Nowadays, people carry their phones everywhere, even while exercising at the gym. Only recently have equipment manufacturers noticed this and started to add a phone holder. For the time being, however, people put their phone on the floor or on top of the weights.
Many wearable fitness trackers already provide functionality of counting equipment exercise reps. But could an accelerometer attached to the structure of the equipment gives more information? If the phone is placed as shown in the image above, the movement measured by the accelerometer along the z-axis gives an estimate of the reps count, the exercise quality (defined below), while more subtle characterstics of the signal can provide information about the weight, the equipment type and consequently which exercise is being performed.
The information from the z-axis movement can be analytically extracted, while the more subtle signal is causes by a complex combination of factors which are not easy to work with (might requires computation intensive FEM calculations of each exercise equipment).
Here is a quick Jupyter notebook that counts reps of an exercise performed on Chest press machine!
Exercise quality measures and equipment identification will be treated in a seperate post.