A Wearable IDC-Based Capacitive Sensing Belt for Real- Time Respiratory Monitoring and Weekly Athletic Performance Evaluation

Breathing is the most constant rhythm of human life, a silent engine that powers every thought and movement. In the world of sports science and medicine, tracking the speed and depth of this rhythm offers a window into how hard the body is working, how quickly it is tiring, and how well it is adapting to training. For decades, measuring this vital sign has relied on bulky equipment or uncomfortable straps that struggle to function when a person is moving. Traditional tools often fail to distinguish between the natural rise and fall of a chest during a run and the jarring motion of the body itself, leaving coaches and athletes with data that is either too noisy to trust or too cumbersome to wear. The challenge has long been to create a device that is as unobtrusive as a belt yet sensitive enough to hear the subtle mechanical shifts of the diaphragm, the primary muscle responsible for drawing air into the lungs, even while the wearer is in motion.

To solve this, researchers at Universiti Malaysia Sarawak have developed a new kind of wearable belt that uses a flat, flexible sensor to listen to the body's breathing in real time. Instead of using heavy electronics or rigid wires, the team built their sensor using a technique similar to printing a circuit on a piece of plastic. They printed a pattern of tiny, interlocking fingers made of conductive carbon ink onto a thin sheet of polyester. This pattern, known as an interdigital capacitor, acts like a delicate electrical net. When the belt is worn around the midsection, just above the waist, these printed fingers sit close to the skin. As a person breathes, the diaphragm moves up and down, changing the distance between the sensor and the body. This movement subtly alters the electrical field around the printed fingers, causing a measurable shift in the sensor's electrical capacity. The system is designed so that when the diaphragm pushes up during an exhale, the electrical signal increases, and when it pulls back during an inhale, the signal decreases, creating a clear electrical map of every breath.

The researchers tested this belt by having a user wear it while performing various physical activities, from light movement to intense exercise. They found that the sensor could detect the breathing cycle with remarkable clarity, even as the body moved. The device showed a high degree of consistency, meaning that if the same amount of pressure was applied, the sensor gave the same reading every time, with very little lag or confusion between the start and end of a measurement. In a continuous test lasting over eight minutes, the belt tracked a steady breathing pattern without losing its signal, proving that the printed carbon ink remained stable and reliable under the stress of movement. The system also demonstrated that it could distinguish between different levels of exertion, showing a faster breathing rate as the physical activity became more demanding, which is exactly what one would expect from a healthy human body under stress.

To make this raw data useful, the team paired the belt with a custom software program that runs on a computer or tablet. This software acts as a filter, using a smart set of rules to ignore the random jiggles caused by walking or running and focus only on the rhythmic rise and fall of breathing. It displays the breathing pattern on a screen in real time, showing a live graph of the breaths as they happen. To make the information easy to understand at a glance, the program uses a simple color-coded system on an animated human figure. When the breathing is calm and within a normal range, the sensor area on the figure glows green. If the breathing becomes slightly irregular or the effort increases, the color shifts to orange. If the breathing becomes too rapid or erratic, the color turns red, signaling a critical state. This visual feedback allows an athlete to see their physiological state instantly without needing to interpret complex numbers.

Beyond immediate feedback, the system is designed to track progress over time, offering a way to measure how an athlete's body adapts to training over the course of a week. By recording the breathing rate every day under the same conditions, the software can calculate whether the athlete is becoming more efficient. If the breathing rate drops over the week while the exercise intensity remains the same, it suggests the body is getting fitter and requires less effort to perform the same task. The researchers validated this approach by comparing the breathing rate on the first day of the week against the average rate over the entire seven days, providing a more reliable picture of improvement than a single snapshot could offer. This method allows for a personalized view of performance, moving away from generic standards to a system that learns and reports based on the individual's own baseline.

The result is a low-cost, non-invasive tool that bridges the gap between high-tech sensing and everyday athletic training. By combining a flexible, screen-printed sensor with intelligent software that filters out noise, the system offers a way to monitor respiratory health and performance continuously, without the discomfort of traditional medical devices. The study confirms that this approach works reliably, providing a stable and repeatable way to measure breathing patterns in dynamic environments. While the current testing involved a single subject for self-assessment, the technology demonstrates a clear path toward a future where athletes and coaches can rely on a simple belt to gain deep insights into the body's most fundamental rhythm, turning the invisible act of breathing into a visible, actionable metric for better performance.