A lot has been made of the importance of the heart rate zone you train in. Mostly that zone 2 is good & that zone 3 is bad! A grey zone, which should be avoided. But why? What’s the reason for this? And should you avoid the grey zone when trying to improve your fitness levels? Mark is here to investigate!

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📹 Why Is Everyone Talking About Zone 2?! 👉    • Why Is Everyone Talking About Zone 2?!  
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