Building on the theme of the first part of this series, this post looks at the benefits of strength training for longevity. (Around 3.500 words, estimated reading time: 15-18 minutes.)
Let’s keep pretending that you need to start training from scratch. You know that you should be to starting with cardio but also that not all cardio will do. So, what’s next?
Let’s assume that your reasons for reading this post are the same as for reading the previous one (you’ve never trained and you don’t know where to start, or thought you knew but you’re not getting where you thought you would, or you’re just fine and it’s ‘just for a friend’, or you paid for it on Patreon, etc.). Let’s also assume that you’ve emptied your cup of tea one-half (the ‘cardio’ half) and you’re curious about what I have to say about the other half (the ‘strength’ half).
That’s a lot of assumptions, I know, but they won’t hurt, because I’m not assuming that I’m preaching to the choir. I’m glad you’re still tagging along, whatever the cause of your interest may be. I explained the origin of my own interest in the first post of this series, and there’s no real point repeating stuff, so let’s move on.
In that same post, I mentioned that life expectancy is only half of the picture and the other half is quality-of-life. It wouldn’t do anyone any good to live to their 100s only to be pushed around on a wheelchair for the last 30 years of their natural life. Avoiding that outcome seems to depend on how jacked, strong, and mobile you are.
The above qualities are not well-promoted by popular options for ‘cardio’ (running, cycling or swimming). And so, there seem to be common sense independent reasons to pursue jackedness, strength, and mobility. And at the end of the day, science validates that particular piece of common sense.
But don’t hold your breath.
How and why it validates it may not be what you think.
Growing old ain’t for sissies
Strength has undeniable benefits for longevity. They are not as well-understood as the benefits of cardiovascular fitness but they are measurable and there are some possible explanations
There is ample evidence that strength is a predictor of lower risk of all-cause mortality irrespective of age. Unfortunately, the standardized measures for strength are not as straightforward qua measures of strength as VO2max qua measure of cardiovascular fitness (CVF). And the relation between strength and longevity is less straightforward than the relation between CVF and longevity. But let’s begin with some good news.
Strength and longevity
The relation longevity bears with strength is established by the same means as its relation to endurance (hazard ratios) and is supported by the same kind of high-quality evidence (meta-analyses). Below is a visual summary of what current science tells us about strength and longevity from the same recent (March 2018) review published in Frontiers in Bioscience I used in the last post (Survival of the fittest: VO2max, a key predictor of longevity?) illustrating the “Hypothesis of physical fitness on Healthy Life Years” (hereafter simply the “Fitness Hypothesis”).
An important thing to notice is that strength and CVF are lumped together to define ‘fitness’. I’ll come back to reasons to do that soon, but they ultimately boil down to the fact that they may not be completely independent. For now, I’d just like to put things in a nice, non-scary way (for a change). Assuming the Fitness Hypothesis,
- Fitness-wise, on average, a well-trained 80-year old is no worse than a sedentary 30-year old.
- Fitness-wise, on average, a well-trained 70-year old is strictly better than a sedentary 30-year old.
Now, let’s put some first-order logic skills to work to obtain some equivalents to the above. Assuming the Fitness Hypothesis,
- Fitness-wise, on average, a sedentary 30-year old is no better than a trained 80-year old.
- Fitness-wise, on average, a sedentary 30-year old is strictly worse than a trained 70-year old.
Perform the mental gymnastics of switching from the first pair of statements to the second pair a couple of times. There you go. If you’re a young punk that spends a lot of time sitting, that should sound a little scary.
But don’t give up yet. There’s enough evidence that with the right training protocol late bloomers may very well end up in better shape at 70 than 30. Of course, the devil is in the details of the “right training protocol” (I’ll come back to that too).
Before moving to the substance of the Fitness Hypothesis, let’s add to it the weight of an example (pun intended): Michèle Wauquier, 71-year old kettlebell lifter, who started kettlebell lifting around 60, then underwent hip replacement surgery, and then went on to win world championships multiple times. She can be seen in the video below putting 74 times over her head about ⅓ of her 49kg competition bodyweight (make a mental note of that figure).
Studies that focus on the link between strength and mortality use handgrip strength and knee-extension strength. A review and meta-analysis of these studies, titled Muscular Strength as a Predictor of All-Cause Mortality in an Apparently Healthy Population, was recently published (Feb. 2018) in the Archives of Physical Medicine and Rehabilitation. Looking at its conclusions clarifies why the Fitness Hypothesis cannot disentangle strength and CVF.
The Archives… meta-analysis showed that higher muscular strength is associated with a lower Hazard Ratio (HR) of all-cause mortality. Taking the population with the lower prospect (lower strength) as reference and lookings at HR of the population with the best prospect (higher strength) in comparison yields the following figures:
- Relative to handgrip strength, stronger people are at a 31% lower risk (HR 0.96) than weaker people, with the effect being more pronounced for women (40% lower risk).
- Relative to knee-extension strength, stronger people are at a 14% lower risk (HR 0.86) than weaker people, with no significant difference found between men and women.
I’ll come to the correlation between handgrip and knee-extension strength and overall strength but before I get to that, let’s look at how the authors explain the link between strength and risk of all-cause mortality.
Our meta-analysis shows that lower levels of handgrip strength increase the all-cause mortality risk, supporting the growing body of literature that has linked muscular strength and risk of mortality. However, in our study, the figures for heterogeneity statistics were large. At least a substantial part of the differences across studies might be explained by the differences in socioeconomic status among populations differences in muscular test protocols (repetitions, hand used, and so on), and the dynamometers included in the test. Furthermore, the observed associations and heterogeneity could be explained by confounding factors such as comorbidities other than diabetes, cardiovascular disease, or by unknown comorbidities. However, attenuated but significant associations were also found after adjustment for the above-mentioned factors; therefore, confounding cannot fully account for the observed associations.
The underlying mechanisms are not fully understood, but some possible explanations have been proposed. It has been hypothesized that the negative association between muscular strength and chronic inflammation is a potential mechanism behind the favorable influence of muscular strength on health. Another possible mechanism through which poor muscular strength may influence health includes an increase in the lipoprotein lipase enzyme, which is related to increased accumulation of triglycerides and decreased high-density lipoprotein cholesterol. 
In lay(wo)man’s term, while healthier people are quite stronger than not-so-healthy ones, it also seems that stronger people are healthier than not-so-strong ones. Hence, strength may have its own protective effect on health. But we don’t know why.
Now, the above quote is a conclusion section and thus understandably short on the details. So let’s qualify it: strength per se does not lower chronic inflammation, nor does it reduce the accumulation of triglycerides. These hypothetical mechanisms are side-effects of strength-training. So that’s a good argument for pushing for it.
Then again, drinking baking soda also reduces inflammation and endurance training has been known to increase lipoprotein lipase activity for at least 35 years. So, these are by no means unique selling points for strength training.
So, is there anything else?
Surprising (?) conclusions
A surprising finding of the Archives… meta-analysis is that lower-body strength has a relatively lower impact on HR that upper body strength. In fact, it is too surprising. The authors try to downplay it by mentioning cases in which the magnitude of impact is reversed before they even mention it.
Although lower limb strength is deemed to be of great importance for daily life (i.e. legs for the ability to walk), the magnitude of its association with mortality risk remains controversial. Strength losses in lower limb muscles determine the whole-body functionality and may prevail over upper limb muscular strength in its relationship with mortality. Our meta-analysis shows that stronger adults, as assessed by knee extension strength test, had a 14% (HRZ0.86, 95% CI 0.80-0.93) lower risk of death than the weaker individuals.
In fact, the authors’ strategy is rather strange, because: (1) the reversal showed up in only one study out of 36 and concerns only elderly people; and (2) there are more interesting ways to downplay this difference. Simply put, knee-extension strength is a very poor measure of overall lower-body strength: it leaves out the hip extensor, including the largest muscle of the lower body, the gluteus maximus). Some of the studies reviewed in the Archives… meta-analysis actually measured hip-extension but the data was sparse (8 studies out of 36) and somewhat heterogeneous (measuring method differed more than for handgrip) and only so I’m tempted to leave it at that.
Second, handgrip strength measures much more than upper-body strength. The handgrip is really a topic of its own which I’ll cover some day. Suffices to say that biomechanics and neurology support the hypothesis that handgrip strength is better correlated to “whole-body functionality” than knee-extension strength and perhaps even lower-body strength. Handgrip also reflects the general state of the central nervous system (CNS) due to the density of receptors in your hands (check the Wikipedia article on the cortical homunculus to learn more). Variations of handgrip strength test make a useful test of CNS fatigue, and subsequently of overtraining, even for endurance athletes who do not train grip strength.
So, textbook biomechanic and neurology entail that the Archive… meta-analysis does not tell us much about the specific contribution of lower- and upper-body strength to HR. Still, handgrip strength being well correlated to whole-body strength, none of the above remarks affects the authors’ final hypothesis about the connection between strength and longevity.
Overall, adults with low muscular strength have more difficulties to perform activities of daily living. As a consequence, their physical activity levels are decreased, leading to greater muscle mass losses (sarcopenia), a decrease in contractile protein content and excessive intracellular and extracellular lipid accumulation. This could make adults more vulnerable to accidents, such as injurious falls, or other adverse events; therefore, their recovery from acute diseases, injury, or surgery may be compromised.
Strength, uh! What is it good for?
The conclusion of the Archives… meta analysis is that strength losses reduce the level of physical activity, and thus ultimately the number of MET-h accrued. Therefore, that being strong enables you to do your cardio later in life.
As far as data can support, there may not be more to the benefits of strength for longevity than that. So why bother with strength? Why not, for instance, stick to some form of cardio that incorporates a wee bit of resistance from a mechanical devices (cycling), gravity (walking/running hills) or the surrounding milieu (swimming, rowing) and be done with it?
Well, the reason is simple: it’s called the Law of Adaptation.
The Law of Adaptation
The Law of Adaptation is an elegant mathematical law that describes adaptive systems. And no, it’s not circular. It’s just a matter of definition. A system is ‘adaptive’ if and only if its behavior is described by the mathematical law. The law embodies the notion of adaptation, it’s called the law of adaptation. Whether a system is in fact described by the law is an empirical matter (the hypothesis that it does has to be tested).
We can put further clarifications at rest, because the hypothesis that the human body is an adaptive system is well-entrenched. As for the Law of Adaptation, its vernacular English is this:
Every adaptive system converges to a state in which any stimulation ceases
Below is a short elaboration on the Law of Adaptation for those who want some details. If that’s not you, skip it.
I pulled this formulation out of the Wikipedia article where it’s quoted from legit research (this one). If you check, you’ll find that said research is theoretical computer science, more specifically biologically-inspired computer science. In case you wonder, the “computer science” part is what makes me competent to talk about it (theoretical computer science is basically applied logic) and the “biologically inspired” part is what makes it relevant to the discussion here. Now, for the math part, what follows is just an elaboration on the two-formula definition from the Wikipedia entry. So if you found it crystal clear, you can skip the rest of this excursus.
The Law of Adaptation is a straightforward corollary of the definition of an adaptive system. So let’s define that first. What a “system” is here does not matter (that’s why the formulation is for an arbitrary system), but let’s say that it’s a thing that can change state and go from a state S to a state S’ while still being recognizable as the same thing. Like you and me, for instance, who can go from sleeping to awake, from fasted to fed, or from young to old. Or a pool of water, that can go from liquid to frozen, or from still to agitated.
Let’s the notation S⟶S’ denote the transition from S to S’, and the notation Pt(S⟶S’) and Pt(S⟶S’|E) denote, respectively, the probability that S transitions at time t to S’ spontaneously (whatever that may mean) and the probability that S transitions at time t to S’ given the event E. We can say that E is a stimulus for S at t if and only if S is more likely to transition to (some) S’ when E occurs than on its own. The latter translates into part (1) of the definition in the Wikipedia entry, namely:
(1) Pt(S⟶S’|E) > Pt(S⟶S’) > 0
The “>0” is just there to rule out trivial cases, but we need not worry about that,because it’s a consequence of how conditional probability is defined, and we could shuffle the math around to avoid that assumption. Note that E can be anything, and its influence on the relation between S and S’ need not be causal (if you’re not a philosopher, don’t worry about that last sentence: I’m just covering my ass in case some other reader is).
Example 1. Let S denote you; S’, a bigger, stronger or jackeder you; and E, a challenging but manageable training session. Clearly, completing E makes it more likely that you’ll transition from S to S’. We have to assume that the probability that you transition on your own from S to S’ is non-zero, and it probably is. But don’t get over enthusiastic: if it is, it’s super-small (and if not, like I said we can shuffle the math around).
Example 2. Assume that S is a liquid pool of water; S’, the same pool of water, frozen; and E, the event of the temperature around S dropping below 0°C. Then E makes it more likely that the pool of water will freeze. In that case, physics agrees that it could happen spontaneously (but the probability is negligible).
Part (1) merely defines a stimulus E for a system S. Part (2) captures what makes S adaptive relative to E (like you, relative to a training session, and unlike the pool of water relative to drops of temperature). In vernacular English, Part (2) says that as time goes by, S becomes less likely to transition to S’ under stimulation E. This is mathematically expressed as follows:
(2) (lim t→∞) Pt(S⟶S’|E) = Pt(S⟶S’)
where “(lim t→∞)” is just a fancy way to say that we are considering ideal time (which has no end)..
You satisfy (2) relative to training, while a pool of water does not relative to temperature (as time goes by, it does not become less likely to freeze when the temperature drops). Now, if you satisfy (2), then assuming that you are going to train with any program that instructs you to do E today (t0) and you aren’t already adapted to E, or mathematically:
(3) Pt0(S⟶S’|E) > Pt0(S⟶S’) > 0
then there is a t sometimes in your future (i.e. such that t>t0) such that doing E would not make it more likely than you become bigger, stronger and jackeder than doing nothing, or mathematically:
(4) Pt(S⟶S’|E) = Pt(S⟶S’)
The art of training consists in switching from E to some E’ such that it would still make a difference at t some time before t (the sooner, the better).
Assuming that the human body is an adaptive system relative to training (more on that soon) the Law of Adaptation is equivalent to the so-called Law of Accommodation from exercise science. You can find it in the first chapter of Zatsiorsky & Kraemer’s Science and Practice of Strength Training from which I pulled the following figure (used without permission, but it’s fair use).
The assumption that the human body is an adaptive relative to training is an empirical hypothesis which is supported by millenia of observations, so let’s just assume that it’s correct. As to why, quite frankly, we don’t know. If you want to understand why we don’t know, check this post. Then again, it does not matter much: even without an explanation, a true hypothesis remains true.So, over time, if you impose the same training stimulation to your body over and over, it will eventually cease to produce any effect.
Why not just cardio-with-resistance?
Whenever someone suggests to simply cycle harder, run/walk hills with a heavier backpack, or swim/row more, I just say: think twice.
There are mechanical and physical limits to the resistance you can add to cycling (your bike’s gears), run/walk hills (your bodyweight and the weight of your backpack) or swimming (the resistance of the water). Hence, any type of cardio that incorporates some resistance will eventually cease to produce any resistance stimulus, and will become ‘just cardio’.
At which point, your body would try to adapt to cardio the way it does when resistance is negligible: improving the efficiency of the delivery system by decreasing the amount of tissue to deliver stuff to (I covered that issue in Part I). And, as I just reminded you, the adaptation to ‘just cardio’ is functionally equivalent to sarcopenia, which happens due to age anyway (if not counteracted by resistance training).
So, an exclusive focus on cardio would simply make you age faster. And eventually, it would prevent you to do the cardio you’d need to live longer. So, too much cardio would kill you by preventing you from doing the cardio you’d need to live longer. Define: irony.
Conclusion (for today): The Longevity Workout™
Extrapolating a training regimen from the benefits of strength for longevity is not as straightforward.
Cardio-wise, science-based recommendations are easy: anything that raises your VO2max is good for your health. Preference-wise, if you are on a tight time-budget, a combination of high-intensity anaerobic and lower-intensity aerobic exercise (like the original Tabata protocol) might get you covered. If you have a little more time, straight-on low-to-moderate intensity steady-state aerobic training might fit better your idea of exercise that doesn’t suck.
Strength-wise, there’s no straightforward science-based recommendation. Of course, there’s a simple-minded solution like: “run, walk, cycle or swim, but buy a hand-gripper and go to a gym to do knee extensions every once in a while”. But that wouldn’t do, for the all the reasons I mentioned earlier.
Now, would anyone suggest that? Well, I’ve read an “evidence-based” bench press program flashing a diagram from some study that correlated pectoralis major thickness and bench press performance, and then recommend pec flies because they improve pec thickness. So yes, I suspect that someone could try to sell a leg-extension-and-hand-gripper program as The Longevity Workout™.
There is, however, a better way to exploit the science.
Let’s first consider the kind of whole-body strength that really matters. When I mentioned the amazing Michèle Wauquier, I also noted that she’s lifting ⅓ of her bodyweight for reps. And if you revisit this post, you may notice that Roman Legionnaires were carrying at least that fraction of their body weight, assuming that they weighed around 75kg on average (I’ll cover the assumption in the “Old School Strength” series). And if you know a thing or two about physical adaptations to rucking (or don’t but care to check) you might suspect that a pattern is emerging that involves loaded carries at ⅓ bodyweight and above.
Now, after you check all of the above and use the power of your imagination, you may still be wondering about grip strength. After all, you don’t train with gladium and scutum at the post every day, or dig ditches, chop wood, plant posts, etc., all of which took care of Roman legionnaires’ grip strength. So let me offer that hint: properly performed tug-of-war and trains hip- and knee extension and grip strength and it can be emulated with a prowler. So can wood-chopping, ditch-digging, and post-planting, with a mace and a tire. And so you might suspect that a pattern is emerging that involves pulling heavy stuff and hitting stuff repeatedly.
I’ll leave things there for today, but I’d bet that when I pick up this series where I left it, you’ll see me coming.
^ García-Hermoso, Cavero-Redondo, Ramírez-Vélez, Ruiz, Ortega, Lee, Martínez-Vizcaíno (2018), Muscular Strength as a Predictor of All-Cause Mortality in an Apparently Healthy Population: A Systematic Review and Meta-Analysis of Data From Approximately 2 Million Men and Women, Archives of Physical Medicine and Rehabilitation, in press, Available online 7 February 2018 (https://doi.org/10.1016/j.apmr.2018.01.008).