There are many people who believe there is a difference in the way you train to build strength versus the way you train to build muscle size. The truth is there is a direct correlation between a muscle’s size and its strength. For a muscle to be stronger it has to be bigger and vice versa.

Tired gym lore like “positives for strength and negatives for mass” is ridiculous. Think about it – if it were true it would be possible to build big 20-inch arms but not be able to bench press 100 pounds, or it would be possible for a guy with skinny 12-inch arms to bench 500 pounds. That just ain’t gonna happen, my friends.

However, even though there really is a direct relationship between the size of a muscle and its strength many trainees complain of making good gains in strength but not seeing good gains in muscle size. Maybe this is what gives rise to myths about needing different ways to train. But the truth (most of it) is way back in your high school geometry class.

The strength of a muscle fiber, like the strength of a steel cable, is proportional to its cross-sectional area. In basic terms, if a muscle is to be twice a strong it has to have twice the cross-sectional area. But when we look at the geometry of that there is some bad news for guys wanting to look bigger:

The figure on the bottom has 50% more area but has only slightly more “size” in diameter.

Without going into all the math, when we double the diameter of a muscle fiber or a steel cable, the cross-sectional area is not just doubled – it’s increased four times! So a 2-inch cable can support four times as much weight as a 1-inch cable.

So when you get stronger, say 50% stronger, your related muscles only need to get 22.6% bigger in terms of what you measure with the tape. So size gains always lag behind strength gains. It’s a geometric law.

But It Gets Even Worse

Every muscle is actually made up of millions of individual muscle fibers bundled together. If there is fat (called intramuscular fat) in between these fibers they affect the size you measure. So if you’re doing everything right with your training you will lose this fat from inside your muscles and guess what? Your muscle will actually get a bit smaller!

You could also lose the more plentiful subcutaneous fat of which most of us have too much. So if you put an inch of muscle on your biceps and lose an inch of fat off your biceps the tape measure says you’ve made no progress.

Also, your arm, leg or whatever is not made out of only muscle; there is also bone, blood, ligaments, tendons, skin and blood vessels that all take up space. Those don’t grow with training so even when you add 50% to your muscle area the effect on a leg containing all that other stuff is mitigated.

Part of your strength increase could also be attributed to increases in your neuromuscular efficiency. That means your muscle did not actually grow but your neural pathways got more efficient at sending their signals between your brain and muscles.

If all of this isn’t depressing enough, 60% of muscle is water so if you’re a little dehydrated when you take your measurements you won’t see all the increase you could.

Keep Punching!

All of the above elements conspire to make size gains a lot harder to achieve than strength gains. But none of this changes the reality that to get one you need the other. Just be glad that with Static Contraction training strength gains are easy to measure with meaningful precision. That will keep you on the road to steady progress.

And the next time a guy in the gym tells you the way to build “size” is with negatives only, or positives only, or supersets, or periodization, or this or that exercise, ask him how his technique will overcome the laws of geometry.