Hypertrophy Differences

If you've ever read a bodybuilding magazine (you have, it's OK, I forgive you) or some other training-related article online, then I'm sure you've heard that for functional gains, you need to be lifting in the 5-8 rep range, and for structural gains, you need to be in the 9-15 range (or something like that).

I definitely want to note that these rules are not set in stone. There are people who grow like weeds keeping everything under 5 reps and others, whose legs grow like they're being fertilized by Mother Nature herself doing nothing but sets of 20-rep squats. With that being said, they are a good general rule for most people.

Now, what is the reasoning for these adaptations and what exactly do they mean? Structural gains refer to actual increases in the size of the muscle. To keep it as direct as possible, training in the 5-8 rep range forces your muscles to partake in very high levels of tension. Your body, being the genius that it is, responds to this by attempting to prepare itself for the next time they have to display such high levels of tension. It does this by increasing the size of and/or adding more contractile proteins to the muscle.

When you lift weights in a rep range beyond 8 reps, and maybe even stretching into the 15+ rep range, your gains in hypertrophy will differ from those mentioned in the above paragraph. Whereas before, the muscle actually increased the size of its contractile elements, it will now respond by storing more "energetic" components in the muscle.

Why? Same reason as before, it just adapts to whatever you tell it to do. Since you did some sets with a weight that required good endurance, it responds by storing more energy in the muscle, so that it can better handle those endurance-related activities, that it expects to see again in the near future. This type of growth is more temporary and short-term than the functional gains talked about before. The famous "pump" will often rear its head in situations like this. And like Arnold said, the pump is definitely a cool feeling, and your muscle will look bigger, but, as you now know, it's very temporary.

If you are interested in looking bigger on a regular basis, you'd be much better off spending time trying to increase the size of your muscle fibers (5-8 reps), not wasting your time with a bunch of high-rep sets that'll send a bunch of glycogen and blood to the muscle, and not much else. To hypertrophy!