Pulse measurement sensor. Do you need a wireless heart rate sensor for your treadmill? Heart rate monitor: what is it for and what are the benefits
In this article, you will learn about a few details to look out for when developing sensors for a photoplethysmograph.
Introduction
In the previous article, you got acquainted with the design of the sensor that measures the heart rate monitor. Today I will share some of the best practices that can be useful when choosing element base plethysmograph and its development electrical circuit... They will help improve the quality of the desired signal, which is primarily influenced by the following factors:- lack of artifacts;
- the presence of a pronounced pulse wave at the registration point;
- design of the sensing element.
There are several sources of artifacts:
- movement of the person using the photoplethysmograph, relative light source, natural or artificial, for example, moving the shadow from the sun during sports;
- moving the light source relative to a person or changing the brightness of this source. For example, flickering of fluorescent lamps;
- non-pulse-related movements of body parts causing movements of the photoplethysmograph or body points in the place where the sensitive element is installed. For example, movements of the bones of the forearm arising from finger movements, movements of the bones of the head associated with speech and facial expressions.
A similar situation is observed when measuring the pulse from the phalanx of the finger. A change in the temperature in the room or a slight change in the posture of a person and the resulting shift of the registration point by a short distance can lead to a decrease in the signal level or even to its disappearance.
When measuring the pulse from the temple, the problem of the lack of signals is exacerbated. The area of the temple is larger than the area of the finger, it is more difficult to find the point at which the pulse is better developed, and the more likely the user is wearing the sensor incorrectly.
Multichannel sensing elements
To solve the described problem, the principle of duplication, which is widespread in technology, can be applied, which in this case implies the use of a sensor with several sensitive elements. Schematic diagram, which implements such an idea, is shown in the following figure.
I foresee the skeptical thoughts of readers about LEDs connected in parallel. Please do not judge strictly, as this is a prototype that should not have been in operation for a long time.
LEDs and phototransistors on printed circuit board are arranged in pairs. The size of the board is chosen so as to cover the entire area of the temple, this allows the amplification and filtering of the signal to be located in the same place. The board may contain holes for attaching to the tape. Appearance a nine-element sensor is shown in the following figure.
A similar solution can be applied to measure heart rate from a finger or wrist. Below is a diagram of a sensor consisting of four phototransistors and one LED.
The emitters of the phototransistors may not be connected and then the signals from each of them are measured independently, in this case a special multi-channel measuring device is required. Multichannel execution can also be useful for removing artifacts. If an artifact occurs only in the area of one photocell, it is fixed and is not taken into account in the overall measurement picture. However, the use of such a scheme is not always convenient, as it leads to an increase in size. It is quite another matter if you connect the photosensitive elements in parallel. In this case, only one measuring channel is required. The following figure shows a prototype of such a sensor. It works according to the "reflection" scheme. The LED is in the center and the phototransistors are at the edges. The sensor can be used to register a pulsogram from the phalanx of a finger or wrist. The printed circuit board is wired so as to be able to connect phototransistors in multi-channel or single-channel versions.
Compauditing
For better fixation of the photocells, the surface of the printed circuit board can be filled with a compound. A special mold is made for filling, which you can also see in the figure. To prevent the compound from sticking to the mold, it is better to make it from fluoroplastic. If the mold is made of another material, for example, metal, then before pouring the compound, it should be lubricated with a special compound. If such a composition is not available, regular petroleum jelly will do. You should also carefully approach the choice of a compound, since an incorrectly selected composition can deform the elements during curing.In addition to fixing, the compound acts as a light filter. Epoxy compounds with colorants are suitable for this purpose. For example, the Epoxicon compound produced by SPbGTI can be used.
An alternative to compounds can be solid filters. They fit closely to the printed circuit board, and grooves are made for LEDs and phototransistors with a cutter or laser. The following figure shows a sensor with elements covered by a milled plate.
The presence of a light filter allows you to minimize artifacts created by external light sources. The following image shows the pre-cure and post-cure optical compounds.
Features of the choice of phototransistors and LEDs
To register the pulse wave, photosensitive elements are used - photodiodes or phototransistors. This article is only talking about phototransistors. Because at the time of my start of work in this direction, there were already several dozen different transistor sensors (clips, clothespins and fingertips) on my hands, and there were also well-developed circuitry solutions. At the same time, the use of diodes is no worse and is widely used in various applications, for example, in common medical sensors of the Nellcor standard.When choosing phototransistors and LEDs, first of all, you should pay attention to the following characteristics:
- wavelength (maximum spectral characteristic) [nm];
- half-brightness angle for LEDs and coverage angle for phototransistors [deg.];
- radiation intensity [mW / sr] for LEDs and sensitivity for phototransistors [mA / (mW / cm2)];
- rated current of phototransistor and LED [mA];
- dark current of the phototransistor [mA];
- the presence of lenses and light filters built into the body.
The wavelengths that are most absorbed by the blood are best for measuring heart rate. These are waves corresponding to the green color 530 nm. The red and infrared ranges are also used. I highly recommend with the classification of methods for measuring the pulse, in the same place you will learn about the absorption spectrum of hemoglobin.
When choosing photocells, you should pay attention to the presence of lenses and light filters that allow you to achieve the desired angle of half brightness and coverage, and, therefore, be less sensitive to radiation from other sources. Built-in filters allow you to work only in the selected spectral range. If you choose a LED with a high angle of half brightness and a phototransistor with a wide angle of coverage, then the light will pass through the surface of the skin. This will lead to a deterioration in the measuring range and the luminous flux modulated by the pulse wave will practically not affect the output signal of the measuring circuit. This situation is illustrated in the following figure.
Angle a2 is acceptable, but angle a1 is too large for an LED with this angle to be used in a heart rate monitor. This example is for a reflection heart rate measurement. The choice of a LED with a large angle of half brightness in devices operating "in the light" will lead to the fact that a large radiation power will pass by the photodetector. This is not desirable, especially on mobile devices.
You should also pay attention to the light intensity of the LED, measured in milliwatts per steradian [mW / sr]. In documents for LEDs, it is usually indicated at currents of 20, 100 and 1000 mA. To save energy, it is better to choose LEDs that have a higher characteristic at the same current consumption. You should pay attention to the magnitude of the photoelectric current of the phototransistor, the larger its value, the better. The last two characteristics are related. As a result, the level of the minimum expected signal should be at least several times higher than the expected noise level in the measuring device.
LEDs and phototransistors are often sold in pairs, suitable friend to a friend constructively and in terms of spectral characteristics. The table shows the characteristics of several pairs of LEDs and phototransistors. The pairs in lines 2 and 3 are not suitable for use in heart rate monitors due to the large angle and low radiation power. Pairs 1, 4, and 5 work well, with the first pair going best. This has been proven by testing. All other things being equal, the best pulsogram signal was recorded using the first pair. It should be noted that if an opaque barrier is placed between the LED and the phototransistor, the angle of radiation and sensitivity will not greatly affect the quality of the pulse measurement.
Conclusion. Three in one
Instead of a conclusion, I will mention a wonderful integral solution, which was given by habrapuser valexey in the comments to the previous article. This is a Si1143 device manufactured by Silicon Labs. Inside it has two photodiodes - red and IR, a control unit for three LEDs, an integrated amplification and filtering circuit, an ADC and an I2C serial interface module. I will not describe other details, since I have not had time to try it yet. Judging by the description, this device is well suited for various measurements related to heart rate monitoring.P.S.
The repository was replenished with drawings of sensitive elements and intermediate amplifiers.If you want to better monitor your overall physiological ability, you need to closely monitor your heart rate. As practice has shown, the best way this can be done with a chest heart rate monitor. In our review, we'll help you choose the best chest heart rate monitor.
Heart rate monitor vs. sports watch / fitness band: what's the difference?
Heart rate trackers in chest straps provide more consistent and accurate heart rate readings than a sports wrist watch. This is due to the higher reading frequency and less vibration on the body. Nevertheless, not all athletes find the belt comfortable, even more so if the user does not know how. It is most suitable for runners and cyclists, but not for fitness rooms. Some swimmers use a chest heart rate monitor, although it is reported to be squeezing chest and brings discomfort.
Nowadays, many fitness bracelets and smartwatches include an optical heart rate sensor. Instead of measuring electrical impulses, as is the case with a belt, it uses light to read the pulse of blood flow through the skin. While these gadgets are more convenient, optical sensors are not as accurate and are not always the best choice... They are not a good companion for people who engage in high-intensity interval training and other workouts that experience dramatic changes in heart rate.
There are three groups of heart rate belts: one wirelessly connects to a smartphone or PC, and the other uses a combination of two sensors that communicate with each other. In this case, a device is used on the wrist - be it a sports watch or a fitness band - that provides a wireless connection to the chest strap. The third group is capable of connecting to smartphones and PCs, as well as fitness bracelets and watches. Communication with peripheral devices is carried out using Bluetooth or ANT +.
By using the first group belt, the athlete will not have immediate feedback when using a chest heart rate monitor as it does not have a display. All data from his memory will be transferred to a smartphone or PC after training. Otherwise, you will have to take your phone with you for a run.
When exercising with the belt of the second group, it is possible to observe the heart rate and other data directly on the watch screen during exercise.
In any case, it's up to you to decide which type is preferable.
Top 5 chest heart rate monitors
There are many models of belts on the market today for accurate heart rate tracking. We offer an overview of chest heart rate monitors, which provide the most accurate heart rate data compared to fitness bands and sports smartwatches.
The Tickr X strap includes a sensor that counts repetitions during strength training and records advanced exercise metrics such as vertical body vibrations and ground contact while running, as well as speed and distance. Cycling enthusiasts will be able to rate cadence using the Wahoo Fitness app.
This heart rate chest strap reliably monitors your heart rate during workouts and sends data via ANT + and Bluetooth to any device you have on hand, be it an Android / iOS phone or a fitness tracker. Tickr X has a built-in memory for up to 16 hours of information, which you can view in the app later.
The device provides user feedback through two small flashing LEDs, one red to indicate that a heart rate has been detected and the other blue to indicate that the Tickr X is connected to another device.
Another type of feedback is vibration during certain user actions. For example, when the tracker is programmed to start or stop a music track when you touch it.
The Fitness Tickr X not only positions itself as a running heart rate monitor with a chest strap, but it is also quite suitable for fitness enthusiasts. It offers more than any other chest heart rate monitor on our list, which is why we ranked it number one in this ranking.
- Work with the large quantity applications
- Water resistance
- User feedback
- There is Bluetooth and ANT +
- On the connected device (sports watch or fitness bracelet), you can view only heart rate data - other indicators are viewed only using applications
- Unsuitable for swimming
Designed specifically for triathletes, the Garmin chest heart rate monitor with a small and lightweight tracker adjusts for comfort both in the water and on land. This strap can be used not only by swimmers, but also by athletes in the gym as a traditional heart rate monitor. The tracker sends real-time heart rate data to your paired watch using ANT + wireless technology (instead of Bluetooth LE).
When you swim, the heart rate sensor stores up to 20 hours of heart rate information, and then when you leave the pool, it sends it to your connected Garmin watch. This is because ANT + signals cannot pass through water.
The HRM Tri chest heart rate monitor is compatible with the following Garmin watches:
In addition to standard running heart rates, the HRM Tri provides movement dynamics including cadence, vertical body oscillation, and ground contact time (using it with the Epix, Fenix 3, and Forerunner 920 XT).
The free Garmin Connect online community lets you store data, plan your workouts, and share results with others. You can view detailed swimming metrics including heart rate graphs, swimming speed, stroke type, mapping, and more. And also track activity statistics: daily steps, distance and calories burned.
The Garmin HRM Tri is an excellent chest heart rate monitor for swimming, fitness, running and cycling with a durable design and accurate readings.
| Water resistance | 5 ATM (50 m) |
| Battery | lifespan 10 months (three workouts 1 hour per day) |
| Price | $129,99 |
- Robust construction
- Suitable for swimming
- Works with Garmin watches
- Expensive
- ANT + only (no Bluetooth LE)
The beautiful and small Suunto Smart Belt chest heart rate monitor matches perfectly with the Suunto AMBIT3 sports watch using Bluetooth 4 Smart LE.
The main feature of this chest heart rate monitor is that it does not show information in real time due to the lack of a display, but writes all the data into memory. You can activate the heart rate sensor on the strap using an app available from your smartphone or Suunto AMBIT3 smartwatch. Then you can go to train: run, swim, do fitness. Accurate data on heart rate and calories burned will be transferred to MOVESCOUNT software for logging and subsequent analysis. You must also turn off the device through the software.
Since the heart rate monitor has Bluetooth technology, it will also work with many other fitness apps on iOS and Android.
Suunto Smart Belt is the smallest Bluetooth Smart compatible heart rate sensor on the market that measures your heart rate with great comfort and accuracy.
- Compact, comfortable fit
- Provides accurate data
- Waterproof
- Compatible with both iOS and Android
- Works with smartphone companion app
- Loses elasticity over time, which leads to poor contact with the skin, and subsequently - inaccurate data
- Poorly designed and awkward MOVESCOUNT app
The Polar H10 chest strap heart rate monitor has built-in memory, allowing you to store one training session for up to 65 hours before syncing with your phone. The sensor turns on using the app in your smartphone, and then at the end of your workout, you can view your heart rate data.
The lack of a screen on the belt device does not allow for real-time feedback. Therefore, it can be used with compatible fitness equipment from the same company, as well as Polar smartwatches and bike computers. The H10 connects with most modern smartphones (iOS, iPhone and Android) via Bluetooth and works with fitness apps.
Polar H10 does not track sleep, daily activity or steps, but when paired with a Polar sports watch, it will greatly improve your reading performance. And with V800, you can get heart rate data while swimming.
The company is known for the good performance of its products, which is why the Polar chest heart rate monitor has an excellent reputation for reliability and accuracy and a place on our rankings.
| Water resistance | 3 ATM (30 m) |
| Battery | replaceable (CR2025), 400 hours |
| Price | $89 |
- Comfortable to wear
- Accurate heart rate readings
- Good battery life
- Waterproof
- Works with third party apps
- Doesn't require the use of a smartphone
- Sends heart rate data to GoPro Hero 4 and 5 action cameras
- Paid general features in a native app
- High price
The MZ-3 chest strap has a unique approach to using heart rate data. It uses the pulse to reward the user based on their individual levels of effort. Basically, you get scores based on beats across different heart rate ranges. The score increases with your intensity.
The application has statistics of competitors, where you can compare your points with friends and acquaintances. This playful approach can be applied to any exercise, whether you are a rower, runner, or cyclist.
The tracker turns on when it detects contact with the skin. There will be no battery drainage problems here if you forget to turn off the heart rate monitor via the app in your smartphone, like with other chest straps. But there is a risk to start the heart rate monitor, just holding it in the palm of your hand. In this case, the device, when turned on and off, emits a characteristic sound signal to notify the user.
Since the MZ-3 tracks your heart rate, not movements or steps, it can be applied to a large extent to any sport - even swimming, as it is waterproof up to 5 ATM. The MZ-3 sensor is ANT + capable, which allows it to work with third-party apps such as Strava or MapMyFitness to transmit heart rate data and GPS routes while running or cycling. There is also a MyZone MZ-50 sports watch that can be paired with a strap to provide live stats during your workouts.
If you need motivation, as well as an accurate indicator of how much effort you are putting in, we recommend the MyZone MZ-3. Efforts are rewarded. This makes the MyZone MZ-3 a reliable choice for everyone from fitness beginner to professional.
| Water resistance | 5 ATM (50 m) |
| Battery | 7 months |
| Price | $130 |
- The competitive element of the MyZone platform motivates and stimulates
- Accurate heart rate readings
- Multisport versatility
- Long battery life
- It's not always obvious that the tracker is on
- May slide during swimming and intense exercise
- The native application needs additional functionality
- High price
- Most heart rate monitors use rechargeable batteries. However, some people use batteries the size of a watch battery, which sometimes needs to be replaced.
- Not all heart rate monitors are waterproof. If you want to swim with a chest strap, choose one that is designed for in-water activities.
- To clean the monitor screen and heart rate sensors, wipe them gently with a soft cloth. To remove stubborn stains, lightly dampen the cloth first.
- Use warm soapy water to clean the belts. Air dry the belts in the sun.
Comparative table of characteristics
For mobile use horizontal scrolling of the table
 |  |  |  |  |
|
|---|---|---|---|---|---|
| Battery | Replacement battery CR2032 | Replacement battery CR2032 | Replacement battery CR2025 | Replacement battery CR2032 | USB, lithium battery |
| Battery life | Up to 12 months | 10 months (three workouts 1 hour per day) | Up to 500 hours | Up to 400 h | 7 months of battery life from a charge |
| Water resistance | IPX7 (waterproof up to 10 ATM) | 5 ATM (50 m) | 3 ATM (30 m) | 3 ATM (30 m) | |
| Sensor | Heart rate sensor, accelerometer | Heart rate sensor | Heart rate sensor | Heart rate sensor | |
| Connection | Bluetooth 4.0 and ANT + (dual band technology) | ANT + | Bluetooth | Bluetooth (supports simultaneous connections) | Bluetooth, ANT + |
| Internal storage | Yes | Yes. Up to 3 hours of workout data | Yes | Yes. Up to 16 hours of workout data | |
| Heart rate | Yes | Yes | Yes | Yes | Yes |
| Heart rate variability | Not | Yes | Not | Not | Not |
| Tracking | Calories, Vertical Oscillation, and Ground Contact Time | Cadence, stride length, ground contact time, ground contact time balance, vertical oscillation and vertical ratio | Real-time heart rate and calories burned data | Tracks heart rate with multiple target zones as well as calories burned, steps taken and distance | Monitors heart rate, calories and time |
| Swimming statistics | Heartbeat | Heartbeat | Heart rate | Transmits heart rate information while swimming to devices that support 5 kHz transmission | Not |
| Peculiarities | Works with apps like RunFit 7 minute workout and more Tracks cadence while cycling paired with Wahoo Fitness app | Specially designed for triathletes | Indoor Gym Compatible GoPro connection Allows you to choose your favorite activity from over 100 sports profiles and get real-time voice guidance during your workout | Live display of data via mobile app, watch or gym equipment Online journal with goal setting, biometrics, tasks, status and social channels |
Remember: if you have any concerns about your health or level physical fitness, check with your doctor. And it's always a good idea to consult with a personal trainer when developing exercises and goals. Take care of yourself.
The Sasmsung Galaxy S5 is an excellent modern smartphone, but nothing in it surprises more than the built-in heart rate sensor, which is linked to the proprietary S Health app. A sensor that has a very small size and located on the back of the device just below the camera gives you a very accurate reading of your heart rate. You can recognize him during your morning run or at any other time. Let's figure out how to use it!
WHAT IS THE ARTICLE ABOUT?
Actions
1. Open the app overview
- Do this by clicking "Applications" in the lower right corner of the screen.
2. Launch the "S Health" app
- In the S Health user interface, you should see icons at the top that tell you your pedometer reading, calories counted, and the calorie consumption you have logged in the app. Below you will see some icons that you can interact with.
3. On the main page of the application, click on Heart Rate
- It is a green icon with a white heart inside.
4. Place your finger on the heart rate sensor under the camera, it will light up in red
Hold it in this position for a few seconds until the data is read. Please note that the first couple of times the smartphone may not read your indicators. The sensor is highly susceptible to movement, moisture and other factors. To improve the quality of reading the indicator, we recommend following the following tips:
- Use the sensor with a dry finger only
- Keep your finger on the sensor as much as you can. Do not hurry!
- Do not Cry! Loud noise can affect the performance of the sensor.
- If the reading does not occur, try holding your breath. Sometimes it helps.
It is interesting
According to Samsung, the installation of a heart rate sensor is a result of the recent trend of close monitoring of health, and one of the ideas of the company is "Samsung's efforts to meet the needs and preferences of people." After explaining technical features measuring heart rate, Samsung talks about why they added a heart rate sensor to the smartphone instead of some other cool feature. “Heart rate is one of the most commonly measured health indicators. The heart rate sensor allows you to check which mode your heart is working in before, during and after exercise. " The flagship and wearable devices are always at hand, which prompted the company to add such a feature to them.
All cardiovascular machines are equipped with heart rate sensors to monitor your heart rate. All normally Treadmills are completed with wired sensors, which have a simple device, but a high measurement error.
Wireless sensors are the most accurate heart rate measurement devices, the error of which does not exceed +/- 1 beat.
Pulse is the number of arterial dilatations at the time of the outflow of blood from the heart per unit of time. It should be noted that pulse and heart rate (HR) are not the same thing, although physically healthy person their meanings will indeed be the same. Heart rate characterizes the work of the lower parts of the heart (ventricles) per unit of time (minute) and can differ significantly from the pulse rate. This phenomenon can be observed when the heart rhythm is disturbed (arrhythmias).
Heart rate values
Every person is different and heart rate values can vary significantly for different people... The factor affecting heart rate is physical fitness, the degree of fitness of the heart and the body as a whole. The body is a complex system in which the heart solves the problem of transporting oxygen to all tissues and organs.
As a rule, the heart of trained athletes at rest beats much less often than the heart of the average person.
The normal range for a healthy person is 60-90 beats per minute. With pulse values below 60 beats per minute, bradycardia occurs, with increased values above 90 beats, tachycardia. You need to know that in a newborn child, an increased heart rate of up to 140 beats per minute is considered the norm, and a woman's pulse is 5-10 beats higher than a man's.
Pulse values rapidly increase during physical exertion, during emotional outbursts (anger, fear, excitement), depends on the statistical position of the body (standing, sitting), increases after eating or after using certain medications.
Table 1 - Average heart rate values for a healthy person.
| Age | Heart rate per minute |
|---|---|
| Newborn | 135-140 |
| 6 months | 130-135 |
| 1 year | 120-125 |
| 2 years | 110-115 |
| 3 years | 105-110 |
| 4 years | 100-105 |
| 5 years | 93-100 |
| 7 years | 90-95 |
| 8 years | 80-85 |
| 9 years | 80-85 |
| 10 years | 78-85 |
| 11 years | 78-84 |
| 12 years old | 75-82 |
| 13 years old | 72-80 |
| 14 years | 72-78 |
| 15 years | 70-76 |
| 16 years | 68-72 |
Why do you need to monitor your heart rate on a treadmill?
For your workouts to be as effective as possible, you need to monitor your heart rate. The efficiency zone is calculated based on the values of the maximum heart rate (MHR). For men, MHR = 220 - age, for women this value is MHR = 226 - age.
Target zones can be conventionally divided into four ranges:
- Area of general health-improving load (sparing mode): 50-60% of the MHR. This zone is recommended for novice users and people with inactive lifestyles.
- Moderate load zone (general mode): 60-70% of the MHR. Suitable for most workouts that aim to burn fat effectively.
- High load zone (advanced mode): 70-80% of the MHR. Recommended for experienced people with a trained heart, the target zone is designed to strengthen the cardiovascular system.
- Zone of anaerobic load (short-term extreme mode): 80-90% of the MHR. Recommended for athletes working on individual programs in the presence of a coach.
Types of heart rate sensors for treadmills
Wired heart rate sensors
The first attempts to electrically measure the pulse appeared in the early 20th century. In 1902, Willem Einthoven received the first electrical cardiac signal using a string galvanometer. Its weight measuring instrument was 270 kg, but the principle of measurement has come down to our times. The heart rate measurements are based on the lead system (Einthoven's triangle), which registers the moment of electrical excitation of the ventricles.
The galvanometer used to measure heart rate in 1902
Modern treadmills are equipped with wired heart rate sensors. The principle of operation of such sensors is simple: two electrodes located on the handrails measure the potential difference, and the information is transmitted via wires to the analog-to-digital converter (ADC) of the console. There the information is processed and displayed on the screen.
The disadvantage of such a system is the high measurement error (20-30%), inconvenience of use and the speed of displaying real values.
It often turns out that only after 30-40 seconds of holding the sensors, one can judge the true heart rate values.
Console has wired heart rate sensors on handrails
Wireless heart rate sensors
Wireless heart rate sensors have a simple device and a number of advantages over wired devices:
- The most accurate heart rate measurements. Accuracy of wireless sensors +/- 1 bpm
- The convenience of use. The cardiac sensor is fixed in the region of the heart using a special belt. With the help of two electrodes, the potential difference is recorded. It is recommended to wet the electrodes with water to good contact... Further, an analog or digital signal is transmitted over the radio channel, which is fed to the console receiver and displayed on the screen.
- The ability to use cardio-dependent programs.
Wireless heart rate sensors have more accurate heart rate measurements. Accuracy of wireless sensors +/- 1 bpm
The disadvantages of this method are insignificant:
- The need to use a battery in the sensor. With daily workouts, the charge will last for 1 year.
- The inconvenience of using a cardiopathy belt during long workouts.
Most popular wireless heart rate sensors
To measure the heart rate, wireless sensors operating in the frequency range of 5 kHz are used. Sensors are coded (used in fitness rooms), and non-coded (intended for home use).
The leading leader in the heart rate monitor market is the company Polar... Along with it, you can find heart rate monitors on sale trade marks Sigma, Beurer, Oregon, Garmin, Suunto. The most budget models have a small set of functions and start at a price of 500 rubles. In the average price range of 3000 rubles, you can find high-quality and convenient heart rate monitors. Expensive models designed for intensive and professional use, often have a coded signal, are sold in the region of 20,000 rubles.
Many treadmill models come with a cordless heart rate belt, predominantly from Polar, that operates at a frequency of 5.4 kHz.
How do you know if you can use a wireless heart rate sensor on your machine?
Before buying a treadmill, it is worth checking the presence of a telemetric heart rate receiver in this model. Such technical information can be obtained on the official website of the seller, or in the instruction manual for the simulator.
Connecting a heart rate sensor
If the heart rate sensor is turned on for the first time, then you need to install the battery, which is also supplied in the kit. Further, the surface of the cardiosensor in contact with the body is moistened with water and the cardio belt is fixed on the chest. After turning on the simulator, the devices are automatically matched.
At a time when medicine did not have modern technical means of diagnostics, the pulse was measured by placing a finger on the artery, and the number of shocks of the artery wall through the skin was counted for a certain period of time - usually 30 seconds or one minute. This is where the name of this effect comes from - pulsus (lat. "Blow"), measured in beats per minute.
There are many methods for determining the pulse, but the most famous are the probing of the pulse on the wrist, on the neck, and in the area of the carotid artery.
After the appearance of the electrocardiograph (ECG), the pulse began to be calculated according to the signal of the electrical activity of the heart, measuring the duration of the interval (in seconds) between adjacent R waves on the ECG, and then recalculating into "beats per minute" using a simple formula: HR = 60 / (RR- interval).
An electrocardiogram can tell a lot about our heart and in addition to the pulse, but to take and decipher an ECG, you need equipment and a cardiologist, which you cannot take with you for a run. Fortunately, in modern world almost everyone can afford a heart rate monitor that measures heart rate while running and at rest.
How the heart rate monitor works
Pulse measurement by electrocardiosignal
The electrical activity of the heart was discovered and described at the end of the 19th century, and already in 1902 Willem Einthoven became the first to technically register it using a string galvanometer.
In addition, Einthoven was the first to record an electrocardiogram (he himself gave it such a name), developed a lead system and introduced the names of segments of the cardiogram. For his labors in 1924 he became a Nobel laureate.
In modern clinical practice, various lead systems (that is, electrode attachment schemes) are used to record ECGs: from the limbs, chest leads in various configurations, etc.
In order to measure the heart rate, you can use any leads - based on this principle, a sports watch was developed that can determine the heart rate.
Early heart rate monitors consisted of a box (monitor) and wires attached to the chest. The first wireless ECG monitor was invented in 1977 and has become an indispensable training aid for the Finnish cross-country skiing team. For the first time in mass sale wireless heart rate monitors entered in 1983, and since then have firmly occupied their niche in amateur and professional sports.
When designing modern sports gadgets, the lead system was simplified to two points-electrodes, and the most famous version of this approach is the sports chest strap (HRM strap / HRM band).
To obtain a stable and high-quality signal, it is necessary to moisten the "electrodes" on the chest strap with water.
In such straps, the electrodes are made in the form of two strips of conductive material. The strap can be part of the entire device or fastened to it with clasps. Heart rate readings are usually transmitted via Bluetooth to a sports watch or smartphone using ANT + or Smart protocol.
Pulse measurement with optical plethysmography
Now it is the most common method of measuring heart rate from the point of view of mass use, implemented in sports watches, trackers, and mobile phones. And the first attempts to use this technology were made back in the 1800s.
The constriction and expansion of the vessel under the influence of the pulsation of the blood flow cause a corresponding change in the amplitude of the signal received from the output of the photodetector.
The method is widely used in hospitals, later the technology was transferred to household devices - compact pulse oximeters that record the pulse and blood oxygen saturation in the capillaries of the finger. Great for intermittent heart rate measurements, but not at all suitable for continuous wear.
Heart rate monitors
The idea of measuring the heart rate from an athlete's wrist using optical plethysmography without the additional wearing of chest straps looked very tempting. The first to implement this idea in the watch Mio Alpha, which proclaimed their device a breakthrough and a new round in the measurement of heart rate. The measuring sensor module itself was developed by Philips.
Optical technology measures the pulse using LEDs that assess blood flow to the wrist. This means you can measure your heart rate without using a chest strap. In practice, it works like this: an optical sensor on the back of the watch emits light on the wrist using LEDs, and measures the amount of light scattered by the bloodstream.
Pulse registration method for photoplethysmographic sensors
For measuring the pulse, the area with the maximum absorption is important - this is the range from 500 to 600 nm. Typically 525 nm ( green color). The green LED for the heart rate sensor is the most popular option in smartwatches and bracelets.
Now this technology is well developed and introduced into mass production. The range of emerging devices with such technology is quite wide (smartphones, tracker bracelets, watches), and manufacturers sports devices are also not lagging behind - all the most significant companies are expanding their line of heart rate monitors with models with optical sensors.
Errors in the operation of optical sensors
It is believed that optical sensors accurately determine the heart rate when walking and running. However, as the heart rate rises to, say, 160 bpm, blood flow so quickly passes through the sensor area that measurements become less accurate.
In addition, on the wrist, where there is not much tissue, but a lot of bones, ligaments and tendons, any decrease in blood flow (for example, in cold weather) can distort the operation of the optical heart rate sensor.
One small study conducted comparative analysis accuracy of chest and optical heart rate sensors. The subjects were divided into two groups, in one group, the pulse was measured using a chest sensor, and in the other - using an optical one. Both groups were tested on a treadmill, where they first walked and then ran, at which time their heart rate was recorded. In the group with a chest heart rate sensor, the accuracy of heart rate measurement was 91%, while in the group with an optical sensor it was only 85%.
According to the head of the company Mio Global, currently no heart rate sensor can be compared to the accuracy of the chest strap.
Do not forget about specific situations when the optical sensor may not work. Wearing a watch over a running jacket, having a tattoo on the wrist, a watch that is loose against the skin, or exercising in the gym can all lead to inaccuracies in the measurement of heart rate using optical sensors.
Despite this, technological progress in heart rate measurement has led to the emergence of a useful alternative to chest straps, and by eliminating a number of disadvantages of optical sensors, we will get another powerful and precision instrument monitoring the pulse during sports.
What running indicators does the heart rate monitor allow?
Strictly speaking, advanced running dynamics is measured with a chest strap. Outwardly ordinary, inside the sensor consists of a transmitter and an accelerometer, thanks to which the runner's movement is analyzed. The same accelerometers are found in phones, footpods, tracker bracelets.
Advanced running metrics include three dimensions: ground contact time, vertical oscillation, and cadence, or cadence.
Ground contact time (GCT) shows how long your foot is on the ground during each step. Measured in milliseconds. The typical amateur runner spends 160-300 milliseconds on contact with the surface. As your running speed increases, the GCT value decreases, and as you slow down, it increases.
There is a relationship between the timing of ground contact and the incidence of injury and muscle imbalance in a runner. Shorter ground contact time reduces the incidence of injury. One of the most effective ways to reduce this is to shorten your stride (increase cadence), strengthen your glutes, and include short sprints in your training program.
Vertical oscillation (VO). Look at any professional runner - you will see that the upper half of their torso does very little movement, while the legs do most of the work of moving the runner.
Vertical wobble determines how much your upper half "bounces" as you run. These bounces are measured in centimeters relative to some fixed point (in the case of a chest belt, this is a sensor built into the chest transducer). It is believed that the most economical running technique involves the least vertical oscillation, and the reduction of vertical oscillation is achieved by increasing the cadence.
Cadence or cadence. As the name implies, the indicator shows the number of steps per minute. Quite an important parameter that evaluates running efficiency. The faster you run, the higher the cadence. A cadence of about 180 strides per minute is believed to be optimal for efficient and economical running.
Heart rate zones Knowing your maximum heart rate, different running watches can break your workout by heart rate zone, showing how much time you spent in a zone during your workout.
Have different manufacturers these zones are designated in their own way, but they can be divided into the following types:
- recovery zone (60% of maximum heart rate),
- zone for training endurance (65% -70% of the maximum heart rate),
- aerobic capacity training zone (75-82% of maximum heart rate),
- TANM zone (82-89% of the maximum heart rate),
- zone of maximum aerobic load (89-94% of maximum heart rate).
Knowing your heart rate zones will help you get the most out of each workout. We will talk about heart rate training in detail in the next article in the heading.
In addition to advanced running characteristics, modern heart rate monitors can measure and track several other interesting indicators:
EPOC (excess post-exercise oxygen consumption). Post-workout oxygen consumption shows how much your metabolism has changed after a run. We all know that running burns calories, but even after the workout is over, calories continue to burn. Of course, to replenish them, you need to recover efficiently.
Monitoring your EPOC can help you understand which workouts are the most energy-consuming and improve your recovery.
Calculated oxygen consumption (est. VO2). The current oxygen consumption indicator, calculated based on the maximum oxygen consumption ( VO2max) and maximum heart rate.
Maximum oxygen consumption (VO2max). The indicator reflects the ability of your body to consume oxygen. This is important because as this rate rises, your body can better and faster utilize the oxygen delivered to the working muscles.
The value of maximum oxygen consumption (MOC) increases with increasing fitness. It is one of the most important running metrics that is directly related to running economy. As in the case of determining the maximum heart rate, the best way VO2 max determination is laboratory testing, but a number of heart rate monitor manufacturers use algorithms for calculating VO2 max. Exercise helps to improve the values of this indicator.
Running performance A metric that uses VO2max (the global standard for aerobic fitness and endurance) to track training progress.
Peak training effect (PTE). Shows the effect of a training session on overall endurance and aerobic performance. The more trained you are, the harder you must train in order to achieve higher PTE numbers.
Instead of output
With heavy use, the heart rate monitor can be a great companion for the runner. It is extremely wrong to consider the heart rate monitor as an expensive toy, which is completely unnecessary for "serious" athletes. Decide on goals for the season, and then start building a training plan.
Remember that measuring and monitoring your heart rate during exercise - reliable way improve results and avoid overtraining.
For those who are just starting their running path, it is recommended to first monitor the heart rate during light runs, and only then move on to any training plan. The data from the heart rate monitor can help you understand how your body responds to stress.
However, there is no need to become a hostage to numbers and gadgets. Learn to listen to your body, evaluate the sensations from each workout, and numbers will become an important additional source of information.