Sometimes I bound out of my front door knowing that running is the best thing ever. Other times, I'd rather lie on my office floor and stare at the ceiling fan than even think about putting on my running shoes.

There are times when that "I don't want to run" feeling is valid: I could be sick or hurt or worn down. But often, I know that I can do it. I just need to take the first step.

Here are four situations where a run may be put in jeopardy, and how to figure out if you should run on, or stare at the ceiling fan instead.

"I'm tired"

What kind of tired? Sluggish, end-of-day tired? I want to hit the snooze button five times tired? Or all around weary?

It's easy to talk yourself out of a run when you're tired, but running can perk you up and wipe away weariness. If you're not sure what to do, try this: in these situations, I tell myself I'm just going to run a mile. If I feel good at mile one (which I usually do), I keep going. If not, I'll turn around and run home to get in two miles, which is still better than none.

One exception: If you need to be focused to run. I ran tired on a trail recently in the semi-dark and tripped on a tree root. I only skinned my knee, but the injury could have been much worse.

"I'm sick"

Old rule of thumb: If the sick is above your shoulders, run. I've run through plenty of head colds and was glad I did. Running was a temporary reprieve from being wrapped up in the misery of that cold. I'll run outside instead of at the gym, though, so I don't get the next person on the treadmill sick. If the sick is below your shoulders — chest cold, flu, upset stomach — take a rest day for your sake and ours. Puke on the trail isn't pretty.

"I'm stressed"

Yes, run. Exercise can help alleviate that stress. It can also give you the brain space to work out the problem that's causing your stress - or the brain space to think about nothing at all.

Be careful of your pace, though. When my stress mixes with anger, I usually go out too fast, and then need to stop and walk before trying to reset my pace, which piles one frustration on top of the other.

"I'm hurt"

This is the hardest one to judge. I've run with a wonky knee and had the wonk work itself out a mile into the run. I've run with a hip screaming in pain, and wound up with a significant injury that required rest and physical therapy to heal. If I'm unsure, I'll put on all my gear and ran slowly up and down the block to test the pain.

If a test run doesn't give you an answer, look at your goals for that run: a race you've been looking forward to? An easy training run? A meet up with a running friend? As my coach once told me when I was struggling with a medical condition while training for the New York City Marathon: "Your goal is to get to the starting line." If that meant taking a rest day to better heal, so be it.

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