This section is from the book "The Hygienic System: Fasting And Sun Bathing", by Herbert M. Shelton. Also available from Amazon: The Hygienic System Vol III Fasting and Sun Bathing.
For a number of years I continued exercise through the fast of most chronic sufferers. My rule was: "Chronic sufferers, unless otherwise contra-indicated, should have daily exercise while fasting." I insisted that the exercise should be mild and carefully adapted to the strength of the patient and preferred those forms of exercise that could be taken while lying in bed. I employed the corrective exercises that may have been needed in most cases during the fast. My rule was that fatigue should be avoided.
I became convinced that this was not good practice in most cases. It is now my practice to require all sick fasters to rest. Only those vigorous individuals who are undergoing a fast of ten days to two weeks as a Spring house-cleaning, and fat individuals who are fasting for reduction of weight are now given exercise while fasting. While the fast is in progress, the emphasis is placed on rest. After eating is resumed, exercise is given.