1. Error compensation during finger force production after one and four-finger voluntarily fatiguing exercise. E. S. Kruger, J. A. Hoopes, R. J. Cordial, and S. Li By Kelsey Christensen

2. Motor Variability Bernstein “repetition without repetition”. Background

3. Motor Variability Bernstein “repetition without repetition”. Degrees of Freedom (DOF) Number of independent elements in a system. Background

4. Motor Variability Bernstein “repetition without repetition”. Degrees of Freedom (DOF) Number of independent elements in a system. DOF Problem/Problem of Motor Redundancy How does the CNS select a particular solution from the infinite number of solutions? Background

5. Introduction Error Compensation DOFs work together to accomplish a given task by compensating for errors made. Utilizing motor variability and redundant DOFs.

6. Introduction Error Compensation DOFs work together to accomplish a given task by compensating for errors made. Utilizing motor variability and redundant DOFs. How is error compensation affected when parts of the motor system are impaired (number of DOFs is reduced)?

7. Methods Apparatus Procedures Data Analysis

8. Methods Apparatus Procedures Data Analysis

10. Methods Apparatus Procedures Data Analysis

11. Procedures 13 young, healthy adults 2 sessions, 2-3 days apart Index finger fatigued All four fingers fatigued

13. 3 6 9 Force (N) Time (s)

14. 3 6 9 Force (N) Time (s)

15. 3 6 9 Force (N) Time (s) F tot F I F M F R F L F tot = F I + F M + F R + F L

17. Methods Apparatus Procedures Data Analysis

18. Force signals from individual sensors to analyze force profiles.

19. ΣVarFi = sum of the variances of individual finger forces VarFtot = variance of total force Error Compensation Index (ECI) = ratio of ΣVarFi to VarFtot. From force profiles:

20. Results

21. Variance (A) and Error Compensation Index (B) averaged over entire force ramp and across all subjects.

22. Average Error Compensation Index over the 1 st, 2 nd, and 3 rd one- second segments of the ramp phase (seconds 4,5,6).

23. Discussion

24. Summary The CNS is able to utilize the abundant DOFs to compensate for motor system impairments to maintain the desired performance. Problem of Motor Redundancy is a GOOD thing. Principle of Abundance – but there is a limit.