Wearable feedback on sports performance
This report describes the process of designing the Globus, a smart shirt that measures that back posture will working out by measuring the stretch in the shirt and uses vibration to give feedback to the user when they have an incorrect posture. A questionnaire has been carried out for this project which showed that fitness is the most practiced sport. This is due to the fact that fitness can be practiced as both a primary and secondary sport. The most important factor within fitness is posture. Mistakes in posture decrease the effectiveness of the workout and can even cause injuries. Fitness related injuries are mainly located in the back and shoulders. Globus is focused on non professional athletes from 18 49 years old that work out 1 2 times a week, with or without a training buddy. Observations in the gym showed that most mistakes that are made are related to the back. An arched back puts too much pressure on the lower back. This can be caused by not looking in the right direction. Looking down forces the spine in the wrong direction and makes you arch your back. This can cause muscle pain or even a hernia, because of damaged spinal discs. A natural curved back is considered to be between 165 and 195 degrees according to research performed for this project. Less than 165 degrees is a rounded back and more than 195 degrees is a sway back. A market analysis performed for this project showed that there are similar products that give feedback on back posture. Most of these products are connected to a smart device and use gentle vibrations as a way of feedback. Prices vary between 60 175. A questionnaire showed that people are willing to spend between 75 125 on a new smart shirt. Research of Mattmann Troster showed that placing stretch sensors in the back of a shirt can be used to distinct between several movements such as lifting shoulders, bending sideward and bending forward. This research was based on changes in resistance of the stretch sensors. A research performed for this project on resistive stretch sensors showed that they do not respond linear to stretch and have a maximum resistance at 25% of the 50% maximum stretch. Moist (sweat and water) have great influence on the sensor readings. Other concepts for stretch sensors are: conductive rubber, capacitive plates or inductive pattern. A comparison was made between these concepts, which showed that the capacitive plates have better washability due to the possibility to laminate the electrodes and it also has a linear response to stretch, which can be measured with ordinary electronics. The capacitive stretch sensor has two parallel moving fabric conductive electrodes. The overlapping area is a measure for the capacitance (as well as the distance between the electrodes) Test are carried out to determine the best location for the sensors in the back of the shirt to distinct between an exercise being carried out with a straight back or a rounded back. The stretch in back of the shirt was measured by drawing a matrix of dots and measuring the distance between these dots. The heat maps of the stretch of a rounded back and a straight back (per exercise) are subtracted from each other to see the optimal location for the sensors. This location is just below the ribs at approximately 60mm horizontally from the spine at both sides. A fully functional prototype was made for testing the performance of the product, which included a Bluetooth LE module, vibration motor, RGB LED and other electronics. The moves during the workout, therefore the device calibrates every time a measurement of back posture is started. Relative stretch is measured from this calibrated starting value. The prototype showed areas for improvement after testing with users, which has led to the final design of the Globus. Manufacturing, packaging and shipping costs are determined. A total investment of 350.000 is needed for a first batch of 10.000 products. The Globus will be sold in a bundle and separate (shirt and electronics) The bundle will be sold for 129, a separate shirt for 49 (independent of the size) and separate electronics for 99. The break even point is at 3.000 sold bundles. A maximum profit of 718.800 can be achieved with the first batch. The company Under Armour is a desired partner for the Globus. They have brand awareness in the fitness market and already sell the shirts that are needed for the sensors of Globus. They recently announced three smart products for the sports market including a fitness tracker at the Consumer Electronics Show 2016 (CES) Under Armour can upgrade their shirts and compete in the rising smart sports market. Future partners could be outside the fitness world, such as companies that prevent RSI or support rehabilitation. Further development for the product could take place on maintaining a constant distance between the two electrodes of the sensor. The current sensor is influenced by pressure from the outside. The shirt should also be kept in the same place to get accurate readings. The accuracy of the readings could also be improved by shielding the sensor or isolating the conductive thread in the shirt.