No Whey? No Problem!

Posted on by

In today’s world of social media “fitspo” blogs and fad diets are at our fingertips more than ever.  The “recommended page” on Instagram, for example, is full of fitness bloggers telling you exactly what to eat and what work outs to do for the best results.  And while their advice is often based on some truth, it is also can be blown out of proportion or can be easily misconstrued.   It is important to remember that diet is based on individual needs and that what works for one person may not work for you- therefore, the best way to choose new meal plans is through education. First off, why are proteins so important?

Figure 1: 9 essential amino acids we must ingest.

Proteins have four layers of structures that all play a role in how they work and  how they interact. The primary structure, is simply the sequence of amino acids (AAs) in a polypeptide chain.  There are essential AAs that we must ingest, non-essential AAs that our body can produce, and conditional AAs that are pertinent in times of stress and illness. Protein is extremely beneficial and unarguably critical to our diets, we excrete excess amino acids, so over eating protein poses to additional benefit.

So knowing this, how do you decide how much protein you should eat? Maybe to some surprise, science have shown that athletes actually require the same general range of protein intake when compared to sedentary persons of the same sex. According to the U.S. and Canadian Daily Reference Intakes,  0.8 g·kg−1 of protein is enough to meet the needs of 98% of healthy adults. “There is not a strong body of evidence documenting that additional dietary protein is needed by healthy adults who undertake endurance or resistance exercise, the current DRI for protein and amino acids does not specifically recognize the unique needs of routinely active individuals and competitive athletes.” They also suggest that for adults 18 years and older,  10%-35% of total caloric intake should be comprised of protein. This supports the accepted ideal that the recommended intake levels can be met through regular diet and without supplementation.

What does this mean for those trying to lose or gain weight? Whilst, in both of these cases, it may be easy to fall victim to one of the fad diets, you should take the time to understand them and to find the truth behind them.  CrossFit is currently one of the most popular fitness plans and many of their athletes use meal templates to guide them in fueling their bodies. The Paleo Diet and Zone Diet are two of the most common choices for these athletes, or a combination of the two.  Paleo (sometimes called the caveman diet) is bases on eliminating processed food and eating a high fat, moderate protein and low carb diet. The Zone Diet is based on “blocks” where you eat a specific number of daily servings of proteins, carbohydrates, and fats.  The “blocks” are structured throughout the day rather than in the normal 3 meals a day.  The diets claim to increase metabolism and when tailored to specific goals, can result in significant weight loss and muscle development.

Figure 2: The 40/30/30 breakdown of the Zone Diet.

Samuel N. Cheuvront found that the Zone Diet does not result in the promised outcomes. He found that any significant contribution of active muscle oxidation was not even found in skeletal muscle.  In another investigation by Tipton, et al,  they looked at the differences between ingesting protein (such as whey protein supplements) before weight training versus after. Their results allowed them to conclude that the timing of supplementation does not matter but that having protein in your system consistently does have positive impacts.

Based on the review of the current literature, the biggest conclusion that can be made is that protein does play a large role in diet and in over all health.  What cannot be confirmed is the benefits of protein supplements or high protein diets. According to daily recommended intakes,  it is much more important to have a balanced diet, and the main benefit of a high protein diet may actually be limiting sugar and carb intake.

 

Further Reading

Orders of Protein Structure

Nutrition and Athletic Performance

Role of Protein in Diet

A Review of Protein Recommendations for Athletes

 

Questions to Consider

  1. How cognizant are you of your protein intake? Do you stagger it throughout the day?
  2. Have you tried any high or low protein diets? Did you notice any difference in your workouts?
  3. What, if any, do these conclusions have on vegetarians?

Breathe In, Breathe Out… Breathing during Exercise

Posted on by

In today’s society, exercise is a part of everyday life. From high school sports and professional sports teams to recreational running and yoga classes, exercise is everywhere. However, many people struggle with breathing during exercise. Gym-goers pant on the treadmill, weight-lifters have trouble lifting their weights, and yoga classes struggle to stay balanced. And, if you’re anything like me, you’ve heard every saying about “breathing in through your nose and out through your mouth” or breathing at certain times while exercising, which can be confusing or overwhelming to do. So, many people ignore their breathing while they exercise and do not regulate their breathing patterns at all. But, many of the exercise difficulties that people experience can be improved by learning to breathe properly while exercising. So, how does this work? And, how does breathing differ between exercises?

The Science Behind Breathing

The process of breathing involves several chest muscles, most notably the diaphragm. The diaphragm is a dome-shaped, sheet-like muscle that lies underneath the lungs. Not only does the diaphragm separate the chest from the abdomen, it is also the primary respiratory muscle. When we inhale, our lungs expand and the diaphragm contracts, or moves downward, as it flattens. At the same time, the intercostal muscles of the rib cage expand. This expansion of the diaphragm and intercostals and the addition of air in the lungs creates a great deal of pressure inside the body, which will play a large role in breath regulation as we will see later. While inside the body, oxygen is absorbed to create energy in the form of ATP. Then, as we exhale, our lungs return to their resting state and the diaphragm returns to a dome shape. As this happens, the pressure built up during inhalation is relieved through the release of gas as carbon dioxide. But what does all this mean for your exercise routine?

The In’s and Out’s of Breathing For All Exercises

Breathing patterns and the timing of breathing differs from exercise to exercise. Many breathing patterns in sports are based on regulating the build-up of pressure that occurs during inhalation, as mentioned above. Other breathing patterns are meant to maximize oxygen-uptake by the body. But, it’s important to note that each sport or type of exercise requires different breathing patterns.

Running

Running is one sport with no singular convention on breathing. Some people say “breathe in through your nose, out through your mouth.” Others say to breathe in-tune to your running, so inhale on one step, exhale on the next. Still others claim that you should breathe however best suits you to finish a run. So, is there no singular optimal way to breathe when running?

Studies have shown that this is false – there are certain ways of breathing that are less energetically costly and more comfortable for runners. One study supporting this was conducted by McDermott, et al. to analyze the connection between breathing pattern and stride rhythm. In this study, ten subjects ran at various paces while measurements of heel strike and inhalation were recorded. The results showed that runners have a tendency to breathe in a 2:1 or 3:2 pattern most often, meaning inhaling for 2 steps and exhaling for 1 (2:1) or inhaling for 3 steps and exhaling for 2 (3:2).

This seems to be a logical pattern of breathing when running. First of all, it is good practice to breathe in sync with your footfalls. When breathing with your footfalls, you time the movement of your body and internal organs with the movement of your diaphragm during respiration. This prevents the development of odd, uncomfortable areas of pressure on the diaphragm which can impede breathing. In terms of the speed of breathing, the more quickly you breathe, the less time your body has to fully absorb the O2 you’re bringing in through respiration. When your body doesn’t have enough oxygen to energize itself, anaerobic metabolism kicks in, which causes lactate to accumulate and decreases the body’s ability to perform endurance tasks. However, when you breathe slowly, more oxygen is drawn into the body, and the body has enough time to absorb the oxygen in your lungs to create energy and keep you energized when running.

Therefore, by slowly breathing in a 3:2 or 2:1 pattern in sync to your footfalls when you run, you have the potential to run more smoothly and for a longer period of time before fatiguing by maximizing oxygen uptake.

Weight Lifting

While there is no standard convention for breathing when running, there is one near-universally accepted standard of breathing for weight lifting exercises. Convention says that while performing weight lifting tasks, one should exhale on exertion and inhale during reset. Easy enough to remember, right? But, is this the best way to breathe when lifting weights?

Studies point to yes. In one study by Hagins, et al. subjects were asked to perform three different breathing patterns while lifting objects:

  1. Inhaling before lift, holding during lift
  2. Exhaling before lift and holding during lift
  3. Inhaling before lift and exhaling during lift

While subjects were doing this, measurements were being taken of change in abdominal pressure and maximum force exerted. These measurements showed that abdominal pressure was lowest during breathing patterns 2 and 3, both of which involved exhalation.

Another study by Lamberg and Hagins looked at breathing patterns when lifting different loads. Subjects were asked to lift milk crates multiple times while a pneumotachograph recorded airflow. This study found that the most consistent natural breathing pattern among individuals was to inhale right before lifting an object, which is consistent with the results of the previous study.

Based on these two studies, it is clear that exhalation is an important part of breathing during weight lifting. By reducing the amount of pressure in the abdomen, exhaling during lifting decreases the chances of sustaining internal injuries such as hernias and vessel strains which can be caused by excessive internal pressure. Exhaling relieves that pressure by releasing some of the accumulated air from the abdomen, ensuring that the abdominal pressure does not reach an unsafe level. So, next time you go to the gym to bench press, remember to exhale when pressing and inhale before letting the weight down onto your chest to regulate pressure build-up in your chest and abdomen.

Other Exercises

The studies viewed in the cases of running and weight-lifting were limited in that they consider only two very rigidly structured types of exercise. The running study had subjects running at specifically selected speeds. And, the weight-lifting studies only looked at subjects lifting specific weights in an up-down direction. But, what about sports where running speed and timing can vary, such as soccer or football? Or exercises where full-body balance is the goal, such as yoga? Is there an optimal breathing pattern for these sports and exercises?

More testing needs to be done to determine optimal breathing for these sports. But, based on the results of existing studies and on common practice in sports, it’s likely that the best breathing pattern for your sport will involve a balance between maximizing oxygen uptake and regulating abdominal pressure.

Recommended Further Reading

For more information about breathing during exercise, explore:

Questions to Consider

  1. Are you aware of your breathing when you exercise? Do you make it a point to breathe a certain way when you exercise?
  2. When you run, what step-breath pattern do you follow most often?
  3. If you lift weights, how do you breathe when you lift? When do you inhale and exhale?
  4. How do you think the breathing patterns covered in this article can be applied to sports/exercises like soccer, football, or yoga?

The Sports Gene Reflection – Malaria & Muscle Fibers

Posted on by

Class Make Up Blog 4/6 – Focus on Chapter 11

Throughout The Sports Gene Reading this week, I wanted to focus on the author’s thoughts on race and muscles fibers. He starts off by mentioning the physical differences between Europeans and Jamaicans. Studies have shown that Jamaicans have longer legs relative to body height and slimmer hips. This is backed by Bergmann’s rule saying that “humans with recent low latitude ancestry will also tend to be more narrow, with slimmer pelvic bones” (pg. 175). The point of these differences was to ultimately look at the reasons behind the running speed scales where both of these physical features proved to be beneficial. However, Epstein found a more anatomical approach by hypothesizing that “malaria in western Africa forced the proliferation of genes that protect against it, and that those genes, which reduce an individual’s ability to make energy aerobically, led to a shift to more fast-twitch muscle fibers, which are less dependent upon oxygen for energy production”. (pg 176)

Cooper found hope in this theory with a 1986 study from Laval University in Quebec published in the Journal of Applied Physiology. The scientists took muscle samples from the thighs of sedentary students , primarily from countries in West Africa. They took the same samples from two dozen sedentary white students  who were identical to the African students in age, height, and weight. The results showed that “a higher proportion of muscles in the African students was composed of fast-twitch muscle fibers, and a lower proportion was slow-twitch muscle fibers compared with the white students. Furthermore, these results showed that the African students had a significantly higher activity in the metabolic pathways that rely less on oxygen to create energy and that are engaged during an all-out sprint”. (pg. 179) This directly relates to the metabolic pathway topic review in class as we were discovering the differences between aerobic and anaerobic exercise. If the study showed that these students had metabolic pathways that rely less on oxygen to create energy, they may be more naturally inclined for sprinting since their bodies naturally choose an anaerobic pathway that doesn’t require oxygen.

In my opinion, I think this is an important study to look into as genetic factors can place people into categories where they may be more successful in certain sports. However, this chapter comments on several scientists who have no interest in investigating it because of the inevitably thorny issue of race involved. (pg. 185)  When our class held a similar discussion about the topic, it came down to whether you would want to know which sports you would thrive in as a child or merely have the freedom to choose your sport/activity based on your love of the sport. Would your parents be more inclined to steer their child towards a sport if they knew they succeed? A study by Lisa Guth showed that “A favorable genetic profile, when combined with an optimal training environment, is important for elite athletic performance; however, few genes are consistently associated with elite athletic performance, and none are linked strongly enough to warrant their use in predicting athletic success.” Therefore, it seems there are a difference of opinions on whether or not genes do play an important role in athletic success. Personally, if I had known I had the potential to be a star tennis player when I was young I would have pursued it. I would be interested to see how my own muscle fiber type relates to the success in certain sports and tweak my training based on that. However, to each his own. However, it seems there is a future of correlating athleticism with genetics that may even change the way we look at sports one day.

 

Sources

David Epstein, The Sports Gene. Chapter 11, Pages 175-185.

Genetic Influence on Athletic Performance

 

Barbells: Withstanding the 1,000-lb Deadlift

Posted on by

Identify

Barbells have been used for strength training for centuries, and the basic design of those used today was invented in 1928, yet they remain one of the most popular and effective exercise tools out there. From the main power lifts of bench, squat, and deadlift, to the olympic lifts of clean, jerk, and snatch, and limitless other movements, a barbell can be used to target any muscle group to improve strength and power. However, it must retain its shape. Through countless loading cycles, years of use, and sometimes extreme bending stresses, a barbell needs to be ready to be picked up and used again right away, and that means it cannot yield, or permanently bend – this would make it more difficult to use, change its motion patterns, and put it at risk of breaking. While typical use of a barbell for most people would not push it to its mechanical limits (Figure 1), those who compete in weightlifting often place so much weight on the ends of the bar that it indeed bends very much (Figure 2).  A barbell must be constructed of the proper material to withstand the loads it is placed under and bend without becoming permanently bent – or, in engineering terms, deform elastically but not plastically.

Figure 1. Use of a loaded barbell to perform a deadlift

Figure 2. Use of an extremely heavily loaded barbell to perform a deadlift

Formulate

When it comes to competition weightlifting, there are actually different dimensions and specifications required of barbells used for different lifts – read about it here. I decided to focus on a barbell for deadlifting because it’s the movement that can be done with the most weight and is not dynamic like olympic lifts. I borrowed dimensions from the most commonly-used barbell for deadlifting, the Texas 7-1/2″ Bar (Figure 3).

Figure 3. Dimensions of the most commonly-used barbell made for deadlifting

I also decided to design for preventing yield failure rather than fatigue failure because it is a more pressing design concern; it would make more sense to constrain for yielding and optimize for fatigue life rather than the other way around.

The world record deadlift is 500 kg (1,102.3 lbs) by Eddie Hall, so I used a weight of 453.6 kg (1,000 lbs), as events involving more weight than this are so infrequent that yielding in that case would not be of particular concern. This weight is divided into two evenly distributed loads at the ends of the bar, treated as a point load at the center of the distribution, while the opposing forces act where the hands would be placed (I assumed this to be the middle of the knurled portion as seen in Figure 3) [Figure 4].

Figure 4. Lifting of a barbell designed as a beam deflection problem

However, the problem can be simplified to fit a common pattern of loading/support (Figure 5), allowing for a few simple hand calculations to find the stress in the bar. This requires ignoring the weight of the bar itself (which, because of its even distribution and relative lightness, is not crucial anyway) and placing the loads at the very ends of the bar. In the end these assumptions will skew the estimate towards a slightly higher stress, giving an even safer design constraint.

Figure 5. Beam ends overhanging supports & two equal loads applied at symmetrical locations – http://www.engineersedge.com/beam_bending/beam_bending7.htm

Solve

By calculating the bar’s moment of inertia, the distance from the neutral axis, and the section modulus of the cross section of the beam, the maximum bending stress can be found to be 587 MPa (Figure 6).

Figure 6. Simplified representation of a loaded, held barbell and calculation of stress

Therefore, the barbell must be made of a material with a yield strength greater than 587 MPa. A look at a plot of materials’ yield strengths shows that metals, ceramics, and composites are all possibilities (Figure 7).

Figure 7. A plot of different materials’ yield strengths compared to their densities (from the text Materials Engineering, Science, Process and Design by Ashby et. al, 2007)

Metals make the most sense, however, because of their density and ductility. Composites’ light weight means they would be difficult, or impossible, to make into regulation-weighted-and-dimensioned barbells. Ceramics are also very brittle, meaning they break before bending at all; it is usually safer for a product to give warning before breaking, in the form of bending, making a ductile metal a better choice. Given its cost compared to titanium alloys, steel is easily the best choice for a barbell.

There is a dizzying amount of different steel mixtures and grades, but based on searching through tables and information sheets such as this and this, it is a safe bet that molybdenum-alloyed steels (steel alloy 4140/4340, yield strength 655/852 MPa) , cold worked austenitic stainless steels (stainless steel grade 301/304/310, yield strength 470-1310 MPa), and martensitic stainless steels (stainless steel grade 410/420/431, yield strength 415-1895 MPa) are all appropriate choices for a barbell that would not suffer permanent deformation even under the most weight a human has ever (dead)lifted.

 

 

Products recalled for children’s

Posted on by

Identify

Many furniture was designed harmful for children, many children were injured or killed due to tip over of the furniture. Dressers designed like this (fig. 1) has killed 7 children and got many injured. In 2016, IKEA recalled many dressers that have potential to tip over while kids climbing it. For a 8-year-old child, is it possible to tip the dresser over when climbing? Unknown: sum of the moment at the center of tip-over.

 

(fig. 1: dresser tip over due to defect)

(fig 2: information of one of the dressers IKEA recalled in 2016)

Formulate

Goal: find the moment at point O.

Formula to use: M = F*d(perpendicular)

The dresser is 134 cm tall, and 48 cm deep. Width is not necessary to measure since we are using a 2-d model.

First, we set up a 2D model to solve the problem (fig. 3).

O: point of tip-over. A: center of mass of the child. B: center of mass of the 3 drawers inserted. C: center of mass of the dresser (without drawers). D: center of mass of the top drawer that is out.

Drawers are 9.25 kg each. Dresser without drawer is 35.97 kg. Mass of a 8-years-old child: 23 kg. A(-55, 75), B(24,50), C(24,67), D(-24, 100)

Assumptions: the dresser is uniformed in weight. weight of the foots and top are negligible. No other things in the drawer. The top drawer is fully out and other drawers are fully inside. Center of mass occur at the geometric center of the main body.

(fig. 3 2-D model for the problem.)

Solve

ΣM= 28 kg* 9.8N/kg* -0.55m+3*9.25kg* 9.8N/kg* 0.24m+35.95kg* 9.8N/kg* 0.24m+9.25kg* 9.8N/kg* -0.24m = -150.92+65.27+84.56-21.76=-22.85N-m

The answer implies that a 8-year-old child is able to tip the dresser over by climbing on the top of the drawer. We assumed that the dresser is empty, and uniformed in weight. However, in real-life the problem could be more specific. Also we simplified the problem as a 2-D problem which implies that the dresser would only tip to the left, but in 3-D world the it could tip at any angle. Further, only one case which the child hangs one the top drawer with other drawers inserted was analyzed, but many other situation could happen in real-life.

The answer is reasonable since all values used were real-life values, and that is why the products were recalled.

In this case, any child weighs over 26 kg has potential to tip over the dresser and get injured or killed.

links:

http://abc7chicago.com/family/safety-group-highlights-recalls-of-childrens-products/1833068/

https://www.disabled-world.com/artman/publish/height-weight-teens.shtml

http://www.ikea.com/gb/en/products/storage-furniture/chest-of-drawers/brusali-chest-of-4-drawers-white-art-20252742/

http://www.ikea.com/ms/en_CA/pdf/Recalled_Chest_of_Drawers_Jun29_EN.pdf?icid=itl|ca|en_secureit_pdf|201606282141595720_1

Increasing the Accuracy of Wearable Heart Rate Monitors

Posted on by

Identify: Many people today look for ways to track their workouts to make sure that they are getting the best possible results whether it is for weight loss or training performance purposes. From high intensity interval training to slow jogging, heart rate monitors have proven to be popular in assisting users with how well they are performing. Furthermore, there are different types of heart heart monitors that are on the market today including chest straps and wearables that have proven to be successful. However, each different type of heart rate monitor has a slightly different method of measurement. So, lets take a peek into how these devices work.

Chest straps are one of the most popular and well known forms of a heart rate monitor that is used today. These straps use a wireless sensor to detect your pulse electronically and then send that data to a wristwatch-style receiver to display. Although these are deemed to be the most accurate, they are not the most comfortable to wear during a workout. Therefore, wearable wrist heart rate monitors have been developed which use an optical sensor built into the wrist unit’s watchband or case back to detect your pulse in a more comfortable way during your workout. The downside to these devices is that they are less accurate than a chest strap. Therefore, we can take a look into how to design an optical sensor that has the most accuracy possible for wearable HRM (heart rate monitor) devices.

Formulate: The main issues that have caused a lower accuracy and unclear signal in wearable HRMs have been the noise, weakness of the measured signal, amplitude of motion, and wide variance between different peoples’ wrists. To look into resolving these issues, it needs to be understood how these devices work. Optical HRM sensing is based on the principle of photoplethysmography (PPG). This allows the wristband to relate the pressure pulse from blood vessels as blood is passing through to each time a heart beats to get the heart rate. The way it does this is by using an LED to emit light into the body’s tissues and and use photodiodes to measure the amount of light that passes through them. The difficulty with this technology is that the measured signal is very small. In order to make a more accurate heart rate monitor, we want to be able to record the signal with the least amount of noise around it due to motion.

The most effective way for reducing the noise is simply the position of the wearable HRM in reference to the skin. The band needs to be worn with a snug fit and maintain an unchanged position throughout a workout. In the figure below, you can see the different interference levels depending on the gap between the skin. On the left, there is more interference shown by more blue lines and on the right there is less interference due to the proximity that the sensor is to the skin.

It is also important to understand that there are other factors that can cause interfere with a wearable HRM to decrease accuracy. For example, wrist curvature, wrist hair density and color, and skin color can all affect an optical signal’s reading. Skin color is a factor of great interest due to the fact that it greatly affects the signal and requires a change in LED brightness. Between the physical gap and skin tone, both factors are large determinants of accuracy for a wearable HRM.

Solve:

In order to design an optical sensor. We will want to minimize the gap between the sensor and sin but also include a sensor that can accurately read a signal with various skin tones.

We can use this equation for photocurrent by breaking it into AC and DC components of the signal. Typically, there might also be ambient light present (AC + DC noise). However, “the DC component of optical noise is usually subtracted due to an ambient light measurement immediately prior or after the LED light on measurement, resulting in an effective signal of”:

Further Readings

Best Heart Rate Monitors and HRM Watches

Heart Rate Monitors: How to Choose and Use

How to design an optical heart rate sensor into a wearable devices wristband

LED – Based Sensors for Wearable Fitness Tracking Products

SFH 7050 – Photoplethysmography Sensor

Using Inverse Dynamics to Prevent Ankle Injuries

Posted on by

Identify:

Ankle injuries are one of the most common injuries that occur in NFL linemen. If these injuries persist, the number of games missed can accumulate and the injuries can potentially end a player’s career. Research is currently being done to figure out how these injuries occur in order to design more efficient equipment such as ankle braces and modified cleats. One common method of injury involves the linemen planting the tip of their foot on the ground with great force. The force that is applied translates over to the ankle which causes the injury. Can we use engineering principles to approximate how much force is applied to the ankle? Yes we can, with the use of inverse dynamics. Inverse dynamics calculates forces and moments at one body segment by using the forces and moments of an adjacent body segment as well as the position, velocity, and acceleration of the connected body segments. By using inverse dynamics, one can solve for the amount of force that is applied to the ankles and potentially create new technology, such as insoles for the cleats, which can absorb some of the force that is applied and thus reduce the risk of injury.

Formulate:

Known Values and Assumptions:

Height = 1.956 m (6 foot 5 inches)* → length of foot (d) = (1.956)(0.0425)** = 0.08313 m

Mass = 141.521 kg (312 pounds)* → mass of foot (m) = (141.521)(0.0143)** = 2.024 kg

Force due to gravity (Fg) = m(9.81) = (2.024)(9.81) = 19.855 m/s^2

Normal force (FN) and force of friction (FFr)***, which are applied at the tip of the foot.

Angle between foot and playing surface (θ) = 15°[1]

Linear acceleration (a) and angular acceleration (α)****

Moment of Inertia (I)

Center of mass = (0.50)(d) = 0.0416 m

*Average height and weight of an NFL lineman during the 2015 season[2]

**Body segment weight and length[3]

***Exact value of FN and FFr can be used if force plate data is available

****Exact value of a and α can be used if motion capture data is available

Unknown Values to be Solved For:

x-direction force applied to the ankle (Fx, ankle)

y-direction force applied to the ankle (Fy, ankle)

Moment about the ankle (Mankle)

Equations to be Used:

∑Fx = max

∑Fy = may

∑M = Iα

Figure 1: Free-Body Diagram of the forces acting on the foot and ankle of an NFL lineman

Solve:

Step 1: calculate moment of inertia

Radius of gyration constant for the foot (Kfoot)[4] = 0.475 m

Radius of gyration of the foot (kfoot)= (Kfoot)(d)[4] = (0.475)(0.08313) = 0.0395 m^2

I = (m)(kfoot) = (2.024)(0.0395) → I = 0.0799 kg*m^2

Step 2: solve for forces in the x and y direction

∑Fx = max → (2.024)(a*cos(15)) = Fx, ankle – FFr → Fx, ankle = FFr+ 1.955*a

∑Fy = may → (2.024)(a*sin(15)) = FN – 19.855 – Fy, ankle → Fy, ankle = FN – 19.855 – 0.524*a

Step 3: solve for moments

∑M = Iα → (I)(α) = Mankle + (dy)*(Fx, ankle – FFr) + (dx)*(FN – Fy, ankle)

where:

dx = y-distance between ankle or tip of foot to center of mass

dy = x-distance between ankle or tip of foot to center of mass

∑M = Iα → (0.0799)(α) = Mankle + (0.0416*sin(15))*(Fx, ankle – FFr) + (0.0416*cos(15))*(FN – Fy, ankle)

∑M = Iα → Mankle =(0.0799)(α) – (0.011)*(Fx, ankle – FFr) + (0.040)*(FN – Fy, ankle)

The solution seems reasonable in the sense that forces are being added on to the ankle. The extent to which the forces are added will depend on multiple factors such as the angle between the cleats and playing surface as well as the height and weight of the athlete being tested. One limitation in this solution was not using exact values of angular and linear acceleration as well as the normal and frictional force. If one is able to accurately obtain these measurements via motion capture and force plate data, they can plug the values into the solutions above to determine exact values of the forces and moments acting on the ankle. For future studies it may be interesting to look at how the other lower limbs, such as the knees and hips, react to translated forces which can accumulate and potentially lead to a greater risk of non-contact injury.

Sources:

[1]: https://www.google.com/patents/US3413737

[2]: http://www.businessinsider.com/nfl-offensive-lineman-are-big-2011-10

[3]: http://www.exrx.net/Kinesiology/Segments.html

[4]: http://health.uottawa.ca/biomech/courses/apa2313/bsptable.pdf

Exercise and Save Money: Turning Exercise Work to Electricity

Posted on by

IDENTIFY:

 

Cycling is a type of popular cardio exercise that can be widely seen in gym, home, and outdoor. This exercise allows exerciser to expend energy by rotating feet around the center of flywheel. Generally, the work done by exerciser just transfer to heat and lost in the air, but can we store the energy and utilize it for our daily life? The answer is yes. In article These Exercise Machines Turn Your Sweat Into Electricity fromIEEE spectrum, it states that Harr, a 21 year old mechanical engineering graduates of University of Florida developed that energy conservation device [1]. By converting workout energy to electricity, electrical bill can be reduced. At the same time, it encourages people to do more exercise to achieve a healthier life. In order to make a real cycling machine to meet this demand, engineers need to identify, formulate, and solve problems. For example, a question would be how long the crank arm of  the cycling machine should be in order to generate 6000 Joules energy in a hour (100watts) ? This question need to be solved because it makes more sense if the machine can generate noticeable amount of energy. The unknown is the crank arm length, and variables are rotating speed of exerciser and exercise duration, which can be assumed as 0.5 m/s and 1 hour, and the work expected is 6000 joules. By solving this problem, engineers would be able to design the machine with proper crank arm length.

Figure 1[2]. This picture express someone is recycling workout energy to lighten bulbs.

 

FORMULATE:

Figure 2. This hand drawing express the flywheel and crankarm park on a normal bike.

Assumptions and Simplification:

(1) The weight of the exerciser’s feet is 1kg (Assume 70kg*1.45%*2)[3]

(2) exerciser’s feet are rotating in a constant speed of  0.5 m/s

(3) The generated energy expected in 1 hour is 6000J (100 watts)

 

The problem is to solve the length of the crank arm of this cycling machine (the radius of this circular motion).

 

Equations for circular motion and work: 

SOLVE:

Since we expect work done is 6000 Joules in a hour, and distance is 0.5 m/s *  3600 s = 1800m,

F = W/d = 3.3 N

F = 3.3 N = (mv^2)/r = (1kg*1m^2)/r

=> r= 1kg*m^2/3.3 N = 0.3 m

Thus, as assumptions made above, the radius of the crank arm of the cycling machine should be about 30 cm, which is realistic.

The variables like feet weight (directly related to force applied on pedal), and rotating velocity can be various for different user. Thus the energy generate can be different for different user too. Generally, more force input the exerciser do, the more the energy generated, and faster the exerciser rotate their feet, the more the energy generated.

One major limitation need to be concerned for this design is that the energy generated won’t be 100% converted to electricity. Thus there is more problems need to be solve to make the conversion more efficient.

Overall, the length of the crank arm of the cycling machine should be about 30 cm in order to generate 6000 joules per hour (100 watts). The solved length is a reasonable value. The energy generated for a single cycling machine might not be a lot, but it can be a more significant number if the system is utilize by gym on multiple cycling machines.

Path forward: instead of a in home exercise device, it can be further designed as a portable energy conservation system attached to a real bike that cycling work can be conserved into battery. In addition, not only cycling machine, the energy recycling system can be applied on other type exercise machines with similar mechanism.

More to read:

Could We Use Exercise Machines As Energy Sources? 

In the Gym: Clean Energy From Muscle Power

These Exercise Machines Turn Your Sweat Into Electricity

There’s more to an exercise ball than you thought

Posted on by

Identify

Anyone who has ever been to the gym has most likely seen or used an exercise ball. They’re big, inflatable balls that many people use to help them facilitate exercise or to stretch. They’re good for strengthening your core and improving your balance. Incorporating an exercise ball into your daily workout will add a challenge to your routine. A lot of people may also use them at home due to the fact that they are very affordable and versatile. While they may seem harmless, there can be serious risks when using one. It is important to use the correct size ball based on your height in order to get the most effective workout. It has to be inflated properly in order to work correctly. An over or under inflated exercise ball will put you at a greater risk for injury. The biggest danger of an exercise ball is having it burst. Over-inflation, improper use, and excessive user weight are some common ways that the ball may burst. The first step in preventing an exercise ball from bursting is choosing the right material. The material needs to be able to support the user and keep the integrity of the ball. Some common materials are vinyl and plastic. It’s important to figure out the force that is being applied to the ball, in order to figure out the strength of the material needed. The material needs to have a high tensile strength to support the user and prevent the ball from bursting and injuring the user.

Example of Exercise Ball

 

Formulate

The first step is figuring out the appropriate size of the ball based on height. When sitting on the ball, your knees should be at a right angle and your thighs should be parallel to the ground. The average woman in the United States according to the CDC is 64 inches tall and 166 lbs (75.3 Kg). According to anthropometric dimensional data, the ground to her knees is .285 (Anthropometric data-197t3u3) of her height.

.285 * 64 inches = 18.24 inches

Proper size for an exercise ball based on height

 

This means that the proper exercise ball should be 18 inches in diameter or 46 centimeters.

To find the best material, we can calculate Young’s modulus based on Hooke’s Law. 

 

Hooke’s Law  

?= stress = Force/Area

E= Young’s modulus

ɛ= strain= Δl/l

Surface Area of Sphere = 4 * π * r^2

Assumptions:

  • Exercise ball undergoes elastic and linear response to force
  • All of the users weight is being applied over the top half of the ball
  • Assume the exercise ball displaces 1 inch when force is applied

Solve

?= Force/Area

Force = 75.3 Kg * 9.8 m/s^2 = 738 Newtons

Half the area of sphere = ½ * 4 * π * 9.12^2= 523 in^2 = .337 m^2

? = 738 N / .337 m^2 = 2190 N/m^2

ɛ= strain= Δl/l

Ɛ = 1 inch/18.24 inch = .0548

 

2190 N/m^2 = E * .0548

Young’s modulus: E = 4.00 x 10^4 Pa

 

From this calculation, an exercise ball would need to be made of a plastic or vinyl with a Young’s modulus of around 4.00 x 10^4 Pa.

The assumption that the user’s total weight is distributed on the entire top half of the exercise ball led to the Young’s modulus to be underestimated. In real life, the user’s full weight wouldn’t be on the ball and it would also be distributed over a smaller surface area. The actual material would have a higher Young’s modulus than the calculated value. 

 

Learn more about the things you can do with an exercise ball!

http://www.webmd.com/fitness-exercise/features/10-fun-moves-to-reshape-your-body-with-exercise-ball-workout#1

http://www.fitnessmagazine.com/workout/exercise-ball/best-stability-ball-exercises/

Exercise Balls – The Ultimate Guide

 

Physical Therapist’s Tool of Choice- Hand Held Dynamometers

Posted on by

Identify

For physical therapists, one of the most important and sometimes most challenging aspects of their job is to track patient progress during rehabilitation from an injury or surgery.  While most of this can be done based on patient reporting (such as 1-10 pain/discomfort scales) or qualitative therapist observations, they collect quantitative data whenever possible.   One of the most common ways therapists can document progress is through strength testing.  For larger muscles, such as the quad and hamstring, larger testing apparatuses, like the Biodex, are used to measure strength. These machines, however, are large and difficult to use. They can be oriented for smaller muscles but almost always therapists will opt for hand-held dynamometers. Over the years these dynamometers have developed from simple spring or strain gauge contraptions to sleek digitalized devices.

The RIHM (Rotterdam Intrinsic Handdynamo Meter)

Taheel Technology Hand- Held Electronic Dynamometer

The above dynamometers are used to test grip strength and for the sake of explanation I will focus on this orientation., It is important to note that clinics often use the device shown below to measure strength of the arm and shoulder region since it allows for measurements to be taken in many different directions. For example, knowing the internal rotation and external rotation strength of a baseball players injured arm in comparison to his healthy one will allow the therapist to decide when the player should be allowed to return to play.

 

As I mentioned, all of these devices are designed on the seemingly simple basis of springs and strain gauges, Therefore, when designing a dynamometers the starting point is to decide what spring to use. If the spring constant is not stable and known, the device cannot be calibrated and will not result in accurate readings.

 

Formulate

For a grip strength dynamometer the patient pulls on a a handle connected to a spring of a known constant. Based on the displacement of the spring from it’s resting position the force they generated can be calculated.  This force is a direct measure of grip strength.  To decide the stiffness of the spring that should be used an engineer must use Hooke’s Law:

Hooke’s law states that the force of extension on the spring is proportional to the displacement of the spring.

The following assumptions can be used to calculate the max spring constant that should be used:

  • Force (Fs)– According to a study done by Top End Sports the maximum grip strength the dynamometer must be able to withstand is 57.5 kg.
  • Displacement (x)- Based on average hand sizes it can be assumed that the maximum displacement of the spring will not exceed 9 cm.

Fundamentally, stiffer springs have higher spring constants. For this reason, we know that the spring constant should be minimized, yet must be able to detect the max force and displacement it may experience. You essentially do not want to make it harder than it has to be for the patient.

Using these two assumptions and an understanding of Hooke’s Law it can be determined what the max spring constant that will be needed.

 

Solve

The following steps are used along with the assumed values to determine the ultimate spring constant:

F=-kx

57.5 N=-k(0.09 m)

k=-638.889 N/m

According to these calculations, a spring with a constant below approximately 640 N/m will suffice in your design of a handheld dynamometer.

Now it is important to understand the implications of the assumptions made here so your design can be altered for maximum efficiency.  It is necessary to consider the patients that will be using your design.  While the calculations above are generalized for average sized patients this may not fit your needs. For example, if your device will be used by pediatric patients the assumed values can be much lower whereas if your device will be used by athletic trainers in professional sports, the numbers should probably be increased.

The development of such dynamometers has been on the rise as their clinical prevalence has also risen.  They are extremely beneficial to clinicians yet are based on such a simple engineering principle.

For more information on the benefits and design of dynamometry I encourage you to check out the following readings:

http://www.prohealthcareproducts.com/blog/handheld-dynamometers-and-manual-muscle-testing/

https://www.ncbi.nlm.nih.gov/pubmed/18796949

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2868792/