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Mildren Et. Al. 2018

Learning to balance on a slackline: Development of coordinated multi-joint synergies

Tags: #slackline #dynamic_balance #joint_symmetries

coordination

Related: [[A Case Study on Balance Recovery in Slacklining - Huber Kleindl 2010]] [[Balancing on Slacklines Modeling and Empirical Evaluation - Vallery Neumann 2013]] [[Improved postural control after slackline training is accompanied by reduced H-reflexes - Keller Et. Al. 2011]]

Key Definitions

  1. In Phase Joint Pair: The same joints on either side of the body having a roughly 0 degree relative angle
  2. Anti Phase Joint Pair: The same joints on either side of the body having a roughly 180 degree relative angle

Key Takeaways

  1. There is limited research on skilled balance control for challenging tasks
    1. There is little understanding of how practice influences balance control
    2. Most research focuses on ankle strategies which rely on ground reaction forces (see [[Balancing on Slacklines Modeling and Empirical Evaluation - Vallery Neumann 2013]]
    3. These strategies are available only in some circumstances, and lead research to ignore multi-segmental control.
  2. Experiment had participants undergo 1 week of slackline practice
    1. As performance increased, trunk and foot oscillations were dampened and movement coordination increasingly reached the further upper body
    2. This was accompanied with joint pair angles either becoming in or out of phase
  3. Hip angle includes movements of spine and hips and thus covers very large balance adjustments, while elbow and shoulder cover much finer balance adjustments
    1. With practice, there was a shift from the grosser, hip and shoulder based movement controls vs to finer, elbow based control
  4. They performed a principal component analysis to identify prominent movement patterns, but only on the tandem stance since the non stance leg movements were not recorded
    1. The prominent movement pattern identified by 'PCA' was opposing movements between left and right shoulders, right and left elbow, and the hips
    2. This is accompanied with the large reduction of hip velocity with practice
  5. Phase plots were used for scaled joint angles, showing scaled velocity vs displacement.
    1. Joint angles settled to either in or out of phase. Because of the lack of lags, this indicates active control rather than passive movement due to internal linkages.
  6. Participant's balance times significantly improved through training, and in both tandem and single leg stance training reduced trunk angular velocity and foot linear velocity.
    1. Training consistently dampened the 4 Hz oscillation seen at the start of trials, as well as reduced angular velocity and frequency across joints.
    2. There was a general reduction in movement velocity across joints during practice with the largest effect at the hips
  7. The slackline trained group had significant improvements on the balance beam transfer task compared to the control group
    1. The balance transfer and skill retention after a week indicate generalized motor learning
  8. This is potentially the first study showing the development of arm based studies to compensate for a situation where lower body synergies are ineffective
  9. Prior research ([[Improved postural control after slackline training is accompanied by reduced H-reflexes - Keller Et. Al. 2011]]) indicated the ~4 Hz tremor may be due to stretch reflex oscillations. But this study showed that the oscillations disappear faster than that study showed the gain of of H reflexes decreasing.
    1. These authors propose it could be due to the development of internal representations of the consequence of body movements while on the slackline.

Limitations

  1. Very limited amount of skill - only one week of practice
  2. Movement of the leg off the line was not recorded (!)
    1. This limits the degrees of freedom of the model
    2. Misses counter balancing strategies found in Federholf Et Al
  3. Balance trials at the beginning of learning were significantly shorter than those at the end