Muscle Weakness & Mortality Risk

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Hi there. It’s been quite a while since the last S&C post and I’m excited to be writing this 2-parter on understanding muscle weakness and mortality risk. The aim in this part 1, is to unpack and explore if there really is an an association between muscle weakness and all cause mortality (i.e. dying). In part 2 (next time), we’ll evaluate if muscle strengthening interventions can influence any increased risk of disease and dying.

Muscle Weakness & The Risk of Dying – or Not!

I’m sure you’ve seen some of the several news articles that have recently, and alarmingly, headlined that muscle weakness might increase your risks of disease and even dying by comparison to stronger counterparts. Here are just a couple of articles that you might have glimpsed:

Is Strength Important?  

So you ask me this question and I’m sure you know what my answer is going to be.  As a reminder, by strength we’re referring to the maximal contractile force a muscle/muscle group can exert in a single contraction (read more on that here).  We can get a measure of this through dynamometry following a maximal voluntary contraction (MVC), or an estimate from something like a 1 or a 3 rep max on a resistance-based task.

If you’ve listened to my webinar leading up to my course S&C For Therapists, you’ll hear me talk about the evidence that highlights the potential importance of muscle strength in the fields of: 

  • Injury avoidance; 
  • OA-related joint pain;
  • Function and quality of life;
  • Decreased dependency for ADLs in later life

And we’re not talking about muscle mass or cross-sectional area here, we’re talking about the contractile capacity of muscle.

Muscle Weakness as a Risk Factor for Disease

So, back to the point, is there a relationship between muscle strength, or lack thereof, and morbidity and onset of disease? 

DISEASE:

Well, yes there is.  Believe it or not, there are may research studies, systematic reviews and meta analyses dating back many years that document this relationship.  Many studies have reported that the strength declines from midlife are highly correlated with new-onset of disease, such as type II diabetes and Cardiometabolic multimorbidity (simultaneously suffering from > 1 of: coronary heart disease; stroke and, or, type 2 diabetes). For example:

Hand Grip Strength – superior predictor than systolic BP in prediction of CVD

The Prospective Urban Rural Epidemiology (PURE) study showed that hand grip strength (HGS) was superior to systolic blood pressure in predicting cardiovascular diseases during a four-year follow-up (Leong et al. 2015).

HGS reduction as risk factor for type II diabetes

A study of middle-aged and elderly people in the USA and China reported that for every 0.05 decrease in the normalised grip strength, the risk of type 2 diabetes increased by 0.49 times (Peterson et al. 2017).

ORTHOPAEDICS

Whilst quadriceps muscle strength was not associated with the progression of osteoarthritis (OA) as determined by x-ray, it was significantly associated with knee pain knee pain in 2566 knee OA patients, after adjustment for age and body mass index. That is to say weaker individuals experienced more pain than stronger individuals (Muraki et al. 2015).

In a systematic review by Xu et al. (2019), several predictors of poor functional outcomes and mortality for patients with hip fracture were observed, one of which was and grip strength.

Clearly this is just a flavour of the literature on the topic, but hopefully enough to make you think that strength, or lack thereof, might be important. References are linked below where possible so you can read further.

Muscle Weakness and All Cause Mortality

RIGHT, down to the biggie – understanding Muscle Weakness & Mortality Risk. Does being weak mean that you’re going to die early?  Bad question to ask. This implies a causal and direct influence of muscle weakness on mortality and that’s something that’s very difficult to ascertain. But evaluating the risk and the association could be helpful; the best way to do this is by following a large population over time in a prospective study design.  So, what are the results of these enquiries?

Just to note here, if you’re pressed for time and you’re looking for the quick salient points, check out the highlighted conclusions in blue.

Lower HGS is Associated with Increased Risk All Cause Mortality & CV Mortality

Newman et al. (2006) evaluated the total mortality rates in the Health, Aging and Body Composition (Health ABC) Study (2292 participants, 70–79 years). Quadriceps and grip strength were strong and independent predictors of mortality. For quadriceps strength (per standard deviation of 38 Nm), the hazard ratio (HR) for men was 1.51 (95% CI 1.28–1.79) and 1.65 (95% CI 1.19–2.30) for women, which was similar for hand grip strength. A hazard ratio, broadly speaking, is a comparison between the chance of an event occurring in one group compared to the chance of the event occurring in another group. A HR of 1.51 means here that a weaker person [and similar in all other respects] had a 15% increase risk of death compared to a stronger person throughout the follow-up period of ~5 years.

This study confirmed that lower muscle strength was a strong and independent predictor of mortality in older adults.

In 2016, Strand et al. reported the findings of the Tromso Study in which 6850; adults aged 50–80 years were followed up for 17 years (prospective design, recruited in 1994).  During the follow-up, 2338 participants died.  Data analyses showed that 1 standard deviation (SD) reduction in grip strength was associated with a hazard ratio (HR) of 1.17 (95% CI 1.12 to 1.22) for all cause mortality (model adjusted for age, gender and body size). 

This means that compared to the strongest group of participants, individuals 1SD weaker were at a 17% increased risk of dying from any cause.

Bae et al. (2018) conducted a prospective observational study to examine whether baseline handgrip strength predicted mortality over eight years of follow-up in Korean adults (45 years/>). Their results showed a robust independent relationship between weaker handgrip strength and higher all cause mortality in both women and men (adjusted for e.g., age, income, smoking, exercise, and comorbidities). Compared to the strongest quartile (the reference), women and men in the weakest group had higher HRs of mortality, 2.5 (95% CI: 1.7–3.8) vs. 2.6 (95% CI: 1.8–3.9), respectively. 

This means compared to the strongest group, the weakest group had an approximately 25% increased risk of dying from any cause over that 8 year period.

One of the most recent studies on this topic is by Lu et al. (2022). They conducted a prospective cohort study involving 493,774 participants from the UK Biobank, median follow-up was 12.1 years.  When compared to the strongest group, the weakest quartile of participants had a HR of all-cause mortality of 1.87 (95% CI: 1.64 to 2.14).  When the model was adjusted to take account of or smoking, physical activity etc. this still resulted in HR: 1.57, 95% CI: 1.36–1.80).

This means that the increased risk of death was 15.7% for those with the weakest HGS vs those those with the strongest HGS over the follow-up period.

Understanding Muscle Weakness & Mortality Risk

As you can see from the studies cited above, muscle weakness is a strong and independent predictor of all cause mortality. Strength matters.

There are several systematic reviews and meta analyses on the topic, which pool the data and reach similar conclusions. Take the study by Lee (2020). Thirty studies with a total of 194,767 older adult participants were included in the meta-analysis. Higher handgrip strength was associated with an 18% decrease in all-cause mortality. Lower handgrip strength was associated with increased all-cause mortality. Interestingly, the minimum handgrip strength in older women that did not increase all-cause mortality was 18.21 kg.

CAUTION!

What these studies are NOT saying is, for example, if you’re weak you’ll live 18% less. Each person faces an annual risk of death – the ‘hazard’. For a hazard ratio of 1.18, for two people alike in all respects other than strength, the weaker one (i.e. the one with the risk factor) has an 18% increased annual risk of death over the follow-up period. To quantify the risk of dying in absolute terms, we need to understand what their background risk of death is over the defined period (NB, this is how the risks associated with taking HRT were inflated and incorrectly reported).

Why Handgrip Strength?

You’ll see from the studies mentioned that some measured quads strength, most measured handgrip strength (HGS). HGS is easy to measure.  You don’t need much kit, money, resources or familiarisation the test by comparison to something like a knee extensor test.  It’s also conventionally considered to be an indicator of global muscle strength and, as we’ve seen, it’s related to various adverse health events. But…

Training Handgrip Strength Won’t Make You Invincible

Clearly handgrip strength is being used as a proxy marker for overall strength and perhaps other things. It would be silly (perhaps!) to recommend based on the aforementioned research that a sedentary overweight person with high BP engage a bout of unilateral handgrip training to protect against premature death. Handgrip strength will increase, or be preserved, commensurate with activities that require grip, whether that be whole body resistance training, or challenging tasks like carrying shopping or lifting grandkids.

Strength is important and the associations seen in these morbidity and mortality studies are likely related, in part, to a higher functional capability being associated with greater strength, particularly in those who have lower baseline strength levels. It might also be related to more favourable hormonal profiles, motor unit recruitment and capture the important aspects of the ageing process.

The rapid downward spiral of strength seen in some populations is also likely to reflect other characteristics such as being older, less active, overweight, joint pain etc. These can lead to fewer activities being performed (as they’re more challenging), then further declines in strength, further diminished functional abilities, disabilities, loss of independent living etc etc … and subsequent premature death.

The Risks of Being Weak on Premature Death

So, where does all of this leave us on our attempt to understanding Muscle Weakness & Mortality Risk? Well, muscle weakness is not only a predictor of reduced quality of life and dependancy in later life, it is also a risk factor for all-cause mortality (likely related to some of the reasons mentioned above). So much so that some studies have recommended strength assessment as a screening tool to estimate mortality risk. Strength matters.

Remember:

Good News

The good news is that we can become stronger and more physically active, and this can have a positive impact on health, pain and dependancy, even in later life. In the next post, we will try to establish whether or not becoming stronger can reverse the premature risk of death and disease.

As always, thanks for reading. Feel free to share.

References

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