The Robust Running Ape: Unraveling the Deep Underpinnings of Coordinated Human Running Proficiency

Abstract

In comparison to other mammals, humans are not especially strong, swift or supple. Nevertheless, despite these apparent physical limitations, we are among Natures most superbly well-adapted endurance runners. Paradoxically, however, notwithstanding this evolutionary-bestowed proficiency, running-related injuries, and Overuse syndromes in particular, are widely pervasive. The term ‘coordination’ is similarly ubiquitous within contemporary coaching, conditioning, and rehabilitation cultures. Various theoretical models of coordination exist within the academic literature. However, the specific neural and biological underpinnings of ‘running coordination,’ and the nature of their integration, remain poorly elaborated. Conventionally running is considered a mundane, readily mastered coordination skill. This illusion of coordinative simplicity, however, is founded upon a platform of immense neural and biological complexities. This extensive complexity presents extreme organizational difficulties yet, simultaneously, provides a multiplicity of viable pathways through which the computational and mechanical burden of running can be proficiently dispersed amongst expanded networks of conditioned neural and peripheral tissue collaborators. Learning to adequately harness this available complexity, however, is a painstakingly slowly emerging, practice-driven process, greatly facilitated by innate evolutionary organizing principles serving to constrain otherwise overwhelming complexity to manageable proportions. As we accumulate running experiences persistent plastic remodeling customizes networked neural connectivity and biological tissue properties to best fit our unique neural and architectural idiosyncrasies, and personal histories: thus neural and peripheral tissue plasticity embeds coordination habits. When, however, coordinative processes are compromised—under the integrated influence of fatigue and/or accumulative cycles of injury, overuse, misuse, and disuse—this spectrum of available ‘choice’ dysfunctionally contracts, and our capacity to safely disperse the mechanical ‘stress’ of running progressively diminishes. Now the running work burden falls increasingly on reduced populations of collaborating components. Accordingly our capacity to effectively manage, dissipate and accommodate running-imposed stress diminishes, and vulnerability to Overuse syndromes escalates. Awareness of the deep underpinnings of running coordination enhances conceptual clarity, thereby informing training and rehabilitation insights designed to offset the legacy of excessive or progressively accumulating exposure to running-imposed mechanical stress.

Full text

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MINI REVIEW
published: 12 June 2017
doi: 10.3389/fpsyg.2017.00892
Edited by:
Duarte Araújo,
Universidade de Lisboa, Portugal
Reviewed by:
Robert Hristovski,
Saints Cyril and Methodius University
of Skopje, Macedonia
Jia Yi Chow,
National Institute of Education,
Nanyang Technological University,
Singapore
*Correspondence:
John Kiely
jkiely@uclan.ac.uk
Specialty section:
This article was submitted to
Movement Science and
Sport Psychology,
a section of the journal
Frontiers in Psychology
Received: 22 February 2017
Accepted: 15 May 2017
Published: 12 June 2017
Citation:
Kiely J (2017) The Robust Running
Ape: Unraveling the Deep
Underpinnings of Coordinated Human
Running Proficiency.
Front. Psychol. 8:892.
doi: 10.3389/fpsyg.2017.00892
The Robust Running Ape: Unraveling
the Deep Underpinnings of
Coordinated Human Running
Proficiency
John Kiely*
Institute of Coaching and Performance, School of Sport and Wellbeing, University of Central Lancashire, Preston,
United Kingdom
In comparison to other mammals, humans are not especially strong, swift or supple.
Nevertheless, despite these apparent physical limitations, we are among Natures most
superbly well-adapted endurance runners. Paradoxically, however, notwithstanding this
evolutionary-bestowed proficiency, running-related injuries, and Overuse syndromes in
particular, are widely pervasive. The term ‘coordination’ is similarly ubiquitous within
contemporary coaching, conditioning, and rehabilitation cultures. Various theoretical
models of coordination exist within the academic literature. However, the specific
neural and biological underpinnings of ‘running coordination,’ and the nature of their
integration, remain poorly elaborated. Conventionally running is considered a mundane,
readily mastered coordination skill. This illusion of coordinative simplicity, however,
is founded upon a platform of immense neural and biological complexities. This
extensive complexity presents extreme organizational difficulties yet, simultaneously,
provides a multiplicity of viable pathways through which the computational and
mechanical burden of running can be proficiently dispersed amongst expanded
networks of conditioned neural and peripheral tissue collaborators. Learning to
adequately harness this available complexity, however, is a painstakingly slowly
emerging, practice-driven process, greatly facilitated by innate evolutionary organizing
principles serving to constrain otherwise overwhelming complexity to manageable
proportions. As we accumulate running experiences persistent plastic remodeling
customizes networked neural connectivity and biological tissue properties to best
fit our unique neural and architectural idiosyncrasies, and personal histories: thus
neural and peripheral tissue plasticity embeds coordination habits. When, however,
coordinative processes are compromised—under the integrated influence of fatigue
and/or accumulative cycles of injury, overuse, misuse, and disuse—this spectrum of
available ‘choice’ dysfunctionally contracts, and our capacity to safely disperse the
mechanical ‘stress’ of running progressively diminishes. Now the running work burden
falls increasingly on reduced populations of collaborating components. Accordingly our
capacity to effectively manage, dissipate and accommodate running-imposed stress
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Kiely The Robust Running Ape
diminishes, and vulnerability to Overuse syndromes escalates. Awareness of the deep
underpinnings of running coordination enhances conceptual clarity, thereby informing
training and rehabilitation insights designed to offset the legacy of excessive or
progressively accumulating exposure to running-imposed mechanical stress.
Keywords: running, rehabilitation, coordination, overuse, variability, plasticity
INTRODUCTION
Running is the most primitively ancient of athletic movements:
critical to competitive success in many sports and, in evolutionary
contexts, critical to survival. Uniquely amongst mammals
humans employ an upright bipedal bouncing gait when running.
A gait characterized by long flight times interspersed with brief
ground contacts during which the shock of impact, equating to
multiple times bodyweight, is absorbed, re-cycled, and steered
through the narrow stabilizing platform provided by a single
supporting foot. Nevertheless, despite these apparent limitations,
we are amongst Nature’s most supremely well-adapted runners
(Bramble and Lieberman, 2004).
The evolutionary innovations bestowing human running
proficiency do not, however, render us invulnerable to
breakdown and running-related injuries are common (van
der Worp et al., 2015). Runners seem particularly exposed to
Overuse injuries, with up to 70% suffering such injury each year
(Clarsen et al., 2013;Saragiotto et al., 2014;van der Worp et al.,
2015). Various definitions exist, amid some inconsistency, and
confusingly ‘Overuse’ describes both a ‘mechanism’ and ‘type’ of
injury (Clarsen et al., 2013). Although definitions vary, published
consensus agrees that Overuse syndromes arise consequent
to progressively mounting micro-trauma accumulated over a
protracted period, exacerbated by insufficient recovery leading
to increasing tissue sensitization in the absence of single
catastrophic events (Clarsen et al., 2013;Saragiotto et al., 2014).
Commonly cited risk factors include elevated running volumes,
prior injury, fatigue and background psychosocial stress (Clarsen
et al., 2013;van der Worp et al., 2015;Ivarsson et al., 2016). Yet
how these factors synergistically interact, leading to Overuse
injuries, has yet to be clarified (van der Worp et al., 2015).
A frequently overlooked distinction between running and
many other sporting movements is that running is one of a
limited sub-set of gaits—along with crawling and walking—that
are so evolutionary ancient as to have mutually co-evolved in
tandem with human neural and biological infrastructures (Kiely
and Collins, 2016). In short: how we run is shaped by, yet has also
contributed to shaping, modern human morphology, in ways that
other sporting movements—a golf swing; a tennis serve; rowing;
the butterfly stroke—, have not. An implication of this synergistic
co-evolution of form and function is that the adaptations
underpinning human running permeate every dimension of our
anatomical, biological, and neurological being. Our capacity to
withstand the extraordinary mechanical and stability challenges
imposed during our bouncing bipedal running gait is not
attributable to any single evolutionary adaptation. Instead human
running robustness emerges as a consequence of our slowly
developing capacity to seamlessly harness, orchestrate and
integrate the outputs of multiple biological and neurological sub-
systems to accomplish running objectives. In short: our ability to
coordinate the running action.
The core defining feature of coordination is that multiple
components work together to realize an objective (Diedrichsen
et al., 2010). Conventionally, within the Sports Sciences,
coordination is perceived through the lens of Dynamical Systems
Theory (DST). Recently, through the lens of Optimal Feedback
Control Theory (OFCT), conventional interpretations of DST
have been criticized for obscuring the fundamental priority of
sensory feedback in shaping effective movement coordination
(Todorov, 2004, 2009). The OFCT framework subsequently
claims to more prominently highlight the relationship between
high-level goals, and the real-time sensorimotor control strategies
most suitable for accomplishing those goals. Recent ecological
dynamics perspectives have similarly advocated the prominent
role of emerging sensory ‘information’ in regulating on-going
motor behavior (Seifert et al., 2013). As in other scientific
domains, however, debates and disagreements exist and the
need for on-going argument, skepticism and scrutiny remain
obvious. Various perspectives, accordingly, have been expertly
and extensively discussed within their respective motor control
and neuroscientific literatures (see for example: Davids and
Glazier, 2010;Nagengast et al., 2010;Kelso, 2012;Proske
and Gandevia, 2012). The problem, for the vast majority of
practical Sports Scientists, Sports medicine practitioners and
evidence-led Coaches is that while these academic debates
are essential, by necessity they are abstract, highly technical,
typically obscured by the in-house terminology of the specific
academic realm and often too narrowly focused to provide
practically implementable insight. Accordingly, any attempt to
construct a coherent overview of such a diverse and contentious
topic will, inevitably, be flawed and incomplete. Nevertheless,
the overarching objective of this review is to provide this
targeted group with an updated evidence-led synopsis of the
key linked dimensions of the running coordination phenomenon
deemed most relevant to performance, resilience and injury
rehabilitation.
THE EVOLUTIONARY UNDERCURRENTS
OF COORDINATED RUNNING
ROBUSTNESS
Evolutionary survival demands that biological systems, operating
in unpredictable environments using unreliable components and
finite energy sources, are robust to the challenges to which they
are most commonly exposed (Kitano, 2004). Accordingly, from
an evolutionary perspective, running coordination’s overriding
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imperative is to deploy available resources to satisfactorily achieve
desired outcomes, while preserving an acceptable robustness
to any running-imposed ‘threat’ serving to reduce survival
probability.
This ‘threat’ takes many forms. If energy depletes; if
mechanical tissue tolerances are exceeded; if neural processes
are overloaded to the extent that movement precision
and/or cognitive clarity declines, then inevitably survival
probability diminishes. No single survival imperative necessarily
predominates. Instead the neurobiological system seeks to
satisfactorily resolve multiple partially overlapping, partially
competing organizational constraints (Skoyles, 2008;Hodges
and Tucker, 2011;Miller et al., 2012). In negotiating this complex
organizational problem, evolution has arrived at a typically
ingenious resource-sparing set of solutions.
Interpretation of Sensation Shapes
Movement
As running increases in severity we are made consciously
aware of mounting ‘threat’ through increasingly discomforting
interpretations of arising sensory information (Marcora et al.,
2009;Smirmaul, 2012). At the whole-body level growing
discomfort influences psycho-emotional state, amplifying
perceptions of anxiety, ‘pain’ and diminished attention which
in turn intensify the inner conflict between motivational drive
and perceived effort that, collectively, we interpret as mounting
‘fatigue’ (Marcora et al., 2009;Seay et al., 2011;Smirmaul,
2012). At the local level, muscle activation patterns are subtly
modulated to offload sensitized tissues, thereby moderating
regionalized discomfort and alleviating tissue irritation (Mizrahi
et al., 2000;Gerlach et al., 2005;Seay et al., 2011). Through
these mechanisms our interpretation of arising psychobiological
discomfort informs us of increasing risk—of impending tissue
damage, elevating metabolic costs, increasing neural processing
demands and cognitive effort—, thereby providing a direct
means through which the perceived relevance of changing
sensation directly influences running behavior (Marcora et al.,
2009;Wolpert et al., 2011).
Prompted by subtle, but persistent, sensory signals the CNS
continually searches for economic trade-offs between desired
outcomes, available resources and discomforting perceptions of
‘threat’ (Hodges and Tucker, 2011;Miller et al., 2012). As we
accumulate running experiences, we learn to more precisely
triangulate between sensory feedback, feedforward activation and
desired running outcomes and gravitate toward coordinative
solutions more satisfactorily resolving these multiple competing
constraints. Progressively, with practice, sensory information
and muscular activation strategies co-evolve into a seamlessly
integrated sensorimotor system: whereby changes in sensation
directly modulate muscular activations, and changes in activation
directly modify sensation (Wolpert et al., 2011; see Figure 1).
Through this elegantly efficient process, sensory feedback
information and feedforward activation instructions become
irrevocably mutually entangled: preserving running robustness
within acceptable limits through an integrated sensorimotor
process of ‘self-organizing optimality’ (Glazier and Davids, 2009).
Organizing Neuro-biological Complexity:
Modularity Facilitates Degeneracy
Biological lifeforms are reflectively characterized as complex
adaptive systems. Complex: as the behaviors of individual
components are inextricably linked to those of multiple others
through arrays of processes, cycles and regulatory feedback
loops. Adaptive: as the behaviors and collaborative outputs
of collections of components flexibly modify their concerted
contributions to best fit current context (Manor and Lipsitz,
2013).
Each individual entity within the complex organism is
linked, physically or functionally, to every other. Nevertheless
there remains an evident modularity, whereby collections of
elements are more densely networked to each other than to
elements within other modules (Whitacre, 2010;Mason, 2015).
All modules are inter-connected, yet are simultaneously partially
insulated and functionally semi-autonomous. Modularity,
accordingly, facilitates robustness as modules can evolve,
reshape, rewire, and repair in tandem, or independently, without
jeopardizing survivability of the entire organism (Maleszka et al.,
2014;Mason, 2015).
Modularity is a fundamental neuro-biological organizing
principle, greatly simplifying otherwise overwhelmingly
disordered complexity. Related modules exhibit extensive
functional overlap, such that alliances of neural networks and
peripheral tissues can spontaneously modify behaviors to achieve
equivalent ‘outputs’ through a multiplicity of pathways. This
functional agility is often conflated with redundancy, but is
perhaps more reflectively termed degeneracy (Glazier and
Davids, 2009;Mason, 2015;Seifert et al., 2016). Degeneracy
describes the ability of alternate structural pathways to achieve
similar functional outcomes in one context, or dissimilar
functional outcomes in divergent contexts (Seifert et al., 2016).
Degenerate systems are composed of diverse elements, capable
of alternately fulfilling similar or overlapping functions and
are fundamental facilitators of complexity, robustness, and
evolvability (Whitacre, 2010; Maleszka et al., 2014;Mason,
2015). Redundancies, in contrast, occur when sub-sets of
identical elements combine to achieve similar outcomes
and are subsequently rare, as there are few identical neural
and/or biological entities. Degeneracy describes a more flexibly
adaptive phenomenon, whereby collaborating communities of
fundamentally distinct components produce reliably consistent
outputs under fluctuating conditions (Mason, 2015;Seifert et al.,
2016).
The human runner represents a highly degenerate system.
Consider the phenomenon of leg stiffness during ground-
contact—the accurate calibration of which facilitates the
protective dampening and economic re-cycling of impact shocks.
Our highly degenerate neuro-biological design can produce
equivalent leg stiffness’s using diverse coordinative strategies:
muscle-tendon units (MTU’s) vary individual contributions
whilst, collectively, whole-leg power outputs remain consistent;
individual MTU’s achieve similar force outputs by summating
different muscle and tendon contributions; individual muscles
vary activated motor unit populations under differing contractile
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FIGURE 1 | Mechanisms through which pain leads to re-distribution of activity within, and between, muscles. Used by permission from Hodges and Tucker (2011).
conditions to produce identical tensions; multiple combinations
of torso, leg and foot postural orientations and pre-set
tensionings deliver equivalent propulsive and stabilization-
enabling contributions (Wickham and Brown, 1998;Roberts
and Azizi, 2011;Turvey and Fonseca, 2014). This option-rich,
highly degenerate movement landscape provides a multiplicity
of avenues through which collaborating modular alliances
combine, and re-combine, to flexibly satisfy dynamically shifting
demands.
This degenerate design offers multiple means to accomplish
running objectives. Historically, the apparently overwhelming
complexity presented by this proliferation of movement ‘options’
was famously interpreted as a control ‘problem’ (Bernstein,
1967). This potentially complex problem, however, is reduced
by the gradual construction of synergies—coordinative structures
comprised of highly context-specific, context-sensitive functional
linkages serving to temporarily constrain collaborating elements
such that they act as single coherent units (Latash et al., 2007;
Wu and Latash, 2014). Through the formation of synergies
the control ‘problem’ is greatly simplified, while simultaneously
retaining the benefits of complexity and degeneracy. As such,
more recently, the apparent problem of excessive choice has
been reframed as the ‘bliss’ of motor abundance (Latash, 2012).
When running, this abundance of potentially over-whelming
movement ‘choice’ can be, through effective coordination,
productively deployed to disperse the running work-burden
among networks of collaborating tissues: thereby promoting
efficiency and robustness.
Fractal Variation: Deploying Coordinative
Abundance
Conventionally, we equate skilful running with metronomic
regularity. As proficient runners achieve reliably consistent stride
outcomes, it seems sensible to assume experts precisely replicate
running stride characteristics. In recent years, however, close
scrutiny of running behaviors illustrates that, even when experts
run at steady paces, movement parameters persistently vary
(Stergiou and Decker, 2011). Through the lens of traditional
motor control paradigms such variability was initially interpreted
as ‘noise’—meaningless error arising from the intricacies of the
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engineering challenge, measurement inaccuracies and fallible
biological components. Intriguingly, however, more recent
investigations reveal the structure of gait variability to be neither
randomly erratic, nor independent of prior events. Instead, the
architecture of past, current and future stride variability’s appear
statistically linked through, as yet incompletely understood, long-
range correlations (Hausdorff, 2007;Stergiou and Decker, 2011;
Hamill et al., 2012).
Structured Non-random Variability
Mandelbrot’s classic work, The Fractal Geometry of Nature
(Mandelbrot, 1982), first popularized the term ‘fractal’ to describe
the phenomenon, pervasive in Nature, of recurrent structural
self-similarity. The unifying characteristic of fractals is scale-free
structural replication: whereby individual entities are composed
of sub-units of a shared structure, while themselves forming
super-ordinate entities conforming to a similarly patterned
design. Examples include the branching networks of the vascular
system and convoluted folding surfaces of the neo-cortex: both
fractally replicating architectures exponentially increasing tissue
surface area.
Fractal self-similarity is not, however, confined to physical
architectures and also manifests as time-series or organizational
replications. Thus sub-regions may be exact or distorted
copies of the all-encompassing over-arching structure, or may
simply share quantitative, qualitative, or statistical properties
(Goldberger et al., 2002;Newell et al., 2005;West, 2010;
Vázquez et al., 2016). Fractal signatures are ubiquitous in
neurophysiology, with multiple phenomena exhibiting self-
similarity across observational scales. Famously, the time series
of inter-heartbeat intervals—heart-rate variability—is a fractal
phenomenon. Although each beat is unique, its uniqueness is not
random but shaped by an innate, neurally embedded background
algorithm blending the organism’s unique idiosyncrasies with
past experiences, current status, and transient momentary
demands, to collectively shape the time-series architecture of
the emergent heartbeat (Goldberger et al., 2002). Accordingly
the beat-to-beat ‘solution’ to the circulation ‘problem’ is neither
tightly prescribed, nor loosely erratic.
Expert running coordination is similarly characterized by
the tuned inter-play between predictability and responsiveness
bestowed by the fractally fluctuating deployment of option-rich,
functionally overlapping degenerate networks. Together, these
networks provide the diverse repertoire of behavioral responses
essential for survival in chaotic, unpredictable environments (Van
Orden, 2007;Nakayama et al., 2010;Stergiou and Decker, 2011;
Vázquez et al., 2016).
RUNNING VARIABILITY: SHARING THE
RUNNING WORK-BURDEN
As with other neuro-biological processes running dynamics
exhibit robust fractal characteristics: suggesting stride-to-stride
variability is neither random, nor dictated by the fluctuating
idiosyncrasies of current conditions. Instead on-going stride
variations are meaningfully related—in a decaying Power law
FIGURE 2 | Inter-relationships between complexity and injury resilience.
fashion—to past variations stretching back over thousands
of strides (Meardon et al., 2011;Hamill et al., 2012). This
pervasive fractal variation ensures the mechanical stress of
running is distributed in ever varying, yet non-randomly
organized, patterns: patterns tuned, through practice, to the
runner’s unique architectural and experiential peculiarities.
This structured variability enables the well-trained runner
to disperse the running ‘work burden’ amongst expanded
networks of biological tissues, whilst simultaneously retaining
the agility to spontaneously respond to emerging challenge
(Figure 2). Healthy running, accordingly, is characterized by
an optimal bandwidth of movement variability: neither too
much, nor too little (Meardon et al., 2011;Hamill et al.,
2012).
Accordingly proficient running coordination is not the
capacity to monotonously replicate an idealized stride pattern,
but the ability to continuously recombine expansive, yet
conditioned, populations of collaborating neural and biological
components. Thereby, enabling the achievement of reliably
consistent running outcomes through a diversity of subtly
shifting movement permutations.
Diminishing Complexity, Drives
Dysfunctional Variability
As we move through a running life, accumulative cycles of ‘wear
and tear’—of injury, overuse, misuse, and disuse—gradually
degrade both the material integrity of biological components
and the networked richness of neural connectivity (Elbert and
Rockstroh, 2004;Taubert et al., 2010;Hoppeler et al., 2011).
As neuro-biological complexity contracts, the landscape of
viable degenerate permutations, capable of satisfying running
demands, deteriorates. Now, the mechanical stress of running
must be distributed amongst shrinking networks of collaborating
components (Pelletier et al., 2015).
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FIGURE 3 | Relationships between running gait variability, risk and efficiency.
Reductions in viable degeneracies do not, however, inevitably
decrease running variability. Instead, as the neuro-biological
systems struggles to proficiently manage imposed loadings,
mechanical stress becomes either more tightly focused on
restricted populations of working tissues, or is erratically
dispersed amongst expanded webs of unconditioned tissues (Van
Orden, 2007;Hamill et al., 2012). As illustration, ACL-deficient
knees typically exhibit reduced, whereas ACL-reconstructed
knees exhibit dramatically expanded, inter-stride variability
(Stergiou and Decker, 2011;Hamill et al., 2012). Such deviations
from habituated variability ranges, oscillating between overly
formulaic constancy and wild randomness, signify an impaired
capacity to absorb, disperse, and purposefully recycle and re-
direct impact momentums (Nakayama et al., 2010;Figure 3).
As coordinative fluency deteriorates, vulnerability to Overuse
syndromes and unexpected perturbations escalates.
Global Accommodation of Local
Perturbation
The entangled nature of complex neurobiology ensures that
when variability changes at any discrete location, accommodating
compensatory behaviors occur elsewhere in the system. As
illustration: active injuries typically reduce habitual running
variability in the injured leg—constraining control to protect
sensitized tissues—, while simultaneously inducing expansions
of variability in the non-injured leg (Hamill et al., 2012).
Such evidence illustrates that, although running injury is a
site-specific event, the accommodation of injury is a system-
wide phenomenon occasioning system-wide coordinative
adjustments. Importantly, these behavioral modifications,
although temporarily functional, inevitably expose compensating
tissues to unhabituated loadings. What has not been discussed
within the running-related literature, however, are the neural and
biological mechanisms which structurally embed running habits
and which must be micro-architecturally altered to support
coordinative change.
PERVASIVE BIO-PLASTICITY: THE
EMBEDDED LEGACY OF PRIOR EVENTS
A fundamental dimension of human neuro-biology is life-
long experience-dependent plasticity: the capacity within the
CNS and tissues of the periphery to lastingly respond—
structurally, chemically, electrically and materially—to repeat
experience (Elbert and Rockstroh, 2004;Taubert et al., 2010).
Throughout supra-spinal and spinal branches of the CNS
persistent patterns of neural activation induce experience-
dependent plastic re-configurations, micro-architecturally
embedding relationships between regularly co-operating
neural components and associated motor units. Plasticity in
the CNS is mirrored in the periphery, as tissues re-model in
response to habitual loading patterns (Hoppeler et al., 2011).
Experience-dependent plasticity refines and economizes
communications linkages between collaborating neural
networks, and conditions peripheral tissue structures to
better cope with regularly encountered movement contexts
(Pelletier et al., 2015).
As we converge on individually unique running styles,
pervasive neuro-biological plasticity embeds movement habits:
thereby constraining the landscape of degenerate movement
options to manageable proportions and increasing the probability
previously successful ‘solutions’ will be recycled in the future.
Plasticity, accordingly, drives the physical embodiment of
coordinative change: thereby sculpting the micro-architectural
basis of coordinative synergies, linkages, and attractors.
Inevitably, however, plasticity is both blessing and curse,
and the engraining of new habits inevitably degrades old
habits.
The Plasticity of Over-Specialization
As running experience accumulates, the sensorimotor apparatus
becomes ever-more efficient at executing the running task. But
neural resources are evolutionarily precious and fundamentally
limited commodities and, as such, are persistently re-deployed to
fulfill varying roles within diverse tasks. Such conflicting usage
patterns drive competitive plasticity processes, as neural networks
strive to persistently re-model neurological ‘form’ to best fit
currently prioritized ‘function.’
Consequently, as we progress from novice to ‘skilful,’
a by-product of on-going neuroplastic refinement is that
fewer networked collaborators are required to manage
the evermore highly practiced running pattern (Coq and
Barbe, 2011;Avanzino et al., 2014;Pelletier et al., 2015).
Subsequently it becomes evolutionarily wasteful to continually
dedicate expanded sensorimotor networks to task execution.
Accordingly, when the range of running behaviors to which
we are regularly exposed becomes monotonously stereotypical,
evolutionary pressure to economize resource uptake ensures the
landscape of conditioned neural and biological collaborators,
dedicated to executing highly practiced running patterns,
progressively diminishes as under-utilized resources are re-
allocated elsewhere (Elbert and Rockstroh, 2004;Avanzino
et al., 2014). A drawback, therefore, of engaging in only a
narrow band of overly stereotypical running tasks, is that we
become hyper-efficient at deploying reduced populations of
degeneracies to execute a narrowing band of self-similar running
patterns. As direct consequence, we become increasingly
vulnerable to both overuse syndromes, and unhabituated
challenges.
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The Plasticity of Disuse
Prolonged abstinence from running drives a progressive loss
of physiological conditioning, and also dims the regular flow
of running-related sensorimotor information. Consequently, the
cortical circuitry normally maintained by consistently processing
running-related sensorimotor information is eroded as voracious
competitive plasticity re-models neural connectivity to best fit
current usage patterns (Elbert and Rockstroh, 2004;Pelletier
et al., 2015). Subsequently when we return to regular running
coordinative control is slightly less proficient and slightly less
resilient.
The Plasticity of Misuse
When we run in injured or irritated states we subtly alter
coordination patterns to divert discomforting mechanical stress
away from sensitized tissues: alleviating negative sensation,
tempering structural damage, and facilitating healing. If,
however, we continue to run in compromised patterns for
prolonged periods, newly adapted remedial strategies become
progressively more plastically engrained within CNS and tissue
architectures (Engineer et al., 2012;Avanzino et al., 2014).
The dynamic inter-play between experience-driven and
competitive plasticity processes ensure the traces of temporarily
functional coordinative compensations typically remain
plastically embedded within neuro-biological structures:
thereby becoming the new ‘normal,’ and exerting a legacy not
easily erased within the abbreviated timeframes offered by
conventional rehabilitation paradigms (Pelletier et al., 2015).
Promoting Positive Plasticity
Ultimately plastic re-modeling, as it consumes precious material
and energetic resources, is evolutionarily expensive (Merzenich
et al., 2014;Clark et al., 2015). Within the adult-brain it
is not evolutionarily economical to plastically adapt to all
stimulation—valuable neural reserves would be immediately
depleted. Accordingly, structures in the mature cortex plastically
remodel only when specific criteria—regulated by modulatory
neurotransmitters such as acetylcholine, dopamine, serotonin,
and norepinephrine—are satisfied (Merzenich et al., 2014;Clark
et al., 2015). Operating collectively these neuro-modulatory
enablers act as “on–off” switches, engaging excitatory and
inhibitory processes and temporarily opening plasticity-enabling
‘windows of opportunity’ within which sensorimotor inputs
contributing to ‘success’ are selectively amplified; while signals
from competing inputs, uncorrelated with that success, are
selectively dampened (Merzenich et al., 2014).
Over time, the continued amplification of relevant
sensorimotor inputs provides a competitive advantage;
greatly enhancing the representational detail embedded in
the cortical territory dedicated to processing running-related
sensorimotor information (Wolpert et al., 2011;Engineer et al.,
2012). Crucially, a core finding emanating from this research
domain is that repetitively non-varying, non-challenging
‘mindless’ movements—those not demanding focused attention
for satisfactory execution—are insufficiently stimulating to
reliably release the cocktail of neuromodulating chemical
catalysts necessary for plastic re-modeling within the mature
motor cortex (Merzenich et al., 2014;Clark et al., 2015). In
contrast, positive plastic re-modeling is optimized in response
to behaviorally relevant intense practice, executed at the limits
of current abilities and therefore demanding high attentional
and motivational drives (Avanzino et al., 2014;Merzenich
et al., 2014). Thus positive neural re-modeling is promoted
only when tasks are neither so easy that they fail to stimulate
focused attention, nor so difficult that continuous failure
undermines motivation. In essence coordination improves
through engaging challenge, not mindless routine. A rationale
perhaps explaining why rehabilitation processes employing non-
challenging coordinative tasks typically fail to generate optimal
recovery (Elbert and Rockstroh, 2004;Merzenich et al., 2014;
Clark et al., 2015).
CONCLUSION
As we accumulate running experiences, sensory feedback biases
us toward personalized styles more satisfactorily resolving
achievement of the running objective against an acceptable
investment of survival-relevant resources. Guided by innate
evolutionary influences, individualized coordinative habits
progressively shape around our unique anatomical, biological,
neurological, and experiential idiosyncrasies.
Subsequently, as we progress from “novice” to “skilled”
runners we more sensitively and smoothly respond to small
perturbations, thereby offsetting the need to periodically
and clumsily respond to larger challenges as minor errors
accumulate. We adjust activation patterns to navigate away from
discomforting sensation, thereby moderating tissue aggravations.
We gravitate toward activations more proficiently poising bio-
composite tissue structures to productively absorb and re-cycle
impact momentums, thereby reducing energetic investment and
dampening shock decelerations. We learn to exploit our layered
landscape of degenerate movement options by fractally varying
stride parameters under the integrated influence of historical
events and current context, thereby dispersing running work-
burdens amongst expanded webs of conditioned tissues. As we
accumulate running experience plasticity-processes progressively
embed working relationships between regularly collaborating
neural components, and embed the tissue features most
adaptive to running-specific loadings. As such plasticity is the
mechanism that engrains synergies and linkages, and embeds
the attractor states underpinning running coordination habits.
A key observation, accordingly, is that running coordination
change is supported on a platform of neuro-biological plastic
modification.
The evolutionary neuro-economics that embed efficient
habits, however, eventually encase us within limiting constraints.
Plasticity facilitates learning by engraining efficient habits,
yet also retains the residues of past traumas and prolonged
sensitivities: subsequently ensuring injuries are rarely transient
peripheral events, but long-lasting insults etched into cortical
tissues of the CNS (Elbert and Rockstroh, 2004;Coq and Barbe,
2011;Pelletier et al., 2015). Similarly the enduring traces of
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repeated cycles of over-specialization, disuse, and misuse, impose
plastic re-configurations not automatically reverting to original
conditions once discomfort diminishes and pain-free running is
resumed.
As we progress through our running lives, the sensorimotor
landscape is in perpetual plastic flux as the integrated influences
of health, training, and injury subtly re-configure neural
connectivity and biological tissue architectures. Chronically, the
progressive accumulation of plastic mal-adaptations drives the
creeping decay of networked neural connectivity: compromising
sensorimotor information flow, blurring cortical representations
of peripheral structures, prompting mal-adaptations in neuronal
excitability, and driving disorder within the primary motor cortex
(Coq and Barbe, 2011;Avanzino et al., 2014). As a consequence,
coordinative control degrades.
When other lifestyle and training considerations—
background psycho-emotional stress, monotonous running
volumes, generalized and localized fatigue—, are overlaid on
already compromised operating conditions, access to expansive
populations of viable movement degeneracies further diminishes.
As this self-perpetuating cycle escalates, coordinative proficiency
decays, susceptibility to tissue irritations grows and we become
increasingly fragile to Overuse syndromes and non-formulaic
perturbations.
Practical Insights and Relevance
Deeper appreciation of the various phenomena underpinning
running coordination potentially informs many aspects of
conventional theory and practice. The topics below are offered
as tentative examples:
Overuse Injury
Documented incidence rates suggest running-related Overuse
injury is neither a ‘solved,’ nor perhaps clearly articulated,
problem. Contextualizing Overuse as a direct consequence
of chronically compromised coordination emphasizes the
necessity of balancing the monotonous stagnation, often
implicit in conventional endurance running programs, with
the unhabituated challenging stimulation essential to promoting
positive neuro-plastic re-modeling. Furthermore, this rationale
suggests that introducing coordinative diversity into high-
volume running programs may be an effective prophylactic
against Overuse occurrence.
Enforcing Technical Change
A deeper appreciation of the embedded undercurrents that
shape running coordination also questions the long-standing
practice of attempting to change technique simply by instructing
the runner to consciously re-configure established coordination
patterns so as to better conform to an aesthetic ideal.
Suddenly altering engrained running habits diverts mechanical
stress along unhabituated pathways: thereby inevitably exposing
unconditioned tissue to unaccustomed loadings and elevating
injury risk. And although empirical evidence remains scarce,
there is a suggestion of rising injury rates following short-term
technical interventions (see Tucker, 2007).
Driving Neuro-plastic Change
Crucially, the perspective presented here suggests we should
perhaps pay less attention to how running styles look, and more
attention to designing interventions that provide the coordinative
challenge necessary to sufficiently stimulate the neuro-plastic
re-modeling necessary to persistently refine communicative
clarity between CNS and the peripheral musculature. Although
such interventions typically fall outside the scope of conventional
run-training dogma, many coaches, past and present, have
intuitively designed training practices fulfilling the criteria
for optimally stimulating neuro-modulatory processes (see for
example: Kiely, 2013; Pfaff, personal communication; Smith,
personal communication). What emerging scientific insight
does add, however, is a growing appreciation of the value of
regularly challenging running coordination through the design
and implementation of appropriately constructed practices.
Visual Evaluation of Running Technique
Conventionally, we associate running coordination with running
technique—the visual evaluation of running style evaluated
against an aesthetic ideal. This pervasive assumption, however,
has never been satisfactorily demonstrated, and no empirical
evidence supports a direct relationship between looking ‘better,’
and actually being ‘better.’
When we visually assess a runner’s technique, and extrapolate
these observations to running efficiency and injury risk
conclusions, we make judgments based on very superficial
information. Typically we fail to acknowledge the unseen
underlying terrain—the idiosyncratic neurology; the embedded
fractal signatures; the unique anatomical architectures and tissue
structures; the plastically personalized legacy of historical habits
and traumas—upon which coordinative habits are founded.
And while it is feasible that, to the highly practiced eye,
visual evaluation may provide clues, generally how these
clues are interpreted is rooted in assumptions currently
lacking an evidence base. Certainly, visual assessments of
running proficiency seem unavoidably subjectively biased and
previous investigations demonstrate differences in technical
ratings between coaches, and even when the same coach
evaluates the same footage at different times (Norris et al.,
2014).
Would performances improve if running form more closely
conformed to perceived technical ideals? Are more aesthetically
pleasing runners less injury prone; more economical? While
opinions are plentiful, evidence is scarce. Anecdotally, renowned
coach and physiologist, Dr. Jack Daniels, once sent video of 20
physiologically evaluated competitive runners to a selection of
coaches and exercise scientists, asking them to—on the basis of
visual inspection—rank athletes in order of running economy but,
“they couldn’t tell, no way at all” (Kolata, 2007).
Finally. . .
The perspective offered within this review is that coordination
is the overarching super-capacity ultimately orchestrating how
proficiently neural, muscular, cardiovascular, and metabolic
reserves are purposefully harnessed, or wastefully squandered.
In relation to running: coordination is the learned deployment
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Kiely The Robust Running Ape
of available neuro-biological resources to satisfactorily realize
running objectives for an acceptable ‘cost’—in terms of depletion
of energetic and neural reserves, and exposure to risk. It is the
physical expression of a confluence of psychological, emotional,
neural, and biological constraints emerging in response to the on-
going interplay between intention, motivation, and perception
of risk; informed by emerging sensory feedback; modulated by
prior experiences and expectations; biased toward repeatedly
re-employing plastically embedded coordinative solutions to
current running ‘problems.’
Ultimately, running performance is underpinned by
a conglomeration of assorted capacities—cardiovascular,
neurological, psychological, physiological, anatomical, muscular,
and biomechanical. Yet it is the super-capacity of coordination
that regulates how proficiently these overlapping performance
contributors are collaboratively expressed to generate propulsive
power, promote efficiency, preserve robustness, and accomplish
running objectives for an acceptable exposure to discomfort and
risk. A deeper appreciation of the underpinnings of the running
coordination phenomenon will hopefully enable practitioners to
more judiciously design interventions to promote, nurture, and
preserve coordinative proficiency in the face of the inevitably
accumulating ‘wear and tear’ endured over the course of a
running lifetime.
AUTHOR CONTRIBUTIONS
The author confirms being the sole contributor of this work and
approved it for publication.
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Conflict of Interest Statement: The author declares that the research was
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