The Correlation Of Acceleration Between Different Parts Of Human Body

BackgroundThe accelerometer is the most common used transducer in sports. The waveform of body’s acceleration can be tested using accelerometer, but the signal will be different according to different parts of body. Two aspects should be considered when placing the accelerometer:Firstly, the conveniences. The wrist and clothes are both appropriate places to fix the accelerometer easily, but the accuracy of the results may be affected because of the large range of motion. The second aspect is the accuracy. It will be good to accurately reflect the motion of the center of gravity. However, it will not be accurate if the motion is nothing about variation of center of gravity like biking or other sports mostly dominated by upper limbs.Therefore, the acceleration waveform is related to the placement of accelerometer and different movements. Even doing the same motion, different acceleration waveform will be shown if the wireless triaxial accelerometer is placed in different parts of the body. Additionally, the waveform will be also different according to different testing time. The similarity of waveform is indeed the correlation between them.ObjectiveThe higher correlation coefficient should be the criterion to determine the position of triaxial accelerometer. The main aim of this study is to explore the following four questions by wearing a triaxial accelerometer in different parts of human body with different movements:1. The repeatability of triaxial acceleration data in various parts of same person in different testing time.2. The repeatability of triaxial acceleration data in various parts of same person in different types of activities.3. The repeatability of triaxial acceleration data of the same part with one person in different time during walking.4. The repeatability of triaxial acceleration data of same part of different subjects during walking.MethodExperiment 1. Four wireless triaxial accelerometers (Noraxon company) were respectively worn on the left chest, right ilium, right shoe and left shoe. A wireless ECG sensor was used for testing of ECG. Experiments were carried out four times. Every time the participant need to do walking, running, jumping, riding bike and stair-climbing in the same place in morning for four days. Then assess the repeatability of different positions’acceleration data by calculating correlation of the data in the 4 time’s experiment.In experiment 2 we choose walking for further detailed investigation. We use 16 wireless triaxial accelerometer (Delsys company,1.5g range,296Hz sampling frequency) on 4 males of Shanghai university of sport. Positions of 16 accelerometers: one on the middle of the forehead, one on occipital median, one on each side of the intersection of mid clavicular line and the seventh rib, two on right chest and left chest, two on right iliac crest and left iliac crest, one on each back of wrist, one on each founder of thigh, one on each ankle, one under each arch of foot. Four subjects need to do walking 3 times a day, each time for 30 seconds, and the test last for: consecutive days.Result1. We respectively calculate the correlation between the average value of each experiment and average value of all experiments. We calculate the correlation between the average of five steps in experiment 1 and the average of all four experiments’, and the results show that the repeatability of data of different parts is stable.2. The correlation between the various projects in experiment 1 show that the repeatability of walking, running and stair-climbing is high. For jumping, the repeatability of right hip is better, and it’s also good in the direction in front of the chest, but it is not okay in other directions. The repeatability is better when fixing the accelerometer on hips than shoes. The repeatability is lower when subjects did biking than other activities. However, for biking, the repeatability is best when the accelerometer was fixed on shoes.3. For the same person in experiment 2, the acceleration curves of each gait cycle in different parts of the body during walking are highly similar.4. In experiment 2, the average of correlation coefficient between different body parts is still stable and highly similar. The similarity is only slightly lower when it’s fixed on wrist, which probably due to the higher freedom of swinging arms.5. In experiment 2, correlation coefficients between different subjects are various, this may be due to the difference between individual walking motion.Conclusion1. The triaxial accelerometer can be placed on all parts of the body if just consider the steps recorded only, and the data we got could be in high accuracy.2. The triaxial accelerometer can’t be placed on the clothes because the accuracy of the data may be affected.3. The triaxial accelerometer should be placed under the soles to get stable data in view of different people and different kinds of sports. If we want to make it more easier to use the triaxial accelerometer, we can just place it on wrist. The data we got from soles will be more stable than wrist.