Consitent cardio is a sure fire way to lower your testosterone levels. Your body doesn't know whether you're running a five K, or running for your life. The internal environment of the body is effected negatively either way. Cortisol shoots through the roof, you go catabolic, and your testosterone gets fried. That's why HIIT is the "cardio" of choice. It effects the body in the complete opposite way of steady state cardio.
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Um...that depends on if you like the feel of loose sneakers?