For the study, sex researchers William Masters and Virginia Johnson observed 21 young heterosexual couples having sex and discovered that heart rates reached as high as 180 beats per minute, Live Science reported.
Participants in the study were asked to don an armband, called SenseWear, that would help researchers keep an eye on their energy expenditures while they had sex.
Before being sent home to have sex at least four times in a month, each person was required to do a 30-minute moderate-intensity workout on the treadmill to provide a baseline measure of their calorie expenditure during exertion.
The findings showed that men, on average, spent 101 calories while having sex, as compared to 276 calories on the treadmill.
Also, women spent an average of 69 calories during a sex session, compared to an average of 213 calories on the treadmill.
According to researchers, the results of the study suggest that sexual activity may potentially be considered, at times, as a significant exercise.
The study was published online in the journal PLOS ONE.