Why Muscle Strength Decreases with Age
Many studies have sought to determine what factors contribute to a decrease in muscle strength as we age.
It is no secret that muscle strength remains a factor in longevity and good health. But unfortunately, as the human body ages, muscle strength and muscle mass naturally decrease, leaving scientists and fitness experts to wonder, what can be done about it?
Two significant studies on the topic are found here and here, illustrating the extent to which muscle loss related to age is experienced.
According to the studies, the loss of muscle strength and muscle mass accelerates with age. However, muscle strength loss occurs faster than muscle mass loss. While muscle mass doesn't affect overall muscle strength, the above-referenced studies suggest that something else plays a role in age-related loss of muscle strength.
Why, with age, do we experience a loss of muscle strength?
It takes a series of complex and coordinated events for the skeletal muscle to produce contractile force.
First, our muscles become innervated by the motor neurons in our brain and spinal cord, thus signaling the muscle to contract. That motor neuron delivers an impulse to the muscle at our neuromuscular junction, causing a signal to propagate and excite the muscle fibers. That impulse triggers a calcium release into the muscle fibers, inducing actin and myosin protein reactions that result in muscle contraction.
After exploring many cellular, molecular, and systemic systems to figure out why humans experience a decrease in muscle strength as we age, most researchers agree that answer lies with two significant issues:
Muscle Quality Loss
The bad news is that muscle quality loss is inevitable. It progresses intrinsically on a cellular level through numerous steps along that contraction pathway outlined above. For example, when it comes to older muscles, the activation and contraction coupling ultimately becomes inefficient as calcium ion channels decline within the fibers of the muscle.
Age can also be a contributing factor in myosin structural change thus reducing the ability to stay in its strong-binding and force-generating state needed for proper muscle contraction.
Furthermore, as our bodies age, they accumulate oxidative DNA damage related to stress, resulting in lower mitochondrial density and the decline of muscle mitochondrial functions, leading to the insufficient production of ATP necessary for proper muscle contraction.
However, there is one other unavoidable factor that contributes to a decline in muscle quality with age related to the "slow twitch" (type I) and "fast twitch"(type II) fibers making up our muscles.
During lower-intensity endurance-type activities, our bodies use slow twitch fibers, which contract more slowly and are more fatigue-resistant. Conversely, fast twitch fibers are used in more rapid, more powerful movements using more force to produce higher tension outputs. These powerful muscles facilitate activities like jumping or sprinting. Unfortunately, our proportion of fast twitch fibers decreases with age, resulting in a loss of muscle strength.
On top of losing muscle quality as we age, we also lose neuromuscular innervation. In our lifetime, our nerves constantly cycle through the process of innervating and denervating our muscle fibers. Muscles experiencing high usage from repetitive motions or great tension end up having more nerve and muscle connections that support increased muscle activation.
In other words, the more we use a muscle, the more it develops neuromotor connections, improving contractile strength. However, the opposite can also be true. Muscles that are not used enough will end up less innervated. Prolonged denervation of the muscle will lead to decreased function and neuromuscular communication.
Healthy young people who regularly exercise typically strike a balance in muscle innervation and denervation as a response to use. However, denervation outpaces reinnervation among older people, regardless of their activity level. That is likely the result of motor neuron failure associated with aging, unstable neuromuscular junctions, and our neurons' impaired ability to reinnervate muscle fibers. Ultimately, this decreased communication between the brain and the muscles results in a lowered force, slower speeds, and compromised overall performance.
How to Combat Muscle Strength Loss
There isn't much we can do to mitigate age-related muscle quality decline, but we have limited control over their neuromuscular remodeling. The increased activation of your muscle fibers as a result of physical activity will initiate events that can diminish the loss of muscle strength. Active muscles release biochemical signals promoting motor neuron fiber growth. Therefore, inducing them forms muscle connections and enhances the excitatory signal transmissions along our neuromuscular junctions.
Those combined effects will improve our neuromuscular communication, leading to increased strength and better control of muscle contractions to counteract the impact of an aging muscle.
Specifically, power training and endurance training can significantly contribute to neuromuscular remodeling. In fact, we simply need to look at life-long athletes as an indicator that regular exercise later in life can improve muscle strength and function.
In other words, for optimal health, we should exercise throughout our lives because it is the best defense against health deterioration and the best way to extend our lifespan.
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For anyone in the Seattle area who wants to get started on combating age-related muscle loss, make an appointment to meet with one of our private trainers in Seattle at Demco Fitness.
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