Which balance conditions had the largest difference between them?
- normal surface eyes open
- normal surface eyes closed
- foam surface eyes open
- foam surface eyes closed
- biggest difference was between eyes open and eyes closed on a foam surface. because of the difference in proprioception.
- Not the best measure of balance was used as only incorporated 1 trial and 1 participant.
Examine the pros and cons of measuring static balance using:
- SD
- range
- sway velocity
- ApEn
- Lyapunov Exponent
What trends can be seen?
- SD: increases throughout the conditions
- range: also increases throughout the conditions
- sway vel: increases throughout conditions
these are the trend we would expect to see - ApEn: fluctuates, increasing then decreasing
- Lyapunov Ex: also fluctuates throughout
these measures are more sufficient for measuring a dynamic eq
Although using these comparison measures makes balance able to be compared with all members of the population
Balance is often referred to as COM, but static balance is measured in COP. Can these be used interchangeably based on your lab results?
- NO, as results show similar trends but not the same results.
- cannot be used interchangeably but e.g.: sway vel can be applied to other measures
Using a PID controller (Peterka, 2000) how does changing the proportional, integral and derivative affect the COM and COP motion?
Increased Proportional:
* increased COP amp & freq
* increased COM, freq & amp stays same
* Increased sway vel
Increased derivative:
* Damped COP
* Damped COM
* Reduced sway vel
Increased Integral:
* COP towards the zero-line reducing drift
* COM towards the zero-line reducing drift
* higher sway vel to start with then decreases
What are some issues with the way the lab implemented the field and lab based hop and stick test?
What could be improved?
- Normalise hop distance by taking max rep and have it as a percentage of max hop distance
- Normalise jump height and get participant to jump over something
Define:
- COM
- COP
- Entropy
- ApEn
- the weighted sum of all the mass in the body
- a point on the ground where resultant forces act (sum of all forces exerted by ground)
- a measure of unpredictability of info and relates to the loss of info over time
- estimate of the entropy in a signal (complexity/regularity of data). 0 = periodic signal, increased value = less predictability.
–> measures how small sections of a trajectory repeat over the whole trajectory
Define:
- Lyapunov Exponent
- Time to stabilisation
- measures exponential divergence of nearby trajectories. Relating to the chaos theory. LyE = 0 (periodic signal, with 0 trajectory divergence), as value increases trajectory paths become more chaotic and random
- a measure of dynamic balance, the time it takes a person to return to a stable balanced position after landing (using 3 velocity vectors: Fx, Fy, Fz-BW) to get the magnitude of force.
–> a 5% threshold of BW is used to determine when a person has regained balance
What was the rationale behind the (Harbourne & Stergiou, 2003) study?
- assumes that posture is controlled by 2 CPGs, selection of an appropriate pattern and the modulation of that pattern.
- a genetically determined behavior, revealed as the NS matures.
- independent sitting requires dynamic stabilization of all linked body segments (complex learning & adaptation to environmental forces) = visible from 5 months (tested at 3 points) -> As infants begin to walk, they begin to decouple the whole leg synergies seen in kicking to allow crawling and walking
How does age impact ability to maintain posture stability (Harbourne & Stergiou, 2003)?
- at 3-year-old children restrict the degrees of freedom by decreasing dimensionality and complexity.
- at age 5, the child is able to have more control over the body’s degrees of freedom, and shows increased dimensionality and complexity as reflected in the COP time series (an adultlike behavior).
- dynamic stability was measured using LyE
What is meant by
Surrogation?
The correlation dimension?
- a technique that can accurately determine if the source of a given time series is actually deterministic in nature
- a method to evaluate the number of degrees of freedom during posture or, in other words, to determine the dimensionality of the COP time series
What were the findings from the infant study (Harbourne & Stergiou, 2003)?
- The LyE values reduced (toward zero) with sitting emerging (a more periodic path of the COP - not random/noise).
- infants increasingly occupied trajectories close together within the state space. = more locally stable with experience
- correlation dimensionality decreased through the stages(freezing DoF), increasing adaptability/flexibility in maintaining postural control over the base of support in sitting
- ApEn decreased complexity of sitting, but increased complexity in exploring getting in & out of sitting, but only 5 study participants
What are the key finding of Peterka, 2002?
Postural Control Mechanisms (adaptive):
- achieved through dynamic feedback of visual, vestibular, and somatosensory system.
- study used pseudorandom rotations of the visual environment to induce (AP) body sway in participants = analysis of sensorimotor system’s response to control perturbations.
- sensorimotor system dynamically reweights sensory inputs depending on their reliability and context. e.g.: when visual becomes unreliable, system relies more on vestibular/ somatosensory inputs.
What are the clinical applications for Peterka, 2002 study?
- Understanding the principles of sensorimotor integration can help in developing better rehabilitation strategies for individuals with balance disorders.
- The findings can inform the design of assistive devices and interventions aimed at improving balance in populations such as the elderly or those with neurological impairments.
What was the key finding from the (Ross et al., 2005) paper?
- Subjects with functional ankle instability (FAI) exhibited significantly longer stabilization times compared to the control group.
- This indicates a compromised ability to quickly stabilize after landing, which is critical for preventing further ankle injuries.
- The study discusses several factors that may contribute to prolonged stabilization times in individuals with FAI, including deficits in neuromuscular control, proprioception, and muscle strength.
What are the clinical implications from the (Ross et al., 2005) study?
- The primary goal was to evaluate the differences in jump-landing stabilization times between subjects with functional ankle instability (FAI) and those without.
- These findings highlight the need for targeted rehabilitation programs focused on improving neuromuscular control and proprioceptive training to reduce stabilization times and prevent recurrent ankle injuries in individuals with FAI.
What are the key findings of the Abernethy & Russell, 1987?
- Experiment 1: manipulated the duration of visible stroke sequences, Experiment 2: masked specific display features.
- Results = experts extract more relevant information from earlier cues (167 ms & 83ms pre-impact), from playing side arm and racquet, so are better at predicting stroke outcomes than novices(only extracted info 83ms pre-impact).
- experts had better lateral and depth error but the extent of their superiority depends on the severity of the temporal occlusion.
What are the main conclusions from experiment 1: manipulating duration of visible stroke sequences (Abernethy & Russell, 1987)
- the critical time for extracting directional information = between 83 ms before & 83 ms after racquet-shuttle contact
- the critical time for extracting depth information = last 83 ms before racquet contact
- advance cues resolve depth uncertainty (forcefulness), early flight cues resolve uncertainty of the shuttle direction
- There are consistent differences in prediction accuracy between expert & novice players for all occlusion conditions (t2-t5), difference that experts better extract early lateral & depth information (167-83 ms prior to contact)
What are the conclusions from experiment 2: masked specific delay features (Abernethy & Russell, 1987)?
- Novices relied on the opponent’s racquet for anticipatory information = ignores cues from opponent’s playing-side arm,head, or lower body
- Experts extracting no information from opponent’s head and lower body, but get anticipatory information from raquet arm & raquet = stroke force & direction prediction
- distal racquet cues(raquet action) = more reliable than proximal arm segment cues(arm action, available earlier than the racquet), so is a better preparatory cue.
What were the main findings from the (Savelsbergh et al., 2002) study?
- used gaze-tracking technology to analyze the visual search patterns of goalkeepers during penalty kicks.
- Expert = more efficient visual search pattern, focusing on specific kicker’s body movement and ball positioning + better anticipation skills compared to novices, accurately predicting the direction of the penalty kick more often.
- Because they picked up early visual cues from the kicker’s approach and movement, processing relevant visual information more quickly and ignore irrelevant cues = faster and more accurate decision-making.
What are the implications for training from the (Savelsbergh et al.,2002) study?
- The findings suggest that training programs for goalkeepers should emphasize the development of visual search strategies and anticipation skills.
- Specific drills that mimic game scenarios and require quick decision-making based on visual cues could be beneficial.
A methodological approach: - The novel methodological approach of using gaze tracking provided insights into the cognitive processes underlying expertise in sports.
- This approach can be applied to other sports to understand the visual and cognitive skills required for high-level performance.
Define:
- Temporal occlusion
- Spatial occlusion
- Reaction time paradigm
- where a movement sequence is cut short, the viewing time of an activity is controlled to see how participants use advance cues
- where physical movement aspects are removed to determine what advance cues are being used
- where subject makes a decision on what action to take, in sufficient time in order to respond to a stimulus. e.g.: penalties
How does success in determining shot direction change with length of occlusion?
Is there a point where visual info is redundant?
- after impact & after +80ms
- as length of occlusion decreases before impact success rate increases
- after impact there is no change so info becomes redundant
is there any evidence that badminton players are better able to use info earlier in the sequence of actions?
- higher at all occlusion aspects than class avg, as they are able to use info at all parts shown by their higher success%
When spatial occlusion was added, was there any change in the badminton players or class performance?
Why might this have happened?
- yes for badminton player
- on avg class gets better when spatial occlusion is introduced, as we are getting rid of useless info.
- there is some learning effect from multiple trials before spatial occlusions
