According to Charles Pulliam-Moore gyms are hotbeds for all kinds of workouts:

• According to a survey 25% of people have considered having sex at their gym.
• 70% of women have thought about having sex with their personal trainers.
• 66% of people say that part of the reason they go to the gym is in the hopes of having sex there.
• 10% of the gym bags you see have condoms in them…just in case.
• This might be because workouts cause your serotonin and dopamine to spike, putting you in the mood.

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Source: Fusion