Muscle density is about more than simply having big muscles. It is about the quality of the muscular composition and its ability to perform. The difference between muscle density and mass requires an understanding of how muscles gain their appearance.
Sarcoplasm is a fluid within each cell. Hypertrophy simply means growth. The theory is that when a bodybuilder chases “the pump”— the point where a muscle has been worked until it has filled with blood and looks as if it’s going to burst — that sarcoplasmic hypertrophy will occur.
Eventually, with an ever-greater volume of sarcoplasm in the cells, the muscles will appear to be bigger, even though the muscle tissue has not increased. If you have ever seen someone with muscles that appear balloonish, or inflated, you are most likely seeing the results of sarcoplasmic hypertrophy.
However, there is still debate about exactly how, to what degree, and whether sarcoplasmic hypertrophy can be directly influenced by training. For this discussion, the trenchant points are that muscle density is not contingent on sarcoplasmic hypertrophy, and that muscle density is better measured through performance than by appearance.
Actual muscle growth relies on what is called myofibrillar hypertrophy. Myofibrils are essentially the muscle fibers that result in muscle striations – when you see someone with well-defined muscles, the thread-like appearance in the surface area of the muscle is referred to as the striations.
Myofibrils are actual muscle tissue. Myofibrillar growth results in a muscle that is literally bigger and has greater muscle density, not just one that has the appearance of greater volume across its surface area. It is denser because the fibers grow and are packed more tightly together with continued, progressive exertion.
Athletic performance is contingent on the ability to contract muscles in harmony with the rules and aims of the sport. Basketball players must be able to use their contractile tissue to leap. Sprinters must sprint. Tennis players must have insanely powerful lateral movement capabilities, and so on. According to Mel Siff’s book Supertraining, the more contractile tissue athletes have, the more power they can potentially generate.
Muscle Growth and Muscle Stimulation
It is possible to grow larger without growing significantly stronger. An elite bodybuilder focuses on stimulating the muscle. The stimulation doesn’t always come from heavy weights and impressive lifts, no matter how strong the bodybuilder looks. When the desired result is a larger muscle with a full, round muscle belly, it doesn’t matter to the bodybuilder whether it is achieved with 10-pound dumbbells or a 500-pound deadlifts, or whether the muscle was formed via sarcoplasmic or myofibrillar hypertrophy.
A round, full muscle is not necessarily a dense muscle, or a strong muscle. A body full of dense muscle looks powerful. If you have ever seen a broad, dense back that was built with deadlifts, you know the power look. It has to be earned through muscle growth.
Which Should You Choose?
It depends on your goals. If you train primarily for aesthetics, you can go far with a focus on sarcoplasmic hypertrophy. If this is your goal, you’ll do best with higher reps sets and plenty of isolation exercises that result in a good pump. Stimulating the muscle should be your focus, which requires you to really learn how to feel the muscles and choose the appropriate movements to work them to exhaustion.
If you are more interested in improving your muscle density – again, don’t think of it just in terms of looks, but also in terms of athletic performance – focus on heavier lifts with lower reps. With increased strength comes greater muscle density.
Unfortunately, many lifters get stuck thinking that they have to choose one of the other. The best of both worlds for most people would be a mixture of the two. Sure, you can get bigger without getting much stronger, but doesn’t it make more sense to get bigger and stronger? If you are always striving to increase your muscle density, as long as your nutrition is on point, you will probably like the way you look.