A recent study has found that there is an inversely proportional relationship with the male libido and the intensity and duration of endurance based exercise. 

Quoting Wikipedia, Libido is a person’s overall sexual drive or desire for sexual activity. Libido is influenced by biological, psychological, and social factors. Bored? Play blackjack online. Biologically, the sex hormones and associated neurotransmitters that act upon the nucleus accumbens regulate libido in humans.

Prof Anthony C Hackney of the University of North Carolina and his researchers conducted a year-long online survey compiled a range of data from 1,077 healthy adult males involved in endurance sports such as running, cycling and triathlons. 

They concluded that “men engaged in higher intensities and greater durations of endurance training on a chronic basis (ie years) are significantly associated with decreased libido scores”; speculated that the physical and mental fatigue induced by prolonged intense training may contribute to an individual’s reduced libido; and advised that clinicians who treat male patients for sexual disorders and, or council couples on infertility issues should consider the degree of endurance exercise training a man is performing as a potential complicating factor”. – (Medicine & Science in Sports & Exercise).

The reality is that low to moderate levels of endurance exercise don’t generally appear to have a negative impact on sexual health — at least to a noticeable degree.