Dynapenia is the age-related loss of muscle strength and force. Tough it is a normal process that happens with aging, as the population grows older, dynapenia is gaining in importance, just like many other geriatric conditions.
In 2008, CDC reported that 16-18% of women and 6-8% of men cannot stoop, kneel, or lift 10lbs (ca. 4,5kg). A 1988 research by Himann and associates showed that with every decade after the age of 63, the walking speed decreases by a staggering 12.4% for women and 16.1% for men. This low physical performance greatly affects the life quality, and can even lead to an early death. It makes dynapenia a great challenge of modern medicine.
Dynapenia VS. Sarcopenia
Although these terms are often used synonymously, they don’t mean the same. While dynapenia is the age-related loss of muscle strength, sarcopenia is the age-related loss of muscle mass.
It has been considered for a long time that the loss of muscle strength was a result of muscle atrophy that happens with aging. However, recent experimental and longitudinal studies have shown that the loss of muscle mass, or sarcopenia, is responsible for only 6-8% of muscle strength decrease. This suggests that other factors contribute to dynapenia to a much larger extent.
If not Sarcopenia, what is the cause of Dynapenia?
The underlying factors for dynapenia are commonly classified as those related to the nervous system, and those related to the muscles.
Factors related to the nervous system
Normally, skeletal muscles are under the voluntary control of the brain. To perform a movement, neurons from certain areas of the brain cortex send a signal to the alpha motoneurons of the spinal cord. The signals travel down the spinal cord to activate the muscles. An alpha motoneuron and the muscle fibers it activates are called a motor unit. The more motor units are activated, the greater the muscle force is. The generated force can also be increased if the neurons of the brain cortex send signals more frequently. These two properties work together to gain the maximum muscle force.
With aging, the activity of the motor neurons of the brain decreases. This decline is associated with many changes that happen in an aging brain: atrophy of certain parts of the brain cortex, reduction in the neuron cell body size, a reduction of the total length of the neural fibers, etc. The capability of brain motor neurons to activate the alpha motoneurons of the spinal cord is also compromised in older adults compared to young adults. That is why older adults also require a greater relative effort to perform simple tasks.
Similar changes happen with the alpha motoneurons of the spinal cord as the number and size of the motor units show a decline with aging. Taking everything into account, even a moderate change in the function of cortical and spinal neurons can lead to a significant reduction of physical performance.
Factors related to the muscles
As mentioned, sarcopenia is another contributor to the decline of the muscle strength. Of greater importance are the qualitative changes in muscles; with aging, muscles become less able to process the signal from neurons and perform movement. Muscles of older adults are infiltrated with fatty cells and linked to reduced muscle strength.
Why is Dynapenia Dangerous?
Until recently, medicine aimed toward expanding the life span, and this was successful. But, what is the use of living long if one is not satisfied with his/her life?
Several studies have shown that low muscle strength is strongly linked with poor physical performance and disability. This is particularly important when it comes to gait – the gait of the people with dynapenia is slow and unstable, they are frail, and experience fatigue more often during everyday activities. People with dynapenia are prone to falls and fractures, they are often functionally dependent and have to use a cane, a walker, or even a manual wheelchair. Gait disability itself to the risk of mortality.
The decreased handgrip strength, which is a marker of dynapenia, was linked to a decrease in performance of the more complex daily activities. Handgrip strength is recognized as an important predictor of life satisfaction and quality. This means that a person with a weak handgrip is often denied the pleasure of working, driving, or playing games.
Finally, many studies, such as the famous InCHIANTI study, have shown that a decrease in muscle strength and a slower gait are associated with higher mortality. Unlike sarcopenia, these are also powerful predictors of health-related events in elderly patients.
What can be done to Prevent and Treat Dynapenia?
Physical activity is the most effective intervention to prevent, slow down and treat dynapenia. However, not every type of physical activity is equally beneficial – studies have found that resistance exercise training (RET) is the most successful in combating muscle weakness and wasting associated with aging.
Resistance exercise training is any physical activity in which muscles are forced to contract against an external resistance, for example, gravity, weights, or machines. It is the best type of activity to improve muscle strength, endurance, and thickness. For the best results, the intensity, duration, and frequency of training sessions must be adequate. It is recommended to perform RET under professional supervision – this particularly stands for the elderly, who often have associated health problems such as lung and heart diseases, instability, osteoporosis, etc.
The ideal training regime includes 2-4 exercise sessions per week, performed on alternating days. A session should last between 30 and 60 minutes. In the beginning, the trainings should include exercises for all major muscle groups. As the fitness and muscle strength become better, the intensity of exercises should gradually increase, and the regime can later be switched to performing exercises for only several muscle groups in one training session. The number of repetitions in a set should also increase, as well as the number of sets.
The following table shows some of the common RET exercises.
Flat Chest Press Push-Ups
Pull Downs Pull Ups Shrugs
Seated Hammer or Preacher Curls Triceps Extension
Overhead Press Upright Rows Lateral Raises
Leg Press Leg Extensions and Curls Lunges Machine Squat
Standing Calf Raises Seated Calf Raises
RET outcome can be boosted if the protein intake is higher, or the proteins are supplemented. However, this is not recommended for older people as their kidney function is often impaired.
Scientists have screened various nutrients that could improve the nervous and muscle system and help combat sarcopenia and dynapenia. Vitamins D and E, selenium, and carotenoids are most commonly employed in this context. The results of studies in this field remain inconclusive– to date, no nutritional supplement has shown significant improvement in muscle strength and force without concomitant exercise. Therefore, resistance exercise training continues to be the best and paramount intervention for treating and preventing complications of dynapenia.
Marina is a medical doctor from Belgrade, Serbia. She graduated with high honors in 2020 and is aspiring to become a pathologist. During her studies, she took part in several scientific researches, mostly in the pharmacology niche. She was also an assisting teacher at the Department of Histology and Embryology for 5 years (2015-2020).
Marina has years of experience as a writer on health-related topics. Apart from English, she fluently speaks several languages, including Spanish, Russian, and Czech.
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