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The second wind phenomenon in McArdle's disease.
Brain : a Journal of Neurology
|December 1, 1986
Summary
Patients with McArdle's disease experience an adaptation phase during exercise due to impaired muscle glycogen use, followed by a "second wind" phase where metabolism normalizes. This study details the physiological responses during these distinct exercise phases.
Area of Science:
- Exercise Physiology
- Metabolic Myopathies
- Neuromuscular Disorders
Background:
- McArdle's disease is a metabolic myopathy characterized by the inability to break down muscle glycogen.
- Exercise intolerance is a primary symptom, but the physiological adaptations during exercise are not fully understood.
Purpose of the Study:
- To investigate the physiological and metabolic responses during exercise in patients with McArdle's disease.
- To characterize the adaptation phase and the subsequent "second wind" phenomenon.
Main Methods:
- Three patients with McArdle's disease exercised at 30% VO2max for 2 hours.
- Physiological parameters including cardiac output, muscle blood flow, metabolic substrate utilization (FFA, glucose), and electromyography (EMG) were monitored.
Main Results:
- During an initial adaptation phase (15 min), patients experienced fatigue but recovered, entering a "second wind" phase.
- Adaptation involved increased cardiac output, altered metabolic pathways favoring free fatty acids (FFA) and glucose, and increased EMG activity.
- During the "second wind" phase, muscle metabolism normalized, showing no significant difference compared to control subjects.
Conclusions:
- Patients with McArdle's disease exhibit distinct physiological and metabolic adaptations during exercise to compensate for the lack of muscle glycogen utilization.
- The "second wind" phenomenon represents a successful compensatory state, allowing for sustained exercise.
- Central command plays a role in regulating cardiovascular responses during the adaptation phase.