Exercise places serious demands on the body. These demands are fundamentally caused by increases in oxygen demand and the consequent increase in body temperature. These demands are met by several physiological responses, including increases in heart rate, blood pressure, breathing and blood flow. These responses must be proportional to the increase in demand and some signal must relay information from the muscle to the brain. Group III/IV afferents do just this. They relay information about the muscle (movement, temperature, acidity, etc.) up to the brain so that appropriate responses are mounted. There is strong evidence in animals that group III/IV afferents play a key role in making breathing easier (decreasing airway resistance) and initiating sweating and blood flow responses. There has been no research on the role of group III/IV afferents on these fundamental exercise responses in humans. The investigators propose to isolate the role of group III/IV afferents on regulate airway resistance, sweating and blood flow responses to exercise in humans.