Down to the Bear Bones: How Polar Bears evolved from Grizzlies to hunt in the Arctic

Katmai National Park in Alaska holds an annual “Fat Bear Week”, in which Twitter followers are asked to vote for the fattest bear in the park. This year’s winner was Holly, somewhere in the range of 500 to 700 lbs. That’s a big bear. However, in 1960, a male polar bear in Kotzebue Sound, Alaska, weighed in at 2,209 lbs. In fact, on average, polar bears weight up to 60% more than Grizzly bears, their closest animal relative. 

A very fat grizzly bear standing on rocks.
Holly, aka Bear 435, the 2019 winner of the Fat Bear Contest. From Katmai National Park via Twitter.

So just how did Polar Bears get so big? Well, as anyone in the Midwest knows, a harsh winter requires a good winter coat. The advantage of thick skin and fur, as well as a higher capacity to put on weight made heavier polar bears more adept to survive. However, bigger bears that could survive the cold were more likely to fall through the ice, so these adaptations required better foot mechanics.

Consequently, polar bears developed a distinctive gait. A rotary gait is a “double suspension” gait, meaning the animal bounces both off the hind limbs and then the fore limbs . This is contrasted from the grizzly bear’s transverse gallop, which involves only one “bounce,” — this loads each limb for a longer time and more vertically. The rotary gait improves stability, giving the polar bear the ability to travel quickly and smoothly on icy surfaces. 

A series of drawings depicting the gait of a galloping polar bear.
A series of drawings depicting the gait of a polar bear. Modified from S. Renous, J.P. Gasc, and A. Abourachid, Netherlands Journal of Zoology (1998).

Another significant difference between the species are their skulls, which, while similar in size, vary greatly in bite force and bone strength. The polar bear has a stronger bite, but a weaker skull. Polar bears are one of the most rapid instances of evolution in surviving species of animals, having evolved from the grizzly bear within the last five hundred thousand years. So why are their skulls weaker if their bite is stronger? 

Simply put: seals are easy to chew. Grizzlies are omnivores, as most bear species. Their diet subsists of salmon, elk, and small game, but includes a hefty amount of vegetation. Polar Bears, in the ice and cold, were forced to eat seals (as well as penguins, fish, even belugas). Seals are largely blubber, providing the caloric intake necessary to sustain these large beasts, but offering little resistance in the chewing process. 

Two line drawings of skulls, one of a polar bear and a grizzly bear
Skulls of the polar (left) and grizzly bear (right). Modified from P. Christiansen, Journal of Zoology (2006).

The polar bear’s skull morphed quickly, elongating to allow it to hunt for seals and fish through small holes in the ice. This weakened and lowered the density of the skull; however, because the seal-heavy diet required less effort to chew than vegetation, there was no selective advantage to a skull reinforcing. So, with a more efficient gait and a stronger bite, the polar bear developed into a killing machine in the icy north.

Interested in more of the polar bear’s hunt? Learn about how they can swim for hundreds of miles, or to see these arctic advantages in action, check out this video of a polar bear hunting a seal.

What Makes and Breaks the World’s Tallest Trees

Trees have the potential to be the largest organisms on Earth. The world’s tallest tree, dubbed Hyperion, is 380 ft tall and weighs over 1,600,000 lbs. Compared this to the world’s largest animal, a particularly massive blue whale which was 100 ft long and weighed 380,000 lbs, the simply massive size of this tree should be obvious. And unlike a whale, a tree is much less likely collapse and crush itself under its own weight. Trees need to be tall, even if doing so consumes a lot of resources, in order to compete for sunlight. So what lets trees get this big, and what limits their height?

A diagram showing a space shuttle, which when prepared to launch is less than half the height of Hyperion, General Sherman, a wider but slightly shorter tree of a different family sequoia, a blue whale that is much shorter than either tree, and the statue of liberty, whose torch barely comes close to the shorter of the two trees
Comparison diagram of the World’s largest trees – Sequoia Tree Comparison Chart, Sequoias

There are two primary rules that govern tree sizes. The first is mechanics, the way the trunk of the tree is built and how it responds to weight. The wood of the biggest trees has a very high strength to weight ratio, which enables a tree to carry its own massive weight without collapsing. The layout and structure of this wood is analyzed at length in the journal by M. Ramage, but in summary, tall trees have internal cells called tracheids. These tiny circular tubes are 2-4 mm long and around 30 μm wide and provide support to the tree and allow water to flow throughout it, without adding as much weight. 

an image showing the tracheid cell structure of wood, many small cylinders stacked on top of each other.
A section of the annual ring of a conifer- M. Ramage’s The wood from the trees: The use of timber in construction and Dr. Krzysztof Wicher.

The high strength to weight ratio of wood allows trees to support themselves at incredible heights. Using B. Blonder’s research about the scaling of trees, it can be shown that trees are so strong and yet comparatively light weight that a tree would not actually collapse under its own weight until it was almost 15 Empire State Buildings tall. Obviously no tree is this tall, meaning some other factors must limit their height, but the incredible strength of wood should now be clear!

A diagram showing the decreasing size of pine needle branch segments. They decrease dramatically as height increases.
Leaf samples taken from the same type of tree with the height they were taken from listed adjacently in meters, – G. Koch’s The limits of tree height

The second primary rule that governs tree size is hydraulics, and it restricts the height a tree can reach. Hydraulics defines a tree’s ability to move water from its roots to its upper leaves in order to perform photosynthesis. The taller a tree gets, the more difficult this process becomes until the tree becomes incapable of growing any taller. G. Koch’s article, The Limits to Tree Height, explores how this hydraulic system works and how it restricts the heights a tree can reach. Xylem, tiny internal pipes that run from the roots to the tops of the tree, and carry water in a long continuous column this whole length. The longer this column becomes, the more difficult it is to maintain and the greater suction pressure that occurs at the highest leaves. Koch studied how properties in leaves changed the higher up they could be found, determining that the efficiency of Photosynthesis decreased, the pressure at the end of the xylem increased, and the size of leaves decreased. At great heights, the status of leaves seemed remarkably similar to those of a tree undergoing a severe drought.

 

Koch determined that these changes with height would eventually hit a maximum limit which they could not exceed, a limit that was determined to occur between 122-130 meters. So while the efficient properties of wood allow trees to reach incredible heights, their restricted ability to move water limits just how tall they can grow.

Sources and Further Reading:

  • Ramage M., Burridge H., Busse-Wicher M., et al. The wood from trees: The use of timber in construction. Renewable and Sustainable Energy Reviews 68, 333-359 (2017)
  • Blonder B. The size of trees: exploring biological scaling (2010)
  • Koch, G., Sillett, S., Jennings, G. et al. The limits to tree height. Nature 428, 851–854 (2004)

Soft Robotics: Humanizing the Mechanical

Cassie the robot, created by Dr. Mikhail Jones at Oregon State University
Cassie the Robot, developed by Mikhail Jones, Faculty Research Assistant in Mechanical Engineering at Oregon State University.

In media and science-fiction, robots have stereotypically, and perhaps somewhat unfairly, been depicted as mechanical, stiff assemblies of moving joints and complicated circuitry. While this still holds true for many robots designed today, whether for industry or research, the past few years have seen a growing interest in soft robotics in academia, industry, and popular culture. As the name implies, many research groups have begun investing in constructing robots from compliant, softer materials.

Stickybot, a gecko-inspired robot.
Stickybot, a biomimetic robot.

Inspired by the way organisms in nature survive and adapt to their surroundings (formally known as biomimicry), the advantages of soft robotic components lie in their flexibility, sensitivity, and malleability – delicate tasks or interactions involving other people would be better accomplished by robots made of compliant materials rather than one that could potentially cause harm to the object or person. To that end, many of the applications of soft robotic research have already seen results in the medical industry, from invasive surgery to assistive exosuits. By taking inspiration from biological creatures or mechanisms, softer materials like rubbers and plastics can be actuated to accomplish tasks conventional, “hard” robots could struggle with.

Animation of pneumatic muscle.
Animation of pneumatic air muscle used as robotic actuators.

The most common method of moving these robotic parts is with changes in internal pressure. By creating a “hard”, skeletal frame, and surrounding it with soft, sealed membranes, changes in pressure allow the designer to control its components precisely. By decreasing the pressure and creating a vacuum, the robotic section would shrink or crumple, and increasing it would do the opposite. Researchers at Harvard developed “artificial muscles” by taking this concept a step further; using origami, they were able to design soft robotic mechanisms that could orient themselves into tunable positions as the pressure was changed inside the membrane (as a side note, origami is used in a surprising number of research fields, one of the most famous being satellite deployment). Compared to the challenge of precisely controlling prismatic (sliding) joints and servos in conventional robotics, the compliance of the materials used allow for finer control and smaller ranges of applied forces that are better suited for precise tasks.

Animation of a person demonstrating the Miura fold on a piece of paper
The Miura fold pictured here is often used to deploy large surfaces while minimizing volume, such as for satellites.

Another significant advantage of soft robots over their stiff counterparts is their adaptability to environmental conditions. Generally speaking, robots do not do well in water (or lava, for that matter), but it would have little effect on robots covered in a sealed, pressurized “skin”. This is what inspired NASA in 2015 to fund research into soft robots that could explore the oceans of one of Jupiter’s moons, Europa.  Similarly, a light-activated underwater robotic manta ray was designed at a centimeter scale to study the effect of environmental cues on controllable robots.

Schematic and pictures of soft robot design.
A soft-legged robot with walking capabilities.

While research in soft robotics is still relatively new, it has the potential to significantly affect the role of robots in our daily lives. As a softer, safer, and more environmentally robust alternative to “hard” robots, wearable robotic devices, exploratory robotic fish, and personal medical attendants could soon become commonplace for the general public.

Continue reading Soft Robotics: Humanizing the Mechanical

Why your scar tissue isn’t an issue

What do knee scrapes, adolescent acne, and paper cuts have in common? They all have the potential to leave a nasty scar. For people who have undergone trauma that results in serious wounds, especially on the face, scar aging is a serious concern. What are scars, and why does scar tissue tend to look different than regular skin as aging occurs?

In 1861, Karl Langer began observing the nature of the skin’s tensile properties. He cut small, circular holes into cadavers, and looked to see where on these holes the skin pulled the most. From these experiments, he developed “Langer’s Lines,” which he asserted were lines of tension all around the human skin. Later, Borges noticed that Langer’s lines only applied to cadavers, and began to perform similar experiments on live people to see if he saw different results. He pinched the skin of live people, and then saw how the direction of pinching impacted the length of the wrinkle formed. From these experiments, he identified RSTL, or relaxed skin tension lines. More and more researchers after Langer and Borges investigated the “tension line” phenomena, and they all noticed the same thing: wounds cut across these lines always led to nastier, uglier scars than wounds parallel to the tension lines. Why would that happen?

Figure 1 outlines the differences of Langer's lines, Kraissl's lines, and Borges's RSTL on the human face.
Image courtesy of MedMedia

To answer this question, let’s first identify the cellular mechanisms at work during healing. According to David Leffell of the Yale School of Medicine, there are three key stages of scar formation. The first stage of scar formation is inflammation. This happens right after the wound is incurred. Blood flows to the site, and tissue called granulation tissue begins to form at the base of the wound. Next is proliferation, when that granulation tissue helps the surrounding fibroblast cells to duplicate as quickly as possible. Fibroblasts are very important; they are the cells that produce collagen, a key protein in tissue formation. During proliferation, more and more fibroblasts fill the site, and they begin rebuilding the collagen networks for new skin. The final stage of scar formation is maturation/remodeling, when fibroblast levels decrease slowly as fresh tissue is rebuilt.

This figure shows each stage of wound healing, as is outlined by the supporting paragraph.
Image courtesy of biodermis.com

Because scars are formed differently than regular skin, they also tend to age differently. Normal consequences of skin aging can be seen around us in older people every day. As you may notice in your parents and grandparents, older skin tends to be dry, rough, wrinkly, and sometimes discolored. While these changes can also occur within scar tissue, the biggest factor in scar tissue aging is the difference in the rate of skin cell renewal. Skin cell renewal occurs when new skin cells travel from the basal layer of the skin up to the epidermis. Scar tissue’s renewal rate is different than normal skin’s renewal rate. This is why adults recover from wounds more slowly than young people – there is a greater difference between their cell renewal rates. The age at which the scar was formed, and the quality of the care provided, are critical in evaluating how well the scar will age.

If you’re interested in learning more about how that cut on your hand might heal and age, watch this video from TED-Ed, or for more detailed reading, check out this article.

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:

[1]https://theclimbingdoctor.com/pulley-injuries-explained-part-2/

 

[2]https://theclimbingdoctor.com/pulley-injuries-explained-part-1/

[3]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3371120/

[4]https://www.sciencedirect.com/science/article/pii/S0021929000001846

[5]https://journals-sagepub-com.proxy.library.nd.edu/doi/pdf/10.1016/0266-7681%2890%2990085-I

 

Ankle Sprains: An Epidemic in the World of Athletics

Have you ever been out running on a gorgeous fall day, only to have the run cut short by a painful misstep on a tree root covered by leaves? I have, and let me tell you – it’s awful! And even if you aren’t a runner, according to the Sports Medicine Research Manual, ankle sprains are a common, if not the most common, injury for sports involving lower body movements. Now, the solution to preventing this painful and annoying injury could be as simple as avoiding tree roots and uneven ground, but the real problem behind ankle sprains deals with the anatomy of the ankle.

The ankle is made up of many ligaments, bones, and muscles. However, when sprained, it is the ligaments that are mainly affected. Connecting bone to bone, ligaments are used to support and stabilize joints to prevent overextensions and other injuries. The weaker a ligament is, the easier it is to injure. There are three main lateral (outer) ligaments supporting the ankle joint that can become problematic: the anterior talofibular ligament, the calcaneofibular ligament and the posterior talofibular ligament. According to a study from Physiopedia, these lateral ligaments are weaker than those on the interior (medial) of the ankle, with the anterior talofibular ligament being the weakest.

An image depicting the various ligaments of the ankle, both lateral and medial.
Anatomy of the ankle, highlighting the lateral and medial ligaments

The next question that has to be asked is why are these ligaments so much weaker than other ones? The answer to this question is based on their physical make up. Ligaments are made of soft tissue that has various collagen fibers running parallel to each other throughout it. The more fibers there are, the more structure and rigidity there is. Think of the fibers as a rope: The rope can stretch to a certain point, but once it hits that point it will snap and break. But if you have a thicker rope (such as the medial ligaments), it becomes much harder to break.

The ligaments on the outer part of the ankle have fewer collagen fibers than those on the inside of the ankle. Thus, when the ankle is moved in an awkward position, it is more likely that the lateral ligaments will break.

Once you sprain your ankle, the focus turns to treatment. Treatment will differ slightly for every individual depending on the severity of the ankle sprain. The simplest way to treat a sprained ankle is to follow the RICE (Rest, Ice, Compression, Elevation) method. Other forms of treatment include taping the ankle or using a brace to restrict movement and to add support and extra stability. Wearing proper footwear is another way that one can prevent and help treat a sprained ankle, as certain shoes are specifically designed to help avoid such injuries. To prevent future ankle sprains, exercises are recommended to help strengthen and stabilize the joint and surrounding ligaments and muscles.

For more information on ankle anatomy and sprains, check out these articles on BOFAS and SPORTS-Health.

Pressurized Vessels Supporting the Spine: Structure and Function of Intervertebral Discs

Back in 1989, it was estimated that about 2.5 million U.S. workers suffered from low back pain, and low back pain has even been talked about as one of the largest causes of disability in the world. Intervertebral disc degeneration is one of the most common reasons for low back pain in adults. In order to understand how disc degeneration occurs and causes pain, it is important to examine the structure and function of discs in the back.

Computer generated image of a healthy lumbar spine
Vertebral Column: Obtained from Smart Servier Medical Art

Discs are structures that sit in between vertebrae in the spine (blue in the image). Their consistency has been compared to Jell-O and the seemingly mythical product called the waterbed. This consistency comes about because of the microstructure of the discs. The main structural component is collagen which not only surrounds the discs but also traverses across the fluid-filled center to give support. Collagen is found all over the body in places ranging from bones to eyes. There are many different types of collagen that are able to account for the softness of the cornea and the strength and stiffness of bones. In discs in the back, the collagen that traverses the middle is the same as that found in cartilage, while the collagen that makes up the outer layer is the same collagen found in skin and bones. This gives the discs a strong, thin outer layer surrounding the gel-like center, warranting the comparison to the waterbed.

Because of this structure, intervertebral discs provide support for the spine in compression. The spine can be compressed by activities as simple as carrying a backpack, sitting, or bending over. When these and other activities occur, the vertebrae press in on the discs, causing pressures from about 15 to 300 psi, or pounds per square inch, depending on the activity. For reference, the recommended tire pressure for a car is 30-35 psi and the pressure inside a champagne bottle is 60-90 psi.

As discs degenerate, either with age or trauma, they respond differently to the large compressive stress applied from the spine. With age, this change in response is most commonly attributed to the inside portion of the disc drying up and changing from a gel to a solid. Discs rely heavily on fluid flowing through their pores, and once they dry up, this no longer occurs. As loads are applied, instead of increasing pressure, degenerate discs can expand outward creating a phenomenon known as a bulging disc. While this is just one of the many medical problems a degenerate disc can cause, it is

Computer generated image of a lumbar spine with disc herniation.
Disc Herniation: Obtained from Smart Servier Medical Art

common and typically leads to an increase in pain. When the discs expand outwards, it reduces the space between the vertebrae causing irritation. If the discs expand far enough outward, they can leave the space between the vertebrae, entering the region where many nerves lie, potentially causing pain throughout the body.

Despite their odd consistency, intervertebral discs play an important role in the spine, sometimes pressurizing to more than 3 times that of a champagne bottle. Both injuries and natural degeneration leads to negative changes in the biomechanical properties of discs, causing an increase in back pain. If you are interested in learning how to take care of your discs, worried you have an injured disc, or simply want to learn more, I recommend going here.

The Benchmark of Upper Body Strength: Injury Prevention During the Bench Press

Who wouldn’t want to look like Captain America? This common desire to attain a strong Herculean physique, either for athletics or aesthetics, has led many ambitious men and women to weightlifting. An egotistical motivation puts these people at risk of injury, however, as they sacrifice proper form to achieve their next personal best. The bench press is one example of an effective but potentially dangerous lift.

This upper body exercise requires an individual to lie flat on a bench while repeatedly lowering and pressing a straight bar loaded with weights on each end. The hands evenly grip the bar slightly wider than shoulder width apart with the feet remaining flat on the ground and the arms fully extended. During the eccentric (or lowering) phase, the bar is brought in contact with the lower chest. The bar is then pressed up until the arms are once again fully extended (concentric phase).

Recreational weightlifters commonly use a wider grip on the bar, believing that this will increase activation of the chest muscles and allow them to mimic Terry Crew’s version of the Old Spice Man. One study performed on 12 powerlifters, however, found that the prominent muscles used during the lift, such as the pectoralis major, triceps brachii, and anterior deltoids (i.e. chest, triceps, and shoulders), experienced similar electromyographic activity despite varying hand spacing.

Diagram of a human upper body muscular system.
Image by OpenStax from Wikimedia Commons.

Although hand spacing does not significantly affect muscular activity, it can lead to injury. A review of several studies on the effects of hand grip found that a grip width greater than 1.5 times biacromial width, or shoulder width, naturally resulted in shoulder abduction, or rotation away from the body’s centerline, greater than 45°. As this angle increases, shoulder torque increases, causing potential injuries. For instance, the inferior glenohumeral ligament, a ligament restricting translational motion in the anterior direction at the shoulder’s ball and socket joint, may tear as abduction increases, causing instability at that joint. Repetitive cycles with this wider grip may also cause acromioclavicular joint (AC Joint) osteolysis – chronic destruction of the bone tissue at the joint between the clavicle and acromion.

Diagram of shoulder joint.
Image by OpenStax College – Anatomy & Physiology from Wikimedia Commons.

Aside from a wide grip, injuries also commonly stem from over-training and using excessive weight. Research on 18 male college students demonstrated that repeating the bench press motion with high frequency until failure resulted in a significant increase in the medial and lateral force exerted on the elbow joint, which could result in injury over time. Furthermore, performing the bench press with heavier loads could result in a sudden rupture of the pectoralis major. At the bottom of the eccentric phase as the bar touches the chest, the muscle fibers are simultaneously lengthening while also contracting, which increases the risk of muscle tear in this region.

Unlike Captain America, people cannot instantly acquire strength or build muscle. Muscular development and improving one’s bench press require time, patience, and proper form. To learn more about injury prevention or variations of the bench press, check out the video below or read these papers by Bruce Algra and JM Muyor.

Sources can be found below:

The Affect of Grip Width on Bench Press Performance and Risk of Injury

The Effects of Bench Press Variations in Competitive Athletes on Muscle Activity and Performance

Elbow Joint Fatigue and Bench-Press Training

An In-Depth Analysis of the Bench Press

 

In the Womb: Alive and Kicking

For a pregnant woman, it can be a thrilling moment when her baby kicks for the first time. Women have described the feeling as a flutter, a tumble, or a gentle thud. However, these movements are not only exciting because they are unpredictable but because they indicate healthy fetal development. 

Although a pregnant woman may not feel her baby’s kicks and punches until 18 to 25 weeks of pregnancy, fetal movement may begin as early as seven weeks and science shows that it is crucial in the development of joints and bones. In fact, a lack of fetal movement can be a sign of abnormal musculoskeletal development and other poor birth outcomes. In the last decade, scientists have begun to wonder how mechanical factors have positive or negative effects on a baby in utero. 

MRI scan animation of developing fetuses
An animation composes of MRI scans of fetal movement during various stages of development. (Image: © Stefaan W. Verbruggen, et al./Journal of the Royal Society)

In particular, researchers Stefaan Verbruggen and Niamh Nowlan at Imperial College in London decided to take a deeper look at the mechanics of these fetal movements through several different studies. As it turns out, neonates can throw a pretty strong punch. In one experiment, researchers saw that fetal kicks can incur an impact of 6 lbs at 20 weeks, 10 lbs at 30 weeks, and less than 4 lbs beyond 30 weeks of pregnancy. The force of fetal kicks decrease after 30 weeks due to the limited amount of space for the baby to move. 

In addition, the force of fetal kicking was also observed in three different neonatal positions: typical (head-first), breech (feet first), and twin fetuses. These studies revealed that twin fetuses can exert the same amount of kick force and motion as a healthy singleton fetus in the typical head-first position. However, fetuses in the breech position showed significantly lower kick forces and lower stress and strain in their hip and knee joints. This discovery might explain why babies in the breech position have the highest probability of being born with hip problems.

simulated strain concentrations in a fetal leg
Simulation of principal strain which indicates that strain increases with gestational age for fetuses in the head first position.  Modified from Verbruggen et al., 2018.

 In another study, three mothers volunteered to have their wombs monitored via MRI so that the researchers could observe the geometry, force, and frequency of fetal motion. It was found that fetal muscles are able to produce nearly 40 times more force than the kick itself. The magnitude of force exerted by these muscles confirms the importance of fetal kicks for proper growth of the hip and knee joints. This information is helping scientists and doctors connect the dots between neonatal environment and newborn joint abnormalities.

Interested in learning more? Check out some of the new technology being developed to further this study!

Attempting to “Knock Out” the Causes of Concussions

This image displays a human head experiencing impact to the forehead region.
This image is licensed under CC BY-SA 3.0 .

Approximately every 15 seconds, a traumatic brain injury occurs in the U.S. A concussion is a form of mild traumatic brain injury produced by a contact or inertial force to the head (or neck) area. A concussion causes the brain to rapidly move around inside the skull, harming natural brain function. According to the Brain Injury Research Institute, roughly 1.6 to 3.8 million concussions occur each year in the U.S., resulting from both recreation and sports related incidents. In fact, brain injuries cause more deaths than any other sports injury.

The high incidence of concussions has made the injury subject to several biomechanical studies in recent years. Kinematic, or motion-based, parameters of the head are used as common indicators to predict brain injury as they are suggestive of the brain’s response to force. Early efforts focused on the linear acceleration of the head during concussion as the primary prediction factor of the injury. The peak linear acceleration of the head is correlated to the peak pressure within the brain, and an increase in pressure within the brain can cause neurological damage. Modern sports protection equipment, including ice hockey helmets, maintain performance standards based on the peak linear acceleration experienced by the head during impact. However, linear acceleration does not entirely reflect the risk of concussion and rotational acceleration of the head must be considered. A shear force acts in a parallel direction to a surface or cross section. Shear forces and subsequent strains in the brain are correlated to peak rotational acceleration of the head. Brain tissue is one of the softest bodily materials and deforms quickly to shear forces. Therefore, rotational acceleration of the head is a common catalyst of severe concussion.

This image presents two human skull and brain combinations. The left skull has red horizontal arrows pointing to the brain to depict the linear acceleration of the head during a concussion. The right skull has red arrows acting in a circular manner around the head to represent rotational acceleration acting on the brain during concussion
This image is licensed under the Creative Commons Attribution 2.5 Generic License. Changes were made to the image in the form of text and red arrows.

A 2015 study introduces the addition of the brain deformation metric maximum principal stress (MPA) in order to aid in connecting kinematics and injury during concussion prediction.  The study used Hybrid III crash test dummy head forms to examine the result of varying forms and severities of impact. Each head form was equipped with nine single-axis accelerometers to study the acceleration of the head and hyperelastic models were used to study brain tissue deformation.

The results of the study revealed the existence of significant correlations between linear acceleration, rotational acceleration and maximum principal stress of brain matter, emphasizing the importance of considering several kinematic parameters in predictive concussion studies. Results of the study exemplified the magnitude of accelerations experienced by the head during concussion: the head forms experienced an average linear acceleration of approximately 40.62g and an average rotational acceleration of approximately 3388 rad/s2, which is equal to about  539 rev/s2. The extent of brain injury is revealed through the immensity of the accelerations experienced during impact.

This image presents a side view of the skull that presents all organs as semi-transparent, enabling viewers to effectively see the inner-workings of the head.
“Years in the making: How the risk for Alzheimer’s disease can be reduced.” (2018)

When determining the probability of concussion, it is limiting to utilize just one parameter. Instead, several parameters and the relationship between each must be considered. Additionally, factors like sex-specific characteristics and under-reporting of injury have been proven to affect the severity of brain injury through study.  While brain injury can never be fully avoided, these studies can help to make equipment more protective and reduce injury.

Interested in reading more?

Neuroscience, Biomechanics & the Risk of Concussion in Developing Brains

Additional Sources:

Biomechanics of Concussion

Brain Injury Prediction

Concussion in Female Collegiate Athletes