BRINGING SCIENCE TO TREATMENT

Neuroplasticity part II: brain matters for effective rehab

In part one of this 2-part series on the importance of neuroplasticity in sports injury rehab, Chris Mallac explained how the ability of the cerebral cortex and cerebellum to reorganize and adapt has implications for athletes in the context of skill acquisition for an effective return to sport. In part two, Chris explores more key principles of neuroplasticity and how they should shape rehab protocols.

As we saw in part one of this series, an understanding of the concepts of neuroplasticity was initially used to direct the rehabilitation of severely brain-injured patients, such as those suffering from a traumatic head injury and stroke. However, these same principles can also be extrapolated to skill acquisition in injured athletes to ensure they learn and retain motor engrams and help prevent re-injury.


Part I of this series outlined the first five principles of neuroplasticity:

  1. Use it or lose it
  2. Use it and improve it
  3. Specificity
  4. Repetition matters
  5. Intensity matters

Part II highlights the remaining five principles:

  1. Time matters
  2. Salience matters
  3. Age matters
  4. Transference
  5. Interference

*Time matters

When rehabilitation is started as soon as possible after an injury, patients experience better retention and functional recovery than in those who have delayed rehabilitation(1,2). The reasons for this dependence on timing are two-fold:

  1. In skill acquisition, molecular, cellular, structural, and physiological events take place in a particular order. For example, when learning motor skills, the sequence of events in order is as follows: gene expression followed by synapse formation, which prompts motor map reorganization (see figure 1)(3). The sooner this process starts, the better it is for learning new skills and avoiding the degradation of existing skills.
  2. Delayed rehabilitation is more likely to result in self-taught compensatory behaviors, which may retard future effective skill learning(3). For instance, after knee surgery patients typically lack terminal extension due to knee stiffness and quadriceps atrophy. They may adopt an antalgic gait that is difficult to correct months after surgery – even though the patient has regained full extension and quadriceps strength. The antalgic gait, which once was a result of pain, now becomes an ingrained motor pattern that is difficult to change.

Figure 1: Cellular and physiological event sequence for motor skill acquisition

 


In the world of professional sport, rehabilitation will likely begin on day one (due to the extensive resources available to the athlete, such as physiotherapists and rehabilitation coordinators). However, the non-elite athlete will often wait until after given the all-clear from the consulting surgeon before visiting the physiotherapist – thus losing the opportunity to start rehabilitation immediately. Ideally, to capitalize on the ‘time matters’ principle, the physiotherapist should:

  1. Educate referring physicians as to the importance of timely rehabilitation after injury or surgery.
  2. Encourage the patient to undergo a pre-operative workup, and ensure they are in the best physical shape they can be the day they have surgery.
  3. Explain to the patient that they need to start safe and optimal loading on the affected injury and commence rehabilitation as soon as possible after surgery.

*Salience matters

Salience refers to the quality of being perceived as important or having some meaningful value. For those who require rehabilitation, the importance of the chosen activities needs to be understood and even rewarded. Simply going through the motions of an exercise is not sufficient to gain long-lasting neuroplastic change in skill acquisition. There are many ways to incorporate the principle of salience into a rehabilitation program. Some examples include:

  • Provide rewards when athletes meet specific physical markers or achievement milestones.
  • Use role models to mentor injured athletes. Elite soccer programs utilize this approach when a young player suffers an injury. For example, they may pair a junior player who suffered an ACL rupture with a senior player who suffered and recovered from a similar injury.
  • Explain why certain rehabilitation exercises are recommended. If the athlete understands why a particular activity is performed, then they will ‘buy in’ to the rehabilitation in a more favorable way.
  • Add competition and interest. For instance, rather than change of direction drills, engage athletes in late-stage ACL rehab in a game of non-contact one-on-one basketball or table tennis.

*Age matters

This principle fits with the adage ‘you can’t teach an old dog new tricks.’ Simply stated, the older the athlete is, the more difficult it is to obtain long-lasting neuroplastic changes in the brain. The molecular, cellular, structural, and physiological changes required during skill acquisition training are not as easy to generate in older athletes(3). As an illustration, rat experiments have shown that some neuronal sprouting in the hippocampus of the brain after brain lesions will start at about 2-4 days after the lesion in young rats, while in older rats, the same injury creates sprouting at 20 days post-injury(4). The practical consequence of this is that older athletes may simply need more time and more intense exposure to rehabilitation to enjoy the same degree of functional recovery as a younger athlete with a brain exhibiting higher levels of neuroplasticity.

*Transference

Transference is the ability of neuronal plasticity in one set of cerebral circuits to promote and encourage plasticity in other areas of the motor cortex(3). The majority of studies investigating this phenomenon in the stroke and head injury population have examined the use of transcranial magnetic stimulation (TMS) in improving motor function. In rats, retraining a motor skill is enhanced if another part of the cortex is stimulated simultaneously(3). The use of TMS in the injured athlete is not an option for the rehabilitation therapist; however, the therapist can modify certain aspects of the rehabilitation protocol to benefit from the principle of transference, including:

  • The use of challenging and multi-stimulus environments. When a brain-damaged rat is housed in a complex environment, they regain functional recovery better than rats housed in simplistic and non-complex environments(4). To utilize this principle in the rehabilitation setting, provide multiple visual and auditory cues for the athlete.
  • The early adoption of aerobic training. Simply encouraging aerobic exercise promotes blood flow responses in the cerebral cortex and cerebellum(6,7). Exercise stimulates angiogenesis, improves neuronal growth, and slows neuron degradation in the cerebral cortex and cerebellum. Therefore, recommend safe aerobic cross-training in the early rehabilitation program to promote angiogenesis and assist in the transference of skill acquisition across the cerebral cortex.

*Interference

This principle may seem somewhat contradictory. This principle explains how plastic changes in the neural circuitry of one part of the cerebral cortex impede the generation of new skills or relearned skills. In other words, rehabilitation that improves the development of one skill may interfere with the performance and development of another skill. This principle supports the principle of specificity.

A practical example of this – and certainly a debatable topic in the rehabilitation world – is the use of unstable surface training to improve proprioception in the knee or ankle injured athlete. Some hypothesize that an over-reliance on unstable surface training, such as wobble boards and BOSU balls, may impede the functional development of stability and proprioception on stable surfaces, such as the football field or basketball court. It may, therefore, be more logical to progress athletes onto firm land training as quickly as possible and avoid polluting the skill acquisition through the use of non-specific training modalities. For more reading on this topic, we refer the reader to this opinion piece written by David Joyce.

The ten commandments

Rehabilitation professionals do not generally utilize the principles of neuroplasticity. However, for the clinician, these principles may play a large part in the successful rehabilitation of athletes. It is possible, therefore, to use the ten principles of neuroplasticity outlined in parts I and II in this series and create the following ’10 commandments’ of rehabilitation:

  1. If unable to strengthen the affected limb, train the other limb (use it, or lose it).
  2. Train it, and then keep training it when the athlete returns to competition (use it and improve it).
  3. Don’t use cookie-cutter rehabilitation programs. Make the rehabilitation activity as specific as possible in terms of planes of motion – sagittal, frontal, and transverse – and directions – vertical, horizontal, and multidirectional- (specificity).
  4. Perform lots and lots of repetitions (repetition matters).
  5. Adequately load and challenge the athlete without creating or exacerbating an injury (intensity matters).
  6. Start as soon as possible after injury or surgery (time matters).
  7. Rehabilitation activities need to be understood, rewarding, and motivating (salience matters).
  8. Older athletes may take longer to rehabilitate (age matters).
  9. Integrate multiple sensory inputs during motor learning and encourage aerobic cross-training exercise during periods of rehabilitation (transference).
  10. Don’t pollute the skill set with unnecessary rehabilitation exercises (interference).

References

  1. Journal of Rehabilitative Medicine. 2003. 35(supp 41), 7-10
  2. Journal of Neurophysiology. 2005. 94, 255-264.
  3. Journal of Speech, Language and Hearing Research. 2008. 51. S225-239.
  4. The Journal of Comparative Neurology. 1982. 205, 246-252.
  5. Progress in Neurobiology. 2004. 72. 167-182.
  6. 2003, 117. 1037-1046.
  7. Proceedings of the National Academy of Sciences. 1990, 87. 5568-5572.
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