In health and fitness, endurance refers to your body's capacity to be capable of a certain amount of stress/workload. In order to find the endurance of an individual, one can do is to perform certain activities until our muscles of the body can no longer do it, and measure how much time we are able to endure that stress. The longer we survive, the higher endurance we have.
The time muscles are able to endure or capable of taking the stress is endurance where is maxing out the the upper limit of endurance of the stress he most repetitions possible with a set weight is maxing out.
In simple terms, your headache is the main area that is your brain is stimulating the pain. When you are distracting your brain from the headache by pinching your leg, your brain is kind of "forgetting" the headache for a second by the pain in your leg.
