The cause of the development of post polio sequealae is not clear, but it may be something called 'neural fatigue'. The poliovirus attacks specific nerve cells(neurons) in the base of your brain and nearby areas of the spinal cord causing the death of a large number of the motor neurons controlling muscles for movement. The enlargement of the remaining motor neuron fibres places added stress on the nerve cell body to nourish the additional fibers. Consequently, years of use in this stressed state leads to the gradual deterioration of the enlarged fibers and eventually of the neuron itself. This results in muscle weakness and paralysis in your body.
Attribution: Avallain