Rack & Westbury Stimulation

Sequential stimulation with equal inputs.

• Used cat soleus muscle with split ventral root stimulation.
  • Denervate other muscles in the limb.
  • Expose ventral roots L7 and S1
  • Split and regroup to get n (typically 6) ventral root bundles that produce equal tension contributions
  • Stimulate these in turn.
  • Stimulation rate for each fibre, p, is low. (Referred to as basic stimulation rate)
  • Tension ripple has its lowest frequency component at np. Keeping this high keeps the ripple amplitude low. (n = 7, p = 3, np = 21 is shown)

Representation of distributed stimulation as a mechanical distributor.

Simulation of Rack and Westbury. Each individual input is a different colour, and produces an unfused train of twitches. The sum of the twitch trains is a near smooth tension. Twitches have a time to peak of 0.3 time units and a time to half relaxation of 0.3 time units.

• If inputs are unequal, then ripple components at p and its harmonics are introduced.

Simulation showing seven unequal inputs

• Limited to slow muscle, as it is much more difficult to get and keep equal components with fast and mixed muscles, due to greater "post-tetanic potentiation" and fatique, especially at low stimulation rates.

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