A Static and Dynamic Study on Balance MacKenzie Sullivan, James Masi

Department of Engineering University of Southern Maine

The study of balance is important to people of all ages, athletic abilities, gender and race. This project assessed the static and dynamic balance of a spectrum of people and record data based on numerous tests. The outcomes of this study are broad-based, and, as can be seen in the extensive testing and data obtained, there are surely applications that it may be useful for, such as norm and abnorm diagnostics, athletic training, concussions, neuromuscular deficiencies, vertigo, etc.,. The study included static and dynamic (still in process) balance testing and analysis of multiple participants as well as analysis of data obtained.

Corresponding Author: mackenzie.sullivan@maine.edu

Introduction/Background

Body movement is the result of forces from within the body as well as external forces acting upon a body. At every moment, a human body is subject to the most influential force on earth, gravity, and the body has adapted to this force very well. By definition, gravity is the force of attraction between two bodies (e.g. the earth and a human). When the objects are small, the resulting gravitational force is also very small, but when the object is large, like planet earth, there is a large effect on the smaller objects that exist upon it. It is important to consider weight of a body as a result of gravitational force when studying the movements and balance of the body. Every part of a body is influenced by gravity, but in mathematical and modeling forms, we can consider the force of gravity to be acting on the point called the center of gravity. The center of gravity is not always in the center of an object, for example a ring, but for every rigid body, the coordinate of the center of gravity is unchanging. If an object, for example the human body, can move, the center of gravity changes with each movement. If a person is standing still with their arms at their sides, the center of gravity is located approximately in the mid line of the pelvis. If the person was to raise an arm to one side, the center of gravity will shift in that direction as well. Because of these phenomena, all body movement causes a rapid change of the center of gravity, and requires quite a support system and constant adjustments to the body itself to keep a state of equilibrium. A vertical line that passes straight through the center of gravity exists, and is called the line of gravity. It follows the changing position of the center of gravity and passes through different regions of the object as its position is changed.

Figure 1 The center of mass of an object

The base of support of an object describes the area over which an object or body is supported. To visualize, the base of support of a chair is the area enclosed by the legs of the chair. For a human body, the base of support includes the area around which the part of the body or walking assistance touching the ground.

Figure 2. Representations of Stability by Changing

Position of the Feet

In the figure above, when the feet are moved farther

apart, stability is improved for the area of base is increased. In the middle representation, medial/lateral stability (side to side) is increased and the right representation, anterior and posterior stability (front to back) is increased. Moving the position of the feet, by walking or moving, changes the area of the base. Using a cane, walker, crutches, or other devices can greatly increase the effective area of the base of support. On the other hand, by walking on toes or one foot, the base of support is greatly reduced. Stability is defined as the property of a body that causes it, when disturbed from a condition of equilibrium or steady motion, to develop forces or moments that restore the original condition (Webster). Stability is affected by the amount of force required to move the line of gravity to a position outside of the base of support, causing the object to topple over.

Figure 3. Human stability criteria

More energy is required to move large masses over greater distances, so it is much harder to move an object with a large mass and a low center of gravity, and easier to move a smaller mass with a high center of gravity. The harder an object is to topple, the greater stability it has. For example, a plastic water bottle is very easy to knock over when empty, but is very stable when full of water. Even though the base of support is the same size, the center of mass in the empty water bottle is much higher than in the full water bottle because of the cap. Stability depends on the position of the center of gravity relative to the base of support. In the human body, a relatively small base supports a constant mass, and both the center of mass and the area of the base are rapidly changing. This requires a complex reflex system combining sensory nerves and motor nerves that control the muscular system of the body. This is why balance is not just a matter of muscular strength; it is greatly affected by the central nervous system.

In the human body, in order to maintain upright balance, the center of gravity must be above the area of the base of support. Any slight disturbance of position can cause the canter of gravity to move outside of the

base, making the body unstable and causing a fall. In the body, any deviation to the center of gravity is constantly monitored by a number of systems. These include sensory mechanoreceptors in capsules and ligaments of joints, stretch receptors in muscles, the vestibular apparatus, which includes the canals within the inner ear, which send information to the brain about the motion of the head, pressure receptors in the skin, and the visual system. All of this information is processed in the central nervous system and signals are sent to muscles to contract and adjust the position of the body appropriately to keep upright and most stable. This whole process includes prediction of body motion in the future so that adjustments are not only reactive but an involuntary action that automatically happens. For example, the body can predict what the next step will be in walking and adjust instantaneously while taking each new step.

Data/Formulation/Methodology

In this static test, a Vernier force plate and Logger Pro software was primarily used to generate and collect data. In the future dynamic study, other instrumentation is used. A list is given below as well as a pictorial representation of the force plate, accelerometer, and clinometer.

Figure 4. Instrumentation

Many functional performance tests exist for static and dynamic balance including static timed tests, and dynamic reaching and stepping tests. In this study, timed tests are used to see how long a subject can remain in a static standing of sitting position without falling over. These types of tests have been used with people who have suffered from traumatic events and diseases like stroke, MS, or Parkinson’s. Timed tests can last anywhere from 15 to 60 seconds and can test balance in different positions such as feet in parallel, one legged, like in this study, and one foot in front of the other, with eyes open and closed.

Figure 5. Testing Procedures: two feet and one foot,

eyes open and closed In this study, a few different activities were monitored, each lasting ten seconds. First, the subject was asked to stand, eyes open with arms at their sides for ten seconds on a force plate to find a baseline for the subjects balance. The next test was repeating the same protocol with eyes closed, which effectively took away the visual receptors that affect balance in humans. Next, the subject stood on one foot with eyes open for ten seconds, then on the other foot, with eyes open first. This took away some surface area of the pressure receptors that contribute to balance. For the subject to remain upright, their center of mass must remain over their base area, which is reduced when balancing on one foot rather than two. Finally, the subject was asked to repeat the one-footed test with eyes closed, reducing two points of stability factors.

Figure 6. The one-footed test

Five subjects were tested, three females and two males, all of varying ages, trauma, and gender. A survey was done and asked about age, gender, and past or present trauma to the head or body. Below is a visual representation of the results of the survey. A tabular form of this can be found in the appendix of this report.

Figure 7 Visual form of subjects tested

The force plate was used to collect data from the test subjects as they performed each test for ten seconds. The results below show the vertical force fluctuation during the test as measured by the force plate.

Analysis

We analyze the rubric for each assessment here…

Figure 8. Raw data from the two-foot test

Figure 9. Raw data from the two-foot test with eyes

closed These two graphs expose the abnormal balance that is

associated with MS. When viewing the raw data of each participant with two feet and eyes open, there is no clear difference between all. Each person has fluctuations in the same range of force and there are no outliers. When the eyes are closed however, and the visual aspect of balance control is taken away, the reduction in the nervous function of the MS patient is calculably apparent. Three times the fluctuation in force can be measured in his test than in the other participants. The effect of MS on his balance is even more apparent when one foot is taken away from the equation, narrowing the area of base to half. This is shown in the graph below.

Figure 10. The right-foot test of balance

The ratio of the measured force divided by the

subjects weight can be displayed. This ratio fluctuates, sometimes dramatically, as the subject tries to stay balanced during the testing period. The standard deviation can be used as a score for balance, and the smaller said deviation is, the better the person’s balance score is. The standard deviation can be noted as sigma, 𝜎. The score can be calculated as follows.

𝑆𝑐𝑜𝑟𝑒 = 𝑤𝑒𝑖𝑔h𝑡 − 𝜎 𝑤𝑒𝑖𝑔h𝑡 ∗ 100%

Figure 11. Equation for balance scoring

Figure 12. Tabular results of balance scoring

Figure 13. Graphical results of balance scoring

The scores indicate that the MS patient scored the lowest overall and the dancer scored the highest overall, especially in the one-footed tests, noted number 3-6. This made sense logically because the dancer had no trauma, and the MS patient had the most trauma of the group. MS Results The role of visual input is heavily relied on with the MS patient, apparent with the difference seen between the eyes open and eyes closed tests. This signifies a very high neuromuscular impairment, and the effect of it is only magnified when the subject is asked to stand on one foot. With this methodology and more testing, we

can numerically characterize the effects of his condition and track how it worsens or improves over time with treatment.

Figure 14. Test results for the MS patient

Figure 15. Two-footed test results for the MS patient

Trainer Results Based on the increased fluctuation in force on the right foot with the eyes closed and open, we can hypothesize that the past concussion damaged the left side of the brain, since it controls the right, and the trainer is very fit and continually works on her strength and balance. With further testing we can characterize the effects of past concussion on her strength in her right side.

Figure 16. The trainer’s test results for the left side

versus the right side

Figure 17. The trainer’s test results for the left side

versus the right side with eyes closed

Dancer Results In the dancer’s results, we can see that the force fluctuations associated with the right and left side are both about equal, therefore no real conclusions about trauma can be drawn. This makes sense because she has had no previous trauma in the survey. These test results can serve as a baseline for a healthy individual with no past trauma.

Figure 18. The dancer’s test results for the left side

versus the right side

Figure 19. The dancer’s test results for the left side

versus the right side with eyes closed

Coach Results Upon viewing the coach’s results, it can be seen that the right foot is clearly and calculably weaker than the left foot. According to the survey, this person injured their right ankle while playing baseball years ago. This testing exposes that injury and could be a way to see how physical therapy could strengthen the joint over time, especially since the coach did not know that he had a deficiency in the right side. We can also see unfelt damage that still exists from past injuries.

Figure 20. The coach’s test results for the left side

versus the right side

Figure 21. The coach’s test results for the left side

versus the right side with eyes closed

Figure 22. The coach’s test results

Athlete Results From the survey, we learned that the athlete has had one diagnosed concussion, and multiple undiagnosed concussions in the past from playing numerous sports. In the results, we can see that the right foot has a significantly higher fluctuation than the left. This testing can indicate that the left side of the brain was damaged when the athlete was concussed. With further testing and study, we can calculate and characterize more of the effects of the concussions on the athlete.

Figure 23. The athletes’s test results for the left side

versus the right side

Figure 24. The athlete’s test results for the left side

versus the right side

Figure 25 The athlete’s test results

In the future, the subjects will undergo dynamic testing of balance. Dynamic reaching tests usually assess the maximum distance a person can reach forward with either their arm or foot and remain stable. This test can be conducted while standing or sitting and in any direction: front, side, back, or vertically towards the floor. Arm raising tests measure a person’s ability to maintain balance while experiencing the destabilizing force associated with raising and lowering the arms. This can also be tested in any direction and for multiple different periods of time. Stepping tests evaluate dynamic stability. During this test, a person is asked to step a foot on and off of a block as many times as possible in a certain amount of time. This can be evaluated in any direction. Along with the number of reps completed, the ability to transfer weight shift from one leg to the other can be measured (Connell). The dynamic testing will utilize two force places instead of one, the accelerometer, and the clinometer to measure the angle of lean. We hope to uncover more of the effects of concussion by separating the two sides and conducting more strength of side tests, as well as the effects of medication for MS and the effects of physical therapy on injuries. We also plan on testing for endurance by lengthening the tests to longer than 30 seconds, and calculating autonomic nervous system response, otherwise known as stabilization time. This can be modeled by a sine wave, and measures the frequency and time between back and forth fluctuations in force caused by regular body response. The length

between these responses could uncover some interesting results and future applications.

Figure 26. The Balance Wear vest Many studies have been conducted to demonstrate

the effectiveness of these vests, but very little research has been done to explain the mechanics behind the results. Gait analysis and other static and dynamic tests can mathematically describe the needs of a patient, and are starting to be measured before and after the vest is worn. This can show just how effective these vests can be in a measurable way.

At the Shriners Hospital Movement Analysis Laboratory, in Chicago, Illinois and Springfield, MA, research into gait analysis and other factors that affect balance is taking place. The tests offered include gait analysis, pedobarography, or analysis of foot pressure, upper extremity analysis of patients using wheelchairs, crutches and walkers, energy expenditure tests, computerized dynamic posturography, strength assessments, high resolution video capture, and foot and ankle segmentation analysis. Depending on the tests performed, the researchers utilize adhesive markers to measure movement shown on the high-resolution video and a backpack electromyography system (EMG) that measures muscle activity. Once the tests are completed and the data is analyzed, the researchers can provide a report to better understand the movement patterns of the patient, and suggest how balance or other impedances can be improved. This can help when choosing prosthetics or other movement assisting devices. Within the period of this project, the Springfield, MA Shriners Hospital Gate personnel will perform similar measurements to validate our findings. At the time of this writing, this study is testing dynamic balance abilities and analyzing data (large set) to form mathematical conclusions about the effects trauma has on total (static and dynamic) balance. The testing is far more complex as are the analyses associated with the movement and resultant forces. The testing utilizes two force plates instead of one, and also incorporate the accelerometer and clinometer into the testing. The normalized dynamic data will be presented along with the static measurements at this ASEE NE conference. Addendum sheets will be distributed to the audience.

Conclusions

Currently, to help patients who struggle with balance, there exist a few different areas of research and devices. First and foremost, many physical therapy options exist to help improve physical strength and increase balance over time. A very interesting approach to improving balance is the development of strategically weighted vests. For example, a company called Motion Therapeutics, Inc. has developed a weighted vest called Balance Wear (Figure 26) that is a non-invasive option that can help improve balance over time by shifting the person’s center of gravity to where a person with a balance disability feels comfortable and stable. Using a diagnostic device like this, along with participation in physical therapy, clinicians can help a person to be mobile and achieve static and dynamic balance over a period of time. There are a number of tests and data reduction methods still to be determined. This project will be continued by the next class of students.

References

1. "Kinesthetic Activities for the Classroom." Kinesthetic Activities for the Classroom. AAPT, n.d. Web. 04 Nov. 2015. <http://scitation.aip.org/content/aapt/journal/tpt/52/9/10.1119/1.4902193>.

2. Connell, Louise Ann. "How to Measure Balance in Clinical Practice. A Systematic Review of the Psychometrics and Clinical Utility of Measures of Balance Activity for Neurological Conditions." Research Gate. N.p., n.d. Web. 04 Nov. 2015. <http://www.researchgate.net/publication/26718994>.

3. Armenti, Angelo. The Physics of Sports. New York: American Institute of Physics, 1992. Print.

4. Profio, A. Edward. Biomedical Engineering. New York: Wiley, 1993. Print.

5. Aston, Richard. Principles of Biomedical Instrumentation and Measurement. Columbus: Merrill Pub., 1990. Print.

6. Carr, Joseph J., and John M. Brown. Introduction to Biomedical Equipment Technology. Upper Saddle River, NJ: Prentice Hall, 1998. Print.

7. Cook, Albert M., and John G. Webster. Therapeutic Medical Devices, Application and Design. Englewood Cliffs, NJ: Prentice-Hall, 1982. Print.

8. Cromwell, Leslie, Fred J. Weibell, and Erich A. Pfeiffer. Biomedical Instrumentation and Measurements. Englewood Cliffs, NJ: Prentice-Hall, 1980. Print.

9. Low, John, and Ann Reed. Basic Biomechanics Explained. Oxford: Butterworth- Heinemann, 1996. Print.

10. Wallace R, Abbott C, Gibson-Horn C, Skubic M. "Result Filters." National

11. Center for Biotechnology Information. U.S. National Library of Medicine, n.d. Web. 02 Dec.2015. <http://www.ncbi.nlm.nih.gov/pubmed/24109846>.

12. "The Mind-Body CorrectionTM." The MindBody Correction. N.p., n.d. Web. 02 Dec. 2015. <http://www.motiontherapeutics.com/>.

13. "Movement Analysis Laboratory." MovementAnalysis. N.p., n.d. Web. 02 Dec. 2015. <http://www.shrinershospitalsforchildren.org/en/Locations/chicago/Additional%20 Services/Movement Analysis>.

Relevant Standards

Currently, there are no specific standards in the ASTM for balance testing procedure. This area of study is protocol based, not standards based. There are some test procedures that marginally apply, but not directly. NCAA standards exist, but not for balance testing specifically. The ASME articles are all similar to the ASTM articles as well. However, a few papers exist that cover a basic protocol for balance testing. The citations for these papers are below, as well as the ASTM articles that have been researched.

1. Lee, Chong-hoon, and Youn-Girl Jeon. "Biomechanics Analysis of Balance and Gait Posture by Obesity Level in Adolescents." IJBSBT International Journal of Bio-Science and Bio-Technology 6.3 (2014): 117-22. Web. 9 Dec. 2015.

2. "Sports Standards and Recreational Standards." ASTM International. ASTM, n.d. Web. 09 Dec. 2015. <http://www.astm.org/standards/sports-and-recreation- standards.html>.

3. "Sports Equipment and Facilities; Pedestrian/Walkway Safety and Footwear; Amusement Rides and Devices; Snow Skiing." ASTM 15.07 (November 2013): Web. "Standards Catalog 2016." ASTM International (2015): n. pag. Print.