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Many of us have been there, felt that: You just woke up from your usual eight hours of sleep, slipped on your cycling shorts and into your shoes, and yet, you’re simply not raring to go. Instead, your gas tank seems to hit “E” for a reason you can’t quite pinpoint. That feeling? It’s called fatigue.

Because this sensation has so many potential causes and symptoms, it’s often tough to tease out what kind of fatigue you’re experiencing. But once you do figure it out, you’re able to tackle roadblocks head on and get back up to speed ASAP.

To get you on the level of fighting fatigue with fury, here’s your guide to what it is, how to differentiate if it’s your mind or your muscles that feel off, and the best ways to tackle extreme tiredness.