Striated muscle, the type of muscle that vertebrates use to move their bodies, makes up about 40 percent of the total body mass in humans, according to Dr. Michael D. Mann of the University of Nebraska Medical Center. These muscles undergo a variety of changes during vigorous exercise, making them some of the most adaptable tissues in the human body.
Muscle Structure and Contractions
The striated skeletal muscles responsible for the movements you experience during exercise are made of masses of fibers. Those fibers are composed of smaller myofibrils, which in turn are made of myofilaments. During exercise, muscle contractions occur when neurons activate the muscle tissue. The myofilaments in the muscle slide past one another to form layers, shortening the muscle. During contraction, the muscle fibers generate small amounts of electrical activity, known as action potentials, which can be measured by electromyography.
Blood Flow During Exercise
Small blood vessels called arterioles dilate when exercise begins, to provide more blood flow to the muscles. Chemical effects in the muscle trigger the dilation when the muscle begins to use more energy in exercise. Blood flow is also increased because the heart begins beating more rapidly. During vigorous exercise, the blood flow to a muscle can reach up to 20 percent more than at its resting state.
Muscular Adaptation
Vigorous exercise, like intense strength training, causes microscopic damage to a muscle’s fibers. When the exercise period has ended and the muscle is at rest, a process begins to repair the damaged fibers. This mechanism employs cells called satellite cells, which multiply and fuse together, connecting with existing muscle. The satellite cells repair damaged fibers and also form new ones, increasing the total bulk of the muscle. This process occurs in much the same way in both men and women, but because of differences in body composition and hormone balances, gender has an impact on the ability to build muscle mass, University of New Mexico researchers explain.
Metabolism and Fatigue
Muscles typically use oxygen for fuel, but when the body exercises intensely, the muscles need fuel more rapidly than oxygen can be provided. When this occurs, the body switches to glucose to provide energy. The metabolism of glucose results in the production of lactic acid, or lactate, as a byproduct. Lactic acid makes the muscles more acidic, resulting in a burning sensation. When lactic acid levels build up and the burning sensation increases, it makes it more difficult for the body to continue exercising, forcing a period of rest to allow the muscle to repair itself.
References
- “The Nervous System in Action”; Muscle Contraction; Michael D. Mann, Ph.D.; July 2008
- University of Washington; Cardiovascular Response to Exercise; Tom Linder, Ph.D., et al.
- University of New Mexico; How Do Muscles Grow?; Young sub Kwon, M.S., and Len Kravitz, Ph.D.
- “Scientific American” magazine; Why Does Lactic Acid Build Up in Muscles?; Stephen M. Roth, Ph.D.; Jan. 23, 2006
Member Comments