When you’re working very hard in the middle of a run, you can sense it even if your windpipe is not burning and there is no pain in your calf muscles. In fact, numbing the legs with anesthesia has no effect on perceived effort. The reason is that perceived effort is literally “all in your head.” Studies have demonstrated that effort perception is mainly a function of how hard the brain is working to drive the muscles. In other words, it is the brain’s perception of its own effort, not the body’s. The harder the brain is driving the muscles, the more intense the effort feels.
