The giant motor units would be caused by reinnervation. Therefore at some point, his calf muscle was denervated and then reinnervated.
Motor units are made-up of an individual axon from a nerve and the group of muscle cells that the axon innervates (think of a nerve as a rope and the axons are the individual fibers that make-up the rope). One axon can innervate anywhere from one muscle cell to about a thousand muscle cells (it depends on the type of muscle).
When your husband's calf muscle was denervated, that means that some axons were damaged and lost contact with the muscle cells they innervated. Nearby axons that were not damaged reached out and reinnervated those denervated muscle cells, thus making the motor units bigger (i.e. those axons now innervated more muscle cells than they once did, making the motor units bigger).
One of the things the EMG measures is the size of the current generated by motor units and if the motor units are bigger than normal (i.e. have more muscle cells than normal), then more electric current will be generated. Therefore, giant motor units will be seen.
The reinnervation in your husbands calf muscle could have happened 6 months ago, 6 years ago, 20 years ago . . . there really is no way of telling.
I hope that helps. If it doesn't, please let me know.
just reading that made me think how wonderfull our bodies are to be able to automatically defend and repare itself.
i never thought medical science could be so awesome.
sadly it can only do this to a certain degree in some injurys/illnesses,well for now anyway.