I’ve tried to summarize for you a great article I just read on IFLScience!
Sex does have some similarities to exercise. Your heart rate increases and so does your blood pressure. But sex only elicits a moderate level of physical stress, about 75% of a maximal exercise. These physical stress levels were intermittent, meaning much of the time was spent at a lower level of stress. Making sex a moderate physical activity such as brisk walking.
Can sex change your physiology such as exercise?
It could! But because most of us don’t sustain sex for long enough and often enough, it does not give you physiological changes. Also, to gain muscle mass you will more likely need resistance training. We don’t yet know if sex brings you this type of muscular training.
What about masturbation? Well, sorry but masturbation is only equivalent to a slow walk. You better get a girlfriend really soon, if you want to make it more of a physical challenge ;P
Exercise affects sex!
Exercise in general mixed with an healthy life style will make you less tired during sex, especially cardio. Women who train their pelvic floor with exercises, will have more control, heightened sensation and less pain during sex. As for men, to train the perineal muscle helps with premature ejaculation.
Sex affects exercise!
Sex has no affects on exercise, but it does have negative affects on recovery. Just wait 2 hours after sex before starting exercising!