Today, probably due to having a not very nutritious lunch, I was able to lift noticeably less (e.g. Benching at 55kg rather than 75kg) weight & reps than normal.
In a situation like this, if your muscles at the time don't have sufficient energy, do they still adapt to get stronger, so that the next time you'd be able to lift (probably) more than the 'normal' amount, or will noticeable muscle adaptation not take effect as you aren't hitting their limit due to a lack of energy?
Obviously I know this isn't a good situation to get into, but is it actually worth going through with the full routine if your goal is to just gain mass, and you're not really worried about the lower weight repetition (endurance) range, assuming your supper or whatever is 'good' meaning you get your needed calorie/protein/etc. for the day?