Fingers Don’t Contain Muscles

Scott 2
female-rock-climber We all have pet-peeves that occasionally happen around us- windshield wipers on when there isn’t enough rain to support lubrication, your husband leaving his dirty laundry on the floor, etc. One of mine is supposed experts in their field saying things about their field that just aren’t true, like a doctor claiming you only use 10% of your brain. In fact, you use all of your brain unless you have brain damage.  (This “brain” myth, incidentally, made it on the list of “Top 7 Medical Myths Even Doctors Believe”- a list compiled by the British Medical Journal after surveying over 1000 doctors.  For the other 6 items, see the Bonus Facts below.)

More to the point of this article, I recently had a rock climbing instructor who told me and two other students, “You need to strengthen the muscles in your fingers.” Being someone who knows a little something about anatomy, I wanted to tell him that would technically be impossible, though not wanting to be a Melvin, I chose to remain silent… at the time. Of course, after the class, I dropped some finger knowledge on my instructor- namely, that fingers don’t contain muscles, at least not ones used to move fingers as he was talking about. (Technically fingers contain many tiny arrector pili muscles, but these have nothing to do with movement of fingers, but rather are attached to hair follicles and can make the hairs on your fingers stand out straight.)

So if there are no muscles in our fingers to move them, what gives all those action movie stars the ability to one-hand a dangling bad guy off a roof? Short answer: magic… err, tendons and ligaments.

Long answer: Each finger consists of three bones (phalanges). They’re named based on where they are in relation to the palm of your hand. There’s the proximal phalange (closest to the palm), the middle phalange, and the distal phalange (farthest from the palm). The first knuckle is called the metacarpophalangeal joint (MCP). (Say that after drinking 3 beers and watch the laughter ensue!) The second knuckle is the proximal inter-phalangeal joint (PIP) and the last knuckle is the distal inter-phalangeal joint (DIP).

In our bodies, tendons generally connect muscle to bone, and ligaments generally connect bone to bone. The tendons that control the bones in our helpful little protrusions are attached to 17 muscles in the palm of your hand and 18 in your forearm- none of which are in your fingers. The muscles that close your hand are known as flexors, and the ones that open your hand are known as extensors. Some are small and help control each individual finger.

The muscles that control your fingers in the palm are known as intrinsic, and the muscles in your forearm are known as extrinsic. The two main extrinsic flexors are the flexor digitorum superficialis and the flexor digitorum profundus. The three main extrinsic extensors are the extensor digitorum, the extensor indicies and the extensor digiti minimi. The muscles in the palm of your hand can be broken down into 4 types, known as interossei, thenar, hypothenar, and lumbricals.

While you probably won’t remember the names of the muscles that control your fingers, you can at least feed your inner-Melvin knowing none of them actually reside there.  This is probably for the best considering the sheer size of the muscles, if they did reside in your fingers, would probably make range of motion almost nothing unless someone had exceptionally weak fingers.

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Bonus Facts:

  • The other six items on the British Medical Journal list of myths that many doctors still believe are, (We’ve already covered several of them on this site, so click the links if you’re interested to know more about each myth):
    • Myth: You Need to Drink at Least 8 Glasses of Water Per Day to Stay Hydrated
    • Myth: Reading in Dim Lighting Will Damage Your Vision
    • Myth: Hair and Fingernails Continue to Grow After Death (It’s actually the body tissue contracting that creates this illusion.)
    • Myth: Shaving Makes Your Hair Grow Back Faster/Thicker
    • Myth: Eating Turkey Will Makes You Drowsy
    • Myth: Cellphones used in a normal way create enough electromagnetic interference to cause considerable problems with hospital equipment, creating false alarms, incorrect equipment readings, and subsequent errors in treatment.  This myth was based on a highly publicized study done in 1993 that offered no actual direct evidence that this was happening, just several doctor’s suspicions that it was happening.  An actual scientific study by the Mayo Clinic in 2005 busted this myth, as did another done in 2007.  Not only this, but, funny enough, according to a survey of anesthesiologists, having a cell phone to use while treating patients resulted in about 22% fewer medical errors than when they had to delay communicating with someone about something pertaining to their patient.
  • For geometry lovers out there, know that when it comes to the biomechanics of our fingers, the muscles helping control them will need to generate a force four times the pressure required at the fingertips to accomplish any task.  Needless to say, the muscles controlling your fingers are exceptionally strong.
  • A study published in the Asian Journal of Andrology in 2011 showed that there is a link between finger length and penis size. No, it has nothing to do with the actual size of your hands, but rather the ratio between the index finger and your ring finger. They found that the shorter your index finger was, compared to your ring finger, the longer the man’s penis. *every man reading this instantly checks ring finger to index finger ratio*  The culprit behind this is thought to be exposure to a hormone called androgen, in prenatal women. The reason why this is thought to be the case is that the 2nd digit-4th digit ratio has been shown to be a predictor of several other traits that are affected by androgen levels, including left-handedness, physical aggression, ADHD, and the ranking of someone’s attractiveness. One study even found a link between this ratio and alcoholism.
  • The average grip strength for men ages 20-75 is 104.3 pounds for the right hand and 93.1 pounds for the left. Women averaged 62.8 pounds and 53.9 pounds respectively. Grip strength is the highest for both sexes between the ages of 25 and 39.
  • 1 in 6 work injuries resulting in a disability involve fingers. The most common reason, finger striking. Put down the hammers! … But not on your fingers!
  • The reason your skin will tend to wrinkle when wet is the subject of much debate. What is known for sure is that the phenomenon is controlled by nerves and the constricting of blood vessels in response to water. If you sever the nerve to a specific part of your finger, that part will never again wrinkle when wet. The theory behind why this occurs is thought to be the evolutionary development that allows for better grip in wet conditions, giving our ancestors to a better handle on collecting food in water and other wet environments. Several studies have shown that it’s easier to handle wet objects when you have wrinkled fingers, than if you have smooth ones.

[Rock Climbing Image via Shutterstock]

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2 Comments »

  1. EC May 5, 2013 at 7:50 am - Reply

    The singular of “phalanges” is “phalanx,” not “phalange.”

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