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No spontaneous second wind in muscle phosphofructokinase deficiency

From the Neuromuscular Center (Dr. Haller), Institute for Exercise and Environmental Medicine of Presbyterian Hospital, and the Department of Neurology (Dr. Haller), University of Texas Southwestern Medical Center and the VA Medical Center, Dallas, TX; and Department of Neurology and the Copenhagen Muscle Research Center (Dr. Vissing), Rigshospitalet, University of Copenhagen, Denmark.

Address correspondence and reprint requests to Dr. Ronald G. Haller, Neuromuscular Center, IEEM, 7232 Greenville Avenue, Suite #435, Dallas, TX 75231; e-mail: rhaller2{at}earthlink.net

Objective: The spontaneous second wind in myophosphorylase deficiency (MD, McArdle’s disease) represents a transition from low to a higher exercise capacity attributable to increased oxidation of blood-borne fuels, principally glucose and free fatty acids. Muscle phosphofructokinase deficiency (PFKD) blocks the metabolism of muscle glycogen and blood glucose. The authors inquired whether the additional restriction in glucose metabolism in PFKD prevents a spontaneous second wind.

Methods: The authors compared the ability of 29 patients with MD and 5 patients with muscle PFKD to achieve a spontaneous second wind during continuous cycle exercise after an overnight fast. Patients cycled at a constant workload for 15 to 20 minutes (3 MD patients, 3 PFKD patients) and at variable workloads in which peak exercise capacity was determined at 6 to 8 minutes of exercise and again at 25 to 30 minutes of exercise (29 MD patients, 4 PFKD patients). Heart rate was monitored continuously, and perceived exertion (Borg scale) was recorded during each minute of exercise. Oxygen utilization and blood levels of lactate and ammonia were determined at rest and during peak workloads.

Results: All variables in both patient groups were similar at 6 to 8 minutes of exercise. Thereafter exercise responses diverged. Each MD patient developed a second wind with a decrease in heart rate and perceived exertion and an increase in work and oxidative capacity. In contrast, no PFKD patient developed a spontaneous second wind.

Conclusions: Patients with muscle phosphofructokinase deficiency are unable to achieve a spontaneous second wind under conditions that consistently produce one in patients with McArdle’s disease. The authors conclude that the ability to metabolize blood glucose is critical to the development of a typical spontaneous second wind.

Received November 25, 2002. Accepted in final form September 8, 2003.

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