How much wood can a woodpecker peck? The Science Behind a Woodpecker’s Anatomy

Woodpecker anatomy: showing the location of the tongue
Diagram showing the tongue of a woodpecker, obtained from “BirdWatchingDaily.com”

Have you ever wondered how a woodpecker is capable of banging its head against a tree so furiously without seriously injuring itself? The impact of a woodpecker’s beak with a tree can exceed speeds of up to 6 meters per second and occur over 12,000 times a day.These kinds of numbers are what allow woodpeckers to smash through trees to get to those tasty bugs that live inside.

How is this possible you may ask? Scientists have studied the anatomy of a woodpecker and have come across an extraordinary discovery: the tongue of a woodpecker wraps completely around its neck before exiting the mouth, constricting the blood flow to and from the brain. This increases the amount of blood volume in the skull, making it, and its precious cargo, filled to the brim with fluid. This creates an effect known as “slosh mitigation”, where an object that is completely enclosed by an incompressible fluid becomes protected from an outside force due to the constant stabilization of pressure within the enclosed system. Thus, the harsh vibrations translated throughout the skull of the woodpecker are mitigated by a cushioning effect induced by the increased volume of blood in the brain. Ever notice how a snow globe always has a little pocket of air sitting on top of the water? Without it, there would be no pressure changes, and the flakes of snow would be restrained from ever creating that magical snowy blizzard we all love.

This incredible discovery is not just a fascinating fact you can pull out to impress your friends. In fact, companies have begun applying the science behind a woodpecker’s anatomy to the sports arena. A company by the name of Q30 Innovations has been on a mission to curb the estimated 3.8 million concussion occurrences every year. Their latest product, the Q Collar, features a tightly fitted neck brace that applies a mild compression to the jugular in the neck, thus creating the “slosh mitigation” effect on the brain. The Q-Collar has already been put to the test, showing positive results on football players and hockey players. Their latest test showed the effects of wearing the Q-Collar for a high school girls soccer team, whose total head impacts were collected via an accelerometer throughout the entire season. Half the team was selected to wear the Q-Collar, and at the end of the season, the accelerometers of both groups reported similar levels of head impact, both in quantity and severity. However, it was shown the group wearing the Q-Collar required less brain activity to complete a concussion protocol than those of the control group. This shows that despite any of the girls having a reported concussion, the high impact loads exhibited on the brain during the season were enough to prohibit the brain from performing at its optimal level.

Want to learn more about breakthrough technologies covering the challenges of concussions? Learn more at Q30 Innovations.

 

References:

  1. “Do Woodpeckers Get Concussions?”http://explorecuriocity.org/Explore/ArticleId/6734/do-woodpeckers-get-concussions.aspx
  2. “Response of Woodpecker’s Head during Pecking Process Simulated by Material Point Method” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4406624/
  3. “What is a Concussion?” http://www.protectthebrain.org/Brain-Injury-Research/What-is-a-Concussion-.aspx
  4. “Q-Collar tests produce positive results in protecting girl soccer players from concussions” https://www.news5cleveland.com/news/health/q-collar-tests-produce-positive-results-in-protecting-girl-soccer-players-from-concussions

Put One Foot in Front of the Other? It’s Not that Easy

From Christmas movies to pop songs to motivational posters, we are encouraged to keep putting “one foot in front of the other.” While the sentiment is inspiring, recent studies show that there is a lot more to the seemingly simple task of walking than this phrase would suggest. Understanding this is especially important for balance and mobility after an injury or as people age.

The steps that make up the human walking cycle. Order of steps: heel-strike right, toe-off left, midstance right, heel-strike left, toe-off right, midstance left, hell-strike right. The body spends the time between heel-strike and toe-off with double support and the midstances are single-leg support.

Image from Wikimedia Commons

The human gait has a set structure that switches the weight between each leg, with only 20% of the typical walking motion distributing the weight across both feet. Maintaining balance throughout this process requires coordination in the muscles controlling the hips, knees, ankles, and feet. Mechanically, these adjustments keep the body’s center of mass (also known as center of gravity) over the base formed by feet positioning.

Obstacles and challenges to balance require a body’s quick response to mitigate shifts in the acceleration and momentum at the center of mass. Lack of efficient control over these parameters results in a fall. Many conditions, as well as age, can affect a person’s ability to respond to mobility challenges.

One specific study looked at how people who had had a stroke and subsequent partial paralysis on one side (paresis) faced mobility challenges compared with healthy folks. This condition effects approximately 400,000-500,000 people in the United States annually. It presents a unique opportunity to compare an individual’s non-damaged stride with their deficient stride at the point in the gait at which only one leg is on the ground (SLS, or single-leg-stride). The timing of the gait, the body’s momentum in all three planes of the body, and the location of the center of mass were recorded in this study.

Anatomical planes of the body. The sagittal plane splits the body left and right. The coronal plane splits the body forward and back. The transverse plane splits the body top and bottom.
Image from Wikimedia Commons

Versus healthy people, stroke survivors had significant trouble regulating momentum in the coronal plane, making falls more likely. Although it makes sense that momentum regulation suffers when muscles are paretic, it is yet unclear why the coronal plane was most affected. Additionally, post-stroke individuals’ centers of gravity were higher, which is also linked to instability. For stroke survivors, the partially paralyzed SLS took longer and extended farther from the center of mass than the regular SLS. While this is not as immediately dangerous as increasing falling risk, it slows mobility, unevenly works muscles (which can lead to injury), and is less efficient.

Going forward, these findings can be used to improve mobility success in people with balance issues or after injuries. This could manifest in better technologies, such as walkers that better help settle a person’s center of mass and partial exoskeletons that would help a person mitigate acceleration and momentum changes, or more targeted and individualistic physical therapies to strengthen weakened muscles and practice patient-specific challenges, such as overcoming obstacles that threaten coronal-plane balance. Understanding more about balance adjustment when walking may make some common phrases trite, but its potential benefits have life-changing impacts for many.

Further Reading and Sources:

Stroke/Paresis Information

Stability of Stepping

ACL Reconstruction: Which Option Is Best For You?

200,000 ACL injuries occur each year, and ACL reconstruction is the 6th most performed surgery in the United States, so to come back bigger, faster, and stronger, the right recovery path is critical.

The anterior cruciate ligament (ACL) is a critical part of the knee joint that connects the femur (‘thighbone’) to the tibia (‘shinbone’). Its main functions are to support the knee joint during side-to-side motion, such as cutting, shuffling, or pivoting, and to prevent the tibia from moving too far forward relative to the femur. When an ACL ruptures, it is very common to reconstruct it to bring someone back to performance level.

Location of the ACL inside the knee joint with other labeled bones and ligaments with another diagram showing a ruptured ACL.
Image from Wikimedia Commons “Anterior Cruciate Ligament”

The basis of ACL reconstruction is using living tissue, also known as grafts, to replace, and function as a substitute, for the torn ACL. There are four types of ACL reconstruction surgeries that use different types of grafts. Those four types of surgeries are classified as autograft reconstruction, allograft reconstruction, xenograft reconstruction, and synthetic reconstruction. Autograft surgeries require one’s own grafts to repair the ACL, allografts require a cadaver’s grafts to repair the ACL, xenografts require an animal’s grafts, and synthetics require manufactured materials. Additional articles on xenograft reconstruction and synthetic reconstruction can be accessed here and here.

Each surgery requires the removal of the damaged ACL, and then the incorporation of a new substitute by tunneling the newly selected graft through the femur and tibia. Within the autograft group, the two popular grafts for reconstruction are patellar tendon and hamstring tendon, with quadricep tendon being another, less popular, choice. The patellar tendon surgery takes the middle third of the patellar tendon, a tendon that connects the kneecap to the tibia, and makes sure to include the bony ends.

The hamstring tendon surgery takes two small slivers of each of the two hamstring tendons, connecting the hamstring muscle to the tibia, coils them up, and then finally bundling them to increase strength.

A knee joint with bones, ligaments, and tendons labeled.
Image from Wikipedia “Knee Joint”

For the allograft surgeries, a surgeon may select an Achilles, patellar, hamstring, or quadricep tendon from the donor.

It is very important to choose the right surgery. While the determination of which surgery and technique to perform falls heavily on the surgeon’s and patient’s preference, there are advantages and disadvantages of each technique which tend to persuade the choice of surgery. The main concepts surrounding the decision of which surgery to perform are the activeness of the patient, muscle strength, and previous knee injuries. Depending on the job, sport, or activity of the patient and the desired return time, one technique may be a better fit.

For a patient participating in low demand activities, allograft surgery may be the best fit due to less post-surgery pain and quicker surgery time, however it is very expensive and offers less tensile strength compared to autografts. As for autograft surgeries, patellar tendon reconstruction allows faster recovery time due to the bone-to-bone bonding and offers a strong substitute for a torn ACL, however future knee pain is very common. Hamstring tendon reconstruction requires more recovery time; however, the post-surgery pain is significantly less than the patellar tendon reconstruction and the tensile strength of the hamstring tendon is the strongest possible substitute.

Additional reading and comparisons between the popular autografts and allograft techniques can be accessed here and here.

Patellar Tendinitis: The Kryptonite of Jumping Athletes

Volleyball is a sport of quick movements. For hitters, one of the most common movements in the game is the jump, whether that be to block or to hit. Although a higher vertical leads to improvement in game performance, it can increase the risk of developing a serious injury that affects many volleyball players: patellar tendinitis. This condition is associated with pain and tenderness directly below the knee cap that is especially apparent during explosive, jumping movements. But what exactly causes this condition? And what can be done to remedy it?

A schematic of the knee and patellar tendon.
Image from Wikipedia “Patellar Tendinitis”

Since volleyball is such a quick game, muscle memory is required to react to different situations that can occur. The main way to build muscle memory is repetition. Therefore, young volleyball players are encouraged to play the sport as much as possible. For many athletes, this means playing for their school during that season and then playing for an independent club for the rest of the year. Although this increases the athlete’s skill level, it also increases the chance of patellar tendinitis, according to a study.

Besides overuse, lack of ankle mobility can also lead to a higher risk of the condition. A study found that players that couldn’t flex their ankle upward past 45 degrees could have 2 times the risk of patellar tendinitis as players with a higher ankle mobility. This is most likely due to the ankle and calf’s role in absorbing impact upon landing. Less absorption by the ankle causes more force to be put on the patellar tendon. This is bad news for volleyball players who often have poor ankle mobility due to a past injury.

There are a few ways to treat patellar tendinitis. For an orthotic approach, players use straps or tape around their patellar tendon. Some think this is simply due to the fact that the strap or tape makes the athlete feel more stable, which allows them to load the tendon more properly. However, a study done in 2011 analyzed the strain in the patellar tendon using a computational model. The researchers found that the patellar tendon strap increased the angle between the tendon and the kneecap, which caused the strain to decrease. Decreased strain means that the tendon stretches less, which would decrease the incidence of patellar tendinitis. Another way to treat the condition is surgically. One of the more simple surgeries is a removal of the dead or torn tissue of the patellar tendon. This allows new, healthy tissue to form.

A strap being put around the patellar tendon that can ease pain.
Image from Sports Injury Clinic “Patella Tendon Taping”

Patellar tendinitis is a serious condition affecting many high-level athletes. Although there isn’t a simple cure, researchers have brought to light different causes and treatments of the condition. These can be used to help athletes remedy the pain they are experiencing and perform at their best.

Sources:

Study on How Vertical Affects Patellar Tendinitis

Study on How Training Volume Affects Patellar Tendinitis

Ankle Flexion Study

Patellar Tendon Strap Proprioception Study

Patellar Tendon Strain After Applying a Strap

Additional Reading:

Clinical Trial on Patellar Tendon Strap

Biomechanics of Pitching: Pushing Limits on the Shoulder and Elbow

Aroldis Chapman of the New York Yankees holds the Guinness World Record for the fastest recorded baseball pitch at 105.1 MPH; a record that has held for almost a decade. Why has no one been able to top his record? — An answer to this question may be found in the biomechanical limits of the human shoulder and elbow during the throwing motion.

As a little background on the subject, the throwing motion can be broken down into six separate phases: windup, stride, arm cocking, arm acceleration, arm deceleration, and follow-through as can be seen below.

Images depicting the six phases of the throwing motion.
Image from the www.physio-pedia.com article “Throwing Biomechanics”

Of the six phases only two are the main instances of injury: the arm cocking phase and the arm deceleration phase.

Injury can occur in the labrum and rotator cuff in the shoulder, as well as in the ulnar collateral ligament (UCL) in the elbow during the throwing motion. In pitchers the stresses are at their extremes due to the unique positions the arm reaches, thus leading to a higher chance of failure in the muscles and ligaments of the arm.

Torques and forces on the shoulder and elbow at the end of the arm cocking phase.
Image from The American Journal of Sports Medicine article “Kinematics of Baseball Pitching with Implications About Injury Mechanisms” by Fleisig et al.

At the end of the arm cocking phase, the arm is in a position of 160° to 180° from the horizontal and puts the arm in the position to accelerate the ball forward. According to one study, extreme torques of 64 N-m and 67 N-m are applied at the elbow and shoulder, specifically loading the rotator cuff and the UCL. Furthermore, the anterior (forward) force at the shoulder of 310 N loads the labrum in such a way that may cause it to tear. The feeling of these loads is equivalent to holding 60 lbs in your hand in the position shown on the right!

Force and position of the shoulder and elbow during the arm deceleration phase.
Image from The American Journal of Sports Medicine article “Kinematics of Baseball Pitching with Implications About Injury Mechanisms” by Fleisig et al.

During the arm deceleration phase the arm is in a position of 64° from the horizontal and the shoulder resists the extreme speed and acceleration it just endured. An article showed that during the deceleration phase the arm experiences angular velocities in the shoulder of almost 7,000 degrees/sec making it one of the fastest known human motions. That is about 1,200 RPM which is comparable to the rotational speed of some car engines during cruise control, while traveling at about 50 MPH! Additionally, the rotator cuff and the labrum take the brunt of the 1090 N (245 lbs) compressive force needed to slow down the arm and it is enacted in just an instant!

According to one article, the limiting factor on pitch speed is that the force pitchers apply to their UCL is at the limit of what makes it tear. This means that attempting to throw any faster would result in the UCL tearing! In summary, pushing to gain more MPH on the fastball would mean even higher loads and thus more demand from the shoulder and elbow despite already being at their limits.

All in all,  biomechanical data shows that limits in the rotator cuff, labrum, and especially the UCL explain why  Aroldis Chapman’s record has been preserved for almost a decade and why the chances of throwing any faster are almost impossible. However, in the world of sports, limits and impossibilities are just waiting to be broken.

 

Sources and Additional Reading:

“Fastest Baseball Pitch (Male)” https://www.guinnessworldrecords.com/world-records/fastest-baseball-pitch-(male)/

“Kinematics of Baseball Pitching With Implications About Injury Mechanisms” https://journals.sagepub.com/doi/pdf/10.1177/036354659502300218

“Biomechanics of baseball pitching: A preliminary report” https://journals.sagepub.com/doi/pdf/10.1177/036354658501300402

“Why It’s Almost Impossible For Fastballs to Get Any Faster” https://www.wired.com/story/why-its-almost-impossible-for-fastballs-to-get-any-faster/

“Throwing Biomechanics” https://www.physio-pedia.com/Throwing_Biomechanics

“Your car’s engine rpm at highway cruising speeds” https://www.team-bhp.com/forum/technical-stuff/171572-your-cars-engine-rpm-highway-cruising-speeds.html

The Spinal Fusion that Reignited a Legendary Career

Can you imagine being the best player in the world at a certain sport and one day, aggravating an injury that not only put your athletic career in doubt, but also did not allow you to do normal daily activities? This is the challenge that faced Tiger Woods.

Tiger Woods is one of the greatest golfers to ever play the sport but has been plagued with back issues over the past few years that have prevented him from winning and also playing in golf tournaments. A golf swing applies a significant amount torque to one’s back. Repeating this motion as many times as Tiger has, through practice and tournaments since he began his career, caused him to have chronic back issues that had to be dealt with. In order to deal with these back issues, he had three back surgeries over the course of three years. After these, he was still unable to not only golf but also do daily activities without pain such as get out of bed, or play ball with his kids. Tiger was at a crossroads, and decided to get a spinal fusion surgery.

An image of the spine with the three regions labeled: cervical (upper region), thoracic (middle region), lumbar (lower region)
Taken from Wikimedia Commons

The spine has three regions: cervical, thoracic and lumbar. The cervical region is in the upper spine near the neck, the thoracic region is in the middle of the spine and the lumbar region is in the lower back. The lumbar region takes the majority of force in a golf swing and is where Tiger had his fusion done. In the spine, discs are in between each vertebra. The disc acts as a shock absorber and allows for slight mobility of the spine. Tiger had a severely narrowed disc in between two of his vertebrae in the lumbar region due to the previous three back surgeries he had. In order to be pain free, that disc had to be removed. This brought about the discussion of him receiving spinal fusion surgery.

 

Spinal fusion surgery is a process which removes the problematic disc from the spine and inserts a bone graft in place of the disc. A plate with screws is then placed in the vertebrae above and below the bone graft. The plate helps with the healing process and over time, it will heal as one unit. The essential goal of spinal fusion surgery is to take two vertebrae in your spine and make them act as one. When these two vertebrae become one through the surgery, it eliminates motion in between them and hopefully, removes the pain as well.

This is an image of a spinal fusion surgery with screws helping to hold the vertebrae together
Image taken from Wikimedia Commons

This spinal fusion surgery was a huge success for Tiger and allowed him to keep playing golf at a high level. Through his win at the 2019 Masters tournament, it’s safe to say that he has at least a few more years of winning tournaments and playing competitive golf before calling it a career.

Additional information and sources used can be found here and here. 

 

Skeletal Support Seekers’ Success (So Far)

Bones break, and broken bones need time to heal, or regrow. Fans of J.K. Rowling’s Harry Potter series are quite familiar with the concept of bone repair, as Harry is once required to drink a Skele-Gro potion to magically (and painfully) regrow his arm bones overnight. Now, as fantastic as it would be to completely fix broken bones in a few hours, modern medicine has not yet discovered that secret of the Wizarding World; however, several treatments have been developed in attempts to speed the rate of fracture repair as well as increase the comfort of the patient (take that, Skele-Gro).

Images of a broken bone and the progression of a callus being formed over time
Image from Cambridge Fracture Clinic

For those unfamiliar with the process of bone repair, a quick overview is in order. In short, inflammation provides stability to a fractured area, and over the course of several weeks fibrous tissue forms a callus around the fracture which is eventually replaced by bone. The mechanical environment at the fracture site is influential in healing, with factors such as hormones, vitamins, minerals, diet, fluid flow, and physical and electrical stimuli affecting healing rates. With these factors in mind, engineers and scientists are attempting to speed bone regrowth.

Low-level laser therapy (LLLT) is one practice found to accelerate bone healing. A study published in Lasers in Medical Science revealed that LLLT stimulates bone cells in fracture areas which increases the rate of callus development. Tests performed on the broken tibial bones of two groups of white rabbits demonstrated that bone mineral density at fracture sites remained higher in the group receiving laser therapy than in the control group throughout healing. 

However, post-mortem tests revealed that bones healed under LLLT endured significantly lower maximum stresses than intact bones or bones healed under normal conditions. This is a controversial result, as other studies have concluded opposite findings, so despite the enhanced growth resulting from LLLT, the authors of this study agree that additional experiments are necessary to satisfactorily settle this issue.

Images of stress concentrations in and around a solid titanium implant and porous titanium implants with various levels of bone ingrowth
Modified from Spoerke, et al., Septermber 2005

Surgical implants are another device used to facilitate bone healing. Most bone implants are made of titanium due to its lightness, durability, and biocompatibility. While these supports effectively immobilize and position bones for proper healing, some patients experience complications later on, largely due to stiffness differences between bone and titanium—resulting stress concentrations increase risk of fracture or implant loosening. Titanium foam implants coated in an organoapatite (OA) layer are a developing solution to this issue, described in detail in an Acta Biomaterialia article.

The porous surface of titanium foam, studied in vitro, substantially decreases implant stiffness, thus enabling stress to be more evenly shared between the foam and surrounding bone. Allowing bone ingrowth into the pores also reduces stress concentrations at the materials’ interface which helps alleviate risk of implant failure. Furthermore, the OA coating on the foam stimulates bonding between bone tissue and the implant, thereby increasing stability. The success of these studies suggest that titanium foam is ready for in vivo testing. 

Check out this video on the advantages of titanium foam:

Although the results of these fracture repair treatments are still a far cry from those achieved with Skele-Gro, further research and development regarding bone regrowth may lead to significant advances in the very near future. Interested in learning more? Check out articles on other developing fracture treatment technologies here and here.

Ways to Prevent and Treat a Common Annoyance: Headaches

Headaches can range from a mild annoyance to a debilitating condition that results in the inability to complete simple daily tasks. Odds are you have experienced a headache since about 50% of the population has suffered some type of headache. While there are many different variables that may have triggered it (injury, stress, chemical imbalances, etc.), the resulting symptoms are always negative. Scientists have been investigating what causes different types of headaches in hopes that they can help people prevent their occurrence and mitigate their symptoms.

One of the most common types of headaches is a cervicogenic headache – a secondary headache caused by referred pain from the neck to the head and facial regions. The high prevalence of cervicogenic headaches – 70% of people who suffer from headaches – prompted one study using a MyotonPRO device to measure and compare the tone, stiffness, and elasticity of the suboccipital and upper trapezius neck muscles in people who have and have not suffered from cervicogenic headaches.

Human suboccipital muscles located underneath the back edge of the skull.
Modified from BodyParts3D, Copyrightc 2008 Life Sciences Integrated Database Center licensed by CC Display-Inheritance 2.1 Japan.
Human trapezius muscle shown spanning the upper back through the neck.
Modified from BodyParts3D, Copyrightc 2008 Life Sciences Integrated Database Center licensed by CC Display-Inheritance 2.1 Japan.

The results showed that the tone – the degree of tension in a relaxed muscle – and stiffness – movement ability of the muscle – values were significantly higher in people who have suffered from cervicogenic headaches in the past. This can likely be attributed to overuse or high levels of past activity of these muscles. This can cause inflammation or other physiological changes that aggravate the nerve fibers in the neck resulting in a cervicogenic headache. The tone and stiffness data can be used to help educate patients on the importance of properly stretching their neck muscles before and after physical activity in order to keep them from tightening and shortening due to overuse. Muscle relaxing medications could also be used as a type of treatment when someone is suffering from a headache.

Tone and stiffness data for people with and without cervicogenic headaches.
Modified from Park, et al., The Journal of Physical Therapy Science 2017.

Another common type of headache is a migraine – a primary headache that has occurred multiple times throughout someone’s life. While a migraine can also have many different triggers, one study investigated the impact of a chemical imbalance of dopamine. This study found patients who suffer from migraines experience a decrease in dopamine levels before they feel the symptoms. There are a couple theories as to why decreased dopamine levels result in migraine symptoms: 1) decreased dopamine increases sensory sensitivity which may result in normally painless signals becoming painful, 2) decreased dopamine impacts motivation and reward/aversion to a point where patients withdraw and seclude themselves. In general, these findings can be useful for the advancement of dopamine regulating drugs in order to combat migraines. Further reading on different chemical causes of headaches in mice can be found here.

Figure showing dopamine levels decreasing during the onset of a migraine.
Modified from DaSilva, et al., Neurology 2017.

Overall, there are many different headache triggers and a lot more research needs to be done before science fully understands how they work. However, there are some things people can do now in an effort to lessen the probability they will suffer from headaches. Additionally, there are  medications and other techniques that work through different paths to mitigate the symptoms of a headache.

Medical Marvel: Robotic exoskeletons enable those with spinal cord injury to walk again

Claire Lomas surrounded by supporters as she walks the 2012 London Marathon
Lulu Kyriacou [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
A fall off of her horse in 2007 caused Claire Lomas to lose all function in her legs. In 2012, she completed the London Marathon, all 26.2 miles. Robotic exoskeletons can literally get people back on their feet shortly after a spinal cord injury occurs, but how exactly do these medical devices not only supplement but restore human performance? What does the future look like for robotic exoskeletons and those with paralysis?

There are approximately 300,000 people living with SCI in the United States, with 17,700 affected annually. So what exactly is a spinal cord injury? A spinal cord injury occurs when trauma, disease, or compression due to tumors causes damage to your spinal cord, which is responsible for your body’s motor functions (voluntary muscle movements), sensory functions (what you feel, such as temperature, pressure and pain), and autonomous functions (your heart beat, body temperature regulation, or digestion). Injuries are classified as complete or incomplete, with complete corresponding to a total loss of function or sensory feedback in areas of the body which are lower than the injury level.

Image showing the area of injury corresponding to the resulting level of paralysis
http://www.living-with-attendant-care.info/Content/Spinal_Cord_Injury_c_Understanding_spinal_cord_injury.html

Studies have shown that people with spinal cord injury, specifically individuals with paraplegia-paralysis who retain function of their upper limbs, prioritize walking as the main function they wish to regain. Robotic exoskeletons, which operate in collaboration with the user to reinforce and retrain certain functions, may be the answer to this pressing need. An exoskeleton  facilitates untethered step repetitions and evenly redistributes the user’s weight to his or her core, minimizing stress on the user’s back, neck, and shoulder muscles. One study testing the exoskeleton from Ekso Bionics also showed an improvement in unassisted balance, since the device only initiates the next step if the user properly shifts his or her weight. Though primarily used for gait or mobility training in rehabilitation facilities, these devices are on their way to becoming everyday mobility aids for people with paralysis.

Rehabilitation for spinal cord injuries is long and tedious. Robotic exoskeletons enable patients to begin rehabilitation early after injury, which helps to prevent joint contracture (which is a limit in a joint’s range of motion, preserve muscle memory and strength, retain bone density, and ensure proper functioning of the digestive and respiratory systems). Humans are meant to be vertical and active, so just the act of standing reduces spasticity (perpetual muscle contraction) and pain, decreases the risk of pressure ulcers or osteoporosis from sitting or laying down for extended periods, and improves bowel and bladder functioning. Moreover, the ability to stand at eye-level and walk again reduces instances of depression.

Despite all of these benefits, current models aren’t perfect yet. The energy demand to operate the devices and consequential fatigue of the user limits long-term use, which restricts use outside of therapy. When people hear exoskeleton, images of Marvel’s Iron Man or soldiers carrying heavy packs come to mind. The advance of robotic exoskeletons may expand their use beyond rehabilitation facilities, allowing them to become integrated into everyday life.