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Adjusting your activity to protect yourself

To those of us with McArdle's our disease often seems irrational and difficult to understand or predict. In fact, how the condition affects our activity IS explainable, and we can learn to look after ourselves, avoid injury and improve our condition. Explaining the mechanics of McArdle's gets a bit complicated.

Doctors tend to use a simplified approach which has the advantage of being easy for everyone to understand and remember:

"Don't do any anaerobic activity (lifting heavy weights, sprinting, etc) but do undertake aerobic exercise (walking, etc)."

However, to look after ourselves as well as we would like, better advice would be:

"Don't empty your ATP reservoir."

But this needs some explaining before we can understand it and follow it.


ATP Reservoir diagram

Energy pathways

The classification of activity into anaerobic and aerobic activity is a simplification. Anaerobic and aerobic actually refer to two energy pathways (ways in which we deliver energy to the muscles). Anaerobic means without oxygen - and this is the pathway which converts muscle glycogen into energy. In McArdle's we can't use this pathway, as we are missing an enzyme (myophosphorylase) which is needed in that process. Aerobic means with oxygen and this pathway converts blood-borne fuels into energy. This is the only energy pathway that people with McArdle's can use.

Energy store in the muscle cell

A chemical called ATP (Adenosine Triphosphate) is used in one of the last steps to activating the muscle. Everyone has a very small store of ATP in each muscle cell. This store of energy is normally topped up by the aerobic and anaerobic pathways. The aerobic pathway is slower at topping up the store than the anaerobic pathway. In McArdle's we can only top up the store through the slower aerobic pathway.

Reservoir visualisation

You can visualise the ATP energy store as a "reservoir". The anaerobic and aerobic energy pathways are like two supply pipes bringing water (energy) into the reservoir. The anaerobic pipe is large and people without McArdle's can turn on the tap to a full fast flow very quickly. In McArdle's that pipe is blocked up and nothing comes through. The aerobic pipe is smaller and slower flowing but works for us just like for everyone else.

When we exercise it is like taking water (energy) out of the reservoir by an outflow pipe. In order to not run out of water (energy) we have to ensure that the outflow demand is in balance with the supply. If the outflow is greater than the supply the water (energy) level will drop, and if we keep going like that the water (energy) will run out altogether. This is when we damage our muscles. When they run out of ATP they start to break down the muscle itself as a source of protein to create energy. (Open enlargeable PDF view.)

Avoid emptying the ATP reservoir

If we exercise at maximum effort (like sprinting as fast as we can, or lifting something very heavy) we empty our ATP reservoir within about 10 seconds. If we exercise less intensely it takes a bit longer to empty the reservoir. Whilst if we exercise very sedately we can keep our outflow and our inflow in balance and thus never run out of energy.

We can use two tactics to avoid emptying the ATP reservoir. Unfortunately we can't see how full the reservoir is, so we have to learn from experience how to gauge this.

1) We can slow down or reduce the intensity of what we are doing so that the demand for energy (the outflow from the reservoir) is slower than the rate at which the reservoir is being topped up by the aerobic inflow.

2) If we can't reduce the intensity (like walking up stairs) then we have to interrupt the demand (outflow) by stopping for a short rest. A few seconds of nil demand will allow the inflow to re-fill the reservoir.

That's it really, but if you would like to learn more... read on.

More information

Some practical examples

1) When using scissors, secateurs or a pump spray, we can change hands - thus fully resting one hand at a time. The ATP reservoir in muscle cells of the rested hand will fill up again whilst the other hand does the work.

2) When carrying something a bit on the heavy side your arms may be using up your ATP quicker than it is replenished. If you can hold the object next to your body, the friction will hold some of the weight and reduce the demand on your muscles. This may be enough to cut your ATP outflow rate to below the inflow rate.

3) When walking uphill, which would normally need anaerobic energy, we can slow our pace and/or zig-zag across the slope so as to reduce the effective incline.

4) When doing something like gardening or household chores, try to ring the changes so that different muscles are used. Maybe do a few minutes of vacuuming (which can be hard on the arms), then swap to say taking something to the other end of the house, which uses your legs and gives your arms a break.

You will soon learn your own techniques.

How much pain?

People with McArdle's tend to describe the sensation in their muscles as they exercise as "getting heavy", "getting tight", "running out of energy", "being exhausted", or "being painful". Unfortunately these sensations lag behind the damage we are doing. The more we push against it, the more pain we will have. Over time we can gradually get better at understanding and anticipating the feelings. It should be our aim to never incur pain which, once we stop what what we are doing, takes more than a minute or two to subside and disappear. If we get pain that lasts longer than that then we have done too much damage and must learn to ease off or stop and rest before this level is reached. We should aim never to have fixed contractures (which tend to last for hours or days), and never to have dark urine from myoglobinuria. Of course, it is not always easy to avoid these things, but one fixed contracture per year should be about the limit. If someone is getting more than that, then they are likely to benefit from a controlled exercise programme. There is some information on starting an exercise programme here. The fitter we get the easier it is to avoid pain.


Some McArdle people report that low-dose creatine supplementation helps them. It may increase the availability of ATP and has been shown to benefit the exercise capacity of healthy individuals undergoing resistance training. However, the Cochrane Review into pharmacological and nutritional treatments for McArdle disease reported "Although there was low quality evidence of improvement in some parameters with creatine ... none was sufficiently strong to indicate significant clinical benefit." If you are interested in trying supplements start by reading the Cochrane Review.

Second wind

At the outset our cardio/respiratory system is at tick-over level so the delivery of oxygenated blood and blood-borne fuels is slow. It takes a few minutes to get this ramped up, so the aerobic energy pathway will be slow to fill the reservoir in the early stages. We are therefore at risk of emptying our ATP stores. We have to be very careful in the first 10 minutes of exercise, until second wind is achieved. (Read about second wind here.) People unaffected by McArdle's will utilise their anaerobic pathway during this period. When we have achieved what is called "second wind" in McArdle's, our aerobic pathway will be working better than in the early stages of exercise and we are able to exercise much more easily.

Good days and bad days

Most of us report having good days and bad days with our McArdle's. Medical science has not yet shown us why this is, but there is a possible approach which some of us have identified and it seems to help. At any stage in the day, but particularly before achieving second wind, we sometimes find that we "just can't get going" - the symptoms seem much worse than normal. We seem to be really exhausted and the cramping sensation in our muscles comes on very quickly, we seem unable to get into second wind. It is likely to be that we are simply running our ATP reservoir almost on empty. We just get a little bit of ATP in and we immediately exhaust it again. We never have enough ATP to get into/back into second wind. The answer is to take a decent rest, preferably sit down for 10 minutes and perhaps have something to eat. After that time our ATP reservoir will be topped up again, perhaps even full. We now have some leeway so won't be at risk of repeatedly emptying the reservoir. As we start off again we should walk as though it was the start of the day and we need to get into second wind. This time we should find that it just seems like a normal day instead if a 'bad' day.

Adverse factors


Stress will tend to make the muscles tense. This interferes with the supply of blood to the muscles and thus activity would normally rely more on the anaerobic pathway - which of course we can't do. We are therefore more prone to muscle damage when under stress, so should perhaps try to postpone significant activity until the stress has passed.


Muscles do not work as well in cold temperatures. This affects us more than others, so keep warm in cold weather and be wary of swimming in cold water (and never in water you can't stand up in).

Each muscle is independent

Remember that the ATP store is in the muscle cell, in every muscle. Any techniques you use are not systemic, but will affect only the particular muscles being used. So slowing down, resting or achieving second wind all need to be considered for each muscle group.

More that you can do to help

The better conditioned we are the easier all activities will be and less likely we are to incur injury. Regular aerobic exercise is the only available solution known today and probably for the foreseeable future.


ATP is made in the muscle cell in things called mitochondria. There are typically about 750 to 1000 mitochondria in each muscle cell. The more mitochondria we have the easier it is to get through our everyday activities and keep up our exercise. The number of mitochondria is increased through muscle conditioning (also called training). At the two extremes, a "couch potato" would increase his or her mitochondria by 20-fold by training up to the level of an athlete.


The more exercise you do the better your cardio/respiratory system will become. The better you will be at delivering oxygenated blood and blood-borne energy to the muscle cells, thus reducing the risk of injury.



Last reviewed: 12 September 2011.