Do you know your grip strength?
I hope to convince you that you should. It is easy and cheap to measure. I bought a hand held dynamometer for less than 30 bucks.
Grip strength is a valuable biomarker. Biomarkers are “medical signs at the level of pathology, body function or structure, or activity/participation that provide an objective indication of medical status.” (Bohannon 2019) Broadly speaking, there are four reasons you should use grip strength as a biomarker: longevity, disease prevention, function and recovery.
We don’t have good, widely available biomarkers of longevity at the blood or cellular level. Tests such as the GrimAge DNA methylation test seem very promising, but are expensive and not ready for population-level implementation. Conversely, anyone can test their grip strength.
Longevity
There is a large body of literature supporting an inverse relationship between grip strength and mortality risk. This systematic review with meta-analysis found that in the 26-50 kg range of grip strength, there was a near-linear inverse relationship between grip strength and all-cause mortality. Another meta-analysis showed a 16% increase in all-cause mortality and a 21% increase in cardiovascular diseases for every 5 kg decrease in grip strength.
Disease
Perhaps more intuitively, grip strength predicts function and absence of disease. Our hands provide the interface for our interaction with the environment. Decreased hand grip strength is associated with increased risk of hip fracture (Denk 2018) and increased odds of developing dementia (Esteban-Cornejo 2022). Depression was found in 8.8% of weak grip adults (<30 kg for men, <20 kg for women) but only 3.8% of those not categorized as weak. (Ashdown 2019) Grip strength is a more powerful predictor of cardiovascular mortality than blood pressure (Leong 2015).
Function
Grip strength can correlate with function without directly being related to that function. Take mobility for an example. A population study looking at adults with difficulty in mobility (defined as self-reported difficulty walking 500 meters or climbing stairs) found 37 kg as a cut-off point for men and 21 kg as a cut-off point for women. Despite the low sensitivity and specificity of that study, walking a half a kilometer is a very low level of functionality that most adults want to exceed for most of their lives.
Recovery
Having sustained a clavicle fracture requiring surgical repair, I’ve been measuring grip strength as a proxy for recovery after upper extremity injury and surgery. Despite a dearth of literature on grip strength after clavicle surgery, there is plenty of research on grip strength after hand surgery, especially distal radius internal fixation. Take for example this small study, where 20 minutes per day of grip strength training resulted in earlier recovery of grip strength. I noticed that my left hand grip strength was stronger than my right pre-injury. This is often the case, as the dominant hand is used for tasks requiring more dexterity. Not surprisingly, my grip strength plummeted after surgery on the affected left side.
For 12 weeks after the surgery, I couldn’t do any weighted training. I began my recovery just by squeezing a tennis ball. If you’re wondering why grip strength can indicate more about you than just the muscles involved in grip, consider the core-through-shoulder stability required to exert a large amount of force in grip. I can attest that, early on, I had to back off grip training entirely, because any grip strength training left my shoulder girdle muscles painfully sore. My left hand grip was around 45 kg pre-injury. After surgery, it dipped as low as 36 kg. In weeks 7 to 12 of my recovery, I dedicated more time to grip strength training. I didn’t do the 20 minutes per day used by Kaji et al. in their distal radius study, but I used a grip strength trainer at least a few times per week. 12 weeks after surgery, the grip strength of my affected hand was up to 46 kg. I've found grip strength also tracks with my day-to-day recovery status, and tends to dip after a hard training day.
Targets
How much grip strength do you need? I don’t think you can be too strong. But we can’t all be in the top percentile. However, I think you really want to avoid being at the bottom. If you’re more than one standard deviation below the mean for your age and gender, it’s worth improving your grip strength. Less than 30 kg for men and less than 20 kg for women will put you in that undesirable range for most adults. As I progress to full activity with the shoulder, I'm aiming for 50 kg of grip strength (with 60 kg as an ideal longer term goal). Another benchmark I’ll be pursuing is the ability to to carry my body weight for at least one minute.
Training
How do you get stronger? Squeezing a grip trainer you bought from Amazon while watching TV is okay if you’re recovering from surgery. But ultimately it’s not going to cut it. Strong grip comes from carrying heavy things, whether in exercise or in life. If you don’t carry heavy things as part of life, grip-strengthening exercises include: farmer’s carry, dead hang (just hanging from the pull up bar), flexed arm hang, pull ups, chin ups, or rock climbing.
There are so many things you could be testing. What gets on your short list? For example, what if you could only test two things? How about grip strength and VO2 max (a measure of cardiorespiratory fitness)?
“Those are probably the two best biomarkers we have…Your VO2 max and your grip strength are better predictors of how long you’re going to live than whether or not you smoke, drink, what your family history is for cancer.”
- Peter Attia, MD
As Dr. Attia points out, there’s no cheating on those two tests. Either you’ve put in the work, or you haven’t.
Most of us are going to test more than two things to assess our health. But some tests are cheap and some are expensive. Some are invasive and some are not. Some are highly predictive and others only mildly so. All these factors play into how often we repeat these tests. For how it shows up in all of the above considerations, I think grip strength deserves a place as a frequent, go-to longevity biomarker.