Lecture 11c, Principles of Speed & Accuracy (Force)

Question 1

Force Variability

Answer 1

as force increases, variability in forces also increases (up to a point - ~70% of max)
- force variability only increases up to a certain point in our maximum force (peaks at 65-70% and will decrease afterwards)

Question 2

With the exception of very fast (near max forces) movement positional variability (We) increases linearly with force/MT

Answer 2

“muscular forces produce movements & variability in muscular forces produces variability in movements”
- need to translate mean movement time to percentage of maximum force
- if you are moving very fast, you would have to apply quite a lot of force - essentially fast movement time means high % of max force applied
- when movement time is slow it means you did not apply much of your maximum force
- maximum force high on left and low on right end of graph
- variability of our movement tends to increase as we apply more force but as some point variability will begin to decrease

Question 3

Scaling force parameter (of football throw) for distance

Answer 3

when we want a certain outcome we will have to adjust our parameters for the motor program
- when we want to throw a football to 10m based on our GMP and schema we may apply a parameter of A which is smaller than parameter of B for an outcome to 30m
- even though we have never thrown a football to 20m we can use a schema to apply C to our force parameter
- since we apply twice the force for 20m compared to 10m we should see twice the variability in our force parameter assigned to 20m compared to 10m - should be greater execution error or effective target width to the 20m (less accurate throwing to 20m than to 10m)

Question 4

In the slower Fitt’s type tasks, we optimize/balance size of initial forces & feedback corrections

Answer 4

• this is known as hybrid control where we combine both open and closed loop processes
  goal: bring the limb to target in efficient way (i.e. shortest time without overshooting)

how? trade-off speed for accuracy by optimizing duration of both the primary force (impulse) and corrective movements (amount of time spent in corrective movements)

primary force/impulse: open-loop
- initial ballistic programmed impulse…intentionally short
corrective submovement(s): closed-Loop
- visual feedback can be used to “home-in” on final target