McArdle's disease is a condition in which the sufferers have glycogen in their muscles, but are unable to access it as a fuel source. Typically they wind up being sedentary (which just makes the condition worse), but there are training approaches that can develop their non-glycogen sources of energy, and allow them to exercise without needing glycogen. (This is a compensation strategy, unlike the gene-knockout mice which have no glycogen stores, the people with McArdles disease will always try to access the glycogen store that they can't get to.)
So how do they train a McArdle's sufferer to not need glycogen?
"By increasing the fat content of his diet to 80% with 14% protein (1 g/kg/d) to totally 1.760 kcal, ketosis of 2-6 mmol/l 3-OH-butyrate was established. The principal effects comprise absence of carbohydrate-based stimulation of insulin secretion leading to activation of glycogen synthesis, and repletion of the tricarboxylic cycle with acetyl-CoA from ketone bodies. With a continuous one-year diet his exercise tolerance was 3- to 10-fold increased dependent of the endurance level...."And then there's this:
"McArdle’s patients easily become sedentary. This just serves to exacerbate muscle breakdown and worsen muscular quality. But you don’t need glycogen to exercise or build muscles. Simple running has proven very effective in one case report . Running also involves eccentric exercise which has a low energy cost for a given level of muscle force."Sadly:
"Although a ketogenic diet seems the natural choice for patients with McArdle’s, there are no real good studies of the strategy. A few small studies have examined high protein feeding with some very modest results , but high protein seems a bit of, as fat and ketones can replace glycogen more easily than proteins."
Of course, we know a high-fat diet will kill you. (I'm being sarcastic, btw.) Surplus protein in the diet is converted into glucose.
Seems like a Maffetone-style training program would be perfect for McArdle's sufferers. Maybe someday it will be tried... Maffetone, of course, is big on warming up:
"If you are one of the 1:100,000 who has McArdle’s, proper warm up is very important. Gradual warm up causes a gradual increase in fat metabolism which reduces the need for glycogen. This is also a tip to everyone on ketogenic diets who like to engage in vigorous exercise. Proper and gradually increasing warm up exercises makes sure as much fat as possible is ready for use. Patients with McArdle’s are known to experience a “second wind” which happens when alternative sources of energy are increasing in availability."