1 Introduction

Currently, according to the World Health Organization (WHO) [11], overweight and obesity have become one of the main factors of disability and death worldwide. Overweight and obesity are defined as an abnormal or excessive accumulation of fat that can be harmful to health.

Overweight and obesity are defined as abnormal or excessive fat accumulation that may impair health. Body Mass Index (BMI) is a simple index of weight-for-height that is commonly used to classify overweight and obesity in adults. It is defined as a person’s weight in kilograms divided by the square of his height in meters (kg/m\(^{2}\)).

World Health Organization [11] continues explaining, Obesity is one of the most pervasive, chronic diseases in need of new strategies for medical treatment and prevention. Obesity is defined as excess adipose tissue. There are several different methods for determining excess adipose (fat) tissue; the most common being the Body Mass Index (BMI). Obesity is a disease that affects more than one-third of the U.S. adult population (approximately 78.6 million Americans).

People who have obesity, compared to those with a normal or healthy weight, are at increased risk for many serious diseases and health conditions. The main causes that origin overweight and obesity is due to the consumption of high-calorie foods very rich in fat and to their sedentary lifestyle [11] and in turn, can cause cardiovascular disease, high blood pressure, diabetes mellitus type 2, hyperlipidemia, different types of cancer, degenerative arthropathy and psychological disorders [2].

Most overweight people want to perform physical activities to lose weight and enjoy good health, but due to the sedentary lifestyle that they have been living and the lack of good physical condition, it can be dangerous to start doing certain physical activities suddenly. Given this, the main cause of death can be a heart attack.

In these situations, there are new technology devices to measure physical activity of a person, that can serve to have control over physical intensity levels that have and consequently establish exercise programs when it is necessary to lose weight or maintain a certain level of exercise derived from a medical prescription [3].

The most used devices to measure the intensity of physical activity are heart rate sensors; since heart rate is an adequate indicator to estimate the level of effort that represents a physical activity. One of these devices is BASIS B1. This device belongs to the Intel company and has a highly effective heart rate sensor.

Another way to measure physical activity is by triaxial accelerometers that measure frequency and magnitude of accelerations and decelerations of body movement to monitor the intensity of physical activity of the subject. Triaxial accelerometers determine intensity and number of movements in three axes (x, y, z).

Some examples of these devices are FitbitBlaze and Applewatch, which are wrist-type watches that allow measuring physical exercises such as running, cycling and cardio. These devices are able to monitor the activity when a person sleeps, their diet, in addition to being able to synchronize with smartphones and are currently competing strongly in the market [4].

One more of these new innovative devices and it will work on this research project to measure the acceleration of movements is GENEActiv [4]. GENEActiv is the raw data accelerometer in form of a bracelet, useful for measuring physical activities and frequencies of movement during daily activities.

Some investigations that use GENEActiv device are related to lack of physical activity and obesity and overweight. A sample is shown in the research project “Project Energise: Using participatory approaches and real-time prompts to reduce occupational sitting and increase physical activity in office workers”, that conducted a study in 57 office workers (age 47 ± 11) who have office work where it shows a sedentary lifestyle who they are living due to their kind of work and this opens the door to possible chronic diseases [5].

An opportunity to perform an analysis that shows the relationship between a heart rate sensor (BASIS B1) and a motion sensor (GENEActiv) is this research project.

2 Related Works

In [8], Calibration of the GENEA accelerometer for assessment of physical activity intensity in children, the study established intensity levels of activity using the GENEA accelerometer and by calibration with oxygen consumption (VO2). In this study, forty-four children, aged 8–14 years, were taken into account, who performed eight activities (ranging from the supine position to a medium-speed race) while carrying three GENEA accelerometers (one on each wrist and another on the right side of the hip), an ActiGraph GTIM on the hip and a portable gas analyzer. The GENEA showed good validity in both wrists (right: r = 0.900, left: r = 0.910, both p < 0.01), but the monitor placed on the hip showed significantly greater validity (r = 0.965 p < 0.05). In conclusion, GENEA can be used in children to accurately assess the intensity of physical activity, either in the wrist or hip.

In [10] is considered an architecture of wearable health monitoring system composed by wearable sensor system, network transmission system and the information processing system on the basis of the three-layer architecture of the internet of things. These data collected are transmitted through Bluetooth technology to a gateway for providing real-time monitoring. All data acquired through network are transmitted in real time to the database server.

Another study [1] entitled: Healthy obesity and objective physical activity, it aimed to examine the differences in moderate to vigorous physical activity between healthy and unhealthy obese groups by using questionnaires answered by the participants themselves, as well as with the evaluations of an accelerometer placed on the wrist.

The analysis was performed on 3,457 adults aged 60–82 years (77% males). The differences between groups in physical activity, based on questionnaires and evaluations with the triaxial wrist accelerometer (GENEActiv), were examined using linear regression. When doing the evaluation with the GENEA (P = 0.002) it was determined that the healthy obese adults did a more physical activity than the unhealthy obese adults. In conclusion, it was found that there was greater physical activity in healthy obese than in obese adults not healthy, when measured objectively (accelerometer), which suggests that physical activity has an important role in promoting health in obese populations.

The work [7] presents a design and implementation of a testbed for AmI using Raspberry Pi mounted on Raspbian OS. It is analyzed the optimized link state routing (OLSR) and wired equivalent privacy (WEP) protocol in an indoor scenario, and mean shift clustering algorithm considering sensing data.

In [6], Physical Activity in Hemodialysis Patients Measured by Triaxial Accelerometer, it published in the journal BioMed Research International mentions that there are several factors that can contribute to a sedentary lifestyle among patients on hemodialysis (HD), including the time that they go on dialysis. The objective of this study was to evaluate the characteristics of physical activities in the daily life of hemodialysis patients through the use of a triaxial accelerometer and the correlation of these characteristics with physiological variables.

Nineteen patients in HD were evaluated using the DynaPort accelerometer and compared with nineteen control individuals (not ill), with respect to the time spent in different activities and everyday situations, and the number of steps when walking. Patients with HD were more sedentary than control individuals because they spend less time walking or standing and spend more time in bed.

The sedentary lifestyle was more visible in the days of dialysis. According to the number of steps given per day, 47.4% of hemodialysis patients were classified as sedentary versus 10.5% in the control group. The level of hemoglobin, the muscle strength of the lower limbs, and the physical functioning of the SF-36 questionnaire correlated significantly with walking and active time.

3 Evaluation Overview

Intensity reflects the speed that an activity is performed or the magnitude of the effort required to perform an exercise or activity. It can be estimated by asking how much a person has to strive to perform that activity [11]. The World Health Organization [11] defines the following types of physical activity intensities:

  • Mild activity: It refers to natural movements, simple, that do not require much effort (walking, getting up from a chair).

  • Moderate activity: Indicates moderate strength exercises (normal running, dancing).

  • Vigorous or intense activity Requires a large amount of effort and causes rapid breathing and a substantial increase in heart rate (playing football or basketball match by actively intervening).

ChooseMyPlate.gov website [9] defines physical activity simply means movement of the body that uses energy. For health benefits, physical activity should be moderate or vigorous intensity.

  • Moderate physical activities include: Walking briskly (about 3 miles per hour), bicycling (less than 10 miles per hour), dancing, golf (walking and carrying clubs), water aerobics, canoeing, and tennis (doubles).

  • Vigorous physical activities include: Running/jogging (5 miles per hour), walking very fast (4 miles per hour), bicycling (more than 10 miles per hour), heavy yard work, such as chopping wood, swimming (freestyle laps), aerobics, basketball (competitive), and tennis (singles).

As instruments to estimate the intensity of physical activity, a BASIS B1 Smartwatch was used, that is a device that calculates the heart rate. This device is a bracelet and is worn on the right wrist. The BASIS B1 is capable of noticing exercises (walking, running, cycling) and keeps track of the heart rate all the time.

We also used a GENEActiv bracelet, that contains a motion sensor. GENEActiv produces raw data, useful for the measurement of physical activities and frequencies of movement during daily activities. This device is scientifically validated by numerous investigations.

GENEActiv device is worn on the hip (GENEActiv is bracelet but was adapted to a belt for wearing on the hip), studies suggest that placing on the hip makes a better estimation of the intensity of movements during physical activities because it is a point close to the center of mass, it also allows to represent values that would be obtained from a smartphone with motion sensor.

Physical activities consisted of performing physical effort, therefore, all participants walked and ran on a treadmill at different speeds and under a certain period of time. In detail, the activities were: walking (speed: 3 Km/h), jogging (speed: 5 Km/h), and running (speed: 7 Km/h). For each speed, the execution time was at least three minutes, that was sought to reflect the physical effort in the motion sensor and heart rate.

Based on the data obtained from both sensors, mathematical methods were applied to show the relationship of the intensity level between both devices. Once different evaluations were made, the model that best reflected the relationship between both devices was selected.

4 Experimental Results

Equipment

To measure the intensity of physical activities, two devices were used: In Fig. 1 (left) BASIS B1 (heart rate sensor) and Fig. 1 (right) GENEActiv (motion sensor).

Fig. 1.
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Basis 1 device (left) GENEActiv device (right)

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As we mentioned, overweight and obesity are defined as an abnormal or excessive accumulation of fat in a person’s body that can be harmful to health [11], while, the BMI (Body Mass Index) is a formula that uses both weight and height to estimate body fat.

All tests were done using a treadmill, the speed in K/h in these experiments was setting on the sensors for collecting values of physical intensity measurement according to each device. Figure 2 (left) shows to the GENEActiv device placed on the hip, it also shows that a belt was used to hold the device. BASIS B1 bracelet device was placed on the wrist as is shown in Fig. 2 (right), each user wears this device on the right wrist.

Fig. 2.
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GENEActiv device placed on hip (left) and BASIS B1 device placed on wrist (right)

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This project used a non-probabilistic sampling, where were chosen participants for convenience, in Table 1 we summarize all data of the participants. To measure physical activity, 11 men and 9 women were selected, who had time to perform all the tests. These studies were conducted on people between 20 and 30 years old, regular or average weight, overweight or obesity (determined according to their BMI) and who did not suffer from any type of disease that could be aggravated during the test or affect the readings of the motion and heart rate sensors.

Table 1. Respondent’s data
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Fig. 3.
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GENEActiv bracelet and BASIS B1 devices placed on wrist and hip, respectively.

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Our tests were carried out at the gym, where a treadmill is located. At the time of the activity, participants wore a BASIS B1 bracelet on their wrist (right hand) and a GENEActiv on their hip, because it is an ideal place to measure physical activity since it is near the center of body mass. See Fig. 3.

GENEActiv device obtained samples at a frequency of 75 Hz generating 75 samples per second. These 75 samples are summarized by the device in such a way that it has only one value per second for each of the axes. Table 2 is a small sample of the x, y, and z values for 10 s. To obtain data from the BASIS B1, it was only necessary to touch the screen of the device and record the amount that reflected the heart rate.

Table 2. Sample of data obtained by the GENEActiv
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Table 3 shows the final results of a female participant, where the intensity levels at the different speeds turned out to be the same with the different devices.

Table 3. Female - intensity level
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Regarding the final results of a male participant are shown in Table 4, where the intensity levels with both devices and at different speeds turned out to be the same.

Table 4. Male - intensity level
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Table 5 lists the final results of a female participant (Number 5), who has the average age corresponding to all the participants. The intensity levels with both devices at the different speeds turned out to be almost the same, the exception was in the 5 km/h test, where the results of the participant number 5 are reviewed, here there was a small difference in level but it is not considered relevant.

Table 5. Average age - intensity level
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Table 6 shows the final results of a male participant (Number 12), who has the average weight of all participants, the intensity levels for both devices at different speeds turned out to be very similar, the exception was in the 5 km/h test, where this participant obtained a vigorous level with GENEActiv and Moderate level with BASIS B1, it could be appreciated that the Vigorous level was the result of the intense style of participant number 12, when running freely on the treadmill.

Table 6. Average weight - intensity level
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In regards the final results of a female participant (Number 4) are shown in Table 7, He has the average height of all the participants, the intensity levels at different speeds for both devices were practically the same.

Table 7. Average height - intensity level
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Table 8 shows the final results of a male participant, who has a light intensity level at all speeds by the BASIS B1 device. The result was produced because participant 11 is a person who practices a lot of sport, and since the BASIS B1 measures the heart rate, this person showed a low rate of heart rate at performing the activities. It is established that usually, people with the very good physical condition have a lower heart rate compared to those who lack good physical condition.

Table 8. Person with unequal intensity level
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5 Conclusions

This article evaluated the relationship between values of motion and heart rate to measure the intensity of physical activity of overweight or obese people. For this, a group of people performed different physical activities.

According to the values showed in the results of different physical activities, through a series of mathematical operations and an analysis to locate the results in the different ranges of physical intensity, it was possible to obtain the physical intensity level from each sensor.

Both the BASIS B1 and the GENEActiv showed a very similar level of intensity for each participant, hence means that at a given moment the movement sensor can be used to estimate the physical activity of a person, specifically an activity where is used the entire body to perform it, or else, an activity where there is no significant muscular effort to try to lift or load a heavy object.

It is also concluded that to estimate physical activity you can make use of the motion sensor contained in a smartphone, thus having financial savings if it already has one. That is, an additional device is not necessary.

As shown in Table 4, the use of a motion sensor is not useful if the person in whom it is applied practices a lot of sport, since due to its very good physical condition it will not be reflected by the motion sensor calculation of the intensity level.