Resistance training is the most effective way to prevent the progressive and inexorable loss of muscle mass and strength that occurs with aging. This process is known as sarcopenia, a Greek word meaning “poverty of flesh’.
Muscle loss begins at approximately age 40 in both men and women. We lose about 8% of our total body muscle mass every decade until age 70. At this point the progressive loss of muscle mass accelerates to 15% per decade. This decline is most notable in the leg muscles, increasing the risk of falls and disability as we age.
What is resistance training? In this type of exercise one is able to increase muscle size and strength by moving the body against resistance which can be provided by one’s body weight, a weight machine, free weights, barbells or resistance bands, to name a few modalities. Resistance training in midlife is an evidence-based method to improve the quality of your life after age 70.
Why does sarcopenia occur? As we get older the rate of muscle breakdown begins to exceed the rate of muscle formation. There are many reasons why this occurs. Aging is associated with decreased levels of certain hormones such as growth hormone (GH) and insulin-like growth factor 1 (IGF-1) which are needed to make new muscle. Testosterone levels drop which also leads to lower muscle mass and bone strength. Fat cells begin to infiltrate the abdominal cavity and surround organs such as the muscle and liver.
To make things worse, older individuals develop anabolic resistance, meaning that the body is less able to respond to existing hormonal signals to build muscle.
There are two different types of skeletal muscle: type I slow twitch muscle fibers which are best suited to endurance activities and type II fast twitch muscle fibers which enable us to perform speed and power exercises. As we age, we lose more type II fast twitch muscle fibers which decreases speed, explosive strength and power.
Other age-related changes also contribute to progressive muscle loss after age 40. Muscles are activated by nerves in a special arrangement called a motor unit. A nerve transmits a signal directly from the brain to a muscle, thereby activating it and causing muscular contraction. Aging is associated with loss of these motor neurons and decreased input from the central nervous system.
Other molecular structures in our body become more dysfunctional as we age. Throughout life, cells in our body release signaling molecules known as cytokines. These cytokines, which are typically composed of very small proteins, can increase chronic inflammation in the body and decrease the body’s ability to make new muscle and save existing muscle mass. Both aging and obesity cause increased levels of inflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-a). Many of these cytokines are released directly from fat and muscle tissue as we age.
So why is resistance training so important? It’s by far the best treatment we have for sarcopenia. Our body begins to build new muscle soon after a workout. The contraction of muscle during exercise activates receptors in the muscle tissue which then stimulate an increase in the release of muscle growth factors. These growth factors recruit skeletal muscle stem cells, also known as satellite cells. Satellite cells migrate to existing muscle fibers and activate new muscle tissue growth by a process called hypertrophy of muscle. To boost motor units, nerves are recruited to activate more muscle fibers. The end result is an increase in muscle mass and strength.
Phillips et al published an important study in 1997 showing us what this means in real life. In their study, just one episode of resistance training stimulates muscle protein synthesis within 2 hours after exercise. In the post exercise period, this increase in muscle synthesis can last for up to 16 hours in trained individuals and up to 24- 48 hours in untrained individuals.
Although aerobic exercise is also important for increasing blood flow to muscle, only resistance training has been shown to increase muscle fiber cross-sectional area and muscle strength and power. Weight training accomplishes this by increasing the number and size of type II fast twitch muscle fibers. There is some muscle breakdown that occurs after exercise but the overall balance favors muscle synthesis, especially when an adequate amount of protein is consumed in the diet.
Proteins are the building blocks of muscle and the body must have an adequate supply of protein in the diet to make new muscle. Because our bodies become less efficient at making protein as we age, research suggests that older individuals may benefit from a higher recommended daily allowance of protein- one gram of protein per kilogram of body weight every day (1 gm/kg/day). The current recommended dietary allowance (RDA) for protein intake for all adults is 0.8 g/kg/day.
It’s important to start slowly with resistance training. Untrained or older individuals should start with using weight machines and then progress to using free weights or barbells if tolerated.
My favorite resistance exercise is the loaded barbell squat because it activates so many different large muscle groups including the gluteals, the hamstrings, the quadriceps, the abdominal stabilizers and the calf muscles. This exercise more closely mimics functional movement patterns which are performed in sports and in everyday activities.
It is possible to significantly slow the rate of muscle loss while continuing to build new muscle. Ultimately, research has shown that regular resistance training in combination with an adequate dietary protein intake will slow sarcopenia and help maintain health and independence with aging.
References
Cruz-Jentoft, A. J., et al. “Sarcopenia: European Consensus on Definition and Diagnosis: Report of the European Working Group on Sarcopenia in Older People.” Age and Ageing, vol. 39, no. 4, 2010, pp. 412–423., doi:10.1093/ageing/afq034.
Koopman, R, et al. “Exercise and Nutritional Interventions to Combat Age Related Muscle Loss.” Sarcopenia – Age-Related Muscle Wasting and Weakness: Mechanisms and Treatments, by Gordon S. Lynch, Springer Science+Business Media, 2011, pp. 289–315.
Martone, Anna Maria, et al. “Exercise and Protein Intake: A Synergistic Approach against Sarcopenia.” BioMed Research International, vol. 2017, 2017, pp. 1–7., doi:10.1155/2017/2672435.
Phillips, S. M., et al. “Mixed Muscle Protein Synthesis and Breakdown after Resistance Exercise in Humans.” American Journal of Physiology-Endocrinology and Metabolism, vol. 273, no. 1, 1997, doi:10.1152/ajpendo.1997.273.1.e99.