Some time ago I wrote an article called Questions on What Is, and What Is Not HEMA, and recently I’ve been thinking about that question a little more. Firstly, I think that a differentiation must be made between historical European martial arts, as in martial arts that were practiced historically in Europe, and HEMA, as in the modern sporting practice. Viking sword and shield, as in the styles of fighting done with a sword and shield by the Scandinavian cultures that we refer to as the Vikings today, was clearly a historical European martial art; it was a martial art used historically in Europe. However, I would also argue that it is not part of HEMA, the modern discipline.
The reason for this distinction is sources. A Norse warrior living in the 9thor 10th centuries had no need to examine written sources to see if the way he was fighting with a sword and shield was historically authentic, whereas a 21st century practitioner cannot just fight with a sword and shield and claim his method of fighting is historically authentic. They must, or at least should, use evidence to back up their claims and demonstrate that what they are doing is likely to be historically authentic.