This claim appears to have been initiated in 1969 by a journalist who interviewed Dr. William Fry, a then leading researcher into the psychology of laughter at Stanford University (emeritus professor of psychiatry and behavioral sciences). In that interview Dr Fry claimed that the body gets a healthy “mini-workout” from a good guffaw. When asked to elaborate, he told the journalist that it took ten minutes on a rowing machine for his heart rate to reach the level it would after just one minute of hearty laughter. The journalist took this data at face value as an accepted scientific fact and simply chose to not mention the size of the research sample in his article that went viral: one person.
What you can say that is scientifically accurate
If you want to quote something about Dr. William Fry of Stanford University then say that he found out that laughing 200 times can burn as many calories as rowing intensely for 10 minutes, boosting your energy and giving you that alive feeling.
The claim itself that laughter is a valid and beneficial form of cardiovascular exercise is true and well documented. Read more.