KPj--I can't quite agree with you on this. Sure, you probably have to reach the "hit by a truck" stage a few times in order to learn your work capacity. But if this keeps happening over and over, it just shows that you don't learn very well. I'd say that the hit by a truck feeling is the indicator that you should have deloaded a few days ago. After a while you should be able to anticipate and plan to avoid it.
I mostly agree with what you said. Everything does "depend". I generally try to avoid CNS fatigue from training affecting peoples every day life. I'd rather they didn't get "achey" and i'd rather they weren't like a half-shut-knife in work.
In terms of work capacity - your work capacity changes as you get stronger (or weaker), it's not always the same. It also obviously depends on how you program your assistance. If you've increased your strength by X% over the last 3 months, then you have the potential for even better work capacity (if you don't have it instantly). To know those limits you need to tread closely to them and, sometimes, that'll result in pushing it a bit too far and getting the strangely enjoyable hit-by-a-truck feeling.
That's not to say this is the only way to make progress, not at all. This is the approach I tend to favour for people concerned primarily with getting stronger.
Maybe it's an age thing, but when I get to that stage, it takes more than a simple deload to get me right again.
I'm not really sure what would define a simple deload. However, age is definitely without a doubt an issue. I actually have two 58 year old clients, one male one female. Some people are a very young 58 in terms of training, especially if they have trained before however these 2 were very sedentary and never done anything before they joined the gym. One basically sits all day the other basically stands all day.
Anyway, with them, I try very hard to avoid the hit by a truck feeling. This is also much easier because they don't have such an aggressive focus on strength training as others. When I do deload them, they get much more of a deload than someone in their 20's (generally less volume and lower intensity). When they have had that hit by a truck feeling, I have noticed that it can take longer than a week to feel fresh again.
On work capacity, lets take the 58 year old female. I can remember a few sets of DL's at 40KG with the bar elevated would create a lot of fatigue. Now, 40KG doesn't make a dent, as she generally does sets with around 75KG from the floor now (in fact the last time she deloaded, she deadlifted 50KG for 3 sets of 5). If I based her potential work capacity on when she was pulling 40KG and really struggling, then she'd just be bored now and, to be honest, probably wouldn't be as strong. What used to create the need for a deload is now considered deload weights.
Deload doesn't have to be for a whole week, or cycle. Sometimes it should be, but it doesn't always have to be.
I agree. There are various ways to do it. I don't use one single approach with everyone. However, I prefer every 4 weeks, prefer to use one whole week, and prefer to over reach before hand. It's just a personal thing. I like to be in control of when I need to deload. I also tend to do more "healthy stuff" in a deload week and teach new movements or lifts so, I get more out of it than just reducing training stress. I'm deloading right now (week 4), and, due to the current program, i'm going to deload in week 7, too. I know that next week i'll be fresh and ready to smash through my sessions, and I know in week 7 i'll be probably be weaker. I know week 5 and 6 are going to be tough and I need to be at my best, so I'm already thinking about trying eat more and ensuring I get better sleep. I know on week 8 (test week) i'll be as strong as i've ever been on this 8 week program as long as I don't screw anything up or something unpredictable happens. If it doesn't work out like that, then something has got in the way. It may be something out with my control like work or family issues, in which case, I need to adjust accordingly, and that's fine. However it may also be that i've slacked off on diet or not got enough sleep, and it acts as the kick in the a$$ that I need - it holds me accountable.