What type of neuron contacts a muscle fiber and initiates a muscle contraction?

Motor neuron.

Explanation:

Muscle contraction begins with signal. The contraction occur when nervous system send signals. The impulse which is called signal is travel through a motor neuron.

The whole process include following three steps:

1) Message is traveled from nervous to muscular system and trigger the chemical reaction.

2) This chemical reaction causes the muscle fibers to reorganize in such a way that shorter the length of them which is called contraction.

3) when this signal is no longer remain , reverse chemical process occur and muscles relax.