I have read all the posts in this thread. I am working on a project for kayaking where an accelerometer is gripped on the athletes wrist and he/she starts kayaking the acc data is collected from the run. The problem statement is the characterise events like paddle entry, exit, velocity, displacement etc. I am using a 3 axis accelerometer by I am assuming that when I collect the data g also plays a role and if I integrate it in either domain g will act in a direction unknown and therefore the results for velcoity and displacement will be inaccurate. Mind you there are no gyroscope or orientation reading available. It would be great if someone could give me an idea on how to do this, and also when the paddle hits the water there is acc jerk ( I like to call it)is produced which I used to characterize paddle entry. But since in kayaking the paddle entry and exit is really fast sometimes the jerk isnt much to charaterise these events. I am using matlab to do this. My basic approach is the pass the extrema function to get the maxima of the signal which is point of max acc i.e when the left paddle goes inside water assuming that the right wrist has the accelerometer on it. At this point the right paddle is in the air and almost static. after this when the right paddle goes inside water there is a decrease in acc and then it reaches the lowest point inside water where the acceleration is assumed to be minimum. Also in my calculations I assumed that the the lowst point inside water is the midpoint between the paddle entry and exit and there the paddle exit time was found out. Since the data wasnt very great many paddle entry and exit points were missed out. I tried all this in the time domain. Any suggestions would be appreciated.