There aren't any clear statistics for the number of people who derive pleasure from the physical pain of an activity (irrespective of any other possible benefit). Nevertheless, it's a well-known, widespread and varied phenomenon.

From an evolutionary point of view, it's not easy to come up with explanations of how and why masochism might have evolved. As far as is known, no other animals show signs of it.

One possible explanation was published in Psychology of Consciousness: Theory, Research, and Practice, 6(4), 386–403.

This appeal can be explained conceptually, phenomenologically, and biochemically as the motivation to reach the highly pleasurable psychophysical altered state called “subspace.”

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Moreover, I contend that from an evolutionary perspective, sexual masochism may even confer adaptive advantages, consistent with evolutionary explanations for the tendency toward submission in conjunction with pain in the context of female reproductive responses such as mating and childbirth.

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Editor's note:It seems there are very few peer-reviewed academic papers on the subject - except in the 'psychoanalytic' press. Wikenigma takes the view that these publications can't currently be seen as science-based.