Muscle Hypertrophy vs. Muscle Hyperplasia

Edited by: Danielle Abel

When you're thinking about your own programming, or programming for your athletes it's important to understand how and when muscle hypertrophy occurs. Understanding this process and timeline will allow you to make better training & nutrition decisions as it relates to your program. 

When you train your muscles, the muscles are either stimulated due to mechanical tension, metabolic stress, or muscle damage or a combination of these. 

Within each muscle fiber there are undifferentiated cells called satellite cells that are awaiting to be formed into new cells or tissue. 

Hyperplasia or no?

If the cells were to form new muscle cells (myofibrils), this process would be considered muscle hyperplasia. There is literature from animal studies that this occurs in animals, but there is controversy in human studies if hyperplasia actually occurs or not. 

Based on the currently available literature, hypertrophy seems to be the most common way myofibrils increases in size. In hypertrophy, new fibers of actin and myosin are added to the myofibril itself, increasing or expanding the individual myofibril's size.

How hypertrophy works 

• Training stimulus occurs
  • Myofibril is damaged
    • Hormones signal satellite cell activation
      • Testosterone signals growth hormone, and growth hormone signals IGF1 (insulin-like growth factor 1)
        • Then, IGF1 signals mechanogrowth factor (MGF)

IGF1 becomes elevated 4 to 6 hours after training has ended, so this process doesn't occur immediately, which makes the whole "eat protein immediately after your workout" recommendation kind of less than helpful. You need protein regularly throughout the day because muscle protein synthesis occurs over time.

IGF1 stays peaked for up to 72 hours after training. 

MGF causes the cascade of muscle protein synthesis (below) from available circulating protein that is broken down into amino acids.

In it's most basic sense, hypertrophy is just adding proteins to existing muscle cells. 

When the satellite cells are becoming differentiated by MGF, they use some of the RNA from nearby myofibrils to adopt the characteristics of that cell. As with the case in hypertrophy, these satellite cells grow into sarcomeres (actin and myosin) that expand the size of the myofibril itself.

The most common additions occur in parallel - which makes the muscle wider. Sometimes "series" additions occur which makes the muscle longer.

Practical Application

Tieing it back to training and nutrition, when you are working with athletes and clients, you can help them improve their hypertrophy efforts by coaching them to ensure they are consuming protein consistently in the 2-3 days following training and that the protein is adequately spaced out throughout the duration of the day to maximize its availability for muscle tissue growth. 

Keep in mind that this process of hypertrophy also occurs in tendons through the laying down of collagen. As more and more collagen is deposited, the tendon becomes thicker and stronger, which increases your tissue tolerance to plyometrics, allowing you or your athletes to do more reps of plyos, increasing their ability to jump higher, run faster, and run longer. 

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