Does anyone remember the definition of wearable fitness or fitness tracker a few years ago? Probably not. FitBit and the other apps that tracked everything from our breathing to our diet were still just ideas. Livestrong bracelets were the closest we came to making statements about our body. But today, fitness trackers have become part of our daily wardrobe. So what exactly is a fitness tracker and what is the excitement all about?
Fitness tracker is a wearable device with sensors embedded in it. It is capable of measuring and analyzing physical activities and body functions. Few are capable of measuring heart rate, body composition, respiration rate as well. Fitness trackers are also known as activity tracker or fitness tracker band.
How does a fitness tracker work?
Many think that the system complexity of fitness trackers are much lesser than a full-blown smart watch. However, that might not be entirely true. A fitness tracker is similar to a smartwatch in lot more ways than you think. Let’s understand a fitness tracker first. It has a 5 layered architecture.
Sensing layer: The sensing layer has sensors embedded in the device, these sensors collect data like number of footsteps, heart rate, body temperature etc. The data collected by sensors are sent to servers using Wide Area Network (WAN) such as Global System for Mobile communication (GSM), General Packet Radio Service (GPRS) and Long Term Evolution (LTE).
Media Access Control (MAC) Layer: This layer is responsible for device monitoring and control, quality-of-service management and power management.
Network layer: This layer takes care for transmission, routing and addressing using Ipv6.With IPV6 address allocation and management can be done more efficiently and hence chosen over other internet protocols.
Processing and storage layer: In this layer the data received from the sensing layer is analyzed and stored in the databases. This layer is also responsible for security control.
Service layer: This layer provides the analyzed and processed data to other services like mobile application on Android or iOS.
Sensing layer is the one differentiating factor which distinguishes one fitness tracker from another. On excavating the sensing layer, we get to see tiny sensors closely watching each move and constantly tracking them. Let’s take a close look at few of these sensors.
Accelerometers
Accelerometers are electro-mechanical device capable of measuring acceleration forces which is intensity and direction of motion.
This tiny sensor of size 1/50th of an inch has a housing that is fixed to the base of the wearable and a flexible comb like silicon tethering in between fingers of the accelerometer. By measuring the motion of the silicon section a change in the orientation and speed can be determined.
The three fingers make up a differential capacitor: That means if the center section moves, then current will flow and the amount of flowing current is correlated to the acceleration.
Most fitness trackers use accelerometer with 3 axes capable of measuring position in 3 dimension, for increased accuracy.
- Global Positioning System
Commonly popular by its acronym GPS. This sensor pins your location by listening to satellite orbiting the earth. According to NASA GPS uses 30 satellites orbiting at a height of 16,000 miles and travelling at a speed of 9,000mph above the Earth.
If the device could identify how far it is from 4 of 30 satellites, then it has successfully pinned down the location on earth.
- Galvanic Skin Response Sensor
Galvanic Skin Response Sensor measures the electrical conductance of the skin with the help of the 2 electrodes attached to the hand. Strong emotion cause stimulus to the sympathetic nervous system resulting in more sweat secretion by sweat glands, hence increases the electrical conductance of skin. When you start to sweat either from exercise or other stimulus the fitness tracker will detect it and after correlating it with data from other sensors the tracker will know the level and intensity of the activity, hence this allows better activity tracking
- Optical heart rate monitor (OHRM)
The optical heart rate sensor uses a method called photoplethysmography (PPG) to measure the heart rate. PPG light is shined on the skin and the light scattered by blood flow is measured. The light gets scattered in a predictable manner depending on the blood pulse and the blood flow volume.
The Optical heart rate monitor has 2 primary components
- Optical emitter: It has 2 LED’s that shines the light on the skin. Because of wide variations in the skin tone, thickness, and morphology associated with diverse set of consumers, most high end OHRM’s use multiple light wavelengths that interact differently with different levels of skin and tissue.
- Digital Signal Processor (DSP): The DSP captures the refracted light and converts it into 0s and 1s that can be in turn converted to meaningful heart rate data.
- Bioimpedance sensors
The bioimpedance measures how well the body resists the flow of electric current. The impedance is measured by applying a small electric current via a pair of electrodes and the resulting voltage is picked-up with an another pair of electrodes.
Tissue consist of many cells and membranes. The membranes are thin but have higher resistivity, but the fluid within and outside the cells have higher conductivity. Membranes with higher resistivity store the charges and behave as small capacitors.
With the help of these electric properties of the cells and membranes, the sensor measures tiny voltage changes at a pair of receiving electrodes and measures the impedance (Z) using the below mentioned formula,
Bioimpedance sensors can measure:
- Skin water content
- Body composition
- Blood volume
- Oxygen in the blood
- Heart rate
Temperature sensor
Just the temperature of the body can give many important insights about your health condition. Raising temperature reflecting on the fitness tracker screen could be a result of high physical activity, but if your heart rate is not increasing accordingly then it is a clear indication that you are getting sick.
The job of fitness tracker does not stop at data aggregation from the sensor. Companies have written complex algorithms to cut noise from the signals sent by the sensors and analyze the signals to come up with meaningful insights about your health and fitness. These algorithms make one fitness tracker better than another.
The system complexity of a fitness tracker looks to be nothing less than a full-blown smart watch, does it?
