Changes in breathing during observation of effortful actions.

Respiration and heart rates were recorded in normal subjects watching effortful actions produced by an actor in front of them. Subjects remained immobile throughout. Two experiments were performed. In experiment 1, subjects watched a weight-lifting performance, either static or dynamic, with increasing weights. In experiment 2, they watched a walking/running performance on a treadmill moving at increasing speed. In both experiments, no change was found in observers' heart rate. By contrast, consistent changes were found in respiration rate. These changes tended to follow the exercise rhythm of the actor, specially during accelerated running (from 2.5 to 10 km/h) where respiration rate increased linearly with speed of the treadmill. Average maximum increase ranged between 25 and 30% above resting rate. This finding demonstrates activation of central mechanisms related to action performance during observation of effortful actions. It could represent a basis for understanding and imitating actions performed by other people.