Popular fitness games designed for home video game consoles like Nintendo's Wii cannot turn couch potatoes into athletes, a study by Muenster University's Institute for Sports Medicine has concluded.

In the study, more than 40 students in the German university's department of sports studies tried out four sports in one such game - each for 15 minutes at a time with 20-minute breaks in between.

Afterwards, those tested rated their subjective sense of physical exertion, and their heart rates and lactate levels were measured. This data was then compared with research-based averages from people performing the actual sports.

The study concluded that the energy expended by the test subjects' motions in front of the console, and hence the workout benefit, was far less than that typically expended during the actual sports. The Muenster University researchers found that only console boxing provided a "physiologically relevant, though merely moderate workout."

Klaus Voelker, director of Muenster's Institute for Sports Medicine, also noted another reason why video fitness games were no substitute for real sport. Students in the study quickly realized that the console reacted to slight movements, he said. During video boxing, for example, vigorous punching was not necessary and test subjects gradually exerted less effort.