I used to have those "can’t put any power behind the punches" dreams a zillion years ago. Never figured out what it was about, they just went away.
I believe that this, and the "try to run/walk but can’t" are due to the fact that most people become paralyzed while asleep. If you are dreaming of moving and your body tries to move in the same way you won’t be able to do it – the dream then picks that up.
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