How finger length influences overall strength

Thursday, October 19, 2017. Author Dr Haran Sivapalan

How finger length influences overall strength

Take a look at your hands.

You’ll notice that your index finger (or second digit) is about the same length as your ring finger (that’s the fourth digit). If, however, you were to take a ruler and measure both fingers, you may notice that your index finger is slightly shorter. This is more likely to be the case if you’re male. But why?

It’s to do with testosterone – the male sex hormone. Higher exposure to testosterone when you’re in your mother’s womb is linked to a shorter index finger in relation to your ring finger. (Viewed the other way, that’s the same as having a longer ring finger in proportion to your index finger).  Scientists call the ratio - of the length of your index finger (2D) to your ring finger (4D) - the “2D:4D digit ratio”. Due to different hormonal environments in the womb, men tend to have lower 2D:4D digit ratios than women. 

For both men and women,  a lower ‘2D:4D digit ratio’ is a marker of greater testosterone exposure in utero. But what has any of this got to do with health and fitness? Interestingly, studies have associated a lower 2D:4D digit ratio with everything from autism, aggression, and heart disease through to left-handedness, facial attractiveness and, of particular interest to our readers, muscle strength. 

Lower digit ratio, greater muscle strength

In a recent study by the University of South Dakota, researchers found that adolescent boys with lower 2D:4D digit ratios tended to have better handgrip strength. And it’s not just in teenage boys that we see this trend. Caucasian men from Germany, Mizos men from northeast India, and Hani women from China have all been shown to exhibit the same pattern: -  the lower the digit ratio, the higher the handgrip strength.

So, what is underlying this relationship?

Again, it’s testosterone. Remember that a lower 2D:4D digit ratio is a marker of higher testosterone exposure in utero. When we’re developing as fetuses in the womb, the basic architecture of our adult bodies is partly determined by the hormones to which we’re exposed. We dub these long-term, structural effects on the body as “organizational effects”. Testosterone has an ‘organizational effect’ on muscle development. This is one reason why males who are exposed to more testosterone in utero compared to females typically go on to have greater muscle mass in adult life.  

For reasons which remain unclear, testosterone in the womb (in balance with estrogen) also has an organizational effect on the ratio of your index and ring fingers. In fact, your 2D:4D digit ratio remains fixed throughout your entire life.

But my digit ratio is high – am I destined to be weak?

Absolutely not! 

Muscle development, size, and strength are influenced by lots of different factors - not solely your prenatal / in utero environment. What’s more important is how often you train and condition your muscles – this will have a much larger impact on how much you can bench-press. Proper nutrition is also a key factor in developing muscle. And, of course, several different genes also contribute to muscle volume and strength: MSTN, VDR, and ACVR1B to name just a few. On that note, if you want a personalized, genetically-tailored nutrition and workout plan to help you get those guns, check out our Build Muscle plan. 

But what about my testosterone levels?

There is a world of difference between testosterone in the womb, and the levels of testosterone circulating in your bloodstream as a fully-formed adult. The latter show considerable fluctuations, both over the course of a single day and over the whole of your lifetime. It’s fair to say that your 2D:4D digit ratio is certainly not an indicator of your current testosterone levels. So worry not.

Nevertheless, it remains the case that your circulating testosterone levels are important when it comes to building muscle. Suboptimal levels of testosterone correspond to lower muscle growth, flabbier body composition, and impaired insulin function. 

Again, FitnessGenes can help here.*  We’ve created a Testosterone Evaluation Template TM for men that analyses your lifestyle and your SHBG1, SHBG2, ESR1 and ACTN3 genes and tells you whether you’re susceptible to low testosterone levels.  Of course, unlike your 2D:4D ratio, your testosterone levels aren’t permanently fixed. Regular exercise, correct diet and losing body fat can all help to boost blood testosterone – all of which are within your control.
So, when it comes to gaining muscle strength and maintaining healthy levels of testosterone, it really is in your hands. 

*If you’re worried about low testosterone, it is advisable to consult a physician. Ordinarily, multiple blood tests are needed to measure your testosterone level directly. 

I hope you enjoyed this story. Please read my other blog post Just Say No to Upselling, which was recently quoted on Inc.com and Unravelling the Secrets of Our Circadian Rhythm

References

Fink B, Thanzami V, Seydel H, Manning JT. Digit ratio and hand grip strength in German and Mizos men: Cross cultural evidence for an organizing effect of prenatal testosterone on strength. American Journal of Human Biology. 2006 Nov 1;18(6):776-82.

Tomkinson JM, Tomkinson GR. Digit ratio (2D: 4D) and muscular strength in adolescent boys. Early Human Development. 2017 Oct 1;113:7-9.

Zhao D, Yu K, Zhang X, Zheng L. Digit ratio (2D: 4D) and handgrip strength in Hani ethnicity. PloS one. 2013 Oct 30;8(10):e77958.

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