Muscles can increase in volume and therefore overall mass… Here is a little underpinning science.
There are two types of muscle growth, hyperplasia and hypertrophy, you might be asking what are you on about? I will simplify these terms and break them down.
Hyperplasia is an increase in the number of fibers in a muscle. This has been proven in animal studies, but not in human studies. However, split fibers are associated with hyperplasia in animals and split fibers have been observed in human studies making this a possibility.
Hypertrophy is an increase in the protein content of individual muscle fibers, making these fibers larger in either diameter or length. This has been proven in many human studies and is the most likely method people put on muscle in the gym…
Many studies have shown increase in muscle fascicle length (bundles of individual fibers) after long term strength training, most often through eccentric only training or when peak muscle contraction occurs at long muscle lengths. This is one reason why I always train clients through full ranges of motion, while increasing or maintaining mobility through this method of training.
Similar gains in muscle size can be observed using heavy or light loads, provided the intensity of the exercises remains hard. However, heavy load strength training also improves strength and hypertrophy at the same time, making this a better training option in my opinion.
The next mini article in this series will look deeper at what stimulates hypertrophy, and how we obtain that within the gym.