nielle Wiener-Bronner -
For athletes of all levels, endurance -- how long they can keep going at their chosen sport -- is made up of physiological and psychological factors. Physiological factors include cardiovascular fitness, and how efficient an athlete is at using energy (their 'movement economy'). A critical psychological factor, on the other hand, is perceived effort, or how hard we feel we are working during an activity. The lower our perceived effort, the easier we feel that an activity is.
original story: http://rss.cnn.com/~r/rss/cnn_health/~3/3w1V5DBMiUE/index.html