Like a fight-or-flight response, a challenge response gives you energy and helps you perform under pressure. Your heart rate still rises, your adrenaline spikes, your muscles and brain get more fuel, and the feel-good chemicals surge. But it differs from a fight-or-flight response in a few important ways: You feel focused but not fearful. You also release a different ratio of stress hormones, including higher levels of DHEA, which helps you recover and learn from stress. This raises the growth index of your stress response, the beneficial ratio of stress hormones that can determine, in part, whether a stressful experience is strengthening or harmful.
From “The Upside of Stress: Why stress is good for you (and how to get good at it)”
by Kelly McGonigal