If you’ve been considering when to start that resistance training programme and / or pondering over whether muscle mass really is that important, then this article is for you – it provides a brief overview of muscle mass and what the research says about muscle mass for health and lifespan.
Lean muscle vs muscle?
There are three main types of muscle: smooth, cardiac and skeletal.
Smooth muscle covers the organs, cardiac muscle supports heart function and skeletal muscle is attached to the bones to enable movement. Usually, lean muscle refers to skeletal muscle and the terms are used interchangeably. The term lean muscle may also be used to emphasise the fact that an individual only wishes to gain muscle, rather than the fat present within muscle – there may potentially be a small amount of fat present within muscles. This has been shown to be beneficial in the case of athletes but harmful in the case of overweight individuals (the fat seems to serve very different purposes).
Lean body mass defined:
Lean body mass is defined as total body weight minus fat mass:
Lean body mass = Total body weight – Fat mass
Lean body mass may also be termed fat free mass (FFM).
Lean body mass consists of: organs, bones, muscles, skin and body water. Although bone density does decrease as you age, unless you are especially underweight or overweight, the size of your organs will stay relatively stable. Thus, it is the muscles and body water that people usually refer to when they consider lean body mass. However, organ size may be more of a consideration with someone who is especially under or overweight, potentially in a more medical setting. Lean muscle mass is lean body mass minus total body water.
Why is muscle mass important?
Before we dive into the multiple reasons that muscle mass is so important, a quick note on sarcopenia, which is defined as a certain loss of muscle mass and strength (approx. 3-5%). Sarcopenia is a very likely outcome from aging, as well as certain health conditions. It is associated with a low-grade inflammatory state, as well as the production of harmful substances (oxidative stress) and impaired muscle protein synthesis. Fast twitch muscle fibres are replaced with fat and connective tissue. As a result, there is loss of structural and contractile muscular function, as well as the loss of metabolic function. Subsequently there is often a strong association with increased insulin resistance, less blood sugar disposal and increased tendency to develop type 2 diabetes.
Now on to the benefits of muscle mass….
More muscle mass for a longer life: muscle mass is inversely associated with risk of death (Abramowitz et al. 2018). Individuals with sarcopenia, defined as the loss of muscle mass and muscle strength, may have a 60% increase in the relative risk of death compared to people without sarcopenia (Zhang et al. 2018).
More muscle mass for better health outcomes: from a longer stay in hospital, to more severe complications, to poorer physical function, low muscle mass is associated with poor health outcomes (Prado et al. 2018). Therefore, increasing muscle mass is key for optimising opportunities for beneficial health outcomes.
To reduce risk of chronic diseases: low muscle mass is associated with increased risk of chronic disease such as heart disease and cancer (Wolfe 2006).
For building and maintaining strong bones: muscle mass is closely associated with bone density (Sutter et al. 2019). The stimulation of bone growth requires the mechanical loading of bone tissues, aka resistance training, which builds muscle (Hong et al. 2018). Bone density is also positively associated with life span, due to frailty and increased risk of fractures being closely associated with reduced life span. You can build muscle mass and bone density together, meaning that you get better health and life outcomes with one investment!
For healthy tissues and organs: adequate muscle mass is vital for maintaining certain levels of the building blocks of proteins (amino acids) in the blood. This is necessary for tissues and organs such as the skin, brain, heart and liver to survive, thrive and be healthy (Wolfe 2006).
For reduced risk of becoming overweight: having less metabolically active tissue, lean muscle mass, can contribute to an energy imbalance over a prolonged time, resulting in energy intake exceeding energy expenditure (Wolfe 2006). For example, the energy released per day as a result of muscle protein synthesis may range from approximately 485 calories per day in a young man who is muscular, to approximately 120 calories per day in an active elderly woman (Wolfe 2006). Although the energy expenditure associated with large muscle mass in being particularly overweight may be insufficient to offset energy intake, increased muscle mass can be capitalised on to increase energy expenditure and promote weight loss.
Recovery from illness: muscle mass plays a critical role in the recovery from illness and an inflammatory response. Muscle strength and function are central to the recovery process (Wolfe 2006).
Increase metabolic rate: resting energy expenditure is the largest component of total energy expenditure and the energy expenditure related to muscle metabolism is the only component that might vary considerably. Large variations in muscle mass are possible and muscle tissue is more energy requiring than fat tissue. Additionally, the rate of muscle protein turnover, the muscle protein synthesis and breakdown also vary and are responsible for the energy expenditure of resting muscle.
To increase and maintain insulin sensitivity: relative to body size, higher muscle mass is associated with better insulin sensitivity (Srikanthan et al. 2011). Increasing muscle mass via resistance training may increase the opportunity for sugar in the blood to be cleared and utilised, as well as reducing the amount of insulin required to maintain normal blood sugar levels (Cuff et al. 2003). This is particularly helpful in contributing to the maintenance of insulin sensitivity long term and increasing insulin sensitivity.
To increase metabolic health: when muscles become unable to uptake blood sugar normally, there may well be the development to poor metabolic health, such as type 2 diabetes. Increasing muscle mass provides a greater disposal for blood sugar as well as the opportunity to increase healthy muscle tissue, Relative to body size, more muscle mass is associated with reduced risk of developing type 2 diabetes (Srikanthan et al. 2011).
For movement: skeletal muscle attaches to bones, tendons and ligaments and facilitates movement. Strong skeletal muscle supports safe, agile and flexible movement.
Muscle weakness may contribute to osteoarthritis: research indicates that low muscle mass may contribute to osteoarthritis.
Muscle mass vs muscle strength?
Whilst we know that there is strong association between lean muscle mass and mortality, research also indicates that low muscle strength is independently associated with increased risk for mortality (Ran et al. 2018). This may translate into it being okay if you have low muscle mass, provided that you have adequate strength. Therefore it may be more relevant to be concerned with how strong you are rather than how big your muscles are. However, muscle size and muscle strength do track very closely and therefore it is likely that the bigger your muscles get the stronger you’re probably becoming too.
How to measure muscle mass
Either a CT scan or MRI scan are considered the most accurate methods of body composition measurements and muscle mass. However, they are not particularly practical options – in terms of radiation and cost.
As part of the body composition assessments we offer in clinic, we assess muscle mass, shown as total muscle mass and then broken down into torso, right leg, left leg, right arm and left arm. This allows us to track total levels in association to norms as well as look for imbalances that may highlight weakness or injury.
We also look at a marker called phase angle. This is also associated with muscle mass but also muscle quality and strength. A low phase angle when one has normal muscle mass, may be an indicator of poor muscle quality and strength.
Our chosen assessment method is a well research BIA device by SECA. You can read more about the method we use, and its comparative accuracy to gold standard assessments like MRI for muscle mass by going to our main page on body composition testing.
Key take aways:
Muscle mass is strongly associated with a host of positive health outcomes including: reduced risk of chronic disease, better recovery from illness, improved health outcomes, longer life span, better metabolic health and strong and dense bones.
Muscle mass may be a key factor in maintaining a healthy weight: contributing to a higher metabolic rate due to being a more metabolically active tissue, and therefore contributing to a higher energy expenditure.
Muscle mass levels can be measured by body composition assessment: through using either DEXA scans or BIA. This can be a useful mechanism to track progress towards health and performance goals.
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References
- Zhang et al. (2018). Sarcopenia as a predictor of all-cause mortality among older nursing home residents: a systematic review and meta analysis
- Abramowtiz et al. (2018). Muscle mass, BMI, and mortality among adults in the United State: a population-based cohort study.
- Prado et al. (2018). Implications of low muscle mass across the continuum of care: a narrative review.
- Hong et al. (2018). Effects of resistance exercise on bone health.
https://pubmed.ncbi.nlm.nih.gov/21778224/ - Darcye et al. (2003). Effective exercise modality to reduce insulin resistance in women with type 2 diabetes.
https://care.diabetesjournals.org/content/26/11/2977 - Scafoglieri et al. (2018). Dual energy X-ray absorptiometry: gold standard for muscle mass?
- Ran et al. (2018). Associations of muscle mass and strength with all-cause mortality among US older adults.
- Wolfe (2006) The underappreciated role of muscle in heath and disease, American Journal of Clinical Nutrition
