Episode #385- Why Grip Strength Predicts Death (And Why You Shouldn't Train It)

0:00Right now, there's a good chance that your doctor is missing the most important vital sign you own. Imagine walking into a clinic and instead of just wrapping a cuff around your arm to check your blood pressure, the physician hands you a small metal device and says, squeeze this as hard as you can. In that one second effort, we can often predict your risk of cardiovascular disease, your rate of cognitive decline, and your overall risk of all-cause mortality more accurately than almost any other single test in the building. But here's the problem. The longevity industry is confusing the signal with the system.

0:28They're treating your grip strength like it's the heater, when in reality, it's just the thermometer. If you train your grip to, quote, live longer, you're essentially holding a match under that thermometer to make the room feel warmer. You might see a higher number on the dial, but the house is still freezing. Today, we're moving past the squeeze of spring mentality and looking at the grip strength for what it actually is, a high-fidelity thermometer for many of the most important systems in your body. We're deconstructing the biomechanics, the predictive power of hand grip strength and disease, and all the nuance in between.

0:57And to help us get into it, I'm joined by the second most handsome doctor in North America, Dr. Austin Baraki. What's going on, dude? Hey, feeling all right. No complaints today. My grip strength is intact and normal bilaterally. So let's get into that. I guess that's right. If I did manual muscle testing on myself, testing my grip strength with one hand onto the other, I could potentially trick myself. I don't know. Well, it's kind of like measuring your blood pressure at home. You know, theoretically, you could do it if you had a validated device and you did it with the correct procedure and everything else.

1:26This is true. We need the same sort of setup for grip strength, and we'll get into that. But first, let's talk about what is grip strength and to understand why the grip is such a powerful diagnostic we got to look at the anatomy first most people think that the power that we create or the force you create for grip strength is in the hand but really it's kind of like a wireless terminal for a motor that's located much further upstream now austin you've done this a few times but now we get to do it for real uh i want to double click on that wireless concept to set the stage for why hand grip strength is getting so much air time in the health and longevity spaces I want you to walk us through the entire pathway from the moment the motor cortex sends the command down through the spinal cord all the way until the muscles actually contract.

2:10What has to go right for that signal to result in a maximal squeeze? Yeah, it's an interesting pathway and one that I outlined in, I would say, a mild amount of detail in our last mystery case where we had the individual who had the foot drop scenario. And this is something that comes up a lot clinically when a patient is experiencing some form of, you know, ideally objective weakness that there is for us to evaluate in a particular area of the body. I'm not going to go through every detail of the neuroanatomy involved for, you know, the sake of our audience. But, you know, the movement starts up in the brain.

2:47There's this combination of, well, there's the like intent, the volitional aspect of deciding to make a movement to the extent that we ever decide anything. but there are also involuntary ways by which a movement can be generated that we do not volitionally choose and all of this is originating well i would say most of it that i can even think of some exceptions there up and up in the brain and so there are a few different kind of converging pathways in the brain multiple different areas the volitional aspects the you know subcortical or subconscious aspects that kind of integrate come together and then their signals travel down through the brainstem down into the spinal cord and then emerge from the spinal cord at a particular spinal root and then that turns into a motor nerve and that nerve sends its signal down to the end of the nerve called a neuromuscular junction where some neurotransmitters are released.

3:38Those trigger the muscle to have some kind of we'll call it some electrical changes and some ions shift around and that leads to what's called depolarization of the muscle and then there's some chemical signals that proceed from there that lead proteins within the muscle cell to interact, leading them to link up, contract, the muscle shortens, and then muscles end in tendons that cross joints. And so when that muscle shortens and it tugs on that joint, it leads to movement of the body. And so from start to finish, that is the pathway that we think about for normal force production in a particular area.

4:12And if someone is telling me subjectively that they feel like an area is weak or if objectively on exam, I am determining that they are weak in an area. My job is to try to figure out where along that entire pathway could something be going wrong. We narrow that down based on the history, the timing, whether there are also sensory versus just motor alone, whether it's symmetrical on two sides of the body or just one or multiple different areas of the body. There's all sorts of ways that we can try to narrow down where could this problem be using history, using exam, and then using forms of imaging and things like that as well.

4:46Yeah. Yeah. I think, uh, outlining that whole, you know, we'll call it a neuro axis or and then myo axis, if you want to get real technical and how those things converge together, it is, is important for understanding like kind of what has to go right for you to actually do a hand grip strength test or really squeeze a barbell, dumbbell person. Um, but the main takeaway here is that all of these command centers are outside of the hand. So for example, if your brain, if there's an issue there, you're not going to get the signal to the muscles that actually are responsible for making a grip, that's not going to fire.

5:20And then further, once that signal actually gets down to the level of the arm, the primary force producers for a hand grip strength test are outside of the hand. We call these extrinsic hand muscles. Mostly these are the forearm flexors, the real motors of the system here. So flexor digitorum superficialis and profundus. If you remember from your anatomy days, these just, you know, big sheaths of muscles with really long tendons. Yeah. But those don't work in isolation. There are muscles on the other side that have to create force to stabilize the wrist joint. And then obviously muscles within the hand, we call those intrinsic hand muscles have to be functioning for you to, you know, fine tune that and make sure you're gripping the right thing and everything else.

6:03But yeah, the other big thing to note here is that the force is transferred through these high tensile tendons. And everyone's familiar with the tendon, you know, connects a muscle to a bone to exert force on the bone and pull it closer. Usually, you know, that's that's the idea here. It goes through the carpal tunnel, the flexor retinaculum. These are more anatomy terms you don't need to know. But effectively, if anything goes wrong in this system, grip strength is going to be compromised. or if you applied this logic to another muscle, strength overall would be compromised. And so when you're doing a hand grip strength test, you're not just testing finger strength.

6:38You're testing the integrity of this entire system from the brain to the bone and position. Well, position of the hand and the wrist that is also matters. So for example, there's this 3-5-3 rule that was told to me by a hand surgeon friend of mine. And to the extent this is a rule or more of just like something to think about, it means that when you are trying to test somebody's grip strength or your grip strength, the wrist has to be an extension. Approximately 35 degrees. This is like a self-determined extension position. So like when you're bench pressing or pressing, you don't need to get out the guineometer and be like, am I at 35 degrees?

7:17It's just going to happen naturally when you squeeze as hard as you can. but if you were to try to test grip strength with a flexed wrist you get what's called active insufficiency it effectively pre-shortens some of the muscles and prevents optimal sort of cross bridging you talked about the proteins in the muscle they have to link up and if they don't link up in a nice way force production or strength is compromised and so in addition to that degree of wrist extension trying to bend your wrist back towards the your forearm there's also some thought that you need to be in three to five degrees of ulnar deviation.

7:50And if you're in anatomical position with your palms facing forward, pinkies towards the inside or medial aspect of your body, if you were to try to deviate your wrist or move your wrist towards your body, that's ulnar deviation. Again, you don't need to consciously think about this stuff. When you just go to squeeze something real, real hard, it just sort of happens. Yeah, well, I'm actively testing this under my desk as you describe it. And I can definitely feel stronger and weaker positions if my wrist is flexed a little bit forward or if it's a little bit more radially deviated, for example.

8:20And listeners can even test this out for themselves at home. Just squeeze your wrist as hard as you can, but then try to put it into flexion and you'll feel like, oh, I'm not actually able to squeeze quite as hard in this position. It just feels awkward to do it this way. So yeah, interesting. Yeah, when I try to teach the overhead press to people, for example, and we talk about the grip and they're like, what should I do? Especially if somebody's really into it, which I can appreciate as a fellow nerd, game recognized game. I tell them put your hands out in front of you kind of like your frankenstein and then just make as tight of a fist as you can and watch what happens to your wrist And it extends and it tends to deviate towards the ulnar side a little bit as well So that's one of the positions that matters another thing.

9:00It's not really positional, but more of just a quirk and feature of the Hand grip strength test. There's this thought that there is a 10 % difference on average between the dominant limb and the non-dominant limb so you'd have differences in side to side. And so this was thought to only be at the level of the hand and then people found it well. No, actually the whole arm, particularly in untrained individuals, that asymmetry tends to narrow when people are trained. However, when you look at the research on this, left-handed individuals tend to not actually have this asymmetry since it tends to be one-to-one, which I thought was interesting.

9:35Is it because we're forcing left-handed people to operate in a right-handed environment? Were they only testing surgeons? They're like, look, we don't have any left-handed instruments. it's only right-handed instruments um that's kind of interesting though yeah it is interesting i mean there was certainly a long time where people who are lefties were forced into a right-handed world and i think these days this is less and less of a thing that tends to happen um i know that lorraine is a is a lefty who actually is quite dexterous uh both literally and and you know she's able to do a lot of things with her right arm um just as well sometimes even even better so there is some interesting adaptability yeah but so if somebody saw if you saw an asymmetry testing somebody's hand grip strength side to side of 10 % or whatever, this wouldn't be abnormal, especially if they're right-handed.

10:17And even if they're left-handed and you see a slight asymmetry side to side, again, not really a cause for alarm. Where we think there's sort of like this line in the sand where you're like, that is odd and I want to investigate that further, is when there's a 20 % difference side to side. There's a thought that that is a kind of red flag clinical sign where look, there could be a pathology at the level of the neck, whether it's a disc herniation, a fracture, nerve root issue, maybe in the brachial plexus, that's this big bundle of nerves that serves your upper extremity or a local nerve sort of issue, because it's just a greater than predicted difference side to side.

10:53Now, of course, based on what Austin's talked about so far, that assumes everything else in the system is good. Brain's working good, tendons working good, bones working good, you know, there's no other issue. But yeah, Yeah, that's just sort of some of the quirks and features of the hand grip strength here. There's other stuff like if somebody has a smaller or larger hand, for example, and the handle on the hand grip strength test, it's this little handheld device, which you guys have probably seen. If it's too far away or too close, that can compromise your reading. If the texture on the actual handle is slippery, for example, that can compromise the output.

11:27And so there's a lot of interesting stuff to do this correctly, not dissimilar to like blood pressure testing. For example, people are like, oh, just take your blood pressure. And it's like, well, is the cuff the right size? It's in the right position. Do you have to pee? Are you in pain? Like all sorts of stuff, you know. Well, an interesting caveat, or I don't know if I'd call it a correction, is when you say like to do it, quote unquote, correctly. And it's not to say that doing it in any of these other ways is incorrect. The issue more so is just, is it something on which you can use our established criteria, right?

11:57So all of the ways that we establish our cutoffs for healthy resting blood pressure are based on it being measured in a particular way. And so if you want to use those cutoffs, you should measure it similarly. The same thing would apply here based on the way that these hand grip strength, quote unquote, cutoffs were determined, be it using maybe a particular device oriented in a particular way with a particular texture. If you want to use those cutoffs, you need to measure it similarly. It's not to say it's like wrong if you were to measure it in a different way, but rather that you would need a new set of cutoffs established on that right so if if the original studies on blood pressure were all done in people who had to pee and were standing up probably 120 over 80 would not be considered the normal blood pressure we would just have a different set of cutoffs and then anytime we wanted to measure somebody's blood pressure we'd have to make sure they're standing up and had to pee yeah exactly yeah so i can envision a scenario like if you went into a clinic maybe a predatory clinic i don't think this exists but you know whatever.

12:51I humans never fail to disappoint. And they were like, we're going to make sure this guy has a low grip strength. We're going to cut them down to size. And they're like, Hey, um, so to test your grip strength, we're going to have you, your elbow is going to be at 90 degrees. You're going to be seated like you should. Uh, and then, uh, flex your wrist as much as possible and then grab onto this thing. And they're like, see, you're low. You need to start TRT. And exactly. Much like testosterone clinics that send you to get your labs done at 5.00 PM, you know, After a meal and a poor night of sleep, yeah, they set you up for failure there.

13:21Yeah. So ultimately, all of these things need to be, quote, correct in order to get an accurate measurement. To use the data that we have, there's a bunch of different things that can be altered, like if your wrist is flexed, if the handle is slippery, if the distance to squeeze is odd. Well, you can get a weak movement, but that doesn't necessarily mean you have true sort of weakness based on this test. So now that we understand the mechanical chain, we need to look at what happens when the chain starts to reflect systemic failure. So Austin, from a clinical perspective, we see grip strength used as a test for sarcopenia as seen in the recent guidelines.

13:55Could you talk about the distinction between dinapenia and sarcopenia and why the signal in the hand often fails before the muscle itself actually disappears? Yeah, I think we both have thoughts on this. and even if the guidelines might describe the use of grip strength as a diagnostic test for sarcopenia, I personally don't use it for a variety of reasons. Practical limitations as well as kind of like when we talk about the use of waist measurement in practice, it's a great measure when it's done properly, but there's a lot of ways that people can mess up a waist measurement. And similarly, as you've laid out so far, a lot of ways that a grip strength test, even using a supposedly validated dynamometer, can be done in a way that limits the validity of the data that you get in terms of how do I apply it to the cutoff.

14:43So I personally tend to use other assessments when I'm evaluating somebody for this, but yeah, it's a very popularly discussed tool in the context of sarcopenia. This other term that you mentioned, dinapenia, is one that is I think a less well-appreciated, maybe we're doing our part in bringing it more to the forefront these days because it is more our interest in that dinapenia refers more specifically to strength and power, much more so than sarcopenia traditionally was thought of as just muscle mass. As we started to realize that health outcomes and things like that were better correlated with strength and power than with muscle mass, they tried to fold in muscle mass and strength into the term sarcopenia, which is how you'll often find it but then i think it's just been split off uh to to this other term dynopenia and so some of the differences as i've laid out so far there's more than just muscle mass that relates to people's ability to produce force obviously having the muscle present is a key component it is you know part of that we'll call it a final common pathway to force generation because it's at the end of that chain but there's a lot of stuff that happens beforehand at least as much if not more that has to happen beforehand starting from the brain all the way down that spinal cord that spinal nerve down to depolarize that muscle and as you have laid out well in some previous content including in our sarcopenia podcast episode that itself is a neurological event and so there are neurological changes that happen that can limit the ability to produce force strength and power kind of disproportionate to the changes in muscle mass that happen and then the last thing to consider here is that not all muscle mass is the same it's kind of like when people criticize bmi and they say well bmi doesn't accurately capture you know my level of muscularity versus body fat and it's like okay well if you wanted to use a similar sort of analogy or argument if you just quantitate somebody's like muscle cross-sectional area that itself doesn't necessarily distinguish the muscle quality how much of that cross-sectional area is comprised of lean you know contractile tissue versus how much of it has fat infiltration into it versus how much of it involves fibrosis or scarring that is non-contractile in nature but still contributes to the overall muscle bulk or muscle size and so there are various other factors that can you know impact the apparent size of the muscle that might not directly contribute to force production so these are all kind of interesting caveats and limitations and why dinapenia is a really interesting way to think about things muscle strength muscle power it integrates that neurological component that may be a bigger factor than just muscle size being lost alone yeah yeah we talked about this a lot on our sarcopenia podcast where it's like it's not just the age-related loss of muscle in fact it's more so the age-related loss of muscular function in this case strength or power i also prefer cratopenia, which is the loss of muscle power or the inability to produce force rapidly.

17:51It depends on which derivative you're, uh, you're taking of the, of the force reduction. Yeah. So yeah, that's the whole point is that when you use one of these like functional tests and you could use other stuff, a timed up and go sit to stand test, these are other sort of functional tests for sarcopenia, which would probably be rebranded as dinapenia or my favorite cratopenia. Um, you're getting a more accurate sort of picture of like, does this person have this condition versus just a loss of muscle mass, which, you know, you can see people whose muscle cross-sectional area decreases, like you said, from a loss of intramuscular fat, you know, this my osteotosis, for example.

18:26And you're like, well, your muscle got smaller, but it works better. So am I concerned or not? The point that we're, the whole reason we're talking about hand grip strength is because we often hear that it predicts how long you live, but we need to be precise about the data. And let's start off with some normal grip strength levels. So like body mass index or BMI, there's no single sort of cutoff that applies to everyone. There are ethnic and geographic differences, also age-related differences. And normative data does exist, but you kind of have to go through that with a fine-tooth comb. What's the population that you're talking about?

18:58And, you know, how are they deriving or creating this normative data? So for like sarcopenia, for example, the latest guidelines suggest that if a man has a hand grip strength of less than 27 kilograms. That's like indicative that person has high risk for sarcopenia and it's less than 16 kilos for women, but that's kind of like pathology. So what is normal? And I think it's helpful to kind of understand this as like an ever-changing or dynamic sort of metric, kind of like bone mineral density. It changes over the course of someone's life. It peaks in early adulthood. There's some like maintenance phase towards midlife area.

19:41That sort of timeline. And it declines from midlife onwards in most folks, particularly individuals who are not remaining active. So, for example, in a large cohort in the United States, so understanding that that's our population, men between ages 29 to 39, that's where they saw their peak value, which was 51 kilos, almost double the sarcopenia cutoffs. and it was 31 kilos for women between ages 26 and 42. Now, after that, the hand grip strength seems to decline at a rate of approximately 1 % per year after age 40, and it accelerates even more than that after age 65. This can be slowed with resistance training.

20:20We're going to talk about the specifics of that later. It tends to be better, meaning that exercise tends to have a better effect when it's heavy, so at least 60 % of an individual's one rep max. there are smaller effects of uh resistance training on grip strength performance when it's indirect meaning you're not someone's not actually doing straight up grip strength training whether it's crushers whether it's plate pinches hold whatever uh and so you get larger effects on how you train so theoretically you could get somebody to go into the gym and maybe they were a quote grip maxer and they were like look i got to get my grip strength up to that uh who was the guy you just climbed the skyscraper, Alex Honnold or whatever?

21:01Yeah. Yeah. Watched it. I have a picture of him on my phone with the hand grip strength test and he's squeezing it. It says 94 kilos. I mean, yeah, I buy it. Strong. Strong. But trying to achieve that is unlikely to improve your sort of health trajectory. And that's going to be a recurring theme throughout this podcast. So if you want to turn it off now, look, you got the, you got the gist of it and you can just turn it off, but we hope you don't because there's more interesting stuff here. So my thought here kind of leave you on a little cliffhanger, is acing the test the goal or should it just be sort of like a part of the process?

21:35So there's some interesting data here. Why does grip strength actually matter? One of the biggest studies to come out in recent times is the Prospective Urban Rural Epidemiology Study, also known as the PURE study. This is a large longitudinal population study designed to assess health outcomes across diverse economic and sociocultural settings. So about 140 ,000 people aged 35 to 70 from 17 different countries, and they were followed for an average of four years to track mortality and health events like developing various diseases. Notably, grip strength was found to be a stronger predictor of all cause and cardiovascular mortality than systolic blood pressure.

22:15That's the top number. For every five kilos decrease in grip strength, there was a 17 % increased risk of cardiovascular death and a 7 % increased risk of non-cardiovascular death. That's the headline. That's what you read in the newspaper or online. I don't know that anybody reads newspapers anymore. Now, interestingly, this was usually not reported. There was no significant association between hand grip strength and incident diabetes, fractures, or injuries from a fall. other evidence on this there are a handful of things that are highly suggestive or highly correlated to hand grip strength like all-cause mortality about a 28 percent risk reduction for those in the highest sort of quartile or segment of hand grip strength compared to the lowest for cardiovascular disease mortality so death from heart disease about 16 percent risk reduction if you have the highest you're in the highest cohort highest group of grip strength compared to the lowest.

23:11And this is particularly true in folks without preexisting heart disease. And then the risk of disability goes down by about 24 % for those that are in the highest bracket of hand group strength compared to the lowest. There were weak or absent associations in a lot of other things, including maybe some things that would surprise you, Dr. Baraki. So leg power, not really associated with it. Walking speed, not really associated with it. Inability to balance, hospital admission, hip fracture, cancer mortality, all weak to absent sort of correlations. So to me, there seems to be this complicated relationship between hand grip strength and health.

23:48On the one hand, pun intended, seems to be a very good test of how the musculoskeletal and neuromuscular systems are working. There's obviously a lot of overlap between the health of those two systems and others, like the heart, for example. On the other hand, pun intended again, it doesn't seem to correlate with health outcomes like cancer. But what's most interesting is that it doesn't seem to correlate well with strength and function of the body overall, as noted by the findings on leg power, walking speed, balance, risk of falls, and so on. What do you make of that? Gosh, it is an interesting observation.

24:22And it illustrates, I think, some of the areas where there's utility to this measure, as well as areas where there are limitations to it. I like the way you described it as kind of like an integrator of neuromuscular function in a similar way to how popular vo2 max measurements have been in recent years and to be fair a vo2 max metric is a really quite good integrator of not just cardiorespiratory and like oxygen delivery physiology but also an integrator of maybe some degree of genetic predisposition and then also an integrator of to the extent you have trained it, it is something that necessitates some degree of training to build up to very, very high levels in most people.

25:06So the use of these tools as integrators is, I would say, interesting. There's some differences between these two, again, in terms of like, say with VO2 max, if you train towards the test, I'm more confident that there are likely to be some health benefits as a result. Whereas if you train very pointedly towards hand grip strength improvements, I'm less confident that they're gonna be like tons of downstream health benefits to it. But yeah, we know that, or we would expect there to be some correlation, for example, between hand grip strength and the amount of overall muscularity and lean body mass that someone has.

25:40And that itself is something that is partially influenced by genetics, much like how I mentioned VO2 max is, is an integrator of other things, general health, endocrine, hormone status, things like that. And to the extent that somebody is well-trained there can be some some impact there but as far as teasing apart why do we see this like variation between hand grip strength as a metric and all of these different health outcomes i think it's going to be very difficult to have a clear confident explanation for why this and not that there's obviously some combination of well how good of a metric is hand grip strength in general and then how much of this is like statistical and like study-based noise if you analyze the data in a different way if you did the study again maybe you do find a slight signal in this direction or that direction for something like that ultimately what we're looking for is one of these things that can be used you know ideally as a as a metric that can give us very confident assessments in our patient's current state of health and gosh it would be nice also if like vo2 max for example if we trained towards it that we would feel confident that somebody's health status is improving i think hand grip strength probably falls a bit short on that on that end.

26:48And I suspect we'll, we'll get more into that here in a little bit. Yeah. Yeah. I, I tend to agree. And I, the way I came at this was like, well, if there's this sort of disconnect, is it a function of the test itself? It's just not actually, actually capturing what we think it is maybe something else. And I kind of went down a rabbit hole and found some interesting stuff. So as you predicted, and as you, you, you know, intuited the biggest factor affecting baseline hand grip strength is the amount of lean body mass that somebody carries. So a bigger car needs a bigger engine. In that case, we're talking about muscle cross-sectional area.

27:22And so consequently, total body lean body mass, the cross-sectional area of the muscles is a single strongest predictor of absolute hand grip strength, explaining more variance than age or height alone. This is presumably why it's used for sarcopenia. If you're like, look, how much muscle does a person have? Squeeze. And it also happens to capture function, which is quite nice. So, you know, gold star for hand grip strength so far. Interestingly, hand grip strength is highly influenced by genetics, as is the amount of muscle mass that people carry. And there's a lot of overlap between the two.