How it Works: Air Displacement Plethysmography

Rachael and My How it Works on Air Displacement Plethysmography… Enjoy!!

Recommended further reading:

http://ajcn.nutrition.org/content/75/3/453.full#cited-by : BOD POD Evaluation

https://www.fda.gov/ohrms/dockets/dockets/05p0207/05p-0207-ccp0001-04-manual.pdf : FDA BOD POD Manual

http://ajcn.nutrition.org/content/95/1/25.long : Dual Energy X-Ray

http://ajcn.nutrition.org/content/69/5/898.long : Comparison of ADP, Hydrostatic weighing and electrical impedance

Breathe In, Breathe Out… Breathing during Exercise

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?

Measuring Breathing Patterns through Strain Gauges

Identify:

One of the major emphases in exercise and athletic training is proper breathing. Should I breath faster or slower? Deeply or shallowly? These are the questions that athletes and gym-goers face every day. And this emphasis on breathing is merited – proper breathing during exercise can better oxygenate the body, which in turn improves endurance, performance, and fat burn during exercise. The problem, though, is that many professional and non-professional exercisers alike do not know how to monitor their breathing during exercise. With the clear benefits of proper breathing during exercise and the lack of athlete experience in monitoring breathing, the need for a device to help monitor breathing during exercise is apparent. One possible device that could be used to monitor an exerciser’s breathing during activity is a strap that wraps around the user’s torso and contains a strain gauge. This strain gauge will measure pressure changes imposed on the strap by inflation/deflation of the torso during breathing, thereby determining the breathing patterns of athletes during activity.

However, designing this device is not a simple task. There are many components that would go into such a device: strap, strain gauge, monitors, and more. Each of these components requires calculations to determine the best type of component to use for the device. One example of this is the process that goes into deciding which strain gauge to use in the system. There are many strain gauges on the market today, but not all of these fit the needs of the system described above. Some strain gauges cannot withstand enough strain to be incorporated in this system. In order to decide which strain gauge is the most appropriate for this system, engineers must solve the problem of determining how much strain the strain gauge will be exposed to when used in the breathing strap and how sensitive their measurements should be.

Formulate:

Before doing any calculations, it is important to understand what a strain gauge is, how it works, and what exactly it measures. First of all, what is strain? Strain is a measure of the amount of deformation an object or material experiences due to an applied force. Strain gauges are designed along this principle of measuring deformation. They can measure either axial or bending strain, as depicted in Figure 1, depending on the type of strain gauge being used.

 Figure 1. Common strain gauge configurations for measuring axial (left) and bending (right) strains.

 

Since the inflation of the lungs will mostly cause axial stretching of the strain gauge, we will look at strain gauges that measure axial strain. When strain gauges are stretched axially, they are displaced. The strain gauge responds to strains with a change in electrical resistance. So, as strain on a strain gauge changes, so does the resistance in the gauge.

One common calculation related to strain gauges is the calculation for gauge factor (GF), represented by the equation:

This relationship can be used in our case to help decide which strain gauge to use in the strap design based on gauge factor, changes in length, and base resistance values in different strain gauges. In the case of our strain gauge strap, we are trying to determine how much strain the strap will experience and what ΔR will give the ideal sensitivity for the strap system. Thinking about the strap system, we can determine the ΔR range that we want the strain gauge to experience based on how sensitive to strain changes we want the gauge to be. As stated before, the gauge responds to strain with a change in resistance. This ΔR will change more drastically as more strain is applied to the gauge. During exercise, the body experiences strain from breathing, small strains from turning of the torso during movement, and other small strains from outside forces like bumping the strain gauge during movement. Given that the strains we want to register and record (strains caused by inhalation) are relatively larger than strains from external sources (strains caused by small movements or bumps), we want our strain gauge to be less sensitive to very small ΔRs and more sensitive to slightly larger ΔRs. And, by using the equation for GF from above, we can calculate estimated ΔRs with different strain gauges to decide on a strain gauge that fits our needs.

In order to solve this, we need to measure or estimate values for all other variables in the GF equation besides change in resistance. These values include:

  • Gauge factor: 2
    • Assumption: Common metallic strain gauges have a GF = 2
  • Length: 50 mm
    • Assumption: This is a large gauge size since strains due to inhalation are likely to be large
  • Change in length: 3 mm
    • Estimated: Based on a measurement of one shallow inhalation, the change in circumference of the torso on inhalation is 3 mm, meaning that the strain gauge will also stretch this much.
  • Resistance: 120, 240, 350 Ohms
    • Variable: These three resistance values are standard for the size gauge we estimate using

Now that we have all the variables needed to solve for the change in resistance, we can begin solving the problem!

 

Solve:

Of these three ΔR values, the value with the 120 Ohm resistance is the smallest, meaning this gauge is the most sensitive to strain changes. Given that we want a resistance that is not extremely sensitive, one might argue that the 120 Ohm gauge may be eliminated from the options. However, none of the above solutions have ΔR values that are extremely sensitive, so it can be concluded that none of them will be hypersensitive to false strain readings. If anything, the gauges will not be sensitive enough to properly differentiate between shallow and deep breaths. Since the 120 Ohm gauge has the lowest ΔR, it is the most likely to accurately indicate subtle changes breathing patterns. The 240 and 350 Ohm gauges have higher resistance change values, meaning they might not be as sensitive to resistance changes caused by strain and may not be able to identify shallow breaths. Therefore, we can say that the gauge that best fits into our parameters is the 120 Ohm gauge.

This solution is somewhat sensible in that the assumptions are reasonable. All assumptions made for this problem represent legitimate conditions that could be experienced in a generic user population. However, while this is a reasonable solution, it is important to note that this is not an absolute solution. The assumptions made in this problem are not necessarily representative of all real-world conditions. For example, the ΔL of the strain gauge may change between users based on different lung capacities and body sizes. Additionally, the strain gauge length may be different; in this problem, one gauge size was chosen, but there are many different gauge types that could have been used. And using a different gauge type will change the problem calculations, changing the resultant strain gauge choice. This problem as a whole is limited in that it is difficult to say which Ohm resistance value is the best without actually trying different resistors in the system and performing physical testing. And, this problem only considers the use of strain gauges; flexi sensors and other pressure sensors may be a more viable alternative given the large resistance change values calculated for these strain gauges. But, with the basic assumptions made in this problem, the solution is a fair estimate of which strain gauge to start the design process with. With the most appropriate gauge decided, work can continue on with the design of the strap system in an effort to help athletes understanding and monitor their breathing patterns.

For more information about strain gauges, visit:

The Treadmill of the Future?

Have you ever been on a treadmill working out when suddenly you almost fall off the back of the machine? Have you ever found yourself struggling to keep up with a treadmill’s pace? Have you ever felt constrained by the preset speeds on a treadmill? You’re not the only one – many individuals have a tough time finding a pace that best suits them when running on a treadmill, to the point that pacing charts have been developed to make it easier for runners to find their ideal pace on the treadmill. But, what if this wasn’t a concern? What if treadmill speeds could be personalized to an individual? That’s the idea behind one US patent, the patent for a user footfall sensing control system for treadmill exercise machines:

Patent title: User footfall sensing control system for treadmill exercise machines

Patent number: US 8480541 B1

Patent filing date: June 23, 2009

Patent issue date: July 9, 2013

How long it took for patent to issue: 4 years

Inventors: Randall Thomas Brunts

U.S. classification: 482/7

Claims: 20

This patent proposes to create a footfall monitoring system to track a treadmill user’s motion, speed, and acceleration to automatically adjust the speed of the treadmill to the user’s ideal pace. As the patent’s classification number denotes, the device is intended to “facilitate conditioning or developing of muscle” through “track, field, gymnastics, or athletic activity.” This device specifically will regulate the user’s “rate of movement” in order to facilitate positive exercise.

This patent consists of 20 claims outlining the main functional components of the treadmill system. The main components of the device include: a tread base, a moving tread belt, a belt motion sensor to measure tread belt speed and displacement, a motor assembly to drive belt motion, a foot sensor to detect a user’s position on the tread belt, and a motor controller that adjusts the speed of the tread belt. The basic design for the system can be seen in Figure 1 below. These main components work together to register a user’s position and motion and then automatically change the speed of the tread belt in response to these measurements. While the details of how the system will measure and calculate differences in position, speed, and acceleration is somewhat complicated, the basic idea is simple – the treadmill will sense where a user is stepping on a treadmill and how long their strides are through capacitive proximity sensors around the tread base, as seen in Figure 1 on the right. By using measurements of timing between footfalls and positioning on the treadmill, the system will calculate the user’s speed, acceleration, and position on the treadmill relative to the “ideal” user position. These measurements can then be compared to the speed and acceleration of the tread belt, which can then be used to automatically fit the speed of the tread belt to the user’s running pace and get the runner back to the ideal position on the treadmill.

This patent is not the first time a speed-changing treadmill has been patented before. Prior patents and art outline similar systems that measure a user’s position and speed on a treadmill. One main difference between this patent and other patents is the sensor type and sensing method used. Other proposed designs and patents used a variety of sensors, including optical sensors and pressure sensors as well as strain gauges, to detect a user’s position on a treadmill. However, these sensors often result in inaccurate or false-positive readings during use. This patent, on the other hand, uses capacitive proximity sensors. Using these sensors allows for higher precision and accuracy in footfall detection.

                    

Figure 1. External appearance of treadmill system (left), assembly and processing schematic for system (middle), and areas of footfall sensors (right).

 

Why does this patent matter? Who is it going to help and how? The answer is – you! This patent has the potential to help everyone from elite athletes to the common gym-goer; anyone who uses a treadmill stands to benefit from this patent. I personally thought this patent was interesting and useful because of my own experiences with treadmills in the past. There have been times when I’m running on a treadmill and my pace changes without me really knowing or thinking about it; it’s a very slight, subtle pace change. But when this happens, I either end up running into the front of the treadmill or creeping backward on the treadmill to the point that I almost fall off the back edge of the machine. Because of this, I think it would be very useful, not to mention safer, to have a treadmill system that automatically adjusts to user pace changes.

This patent and other exciting patents can be found through Google’s patent search or through a government patent search.