Research & Education

Dynapenia: Underappreciated Influence in Healthy Aging


In the functional naturopathic and allopathic medical communities there’s usually a lot of focus on children’s health: autism spectrum disorders the increasing incidence of food allergies proper diagnosis of ADD and ADHD and more. But what about the health and wellness of older people? When there are discussions about health concerns among aging people—which really is every single one of us from the moment we’re born—it seems like attention is given primarily to Alzheimer’s disease mild cognitive impairment and other forms of neurological degeneration that affect the mind. And certainly no one wants to lose control of their memory and behavior. But what about the physical body? When physical degeneration becomes severe it can be just as devastating as mental and cognitive instability and they can have similar ramifications for independent living.

Sarcopenia—the loss of muscle mass during the aging process—gets the lion’s share of attention regarding the physical wellness of older people. Existing quietly in its shadow but no less important is dynapenia. In contrast to the loss of muscle mass dynapenia is the loss of muscle strength. (The word comes from the Greek dyna for “power strength or force” and penia for “poverty” and encompasses both strength and mechanical power—that is how much someone can lift and how quickly or explosively they can lift it.) Having weak muscles and poor strength can affect people of any age but it may be particularly devastating for older people. Quality of life in older age is intimately tied to one’s degree of mobility range of motion and movement without pain. Independent living depends on being able to conduct everyday activities that require a certain degree of muscle strength such as carrying heavy grocery bags from the car into the house walking up or down stairs and getting up out of a chair easily and without struggle.

Some amount of strength loss in one’s twilight years is to be expected but the more someone can preserve muscle mass and power and delay the decline of these the longer they’ll be able to remain independent take care of everyday household maintenance and even see to their own “care and feeding” so to speak. According to one study a staggering 16% to 18% of women and 8% to 10% of men in the U.S. over age 65 cannot lift 10 pounds or stoop or kneel down. This is a grim statistic indeed. It might be nearly impossible for such individuals to get in and out of an SUV without help not to mention a large bag of dog or cat food might weigh ten pounds! (Forget shopping at the warehouse store…)

The age-related loss of muscle strength is not fully and directly correlated with the loss of muscle mass. According to studies muscle strength is lost at a substantially higher rate than muscle mass and gaining muscle mass does not necessarily prevent a decline in muscle strength. For example in a small cohort of men over age 69 with low IGF-1 levels but who were otherwise healthy growth hormone treatment for six months resulted in increased lean tissue mass and decreased fat mass but no improvements in functional ability. And while both sarcopenia and dynapenia are risk factors for functional limitation or physical disability in older adults according to pooled data from several studies dynapenia seems to have a slight edge over sarcopenia in contributing to these outcomes. 

Precise diagnostic criteria for identifying dynapenia are lacking but two commonly used determinants are grip strength and knee extensor strength. And if muscle size isn’t the main issue in dynapenia then what is? Researchers believe the loss of strength is closely related to neurological deficits that affect muscle activation and intrinsic force generation. There may be a loss of ability to recruit and fully engage motor neurons and muscle fibers which may occur regardless of the size of a muscle. Data from post-mortem dissections indicate that individuals over age 65 show as much as a 43% volume decrease in premotor cortex neuron cell body size compared to younger people and it has been observed that older adults have maximal motor unit firing rates 35% to 40% lower than those of younger adults.

As for how to prevent dynapenia unfortunately except in sci-fi movies it’s just not reasonable for people to expect to reach their eighties or nineties with the same strength power and mobility they enjoyed in their twenties. Some degree of muscle decline and deterioration is inevitable and unavoidable. Not much is known about the role of nutrition in dynapenia except that the same healthy diet and lifestyle habits that promote general health and wellness might help stave off the neurodegeneration underlying dynapenia. (And to whatever extent dynapenia may be at least somewhat influenced by sarcopenia protein requirements for older people are likely significantly higher than general dietary guidelines suggest.) That being said with the goal of delaying this what holds true of so many other things in life—use it or lose it—likely applies. To whatever extent possible people should continue to engage in muscle strengthening activities as they age. A walk or jog along a scenic outdoor path is great but for healthy aging lifting heavy things once in a while might be just as important as a good diet.