Tag Archives: Gym class

“How can anyone be so out of shape?” 

“Why don’t they  just try harder?” 

“Don’t they realize they’ll have to run more laps?”

Anyone who has ever ran laps in grade school gym class can probably recall stragglers.  Some were children with asthma or other health issues, but some consistently finished for no obvious reason.  For such children, it may very well have been the case that trying harder simply wasn’t an option.

When a child with no obvious physical infirmity is unable to meet basic physical fitness criteria, effort should be made to rule out McArdle’s disease, a rare and often undiagnosed muscle disorder marked by extreme exercise intolerance.

How McArdle’s Disease Makes it Difficult for Children to Run Laps

Also known as glycogen storage disease Type V or phosphorylase deficiency, McArdle’s disease is an inherited condition which impairs energy metabolism in skeletal muscle. During moderate to intense physical activity an enzyme called glycogen phosphorylase provides contracting muscles with the energy required to do work. In McArdle’s disease this enzyme either is either non-functioning or missing, and the result is premature exhaustion and failure which may be accompanied by cramp-like injuries to muscle tissue.

Screening Children for McArdle’s Disease: Simple Signs to Look For

Even with the wealth of information now available on the web, screening McArdle’s disease in children remains challenging. Undiagnosed individuals may have a healthy appearance and symptoms can easily be mistaken for laziness or behavioral problems.

For this reason, it is critical that the right people know exactly what to look for. Physical education instructors, teachers, school nurses and even other students can screen McArdle’s disease on the basis of one or more of the following criteria:

  • They seem abnormally out of shape despite a healthy appearance.  People with McArdle’s disease have trouble sustaining low- to moderate-impact activities such as climbing stairs or walking steep inclines, and consistently perform below average on standardized fitness evaluations.
  • They have trouble getting in shape.  Because their muscles do not metabolize energy normally people with McArdle’s fail to respond as expected to endurance exercise regimens.
  • They may experience cramping injuries accompanied by dark-colored urine.  As children reach adolescence, increased body weight, musculature and opportunity for competitive sports training may precipitate episodes of muscle failure and injury during activity. Telltale symptoms include painful cramp injuries called rhabdomyolysis, sometimes accompanied by myoglobinuria, a potentially life-threatening condition indicated by urine darkened by proteins entering the bloodstream from damaged muscle tissue.
  • They may avoid fitness evaluations or other physical activities. The conspicuous symptoms of McArdle’s disease can make children self-conscious and embarrassed, and the stigma of feeling different may lead them to avoid participating in physical activities altogether.


If you know of anyone who fits any of these criteria, please reach out to them and learn more about the challenges they face.  Children with undiagnosed McArdle’s disease may suffer from the perception that they are simply out of shape or lazy, so approach them with discretion but be patient and persist in asking the right questions.

Most importantly, always remember that diagnosis and treatment of McArdle’s disease should be left to qualified medical professionals.  Recent advances in medicine make conclusive diagnosis a matter of one or two clinic visits and a minor blood test.

Children and adolescents with McArdle’s disease can live active lives and be physically fit, provided challenges are undertaken safely and within the scope of the limitations of this disease.  Catching symptoms early gives children with this rare disease a better chance to feel normal.

For additional information about McArdle’s disease visit any of our homepage resources or the Muscular Dystrophy Assocation website.