Overtraining will get you further than undertraining. If you’re working out two days a week, you’re not overtraining.
Listen to your body. It’ll let you know when you need to rest. Some weeks I can go 7 in a row without a rest day, but others I need 2 days off.
Nick Momrik 
Some weeks 7: dang you are intense bro!
As an old man I really like the idea of minimum effective dose.
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I used to too. Then I got addicted to CrossFit.
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