I take a historical approach to HEMA, which in turn requires that I also take an athletic approach. I believe that we can never truly understand a topic unless we fully experienced it (and I believe its safe to say none of us experienced the Medieval era). However, we can at least try to get as close a reasonably possible; that is what we do in historical re-creation. Additionally, I believe that if you're going to re-create, do it right or not at all. To understand fully, we must experience fully. To experience fully, we must examine the entire context. Not examining something in its proper and full context is a gross error in historical research.
The subject in this scenario is the knight and his fighting techniques. We must consider the whole context in studying it and in recreating it. The knight trained constantly from the age of 7 and through his knighthood at 21. The knight was an ideal specimen of human physicality; he was a professional soldier. Not only did he learn the techniques of the sword, he honed his body to make it more efficient and better with that sword. If we are to re-create medieval martial arts, we must do this with this full context in mind.
None of us grew up in the hard life of a knight-to-be, and thus we are robbed of truly understanding that experience. Yet there remains many ways that we can get close to understanding to some degree. I can sign up for HEMA lessons and I can exercise. Either one alone does not give me an understanding of medieval martial arts. I can become as strong and fit as a knight through exercise and nutrition, but if I don't know how to swing a sword, I have gained little in terms of understanding the life of a knight. I could master the techniques of Talhoffer, but without being physically fit, I can be overpowered by sheer force and likewise, I have gained little historical understanding. To understand the life of a knight, I must both know the fighting style as well as be physically fit. Just as a knight was fiercely competitive about winning, so too must I be if I wish to recreate and understand the life of a knight.
Justice Charles Gray laid out 7 principles for historians. The 3rd principle is this:
"The historian must be even-handed in treatment of evidence and eschew 'cherry-picking'"
In other words, a true historian covers everything on a topic, not just that which is convenient. To disregard fitness and study on technique is a crime agains historical scholarship and it robs the historian of vital understanding.