Equilibrium Point Hypothesis (EPH) Feldman (1966, 1986, …): λ-Model Bizzi (1978, 1979, …): α- Model ∑F=0 : در حالت تعادل

EPH and Muscle Stiffness F = k ( X – X0) :رابطه يك فنر (عضله) K = σ (α ) X0 = β (λ)

Load Effect βv = Θf - Td/σ

Evidence for EPH (Polit & Bizzi 1978-9)

EPH Generalization

Questions Unanswered? 1- Role of Motor Centers in the Brain? 2- Motor Learning? 3- Environmental Effects?

Fitt’s Law Speed-Accuracy Trade-off

Fitt’s Law Speed-Accuracy Trade-off

Fitt’s Law (cont.) MT = a + b [ log2 (2A/W) ] MT = Movement Time ID ( Index of Difficulty) = A/W log2: Inspired from information theory

Fitt’s Law (cont.)

Fitt’s Law (cont.) Larger limb showed more sensitivity

Learning & Fitt’s Law (cont.) Kelso (1984) Slope was reduced to nearly zero following 40,000 trials.

Aging & Fitt’s Law (cont.) Kelso (1984) Aging increases the slope

Modification to the Fitt’s Law MT = a (A/W)b Modification effect is minor (10%)