Slacklining: An explanatory multi-dimensional model considering classical mechanics, biopsychosocial health and time

Table 1 Summary table of the proposed concept-model

Additional dimensionality		Multiple levels	Description
Time multiplicity: physical/external versus cortical/internal. These can include: (1) Biological neuronal delay; (2) Learning; (3) Process delays of choice; (4) Action responses; (5) Physical external time elapsed; (6) Perceived cortical time; (7) Temporal goal setting; and (8) Instant feedback	Biopsychosocial constraints, these can include: (1) Motivation; (2) Attitude; (3) Context; (4) Experience/Skill (neuroplasticity); (5) Fatigue; (6) Muscle properties; (7) Injury; and (8) Age	4: Neural activity	The manifold of different muscle activity strategies leading to HFM slacklining are the result of a complex integration of top-down control loops, bottom-up reflexes, neural latencies, inhibition loops etc.
		3: Muscle activity	Various muscle activation strategies can be used to control the multi-DoF joint kinematics and stay within the manifold of level 2 (co-contraction to control joint stiffness, agonist/antagonist tuning)
		2: Multi-DoF joint kinematics	Keeping within the manifold of level 1 can be attained through multiple solutions of joint kinematic strategies (abundant movement system). Different positions and orientations of the segments of the extremities and trunk can give the same CoM coordinates; vice versa the same point in the CoM phase space can be obtained through various joint kinematics. The (infinite) set of joint kinematic strategies form a manifold themselves within a high-dimensional topographical space
		1: CoM phase space	At the whole-body level there is > 6D phase space for CoM (position, orientation and velocity relative to the base of support, limbs and diverse body parts) contains a manifold in which the objective of slacklining (level 0) is achieved. There are physical limits to the extent the CoM can deviate from the base of support and to the velocities that can be counteracted. Higher velocities can be counteracted in regions of the manifold where deviation from the base of support is small
		0: HFM slacklining	The basic objective of slacklining is harmonious functional movement on a tightened rope: smooth dynamic stability

The slacklining multi-dimensional model presented above illustrates: the two added dimensions of ‘time multiplicity’ and ‘biopsychosocial constraints’, in the left 2-columns in descending hierarchical order; and the subsequent multiple levels at which these influence the body’s response are presented in the 5-Rows and read from bottom to top in ascending hierarchical order. MDM: Multi-dimensional model (of slacklining); HFM: Harmonious functional movement; CoM: Centre of mass; DoF: Degrees of freedom.