movement patterns from a single neural strategy
Journal of Neurophysiology
An optimal state estimation model of sensory integration in human postural balance
Journal of Neural Engineering
The dynamics of postural sway cannot be captured using a one-segment inverted pendulum model: a PCA on segment rotations during unperturbed stance
Journal of Neurophysiology
Coherence analysis of muscle activity during quiet stance
Experimental Brain Research
Effect of vision and stance width on human body motion when standing: implications for afferent control of lateral sway
The Journal of Physiology
Postural dynamics in the standing human
Biological Cybernetics
A theoretical model of phase transitions in human hand movements
Biological Cybernetics
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