How Weight Training Increases Muscle Fiber Size by Increasing the Number of Myofibrils

The changes you see and feel from weight training are more than skin deep. Yes, you feel stronger and you see the changes in your muscle size, but you are also increasing the number of muscle fibers with new protein strands known as myofibrils. How much change occurs depends on your genetics, your commitment to a training routine and also your rest days for muscle recovery and growth.

  1. Ouch, That Hurts!

    • When you hear the word "trauma," you think of pain. But trauma caused by resistance training is necessary for muscle fiber growth. You challenge the muscle fibers beyond their capabilities, which damages the cells of the muscle fibers. Your body responds to this damage by sending new cells to the trauma center. These satellite cells are on the outside of the muscle fibers. They move to the inside, bond to the muscle fibers, and increase the fiber size, thus increasing muscle size.

    Multiplying Myofibrils

    • Satellite cells change the size of the muscle fiber in two ways: thickness and number. When the new cells bond to the fibers, the thickness of the strands increases. Some cells fuse together to create new myofibril strands. Cells continue to multiply and grow, strengthening the new myofibril strands and increasing your overall strength.

    Protein Power

    • The cellular proteins that make up the new myofibril strands need protein sources to continue their growth. A study presented in the September-October 2012 issue of the American College of Sports Medicine's "Health and Fitness Journal" reports that consuming small amounts of food protein sources throughout the day is the best choice for increasing myofibril growth, which results in a stronger muscular contraction, the ability to lift heavier weights and greater strength gains for you.

    Thanks, Mom

    • Genetics play a significant role in how fast and how much your muscle size improves. For example, the growth factor hormone can affect the cellular activity that leads to new myofibrils. The growth hormone originates in the pituitary gland, and your body makes more or less depending on genetics, similar to the way insulin production varies between people. You can stimulate the release of the growth hormone with resistance exercise. Participate in resistance exercise two or three days a week. Strength train your large muscle groups, such as your chest, back, shoulders, arms and legs, with at least one day of rest between training sessions. With proper training, recovery and eating habits, you should see the results of your new myofibrils within several weeks to several months.