Functional Variability

To achieve performance goals in competitive sport there is a need to strike a delicate balance between movement pattern stability and variability because, although  athletes  need  to  achieve  consistent  outcomes,  they  also  need  to  be  able  to  successfully adapt  their  movements  to  changes  in  the  performance  environment.  To  achieve  these  aims,  the theory of ecological dynamics advocates that there is an intertwined relationship between the specific intentions,  perceptions,  and  actions  of  individual athletes  that  constrains  this  relationship  between movement pattern stability and variability in each individual  performer.  This  intertwined  relation between an individual’s intentions, perception, and action processes needs to be carefully understood because  of  the  insights  it  provides  on  expert  performance in sport.

Traditionally, a high level of expertise in sport has  been  associated  with  the  capacity  to  be  able to  reproduce  a  specific  movement  pattern  consistently and to reduce attention demands during performance  by  increasing  the  automaticity  of movement.  It  was  assumed  that  the  central  nervous  system  (CNS)  functioned  as  an  executive organizer  and  prescriber  of  motor  programs  and action  plans  charged  with  the  task  of  producing stable  movement  patterns  from  an  individual’s effector system. From that viewpoint, expertise in sport  was  associated  with  a  reduction  in  deviations in task performance from an ideal standard or  movement  template  which  was  represented in  the  CNS.  By  harnessing  integrated  feedback systems,  athletes  were  considered  to  modify  the motor  program  entry  parameters  until  expert behavior  was  eventually  achieved  after  many hours  of  practice.  Traditionally,  therefore,  movement variability was considered as noise in performance  and  learning  which  should  be  minimized or  eradicated  to  enable  the  production  of  highly functional  movement  programs  (movement  variability  was  considered  to  be  an  artifact  limiting an  individual  system’s  processing  of  information from input to output).

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However,  research  in  ecological  dynamics  has shown  that  movement  system  variability  should not necessarily be construed as noise, detrimental to performance. Nor should it always be viewed as error or a deviation from a putative expert model, which  should  be  constantly  corrected  in  learners. Inspired by insights from the Russian physiologist Nicolai  Bernstein,  movement  system  variability instead  is  now  considered  to  exemplify  the  functional  flexibility  of  a  skilled  athlete  to  respond to  changes  in  dynamic  performance  constraints. For  this  and  other  reasons,  the  concept  of  functional  variability  has  gained  a  significant  amount of empirical support in the sport psychology field. A  key  idea  is  that  movement  pattern  variability can  be  viewed  as  a  functional  property  of  skilled performers  to  help  them  adapt  their  movement behaviors  to  changing  task  constraints  (see  entry on  “Task  Constraints”).  Traditional  research  has typically  focused  on  the  amount  of  movement variability  exhibited  by  an  athlete  during  performance, assessed by statistical measures such as the standard  deviation  or  variance  around  a  distribution  mean.  According  to  Karl  Newell’s  (1986) Constraints on the Development of Coordination, these  statistics  indicate  the  amount  of  noise  in  a single  measurement—that  is,  the  standard  deviation  only  indicates  the  magnitude  of  variability recorded during task performance (the amplitude, the  spatial  aspect  of  the  scores  in  a  performance distribution.  It  provides  little  information  on  the structure of movement variability exhibited by an athlete, which is needed to understand whether it is  functional  or  not.  For  this  reason,  Newell  and his  co-investigators  recommended  studying  the temporal  structure  of  movement  pattern  variability  by  analyzing  the  spectral  range  of  noise, which  provides  information  on  the  deterministic (preplanned)  or  stochastic  (emergent)  nature  of movement  variability.  Also  pointed  out  was  that it  would  be  wrong  to  consider  that  deterministic processes  specify  the  invariance  of  a  movement pattern   and   that   stochastic   processes   specify its  variance.  Given  these  theoretical  advances  in understanding   movement   pattern   variability, ecological  dynamicists  have  argued  that  there  is no  ideal  motor  coordination  solution  (a  classical technique) that all athletes should aspire to during learning.  Rather,  functional  patterns  of  coordination  emerge  during  practice  from  the  interaction of  constraints  on  each  individual  athlete  (task, environmental,  and  organismic),  leading  to  intraindividual  and  interindividual  movement  pattern variability as consistent performance outcomes are achieved.

Recently,  the  functional  role  of  movement pattern  variability  has  also  been  supported  by research  highlighting  the  property  of  neurobiological  system  degeneracy,  technically  defined  by Gerald Edelman and Joseph Gally as the capacity of  system  components  that  differ  in  structure  to achieve  the  same  function  or  performance  output. This structural property in humans indicates the availability of an abundance of motor system degrees of freedom—that is, the many components of the movement system (alluded to by Bernstein), which can take on different roles when assembling functional actions during sport performance (captured by system degeneracy).

Allied to these ideas on neurobiological degeneracy,  research  on  sport  performance  has  begun to  explain  why  expert  performers  often  display higher levels of intraindividual movement pattern variability  than  novices  in  sport,  data  traditionally  viewed  as  counterintuitive.  The  movement variability  exhibited  by  skilled  individuals  can play  a  functional  role.  For  instance,  it  highlights an  expert  athlete’s  capacity  to  perform  several types of movement or to adopt one of a number of coexisting modes of coordination, that is, exploit system  multistability  (the  many  functional  states of  system  organization)  and  metastability  (the capacity  to  switch  between  functional  states),  in order to achieve the same functional performance outcomes. In the past years, empirical research on sport  performance  has  clearly  exemplified  how intraindividual   and   interindividual   movement variability  can  play  a  functional  role  in  the  performance of team-based and a range of individual physical  activities,  such  as  a  cyclical  movement task  in  an  aquatic  environment  (breaststroke swimming)  and  a  continuous  discrete  task  in  the wilderness  (ice  climbing)  (see  studies  by  Duarte Araújo,  Keith  Davids,  and  Ludovic  Seifert  and coworkers).  These  key  ideas  on  functional  variability  have  now  been  integrated  into  a  motor learning  theory  by  Wolfgang  Schöllhorn  et  al., known as Differential Learning, which advocates adding  noise  to  initial  performance  conditions to  provoke  learning  by  forcing  the  individual  to adapt unexpectedly.


  1. Bernstein, N. (1967). The co-ordination and regulation of movements. New York: Pergamon Press.
  2. Edelman, G.M., & Gally, J. A. (2001). Degeneracy and complexity in biological systems. Proceedings of the National Academy of Sciences, 98, 13763–13768.
  3. Newell, K. M. (1986). Constraints on the development of coordination. In M. G. Wade & H. T. A. Whiting (Eds.), Motor development in children: Aspects of coordination and control (pp. 341–360). Dordrecht, Netherlands: Martinus Nijhoff.
  4. Schöllhorn, W. I., Beckmann, H., Michelbrink, M., Sechelmann, M., Trockel, M., & Davids, K. (2006). Does noise provide a basis for the unification of motor learning theories? International Journal of Sport Psychology, 37, 1–21.
  5. Seifert, L., & Davids, K. (2012, September). Intentions, perceptions and actions constrain functional intraand inter-individual variability in the acquisition of expertise in individual sports. The Open Sports Sciences Journal, 5, 68–75.
  6. Vilar, L., Araújo, D., Davids, K. & Button, C. (2012). The role of ecological dynamics in analysing performance in team sports. Sports Medicine, 42, 1–10.

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