Abnormal muscle physiology Second-wind phenomenon The second wind phenomenon is experienced by individuals with McArdle's disease and can be explained by increased blood flow, optimized delivery of free fatty acids with concurrent activation of their metabolism, and increased utilization of glucose. However, pre-exercise glucose intake can prevent the onset of this phenomenon. The second-wind phenomenon occurs approximately 10 minutes after the onset of exertion, denotes a sudden and significant improvement in aerobic exercise tolerance after a brief rest period, following the development of muscle stiffness and myalgias, enabling the person to continue physical activity with a resolution of symptoms triggered at the start of exertion.