Category Archives: McArdle’s Research

This was forwarded to me today:

http://www.ccad.uiowa.edu/vsr/

They are attempting to commercialize the software. I’m mainly interested to see if computational modeling like they are doing could be applied to McArdle’s Research. I know they use Santos to see how much gear they can load onto a soldier, walk him around and see what he can physically handle. I imagine whatever numerical models drive that could certainly be modified to reflect our energy bottleneck, right?

Simulation capabilities are getting better every day and a high fidelity, biomechanically accurate human model could be really relevant for McArdle’s issues

This link discusses strength and fatigue modeling using a computerized simulation. ?Such a model might one day help doctors visualize the physical limitations imposed by the disease.

Women with McArdle’s disease often express concerns about pregnancy, since childbirth is an exhausting and physically demanding for even healthy individuals.  Below is a list of relevant articles about McArdle’s disease and pregnancy that seem to indicate that, in general, the condition is not necessarily exacerbated by nor does it necessarily complicate pregnancy and childbirth.

Can patients with McArdle’s disease run?  Historically, most of us with the condition have difficulty doing just that – jogging or running, or similarly intense activities.  While scouring the internet for information on the disease, I came across an article in the online British Journal of Sports Medicine titled “Can Patients with McArdle’s Disease Run?” whose abstract follows:

Patients with McArdle’s disease commonly adopt a sedentary lifestyle. This sedentary behaviour, however, usually worsens the limited exercise capacity of these patients. Although eccentric muscle work can be associated with rhabdomyolysis, supervised eccentric training with gradually increasing loads has important advantages compared with conventional concentric work, particularly for patients with a poor cardiorespiratory system. We report the beneficial effects (particularly, increased VO2peak (from 14.6 to 30.8 ml /kg/min) and increased gross muscle efficiency (from 13.8% to 17.2%)) induced by a supervised aerobic training programme of 7 months duration including 3–4 running sessions ((60 min/session) per week in a 38-year-old patient. These preliminary data suggest the potential therapeutic value of this type of exercise in these patients. 

This is encouraging, because it is confirms what I already suspected: that diligent and careful but nonetheless moderately intense exercise may be the only effective therapy for McArdle’s disease capable of improving quality of life.

To read more, click  here: http://bjsm.bmj.com/cgi/reprint/41/1/53.pdf (free registration is required.)

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.

I was doing some casual research online about energy metabolism, as I’m experimenting right now with my diet, etc. I read in a Wikipedia article about glycogen this description of glycogen debt:

Due to the body’s inability to hold more than around 2,000 kcal of glycogen,long-distance athletes such as marathon runners, cross-country skiers, and cyclists go into glycogen debt, where almost all of the athlete’s glycogen stores are depleted after long periods of exertion without enough energy consumption. This phenomenon is referred to as “hitting the wall” or “bonking”. In marathon runners it normally happens around the 20 mile (32 km) point of a marathon, where around 100 kcal are spent per mile,[citation needed] depending on the size of the runner and the race course. However, it can be delayed by a carbohydrate loading before the task.

When experiencing glycogen debt, athletes often experience extreme fatigue to the point that it is difficult to move.

Does that sound familiar?  “Extreme fatigue to the point that it is difficult to move?”  Marathon runners who deplete their muscles’ stores of glycogen get to enjoy a little taste of the ‘ol McArdle’s Disease.  Because the muscle cells encounter that “energy bottleneck”, i.e., there is no more glucose to create ATP to drive muscle motion, their muscles simply stop responding.

What’s the Significance?

This is noteworthy because an another affirmation that, no matter how healthy, fit and capable of normal exercise people may think you are, if you have McArdle’s Disease there are in fact limitations on what you are capable of, limitations that are beyond your control.  It is important for people with McArdle’s to remember this, because years of coping with undiagnosed symptoms often lead people to simply believe they’re out of shape.