Tag Archives: muscle cramps

Muscle fatigue and weakness experienced during even moderately intense physical activity can in fact simply be caused by a lack of physical conditioning, but the human body is a robust machine that, when working properly, responds rapidly and efficiently to changing demands.  When muscle weakness is acute and to the point of failure (non-response), however, it is time to seek medical attention.

People with McArdle’s Disease may experience this type of muscle failure.  It is described in medical journals as “rapid onset muscle weakness and cramping,” but this doesn’t give a very clear description.  More accurately, it can be described as a diminished response from the active muscle group as a function of time.  For example, when someone with McArdle’s Disease tries jogging, their experience is more or less normal for anywhere between 10-30 seconds, depending on factors like incline, recent diet, physical condition, etc.  It is after this initial period that the individual with McArdle’s experiences an abrupt and rapid decrease in energy that is not so much about being “out of breath” as it is about muscles simply no longer responding.

I’ve put together a graphic representation of what this feels like.  Anyone with McArdle’s Disease knows that intense exercise elicits an exponential decrease in energy in a matter of seconds, usually well under one minute:

This is a rough, non-scientific graph that is rather subjective but nonetheless probably an accurate graphical description of the sensation of McArdle’s Disease symptoms.  The exponential curve representing energy capacity as a function of time during intense exercise corresponds to what I know about reaction rates; i.e., there is a fixed concentration of phosphocreatine as well as creatine kinase in the cell atany given moment, so as ATP generated from glucose metabolism is the limiting factor in the overall picture, as the concentration of phosphocreatine (which is used up creating ATP for immediate use) drops dramatically, so too does the “reaction rate” of physical energy available from the active muscle group.

Muscle fatigue and weakness experienced as a result of McArdle’s Disease seems to vary according to the intensity of the activity.  Walking on flat ground, for example, apparently has an energy demand per unit time that is low enough to allow the cell to overcome the obstacle in the traditional energy pathway and create enough energy per unit time to permit the continued activity.  Some physicians speculate that individuals with McArdle’s Disease can experience a “2nd wind” phenomenon following warm-up as a result of adaptive measures the body takes in response to physical activity.  In any event, between walking and jogging there seems to be a rather pronounced drop-off in energy per unit time.  Speaking for myself, I can tell you that no amount of conditioning to date has allowed me to completely overcome the dramatic drop in muscle energy which results from taxing activities such as jogging or climbing stairs.  Walking, however, is a different story.  The graph below compares the sensation of performing these activities with McArdle’s Disease:

As the graphic indicates, walking may elicit some pain and weakness initially but with calculated persistence, this is overcome and walking is easily sustainable for long periods of time.  I am even able to ascend moderately large hills, following such a warm up and using efficient “management” of the terrain and my energy.

The purpose of this page is to give physicians or other health professionals as clear a picture as is possible of what the symptoms of this disease are like.  The more is known about the disease, the better the quality of life for those with it.

As of 2008, the only realistic treatment for McArdle’s Disease is – somewhat ironically – exercise.

The physical (and emotional) discomfort associated with failure episodes characteristic of McArdle’s Disease often pushes people with the disease towards a sedentary life style.  If you consume sugary snacks or beverages as a way to try to up your blood sugar to power through episodes, you probably have it worse because the body ultimately outsmarts itself and interprets those snacks as “break time” and shuts your energy-creating enzymes down essentially, making you even more tired (this is not pseudo-science, but it IS an idiosyncratic characterization…there’s a difference.)

The reason sedentary people with McArdle’s Disease have so much discomfort exercising is the same reason any normal sedentary person does.  Their body has adjusted to just sitting around, and not having demands placed on it.  When you get up and push your body beyond the limits of what it is chemically prepared and equipped to do, you will feel initial resistance.  This is the same for all people, regardless of whether or not they have McArdle’s….only, with those of us who have the disease, this threshold is reached much quicker.

The way to effectively manage the disease is with diligence and patience and caution and perseverance.  There is in fact plenty of empirical data supporting the notion of a “second wind” phenomenon that people with McArdle’s disease experience following very careful, low-impact periods of warm-up exercise such as walking on reasonably flat ground for sustained periods of time.  Such folks are by no means “over” the symptoms, but they are able to walk almost indefinitely without experiencing failure symptoms.  It is in this “golden” period, following the warm up, that individuals with McArdle’s Disease are enjoying the normal benefits of exercise.

The secondary benefit of this is that, to some degree, their large muscle groups are now behaving somewhat like a normal person’s.  Blood circulation increases, the heart rate is up, and energy metabolism is occuring at a fast enough rate to sustain some physical activity.  It is in this “golden” period that an individual with McArdle’s disease MAY, depending upon their physical state of conditioning, be able to:

  • Play sand volleyball or moderately-paced basketball or soccer
  • Dance
  • Perform outdoor labor
  • Ride a bike up moderate or short inclines
  • Hike up and down reasonably large hills without failure
  • Swim (safely)
  • Paddle a canoe or kayak
  • Possibly even jog

It all depends on the individual.  Just like every other physical trait like hair (straight, or curly?), skin color (light or dark?), or height, how your body metabolizes energy and oxygen and how it reacts chemically to exercise is really inherently genetic and different from person to person.  So, know your limits, but by all means to carefully and diligently push your limits because this is how anyone – McArdle’s Disease or not – makes gains.

Keeping your body healthy is a little trickier with McArdle’s Disease, but the patience you are forced to employ in order to get exercise is something you will benefit from.  That’s more or less universal for all people with and without the disease.

Best of luck!