Fitness gives sexual pleasure

Experts from the University of Indiana (Indiana University) found that almost half of the women involved in fitness, faced with an unexpected "side effect" of training.The fairer sex are sexually excited. Professor Debby Herbenick and his colleagues conducted a survey of hundreds of women aged 18-63 years. It was found that during exercise -yoga, cycling, running, swimming - women have orgasms. However, they do not even think about sex. 
Almost 50% of women faced with this phenomenon in more than 10 exercises, writing abc news. Most often, orgasm occurs during exercise in the press (45%), strength training (26.5%), yoga (20%), training on a stationary bicycle (15.8%), jogging (13.2%), walking (9 , 6%), and sometimes during training with a pole or rope. 
The first such case was recorded in 1953. The study is the topic for a long time was not spent. What are the mechanisms behind this type of sexual arousal and orgasm, scientists still could not figure out.