Tag: hands

Why Do Your Fingers Make A “Pop” Noise When You Crack Your Knuckles?

When cracking your knuckles, one tends to hear a “pop” noise that is loud, sharp, and irritating to most. This noise can be addicting in the sense that it makes others want to crack their knuckles. The main questions that I focused my research on were “Does cracking your knuckles or joints cause potential health issues for your future?” and “ Why does cracking a joint such as your knuckles make a “pop” noise?” 

Continue reading “Why Do Your Fingers Make A “Pop” Noise When You Crack Your Knuckles?”

Attention Deficit Handwriting Details: The Effects of ADHD on Handwriting

Imagine you’re in college and struggling to focus during a boring lecture with a monotone professor. Now imagine that same struggle, but every little thing around you is a distraction making it difficult to focus on everyday tasks, not just the boring ones. Individuals with Attention Deficit Hyperactive Disorder (ADHD) battle this inability to focus constantly. Yet for individuals with ADHD, about 1 in 20 children (basically a lot of children), the struggle does not stop there: these individuals who struggle to focus often exhibit fine motor coordination impairments as well.

It just so happens, writing requires fine-motor coordination. Even with computers and evolving technology, writing is a necessary skill used by most individuals throughout their lifetime. It is well-known that when taking notes, you are more likely to retain information when writing notes as opposed to typing them. We have to write when we take exams (hopefully more so once the pandemic is over because I am tired of computer glitches during online exams). We write to communicate different ideas to each other, or even to communicate ideas to future self that we wish to remember.

Writing is still a necessary part of our everyday life, yet when this writing is difficult to read, its effectiveness diminishes. Imagine finally being able to focus enough during that boring class to take notes but not being able to read them. Imagine taking a timed exam but wasting this limited time to ensure the handwritten answers are legible. When compared, the handwriting of most individuals with ADHD is worse than individuals without this disorder.

There are three subtypes of ADHD: individuals are primarily hyperactive, primarily inattentive, or combined type (both hyperactive and inattentive). Individuals with ADHD who are primarily hyperactive are more likely to write faster with shorter strokes and to write more efficiently. On the other hand, individuals with ADHD who are primarily inattentive write with inconsistent letter sizes and spacing between the letters, along with diminished legibility. These individuals will exhibit this inconsistency in their writing due to a greater variability in stroke sizes.

Image of the handwriting with inconsistent letter sizes and spacing. There are 6 letters circled out of 10 letters. The letters are circled because they are illegible and it is difficult to know what the letters are supposed to be. The four letters not circled are: t, v, x, y.
Image of the handwriting with inconsistent letter sizes and spacing, along with illegibility of letters circled.
Source: https://doi.org/10.1177/0883073807309244

Individuals with combined type ADHD experience an inner battle between hyperactivity and inattentiveness, resulting in faster, more efficient writing at the expense of accuracy and legibility of their handwriting. Interestingly, these individuals on Methylphenidate, a stimulant used to treat ADHD symptoms, tend to write in the complete opposite fashion: the quality of their handwriting improves while the speed diminishes. Since the illegibility of the combined type ADHD individual’s handwriting is affected by their inattentiveness, the improved handwriting quality is due to the increased focus provided by this stimulant.

It is believed that the handwriting of primarily inattentive and combined typed individuals are the results of a form of Dysmetria. Dysmetria is a lack of coordination between movements, which would result in the irregular handwriting due to an under or overshoot of the desired writing size. These individuals are unable to process the information that they receive fast enough to generate the desired response.

While primarily hyperactive individuals tend to write faster and more efficiently, their handwriting does not necessarily differ from individuals without ADHD. On the other hand, the difference in quality of handwriting in individuals with ADHD compared to individuals without is more prominent in those with primarily inattentive or combined typed ADHD. There are many individuals out there who struggle with ADHD and are at a disadvantage because of this. Accommodations for individuals with ADHD should go beyond accommodating inattentiveness and hyperactivity since difficulties are only the root of them problem that stem into more obstacles such as reduced writing quality.


Rebecca A. Langmaid, Nicole Papadopoulos, Beth P. Johnson, James G. Phillips, Nicole J. Rinehart. Handwriting in Children With ADHD. Journal of Attention Disorders. https://doi.org/10.1177/1087054711434154. Original Research.

Marie Brossard-Racine, Michael Shevell, Laurie Snider, Stacey Ageronioti Bélanger, Marilyse Julien, Annette Majnemer. Persistent Handwriting Difficulties in Children With ADHD After Treatment With Stimulant Medication. Journal of Attention Disorders. https://doi.org/10.1177/1087054712461936. Original Research

Javier Fenollar-Cortes, Ana Gallego-Martinez, Luis J. Fuentes. The Role of Inattention and Hyperactivity/Impulsivity in the Fine Motor Coordination in Children with ADHD. Research in Developmental Disabilities. https://doi.org/10.1016/j.ridd.2017.08.003. Original Research.

Arthritis is NOT Just For The Elderly: Early Signs Of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease that, according to the Arthritis Foundation, affects 1.5 million people in the US. Women are 3 times more likely to develop RA and are usually diagnosed between ages 30 and 60, while men are rarely diagnosed before the age of 45 . Unlike osteoarthritis which is caused by wear and tear on joint cartilage over time, RA is caused by an overactive immune system that triggers unnecessary inflammation responses. One effect of this is that the body attacks its own joints causing swelling, stiffness, and chronic joint pain as well as irreversible damage. This limits joint mobility and decreases the quality of life for those impacted by it, especially those diagnosed as children or young adults.

This disease cannot be cured but treatments like medicine or dietary/ lifestyle changes are most effective when diagnosis happens early. When joint damage occurs it is irreversible, meaning the only treatment option is surgery. The joints most commonly affected in the early stages of this disease are finger joints which are usually the first sign of inflammation and will be the focus of this article. The image below shows the progression of finger joint damage in a patient with RA starting with no damage (a) to severe damage (c).

As an RA patient, a typical visit to your doctor would always include a pain/inflammation assessment. With a focus is on early stages of RA, fingers and hands would be the most important areas to look at. Each joint of focus would be felt by your doctor to check for swelling and tenderness, but the most important aspect is the patient’s self-assessment of inflammation and pain. It is important for patients to accurately assess their pain and mobility in order to find a medicine or treatment that works effectively. This was the focus of a study that was conducted on 52 RA patients (33 women and 19 men) which used a variety of tests in an attempt to quantify arthritis damage and compare it to the predictions made my patients.

The first test looked at range of motion for fingers flexed (in a fist) and extended (straightened). The next test measured grip strength in different positions like using a pencil, opening a jar or turning a key by using a device that measured the force produced by the hand in each position. Stiffness was measured visually, and pain levels were also recorded, but it should be noted that pain cannot accurately be quantified because pain tolerances vary among patients. The result of this study was that the patients predictions on grip strength and stiffness best correlated to the real results and were therefore the best predictors of hand function. This means that patient reports of strength and stiffness are the most accurate and helpful to be used by doctors when choosing medications or treatment plans.

Because joint damage from RA cannot be reversed, surgery is usually the only option to repair damaged joints, and even surgery will not bring back full mobility. Because RA treatments (both medicines and surgery options) are still very new there isn’t widely available or reliable data on the impact of hand surgery. Additionally, with the increasing use of the newer class of biologic drugs there has been a noticeable decrease in damage to the synovial tissue (the specialized tissue between the bones in any given joint) and the need for hand surgery has significantly decreased because of this. Overall, a variety of surgeries are available and there is almost always a tradeoff between mobility, vanity and elimination of pain. It is up to the patient, doctor, and surgeon to decide the best treatment option.

Overall, it is important to listen to your body and look out for early signs of RA to avoid lasting joint damage. This is especially important if you have a family history of RA. Early symptoms include, redness, pain, stiffness and swelling at joints, a lack of muscle strength, decreased range of motion/mobility, and even unexplained fatigue or fever.

References and Further Reading

Punch like a nerd: Utilizing Biomechanics in Boxing Form

Why we punch and how we do it

You and I are living creatures. Every living creature on Earth has some means of self-preservation, and while society and technology have advanced humans far beyond the norms of the animal kingdom, deep down at our core is the self-preserving instinct known as “fight or flight”. When the moment arises that flight is not possible, that unarmed self-defense is the only option, a human will most likely throw a punch. Unless you are trained in a combat sport or a style of self-defense, that punch will likely be inefficient and ineffective. I’m here to break down, with biomechanics, the most effective way to throw that punch.

This diagram shows 4 main punches in boxing. This blog will focus mainly on the cross, hook, and uppercut. Photo from neilarey.com

In boxing, that sport that deals with punching a good bit, there are three main types of punches: straight (jab/cross), hook, and uppercut. As pictured above, the three motions have varying paths traveled by the fist and they engage different muscles in different ways.

“Hold on a minute, why not throw a karate chop or a big ol’ open hand slap?” A study was done to answer this question, where untrained men and women hit a target with an open hand, a karate chop and a closed fist. For each of the techniques they calculated the effective mass, which measures the impact the target experiences. The results showed that while the open hand slap and karate chop had similar effective masses, the closed fist punch had an effective mass that was more than double the other techniques. So, unless you’re a black belt in karate with a mean karate chop, let’s stick to punching if the need arises.

Which punch to utilize

Now that you have decided that the first step is to clench your fist and rear up for a punch, how exactly do you do that? Biomechanical studies have shown for low-level boxers the cross, which is a straight punch with the dominant hand, generates noticeably more punching force. When elite level boxers such as Olympic athletes are observed, however, all three techniques produce extremely similar punching forces. This suggests that for the average untrained human, the most effective and efficient punch to use is going to be the cross.

While it is not the most scientific diagram, this graphic gives some biomechanically sound tips on how to throw an effective straight cross. Photo from The Art of Manliness.

But why is the straight cross generating more force in amateur boxers, and how can elite boxers generate high forces with the other techniques? It’s all answered by biomechanics.

Each punch is unique in how force is generated due to the motion of our bodies and the muscles each motion uses. For example, elite level boxers generate much more of their punching force from extension of their back leg and the extension of their elbow when throwing the cross. This is similar to how a baseball pitcher generates force by driving off the mound with their back leg in their throwing motion. When throwing hooks and uppercuts, elite boxers tend to utilize their hip rotation much more than lower-level boxers, who rely on their shoulder motion. All of this leads to the fact that while you’re throwing your fist at a target, most of the power comes from your waist and legs, so mixing a leg day into your workout schedule could be beneficial.

Sources and Further Reading

Rock on, Dude!

In the rock climbing world, there is not much that people fear more than the sound of a “pop” coming from their fingers. That sound means months of rehab and can keep you off the rock for up to six months [1]. But what exactly is happening when you hear that dreaded sound? The fingers are so small, how can one injury to the fingers be so devastating? Let’s dive in.

As a review of hand anatomy, direct your attention to the graphic on the right. There are two main tendons that run up each finger to allow the fingers to produce the curling motion. In order to keep these tendons close to the bones to provide for maximum torque,

Diagram of the hand showing the tendons and pulleys
Anatomy of the hand [2]
they are held by pulleys. The pulleys are the culprits of the “pop” when grabbing tiny holds. Without these pulleys, the tendons would “bowstring” and pull away from the axis of rotation of the finger and thus decrease the strength of the system [2]. The important pulleys in climbing are the A2 and the A4, as they are fibro-osseous pulleys (connect bone to bone) and are stiffer than the A3 and A5[3].

In climbing, there are two main hand positions when grabbing

The open hand position
The open hand position [2]
holds: Open-hand and crimp. The open-hand grip relies heavily on the forearm muscles, while the crimp puts a significantly higher strain on the skeleton. The crimp is incredibly dangerous, as it puts three times the force being applied to the fingertip on the A2 pulley [4]. A common mistake I have noticed for newer climbers is to crimp everything as the big muscles in the upper arm and back are much stronger than the forearms. Putting all the weight on the skeleton and big muscles allows you to skip over the limiting factor of weaker forearms. This allows climbers to pull on smaller holds and climb harder routes. New climbers are not as aware of the dangers and they get excited

hand in the crimp position
Hand in the crimp position [3]
to send harder and harder routes, but this reinforces the bad habit of crimping which will eventually get you injured. Of course, sometimes crimping is unavoidable when the holds are very small, but it is best to avoid it as much as possible.


So how strong are these pulleys? In a study performed with recently deceased cadavers, the A2 pulley resisted up to 408 N, which is 91 pounds [5]. This was determined by removing the bone from the hands and pulling on the pulleys until they broke. Based on another study in live humans, the force applied to the A2 pulley was extrapolated to be around 373 N with 118 N applied to the fingertips [4]. This extrapolation was based on a controlled environment. It is easy to see that a pulley could be loaded with much more force than that if a climber’s foot slips mid- move or if you catch a hold with fewer fingers than you mean to. It was also

Me crimping as hard as I can because I'm weak
Me crimping as hard as I can because I’m weak

found that the bowstringing in the intact A2 increased by 30% throughout a warm-up process [4]. This clearly shows the importance of a good warm-up.

Sources and extra reading:








Scleroderma and Raynaud’s Phenomenon: Cold Weather’s Influence on Skin

Anyone who is familiar with winters that are mainly at temperatures in single digit range knows how crucial gloves are to surviving the tough, frigid weather. If one was to go outside without them, their hands become extremely pale (or sometimes almost blue) and, once back inside, take a bit of time to get back to normal. It’s a tough life, I know, but people with a scleroderma have an even harder time surviving the winter. What is scleroderma, you ask? Scleroderma is an autoimmune disease that causes skin and internal organs to thicken, and if that wasn’t tough enough, a good chunk of people with it also experience secondary Raynaud’s phenomenon, which is an exaggerated vasoconstriction of arterioles in response to cold weather and causes a drop in blood flow. The main, visible outcome from this disease is how the skin whitens and swells. Problems must ensue from the combination of thick skin and lack of blood flow to the extremities, right?

Raynaud's Phenomenon in ring finger
Thomas Galvin [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Modified from Balbir-Gurman, Denton, Nichols, Knight, Nahir, Martin, and Black, Annals of Rheumatic Diseases 2002

With the thickening of skin, certain properties of skin will noticeably alter when a person has scleroderma. In a recent study, researchers from multiple backgrounds used a new suction device to compare mechanical properties of skin of patients with scleroderma and healthy patients. In the experiment, the researchers used a modified Rodnan skin score to observe skin involvement. This way of testing focuses on how easy it is to pinch skin and witness how it folds. The skin was tested on 3 parts of the body including back, forearm, and shoulder in order to see how the skin not only differs between patients, but to see how different areas have different properties due to activity and use of those parts of the body. To test the skin of the patients, the new suction device used, the BTC-2000, also proved beneficial due to its non-invasive nature that could be used more frequently to produce data. The biomechanical properties of skin depend greatly on the dermis, or skin thickness, due to the properties being derived from witnessing skin response to pressure and stress. The study that these researchers performed supported the idea that mechanical properties of skin are altered negatively when a patient has scleroderma. The major properties that were observed were less extensibility, stretchiness, and a larger resistance to stress.

So the struggle to go outside in the winter is even bigger for people with scleroderma. But in their case, the damage brought on by cold weather is greater and typically more permanent. Similarly, if this is how the disease influences the mechanical properties of the outer skin, the potential impact on internal organs is intriguing.