What is Sarcopenia?
Did you know that a continuous, lifelong process of muscle loss, known as sarcopenia, begins around the age of 30 and continues with a 3-5% loss of muscle mass and muscle strength with the passing of each decade? Sad but true.
While losing muscle is considered a normal consequence of the aging process, understanding the factors involved in this process can help us slow down the inevitable with the goal of maintaining strength and mobility well into our senior years. Our discussion focuses on four known factors associated with sarcopenia, the medical term for muscle loss due to the aging process.
Four Reasons Why We Lose Muscle After Age 30
- Loss of motor units.
- Conversion of muscle fibers.
- Reduction in protein synthesis.
- The invasion of fat into muscle fibers.
Let’s briefly consider what each of these factors involve.
Loss of motor units. The ability to move and maintain muscle tone depends upon a connection between a neuron in the spinal cord and its assigned muscle fiber(s). Together, the neuron and muscle fibers, known as the motor unit, cause the muscle to contract. As we age, the motor neuron begins to fail due to wear and tear or inactivity. Reduced signaling from the nerve to the muscle leads to muscle atrophy, loss of strength, and eventual loss of muscle fiber when the neuron dies. Although other motor units initially try to take up the slack, they soon become overworked, causing them to become less efficient over time. The loss is gradual but continuous across the lifespan. Loss of motor units leads to reduced muscle mass and muscle strength.
Conversion of muscle fibers. Muscle fibers may be described as either fast twitch or slow twitch. Fast twitch fibers are able to rapidly generate high muscle tension for quick action but they fatigue quickly. Slow twitch fibers are fatigue resistant and are usually associated with fine manipulations. They are the first muscles to be recruited when a minimal level of muscle power is needed. When a motor neuron dies, fast twitch muscle fibers may convert to slow twitch fibers as adjacent motor neurons re-innervate orphaned muscle fibers. A reduction in hormones levels (testosterone, estrogens, growth hormone, and vitamin D) also accelerates the conversion process, affecting muscles and tendons, resulting in a gradual reduction in fine motor activity, balance, and speed of movement. That’s why daily activities like climbing steps or even getting up out of a chair become difficult.
Reduction in protein synthesis. Body structures and tissues are in a continual state of repair, breaking down and building up. With age, muscle protein synthesis and muscle regeneration slows down, resulting in reduced muscle mass. A reduction in hormones also affects the rate of muscle protein synthesis and muscle mass, contributing to an increase in body fat.
The invasion of fat into muscle tissue. As muscle fibers and muscle mass diminish, fat begins to deposit itself in the muscle fibers, significantly reducing muscle strength.
What’s a Body to Do?
Studies have shown that properly designed progressive resistance training, 2-3 times a week, is an effective way to intervene in or prevent sarcopenia. Resistance training supports overall muscle strength, improves gait, and speeds up timed movements by increasing the effectiveness of neuron firing rates and muscle fiber recruitment. It also positively influences muscle protein synthesis and hormone concentrations. Other factors involved in retaining muscle mass and strength is the adequate intake of calories and protein in the diet. This can become challenging as an individual ages, especially if their appetite is waning. If you have experienced progressive loss of muscle mass and strength due to chronic illness or aging, talk to your doctor before beginning a program of progressive resistance training and remember, easy does it!
Sarcopenia: The Mystery of Muscle Loss by Chantel Vella, M. S. & Len Kravitz, Ph.D.
An Overview of Sarcopenia: Facts and Numbers of Prevalence and Clinical Impact by Stephen von Haehling, John E. Morley, and Stefan D. Anker.
Not Being Able to See the Muscle for the Fat by Christopher J. Oliver.