Accelerometer can work here I think - so long as you correct for drift by detecting when the foot
has stopped accelerating (ie is on the floor), and reset the velocity variable to zero. The drift for an
accelerometer over the 1/3rd second or so of a step shouldn't be too huge (for long periods its
horrendous due to the double integration).
You need proper 6DoF device really, the gyro to understand the various rotations so that the acceleration
vector can be integrated in the right direction and gravity subtracted out.
This sort of thing, basically:
