Pain perception after running a 100-mile ultramarathon

To determine if pain perception is affected by an extreme bout of exercise that causes ongoing exercise-related pain.Repeated-measures design.Pre-race registration area and finish area of an endurance race.Twenty-one competitors in the 2005 Western States 100 Mile Endurance Run and 11 control subjects who were assisting at the race but not running.Not applicable.Overall pain and pain ratings on a pressure pain test before and after the event.Mean overall pain +/- standard deviation on a 100-mm scale increased (P.05) from 3+/-6mm before the run to 39+/-28mm after the run among the runners. The faster runners showed a mean reduction (P.05) in pain ratings after the race of 15+/-20mm (on a 100-mm scale), whereas there was no change for the slower runners and controls. Findings were confirmed by model-based analysis.The faster runners in a 100-mile (161-km) running race experience a modest temporary reduction in pressure pain perception that does not appear to be augmented by ongoing pain related to the exercise. The lack of a reduction in pain perception among the slower runners may be because an extreme bout of exercise of this nature can "exhaust" the systems responsible for exercise-induced analgesia in all but the most well-trained of runners, or that these systems were not activated because the slower runners were unable to maintain a high enough exercise intensity during the later stages of the race.