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• Explicit motor learning interventions are still relevant for ACL injury rehabilitation: do not put all your eggs in the implicit basket!: Letter to the Editor
  Anne Benjaminse
  Published on: 17 January 2023

• Published on: 17 January 2023

  Explicit motor learning interventions are still relevant for ACL injury rehabilitation: do not put all your eggs in the implicit basket!: Letter to the Editor

  • Anne Benjaminse, PostDoc researcher / physiotherapist / human movement scientist University of Groningen, University Medical Center Groningen, Center for Human Movement Sciences, Groningen, Netherlands

  Anne Benjaminse,1,2 Alli Gokeler3, 4, 5
  1 University of Groningen, University Medical Center Groningen, Center for Human Movement Sciences, Groningen, Netherlands

  2 School of Sport Studies, Hanze University Groningen, Groningen, the Netherlands 

  3 Exercise Science and Neuroscience, Department Exercise & Health, Faculty of Science, Paderborn University, Paderborn, Germany

  4 Amsterdam Collaboration for Health and Safety in Sports, Department of Public and Occupational Health, Amsterdam Movement Sciences, VU University Medical Center, Amsterdam, The Netherlands.

  5 OCON Center of Orthopaedic Surgery and Sports Medicine, Hengelo, The Netherlands

  Dear Editor,
  We read the recent manuscript by Kal et al.1 ‘Explicit motor learning interventions are still relevant for ACL injury rehabilitation: do not put all your eggs in the implicit basket‘ with great interest. The authors did a commendable job summarizing the current literature and we highly respect them for being critical, to foster academic discussions to move science forward. We do however have some concerns regarding the methodology and interpretations made by the authors.
  Confusing definition: description vs. execution
 First, the authors write: "Elite athletes have shown to successfully use explicit interventions to de-automate, and subsequently improve, problematic movements.“.2 The paper by Toner et al. is largely based on assumptions, case studies and philosop...

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  Anne Benjaminse,1,2 Alli Gokeler3, 4, 5
  1 University of Groningen, University Medical Center Groningen, Center for Human Movement Sciences, Groningen, Netherlands

  2 School of Sport Studies, Hanze University Groningen, Groningen, the Netherlands 

  3 Exercise Science and Neuroscience, Department Exercise & Health, Faculty of Science, Paderborn University, Paderborn, Germany

  4 Amsterdam Collaboration for Health and Safety in Sports, Department of Public and Occupational Health, Amsterdam Movement Sciences, VU University Medical Center, Amsterdam, The Netherlands.

  5 OCON Center of Orthopaedic Surgery and Sports Medicine, Hengelo, The Netherlands

  Dear Editor,
  We read the recent manuscript by Kal et al.1 ‘Explicit motor learning interventions are still relevant for ACL injury rehabilitation: do not put all your eggs in the implicit basket‘ with great interest. The authors did a commendable job summarizing the current literature and we highly respect them for being critical, to foster academic discussions to move science forward. We do however have some concerns regarding the methodology and interpretations made by the authors.
  Confusing definition: description vs. execution
 First, the authors write: "Elite athletes have shown to successfully use explicit interventions to de-automate, and subsequently improve, problematic movements.“.2 The paper by Toner et al. is largely based on assumptions, case studies and philosophers' views.2 The authors presume that with adopting explicit learning, patients are not allowed to know the goal of the exercises.3 For clarity, the correct definition of attentional focus needs to be used: Attentional focus relates closely to what you tell your patient prior to the execution of the exercise. An internal focus would be induced to focus the attention on body parts and movements. Conversely, for an external focus, the attention is directed to the outcome or the goal of the movement. Hence, adopting an external focus is related to the planning of the movement, but has nothing to do with the processing of intrinsic feedback or bodily awareness.4 It does not mean that patients are not aware of their body movements, i.e. the ‘explicit interventions’ the authors refer to. It is important to note that bodily awareness is not necessarily inherent to an internal focus of attention.5 Leaning is not possible without bodily awareness.6 An external focus of attention simply means the patient is focusing on the intended movement effect – while preparing for the execution.6 This does not mean that one must never use body related instructions that elicit an internal focus of attention. Of course you can use it. It will just not result in most optimal motor learning.7,8
 In summary, it is important to differentiate between telling the goal of the exercise (i.e. description - general instruction) and the specific instruction provided just before the execution of the task. For example, in case of rehabilitation after ACLR: “the goal of this exercise is to improve knee bending while landing, as this promotes a softer landing, which is better for your knee.” Then, as the patient is preparing to execute the exercise, it is critical to shift their attentional focus that corresponds closest to the task goal: e.g. “focus on landing with as little noise as possible”.
  Familiarity
 Second, the million-dollar question, do effects of implicit learning depend on the person’s preference? Here, again, the entire picture needs to be presented. Kal et al. conclude “Implicit or explicit learning appears most effective when it is aligned with an individual’s preference“, even though the original authors state: “Due to the well-documented external focus advantage we are hesitant to argue that direction of attentional focus does not have any influence on skilled motor performance.”.9 The preferred focus, often as a result of past experience with coaching instructions,10 is not always the most beneficial solution.11-15
 In addition, retention, a key aspect of motor learning, has not been reported.9 It is thus not possible, and it may give a skewed representation, to conclude learning is most effective when aligned with an individual’s preference, as the definition of learning is ‘a relative permanent change in a person’s capability to perform a skill’.16 To interpret results, the authors need to adhere to the correct definition of motor learning. Directly observable performance improvement is different from sustained improvements over time (retention).16 Often times explicit learning is indicated as being effective, potentially because it shows quick benefits.17
 The authors also write: “People with musculoskeletal conditions strongly prefer to consciously control movements.” But again, we need to ask the question if this preference is of benefit to them? Kal et al. should also have stated the conclusion of the paper they refer to: knee pain was more commonly reported by people with a propensity for conscious involvement in their movements.18 Thus, even it is the case that patients prefer to consciously control movements, it is not per se most effective.19 Loss of function, pain, fear of reinjury and other psychological factors, cause a shift in attentional focus towards the injured area such as the knee.19-22 The process behind this needs to be explored in further detail before we can say whether it is beneficial to consciously control movements. After musculoskeletal injuries neuroplastic changes of the central nervous system occur,23 which induces a focus on the injured joint. An ACL injury triggers neurocognitive disruption,23 demonstrating potentially maladaptive neuroplasticity within the brain whereby (pre)motor cortex areas are more active during simple movement tasks compared to uninjured individuals.24 Concluding, it would be unwise to leave patients to their own focus preference or assume they will find the focus that is optimal for them.

Verbal and visual feedback
 The authors pose that explicit verbal feedback on movement has been identified as a key active ingredient in primary ACL injury risk reduction.25 However, again correct interpretation of scientific studies is crucial here. All these training programs are conducted in a relatively controlled setting (e.g. with supervision from researcher) with no retention and transfer effects measured.25 Also, no studies thus far have comparison included with implicit verbal feedback conditions.
 The authors also state that it is unclear whether improved biomechanics can be attributed to implicit learning per se as this can not proven through self-report.26 Indeed, self-report, although done often,27-29 is not the best way to provide objective evidence.30 But, it is widely known that model learning, as we did in this study,26 or observing and imitating movements facilitates an athletes’ exploration and search for their own most optimal functional task solutions,34-36is part of an implicit learning strategy.34 Studies using Electroencephalography and Transcranial Magnetic Stimulation conclude that movement outcome and efficiency are enhanced when an external focus of attention is promoted, 31-33, likely due to improved neural strategies, such as cortical inhibition.. When providing sound designed research with only the attentional focus instruction being different across groups, including a control group, one can conclude that difference across groups is based on that factor. Vice versa, how can we know athletes in previous research have indeed adopted an internal focus of attention?
 In sum, we feel the authors should have presented the entire picture to the readers based on sound synthesis of the literature and proper use of definitions.

  REFERENCES
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  Conflict of Interest:
  None declared.

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