The arena of an axon

Researchers try piecing together intel until a complete picture of the syndrome's etiology is developed. The earliest clinical evidence is not necessarily the original event! But, in the case of Amyotrophic Lateral Sclerosis, the first apparent event by most authors' reports is the disconnect of an axon from a muscle fiber. This is unlikely the actual first event because such disconnects happen naturally (or by injury) and possibly by necessity.
The Average Life Span of Skeletal Muscle Cells (seattlepi.com)
https://tinyurl.com/MuscleFiberLifeSpan

Thus a neuron's axon must find a way to connect a new muscle fiber (or reconnect an existing one). One of the amazing features occurring at the end of a neuron's axon is the build of a growth cone, which is a primary agent in the build of a synapse. Synapses are very small, estimated at around thirty nanometers:
Size of synaptic cleft - Human Homo sapiens - BNID 108451

Once a neuron's axon's growth cone reaches a location where a synapse could be built, it will literally try building another one . . . these are some of the 'agents' who work on the problem:
Growth cone - Wikipedia

Filopodia - Wikipedia

Lamellipodium - Wikipedia

If successful, the muscle fiber will become responsive to stimulation and contribute to the force the muscle produces.