> The rule is if it doesn't ache for a couple days after, you need to go harder/heavier. That's not a good rule. Once you've past the first few months of resis

> The rule is if it doesn't ache for a couple days after, you need to go harder/heavier. That's not a good rule. Once you've past the first few months of resistance training, not being sore after a workout is not an indication that you didn't work out hard enough. It's very possible to work hard and have little to no soreness while making reliable strength gains. In general you really want to get to place where you're working out more days per week, for a smaller amount of time each session (with a targeted muscle group). There shouldn't be much soreness at all unless you've over-exerting yourself. It's an extremely common misconception that you need to work yourself to soreness to facilitate muscle breakdown and repair. But that's actually inefficient. The only reason it's even so common in people new to training is because they tend to workout with someone who is significantly more advanced (or enthusiastic) than they are.