Muscles are an essential part of motion and action in the lives of all human beings. Understanding the anatomical structure, function and adaptations related to muscles are paramount not only to our knowledge base, but also our deeper appreciation of our participation in activities of daily living. Without muscles our framework of bones would have no means for transporting us from place to place each day.
Structure of Muscles
Internally, all muscles share a basic structure and order. The structure begins with tendons, which connect muscles to bones. Then multiple levels of connective tissues and muscle fibers form the next level of structures internally. These structures include the fascia, perimysium, epimysium, fasiculi and endomysium. Finally, at the last level, myofibrils are located within the cell of the muscle. The combination of these structures all play a role in the function of muscles.
Types of Muscles
There are three types of muscles, including skeletal muscles, smooth muscles and cardiac muscles. Skeletal muscles are considered voluntary muscles, meaning that they can be contracted consciously by an individual. Smooth muscles are considered involuntary, meaning that they contract without conscious control. Smooth muscles are located in internal organs such as the stomach, blood vessels and heart.
Superficial vs. Deep Muscles
Superficial muscles are those that are surface-based or more outwardly located, while deep muscles are located more internally. Superficial muscles, such as the biceps brachii and the quadriceps, are highly visible. The rhomboids, which are located beneath the trapezius, are considered deep muscles.
How Muscles Work
In order for muscles to produce a movement, a series of processes has to take place. Skeletal muscles cannot contract without a signal being sent to the muscles via the neurotransmitter acetylcholine. Acetylcholine serves as the catalyst for beginning the muscle impulse chain reaction. This chain reaction ultimately causes the muscle membrane to be stimulated, causing the release of calcium. Calcium release triggers a shortening of the sarcomeres within the muscle that causes muscular contraction. This muscle contraction will continue to occur as long as there is a signal to the muscle via the neurotransmitter acetylcholine.
Benefits of Weight-Bearing Loads on Muscles
Muscles have an incredible ability to adapt to stimuli that are placed upon them. Weight-bearing loads cause damage to muscles, which results in muscles becoming stronger in order to meet the demands of the stimuli placed upon them. Weight bearing loads play a significant role in reducing the loss of muscle mass as we age, which is called sarcopenia. In the Volume 4, number 3, 2000 "Journal of Nutrition, Health and Aging," researchers Roth, Ferrell and Hurley indicated that weight bearing loads were effective in improving strength and muscle size, which ultimately reduces the effects of sarcopenia.
In the March 2000 "Journal of Gerontology Series A," researchers Ivey, Tracy, Lemmer, NessAiver, Metter, Fozard and Haley demonstrated that the addition of weight bearing loads for nine weeks contributed significantly to increased muscle quality. The study also showed that even with no training occurring for 31 weeks after the initial nine weeks of resistant training, muscle quality levels remained elevated beyond baseline levels for the subjects involved in the study.
References
- Roth, S.M., R.E. Ferrel, & B.F. Hurley. 2000. "Strength training for the prevention and treatment of sarcopenia." The Journal of Nutrition, Health & Aging 4(3):143-155.
- Ivey, F., Tracey, B., Lemmer, J., NessAiver, M., Metter, E., Foxard, J. & Hurley, B. (2000). Effects of strength training and detraining on muscle quality: age and gender comparisons. The Journal of Gerontology Series A: Biological Sciences and Medical Sciences. 55 (3), B152-157.
