MPU 6050 Accelerometer Frequency Response

I am making a project that requires an accelerometer to be attached to the waist of a person that will detect the movement frequency of that subject. I have searched everywhere but I cannot figure out how to extract frequency from the accelerometer. I suppose it has something to do with the frequency response but I am unable to figure it out. Can anyone help me solve this problem?
I want to have these frequencies fed to an Arduino board that will do other operations based on these values.

Frequency would be an indirect calculation.

You collect sample data at regular intervals.
The acceleration readings at each sample allows you to calculate change in speed for each axis, which can be used to determine overall velocity changes.

Plot those (store a number of samples in an continuously updated array) and eg. look for changes in sign, as reversals of direction. The number of samples between those (time) gives you period; the reciprocal of period is frequency.

You could do a similar thing for each axis rather than combining them.

Can I have a specific frequency value? The normal movement frequency is around 3Hz. I want to check if the frequencies are closer to this or not to monitor the movements or walking patterns of a person.

Store enough samples so there is always several seconds of data are in the array, eg. 10 seconds worth.

Then run an FFT algorithm on the array at regular intervals to get the overall frequency / spectral data.