"participants exercised on a stationary bicycle until they were exhausted
- that is, unable to maintain a cadence of 60 revolutions per minute.
On another day, as a control, their physical exercise was preceded by 90 minutes
of watching documentary films about cars and trains.
Even though there were no significant differences in physiological measures
(heart rate, cardiac output and others) under the two conditions, bicyclers consistently tired
about 15 percent more quickly after the mental exercise than after watching the movies.
Apparently, their poorer exercise results after mental effort were caused
not by reduced performance of their bodies, but by exhaustion of their minds",