Gradual loss of skeletal muscle mass and skeletal muscle strength is the most insidious and perilous age change of all
In my first blog, I explained that the trajectory of the aging process depends largely on an individual’s lifestyle choices. It is, therefore, important that every older adult understand exactly what age changes can be expected and secondly, and most importantly, how to negate or minimize them. This blog will describe one of the most troubling and debilitating effects of aging, loss of skeletal muscle mass (also referred to as muscle size) and loss of skeletal muscle strength. I will follow this up with insight 3 (my next blog) on what to do about these changes. Specifically, I will detail successful strategies of progressive resistance training plus consumption of quality protein.
Muscle mass and strength decline over time
It is well established that muscle mass and strength gradually decline over time. A starting point, although variable and depending on the daily level of physical activity, is generally denoted at about 50-60 years of age but may start many years earlier. Loss of muscle mass, termed sarcopenia, is about 1%/year whereas loss of muscle strength, designated dynapenia, is much greater, at about 3%/year. Unfortunately, these changes go unnoticed especially in the case of declining muscle size since fat accumulation sneaks in to replaces muscle cells that either shrink or disappear. This is illustrated in the MRI scans shown below. Often muscle weakness is regrettably accepted as an inevitable and unalterable age change.
Just a brief note on the terms, sarcopenia and dynapenia. A diagnosis of either sarcopenia (loss of muscle mass) or dynapenia (loss of muscle strength) indicates that a measureable quantity of decline in muscle structure and function has been determined. Although not set in stone, there are defined numerical “cut-off” values (e.g. values for mass of arms/legs, grip strength, force of knee extension, speed of walking or rising from a chair) associated with each term that have been established by professional medical research groups worldwide. If a patient undergoes an assessment in which mass and strength are quantified and the numerical values fall below the established cut-off, the physician will make a diagnosis of either sarcopenia or dynapenia or both and propose appropriate therapy to prevent a worsening of these losses. However, the goal for the older adult should be to continuously optimize muscle size and strength so that a designation of sarcopenia/dynapenia is never obtained or even considered.
Consequences of loss of muscle strength (dynapenia) – abundant, negative, and life-shortenin
Why be concerned about loss of muscle strength? Because this change definitely leads to:
(1) increased physical disability; decreased quality of life,
(2) increased risk of falling,
(3) shorter lifespan.
The most destructive change induced by dynapenia is the most obvious: reduced leg, chest, back, shoulder and arm strength/power (speed) that slow and hinder performance in all daily activities from standing to walking to lifting to breathing. As mobility and gait speed decline so does the total level of physical activity, further accelerating the decline in strength and power. This inevitably leads to physical disabilities, loss of independence, and reduced quality of life. Secondly, diminished skeletal muscle strength alters posture, a change which causes unsteady balance and an elevated risk of a fall. Falls are menacing events with a high probability of a fracture, hospitalization and lengthy recovery. Additionally, weakened chest, back and shoulder muscles secondarily compromise the ability to augment the exchange of oxygen and carbon dioxide during stressful activities e.g. climbing stairs. A reduction in gas exchange generally slows or halts the activity and reduces independence. Dynapenia not only translates into poor physical performance and physical disabilities but, sadly, it has been statistically associated with increased mortality (premature death).
Consequences of loss of muscle mass (sarcopenia)
Why be concerned about loss of muscle mass? Because this change definitely leads to:
(1) weight gain,
(2) elevated risk for Type 2 Diabetes
(3) cold intolerance.
Weight gain occurs because skeletal muscles burn up a lot of calories just for maintenance. The totality of muscle mass is huge and exceeds that of all other tissues combined. Less muscle tissue means less calories consumed by muscles and more calories converted to fat storage and hence an associated weight gain. In addition to the increased poundage, accumulated fat in the older adult locates, for as yet poorly understood reasons, to sites (abdomen or waist area; on top of major organs such as the heart) that encourage chronic low level inflammation, a major factor contributing to tissue damage. Clearly an unwanted effect. Secondly, muscles are one of the prime tissue targets that readily acquire ingested sugars, a process facilitated by insulin. Less muscle, less uptake of sugar by this tissue and more sugar remaining to circulate. Persistently elevated sugar levels augment the risk for Type 2 Diabetes and furthermore, promote spontaneous oxidative damage (a type of tissue damage) throughout the body, another unwanted effect that accelerates aging. Finally, an often overlooked function of skeletal muscles is heat production in the form of shivering at low ambient temperatures. Less muscle mass means less vigorous shivering and reduction in expected warmth. This is experienced as cold intolerance which means that at low ambient temperatures, one needs to put on more outerwear to keep warm. This compensates for the loss of extra heat normally supplied by customary muscle mass of young adulthood.
Pictures depict loss of muscle mass
The first illustrates the extent of muscle loss that typifies sarcopenia. The second picture show actual data of the cross-section of the thigh region obtained from MRI scans of 3 volunteers: a 40 year old triathlete, a 74 year old sedentary man and a 70 year old triathete. Triathlete are athletes who compete in the triathlon (competitive biking, running, swimming events). In each cross-section of the thigh muscle, the small white center circle is the bone. It is surrounded by dark material (muscle) and defined by an outer sheath. Thigh scans of the 40 and 70 year old triathlete are remarkably similar. However, major changes are observed with the center photo of a 74 year old sedentary man. Muscle tissue has disappeared and the space formerly occupied by muscle cells has been replaced with adipose tissue, another name for fat. This sobering image emphasizes the actual extent to which skeletal muscle can disappear. Regrettably, as serious as muscle mass disappearance may appear, the associated reduction in strength is several fold greater than the observed loss of mass!
It seems reasonable to assume that if one understands the severe consequences of aging in skeletal muscle, then what must follow is both an interest and a motivation to avoid them with proven interventions. My next blog (Insight 3) will discuss strategies that achieve this goal.