A good way to look at physical adaptations from a big picture perspective is to think of everything your body does as an adaptation that makes it easier to deal with life.

Protective Adaptations

Increases in size are really just adaptations that the body uses to protect itself from ever increasing amounts of tension, or bar weights. Here's an example I heard recently that may elucidate a protective adaptation:

A friend found this stray dog that must've been about a year old. The dog was full grown and normal sized everywhere except it's neck, which was about half the size it should've been. Someone had put a collar on the dog when it was a little puppy and it had never been taken off. As part of the normal growth process the puppy more than doubled in size all over. However, it adapted to the collar by inhibiting growth in his neck to keep him from growing into the collar and choking himself to death. That is a very obvious example of a protective adaptation, but the same thing occurs when our body changes to adapt to any external stimulus.

When we train with weights we send our body a signal that says "OK body you need to protect yourself from all this muscular damage I'm throwing at you." Of course we don't really say that - Ideally we would like our body to get bigger without us doing anything, but that's how our body perceives our workouts. To see examples of this "protective expression" amongst various athletes all you have to do is take a look around:

Various Manifestations of These Adaptations

Gymnasts inherently have well developed lats and triceps in proportion to the rest of their body. What is their body protecting them from? Probably the large volume of pullup and dipping variations in their training. You also notice they have small legs and that can be explained by the fact that they don't create much tension in their legs from training.

Powerlifters tend to have big butts, spinal erectors, traps, and hamstrings. What is their body protecting them from? Probably all the low bar squats and deadlifts they do - which engage a lot of glutes, erectors, traps, and hamstrings. (Interestingly enough, even though powerlifters are not typically after size increases, the amount of muscle they carry in those muscle groups will be better than most bodybuilders).

Then you have bodybuilders, who intentionally create excessive tension in ALL major muscle groups. They tend to have well developed muscles all over.

What We Do

So, we go in the gym and train our butt off in an effort to signal our body to protect itself.

Now, once that signal is sent the body can basically do 4 things. It can:

1. Get bigger and stronger
2. Get stronger (increase neural efficiency)
3. Get better at performing the same workouts (do nothing or stay the same)
4. Go backwards (Overtrain)

Number one is what we want. We want to get bigger and stronger. Number two is what occurs to a large extent with people like lightweight olympic lifters, wrestlers, gymnasts and other people who compete in weight class events. They get a LOT stronger without getting a whole lot bigger. The main difference between someone who gains strength in isolation, or strength with size, is their state of nutrition.

Moving on, number 3 (staying the same) is what occurs with people who do the exact same workouts with the exact same weights with the exact same diets at the exact same bodyweight as they were a month, a year, 5 years, or ten years ago. Number 4 is what happens when people overdo it. They get weaker and may get smaller as well.

Lets say you stimulate your body to get stronger. This is a fairly easy adaptation as it doesn't require much of anything extra to carry out. The body simply makes better connections between your mind and muscles.

But let's say your training creates enough muscular microtrauma that your body also makes up its mind that it must get bigger in order to protect itself from what you're throwing at it. It still needs enough nutrition floating around to carry out that adaptation. Even without that nutrition, your body will still stimulate non-size related muscular adaptations that enable it to tolerate the same workouts in the future with less muscle damage. It will increase the amount of connective tissue in your muscles, which toughens them up like leather. From a bodybuilding standpoint, this is a prime example of spinning your wheels. You're not getting any bigger but you are increasing your muscular resistance to damage. That's why if you're interested in muscle mass and you're not eating in a manner conducive to gaining mass it could be argued that it's better to do very easy maintenance workouts instead of going in the gym and busting your butt.

We've all probably seen very thin people who might have jobs as movers and such who move heavy stuff all day long and are strong as ox. They do get a lot stronger yet don't get bigger because they don't eat enough.

One of the things that anabolic hormones do is lower the threshold of extra nutrition necessary to stimulate muscle mass increases. They make the body more prone to say, "let's get bigger" and also make the food you eat work better. So a person on steroids or a pubertal male will still grow while doing nothing and eating practically nothing.

Conclusion

The main point I want to make is instead of getting overly caught up in the specific nuts and bolts of your training, ask yourself if over the long term you're consistently giving your body a reason to say, "we must protect this house". Look for continual progression in the most basic things that are going to cause those "protective" adaptations. The main one you need to be concerned with is the progression of weight you can lift on various movements over time. These don't necessarily have to be 1 rep maxes, but how much do you improve on various movements over varying rep ranges with a given lifting technique? No matter how intensive and puke inducing your workouts are, if you're the same strength in a given movement 5 years from now that you are right now there's a pretty damn good chance the bodyparts associated with that movement are gonna be the same size as well....because there's no reason for your body to try to build more protection against something it can already handle.

-Kelly