“Ouch!” Who knew the radiator was on? You yank your hand back, wincing.
Unpleasant as it was, pain protected you in this instance. The heat would have damaged your hand. Thanks to a jolt of pain, you removed it from harm’s way.
We owe pain a begrudging thanks but it’s not the only uncomfortable feeling the body uses to keep us safe. Prof. Emma Cohen and her team at the Social Body Lab are researching feelings of fatigue. In particular, the feelings that kick in during exercise. Go for a long enough run and tiredness will creep in, eventually becoming hard to resist. And at some point, you’ll surrender, dropping your run to a walk.
“From an evolutionary perspective,” Emma explains, “sensations of fatigue induced by physical activity or exercise are thought to be part of an energy regulation strategy that maintains expenditure within safe limits.”
After all, in succumbing to fatigue, you stopped spending energy. The body’s resources are limited and careful management of its energy is crucial for survival. It certainly was in our evolutionary past. Overspend your energy now and you may not have enough to fend off that tiger later. Fatigue keeps you safe by preventing you exhausting your energy supply.
But scientists know that neither pain nor fatigue are simple, brute mechanisms that entirely bypass your mind. What you believe, desire, intend etc can affect how you experience pain and fatigue.
The well-known placebo effect illustrates this. Participants told they’ve been given pain-killers, even when the pills are duds, still tend to report a decrease in pain. Similar effects are observed with fatigue. Emma notes one study where participants ingested a capsule they thought was a performance aid. It wasn’t. But they still experienced a performance boost. This was despite no perceived increase in how hard the exercise task felt. “It was easier to put the effort in, there wasn’t any tiredness creeping in,” one participant reported.
Emma explains what she thinks is going on here: believing that you have more energy available leads the body to be less cautious in letting you spend energy. After all, you don’t need to be stingy with something you have in abundance. Hence the feelings of fatigue produced are less intense, allowing you to exert harder and longer.