Failure training can provide hands on experience with muscle fatigue. At a certain point, whatever muscle group you’re working can’t complete a full rep. But when you feel like collapsing to the floor after an especially demanding workout, that’s central fatigue telling you it’s time to hit the showers. An interesting study published online at helps explain the mechanism involved.

The neurotransmitter serotonin is released during exercise, which helps you keep going. But when serotonin builds up to a certain level, your brain puts the brakes on the feel good effect by shutting down signals to muscles so they won’t continue working. Basically, your brain rewards hard work but protects you from taking it too far. Listen to your body.