Why is the aesthetic of gyms, even the good ones, always so lifeless? Always black and grey and white everywhere. I want fans blowing air in my face at 12 km/h and a simulation of running along a forest path in a magical fantasy world .... or at least some plants.

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That's my preference. Some places have 30' temperatures though 🙃

because such loading is not natural, fast exercise is natural and healthy. The founder and promoter of "cardio training" died of a heart attack. Running has been a stressor for most of humanity's existence.