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Deep Dive: Muscle mass, quality, strength - which is more important?

As we age, there is no question that we lose muscle mass as well as muscle strength and function. Ways to mitigate against these changes as we age are key to one’s pursuit of longevity. First, let’s make clear a few definitions.



Muscle mass refers to the size and volume of muscles, while muscle strength refers to the amount of force a muscle can generate.


As we age, we naturally lose muscle mass and strength, a process known as sarcopenia. This can lead to reduced mobility, increased risk of falls and fractures, and a decline in overall health and quality of life.


There have been several studies that have looked at muscles through the lens of longevity. Here we summarise a few key studies from the Health ABC Study, and the NHANES study to name a few, looking the whether muscle mass, muscle quality, or muscle strength are important.


Key Takeaway: Muscle strength and functional capabilities are important for longevity. Maintaining good amount of muscle mass is also associated with longevity in several studies. The overall strategy is to maintain good muscle mass, strength and function and exercise that aim to optimise these metrics will help in your longevity pursuit.


 

Title: Association between muscular strength and mortality in men: prospective cohort study Authors: Ruiz, J. R., Sui, X., Lobelo, F., Morrow, J. R., Jackson, A. W., Sjöström, M., & Blair, S. N. Publication: BMJ, 337, a439 (2008) DOI: https://doi.org/10.1136/bmj.a439


Summary:

This study aimed to investigate the association between muscular strength and mortality in men. The researchers conducted a prospective cohort study involving 8,762 men aged 20-80 years who underwent a comprehensive health examination between 1980 and 1989. The participants' muscular strength was assessed using one-repetition maximum tests for leg and bench press exercises. The study followed the participants for an average of 18.9 years.


The results showed that higher levels of muscular strength were significantly associated with a lower risk of all-cause mortality, as well as a lower risk of death due to cancer and cardiovascular disease. This association remained even after adjusting for potential confounding factors such as age, body mass index, and cardiovascular fitness.


Moreover, the study found that the combination of high muscular strength and high cardiovascular fitness provided additional protection against mortality compared to high levels of either factor alone. This suggests that both muscular strength and cardiovascular fitness are important components of a healthy lifestyle that can contribute to reduced mortality risk.


In conclusion, the study demonstrates that higher muscular strength is associated with a lower risk of mortality in men, independent of cardiovascular fitness and other potential confounding factors. The authors suggest that promoting regular resistance training exercises to improve muscular strength may be a useful strategy for reducing mortality risk in the general population.


 

Title: Strength, but not muscle mass, is associated with mortality in the health, aging and body composition study cohort Authors: Newman, A. B., Kupelian, V., Visser, M., Simonsick, E., Goodpaster, B., Nevitt, M., ... & Harris, T. B. Publication: The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 61(1), 72-77 (2006) DOI: https://doi.org/10.1093/gerona/61.1.72


Summary:

This study aimed to examine the associations between muscle mass, muscle strength, and mortality in older adults. The researchers analyzed data from the Health, Aging, and Body Composition (Health ABC) Study, which included 3,075 community-dwelling older adults aged 70-79 years at baseline. Muscle mass and strength were measured using dual-energy x-ray absorptiometry (DXA) and isokinetic dynamometry (grip strength and knee extension), respectively. The participants were followed for an average of 4.9 years.


The results showed that greater muscle strength was significantly associated with a lower risk of all-cause mortality, even after adjusting for potential confounding factors such as age, sex, race, and comorbidities. However, the study found no significant association between muscle mass and mortality risk after adjusting for these factors.


The authors concluded that muscle strength, but not muscle mass, was independently associated with mortality in older adults. This suggests that interventions aimed at improving muscle strength, rather than increasing muscle mass, may be more effective in reducing mortality risk among older individuals. The study highlights the importance of maintaining and improving muscle strength as a key component of healthy aging.


 

Title: Muscle mass index as a predictor of longevity in older adults Authors: Srikanthan, P., & Karlamangla, A. S. Publication: The American Journal of Medicine, 127(6), 547-553 (2014) DOI: https://doi.org/10.1016/j.amjmed.2014.02.007


Summary:

This study aimed to investigate the relationship between muscle mass index (MMI) and longevity in older adults. The researchers analyzed data from the National Health and Nutrition Examination Survey (NHANES) III, which included 3,659 participants aged 55 years and older. Muscle mass was estimated using bioelectrical impedance analysis, and MMI was calculated as muscle mass divided by height squared. The participants were followed for mortality outcomes over a period of up to 18 years.


The results showed that higher MMI was significantly associated with lower all-cause mortality risk in both men and women, even after adjusting for potential confounding factors such as age, race, comorbidities, and lifestyle factors. The association between MMI and mortality risk was particularly strong among participants aged 65 years and older.


The authors concluded that higher muscle mass index is an independent predictor of longevity in older adults. This finding emphasizes the importance of maintaining and increasing muscle mass as a key component of healthy aging and suggests that interventions aimed at improving muscle mass may be beneficial in reducing mortality risk among older individuals.


 

Title: Objectively measured physical capability levels and mortality: systematic review and meta-analysis Authors: Cooper, R., Kuh, D., & Hardy, R. Publication: BMJ, 341, c4467 (2010) DOI: https://doi.org/10.1136/bmj.c4467


Summary:

This study is a systematic review and meta-analysis that aimed to investigate the association between objectively measured physical capability levels and mortality. The authors searched multiple databases for relevant studies published up to April 2009, which included a total of 57 eligible studies.


The physical capability measures analyzed in this review were grip strength, walking speed, chair rising, and standing balance. The results showed that lower levels of physical capability were consistently associated with higher mortality rates across all four measures. This association remained significant even after adjusting for potential confounding factors such as age, sex, and body size.


The meta-analysis revealed that the pooled hazard ratios for all-cause mortality were 1.67 for the weakest versus the strongest grip strength, 2.87 for the slowest versus the fastest walking speed, 2.13 for the slowest versus the fastest chair rising time, and 1.96 for the worst versus the best standing balance.


The authors concluded that lower levels of physical capability, as measured by grip strength, walking speed, chair rising, and standing balance, are associated with a higher risk of mortality. This finding highlights the importance of maintaining and improving physical capability as a key component of healthy aging and suggests that interventions aimed at enhancing physical capability may be beneficial in reducing mortality risk among older individuals.


On Muscle Quality

A few studies on ‘muscle quality’ are also shown below for those who may be interested using medical imaging techniques to discern muscle quality of an individual. This is an area of active research.


Title: Muscle area and density and risk of all-cause mortality: The Multi-Ethnic Study of Atherosclerosis

Authors: Larsen B, Bellettiere J, Allison M, McClelland RL, Miljkovic I, Vella CA, Ouyang P, De-Guzman KR, Criqui M, Unkart J

Publication: Metabolism, Volume 111, October 2020

DOI: 10.1016/j.metabol.2020.154321


Summary:

This study aimed to examine the relationship between muscle area, muscle density, and all-cause mortality among a multi-ethnic cohort. The researchers analyzed data from the Multi-Ethnic Study of Atherosclerosis (MESA), a prospective cohort study that included 6,814 participants aged 45-84 years from four different racial/ethnic groups (Caucasian, African American, Hispanic, and Chinese). Muscle area and density were measured using computed tomography (CT) scans at the L4-L5 vertebral level.


The participants were divided into quartiles based on their muscle area and muscle density measurements. The researchers followed the participants for an average of 12.3 years, during which they recorded 1,456 deaths. The association between muscle area, muscle density, and all-cause mortality was analyzed using Cox proportional hazards models, adjusting for factors such as age, sex, race/ethnicity, education, smoking status, alcohol consumption, physical activity, body mass index (BMI), and waist circumference.


The results showed that participants in the highest quartile of muscle area had a 27% lower risk of all-cause mortality compared to those in the lowest quartile. Similarly, participants in the highest quartile of muscle density had a 32% lower risk of all-cause mortality compared to those in the lowest quartile. These associations were consistent across different racial/ethnic groups and remained significant after adjusting for potential confounders.


The authors concluded that greater muscle area and muscle density were independently associated with a lower risk of all-cause mortality in a diverse population. They suggested that interventions targeting improvements in muscle area and density could potentially reduce the risk of all-cause mortality among middle-aged and older adults.


In summary, this study found a significant association between higher muscle area and muscle density and a lower risk of all-cause mortality in a multi-ethnic cohort. These findings highlight the importance of maintaining adequate muscle mass and density as a potential strategy for promoting longevity and reducing the risk of death from all causes.


 

Title: Adverse muscle composition predicts all-cause mortality in the UK Biobank imaging study

Authors: Linge J, Petersson M, Forsgren MF, Sanyal AJ, Dahlqvist Leinhard O.

Journal: Journal of Cachexia, Sarcopenia and Muscle

Publication Date: December 2021

DOI: 10.1002/jcsm.12834

PMID: 34713982; PMCID: PMC8718078


Summary:

This study investigated the association between muscle composition and all-cause mortality in a large cohort of middle-aged and older adults from the UK Biobank imaging study. The researchers examined the role of intramuscular fat and muscle density, which are indicators of muscle quality, in predicting mortality risk.


The study included 16,112 participants (average age 62 years) who underwent magnetic resonance imaging (MRI) to assess muscle composition. The participants were followed for an average of 4.5 years. The researchers evaluated the relationships between muscle composition measures and all-cause mortality using statistical models adjusted for various factors like age, sex, body mass index, and lifestyle factors.


The results showed that higher levels of intramuscular fat and lower muscle density were significantly associated with an increased risk of all-cause mortality. Specifically, participants in the highest quartile of intramuscular fat had a 33% higher risk of death compared to those in the lowest quartile. Similarly, those in the lowest quartile of muscle density had a 60% higher risk of death compared to those in the highest quartile.


Importantly, these associations remained significant after adjusting for potential confounding factors, suggesting that adverse muscle composition independently predicts all-cause mortality. Moreover, the combined effect of high intramuscular fat and low muscle density further increased the risk of death.


The findings of this study highlight the importance of muscle composition, and not just muscle mass, in predicting health outcomes. The authors suggest that interventions targeting muscle quality, such as exercise and dietary modifications, could help improve health and reduce the risk of mortality in middle-aged and older adults.


In conclusion, this large-scale study provides evidence that adverse muscle composition, characterized by high intramuscular fat and low muscle density, is an independent predictor of all-cause mortality in middle-aged and older adults. The results underscore the need for strategies to improve muscle quality and potentially reduce the risk of death in this population.



 

Based on the studies summarized above, it appears that muscle strength has a more consistent and significant association with mortality risk compared to muscle mass. While muscle mass has been shown to be associated with longevity in some studies, muscle strength has been found to be independently associated with mortality risk in multiple studies, even after adjusting for potential confounding factors.


It is important to note that these studies do not necessarily imply that muscle mass is unimportant, but rather that muscle strength may be a more critical metric to focus on when assessing health outcomes and designing interventions for older adults. Both muscle mass and strength are important components of overall physical capability, and maintaining or improving both aspects can contribute to healthy aging.


While muscle mass is still an important factor to consider, the evidence from these studies suggests that muscle strength may be a more important metric to measure and target for interventions aimed at reducing mortality risk and promoting healthy aging.


The last 2 studies’ findings suggest that muscle quality, as indicated by muscle composition (intramuscular fat and muscle density), is an important factor in addition to muscle strength for predicting longevity. Adverse muscle composition, characterized by high intramuscular fat and low muscle density, was found to be an independent predictor of all-cause mortality in middle-aged and older adults. This highlights the importance of not only focusing on muscle strength but also on improving muscle quality through interventions such as exercise and dietary modifications to potentially reduce the risk of death and promote overall health and well-being in this population.

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