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There are different kinds of strength. Some people have endurance strength and can count reps with a relatively heavy weight and other have explosive strength and can lift Ridiculously heavy weights 1-2 times. It is partialy genetics, yes - but it also has to do with your lifestyle, how well you sleep...your eating habits, your supplements, worries, wife, children, school, all that shit...I'd say, take a few days off of training before you hit the gym again.
