This is a response more to the question of martial arts links with historical druids than to the idea of physical exercise in druidry.
Have any of you read the Sister Fidelma mysteries? While about an Irish nun/dailaigh in 7th century CE Ireland and environs, and also while being a series of murder mystery novels, the author (Peter Berresford Ellis, writing under the nom de plume Peter Tremayne) behind the series is a well-known and well-respected Celtic Studies scholar, and the Irish culture lived and described by the main character gives a lot of insight into Late Ancient/Early Medieval Irish culture. A culture that may or may not link up with ancient/historical druids, but interesting nonetheless.
Anyways, in this series, the author describes a sort of defense exercise, probably similar to some sorts of martial arts (I know nil about martial arts)? I'm quoting from the series website below. Here is the link: http://www.sisterfidelma.com/FAQS.htm
I hope others find this interesting as well.
TROID SCIATHAGID (Battle Through Defence)
Troid (also troit) = fight, battle, quarrel; sciath = root word for shield, defence, protection, guardian (Royal Irish Academy ‘Dictionary of the Irish Language: based mainly on Old and Middle Irish Materials)’
Prof Joseph Connolly (Orlando, FL), in his renewal letter, asked the following:
“I am a Fellow of the Society of Martial Arts in the UK, a professional society which operates the College of Higher Education of Martial Arts, as approved by Privy Council. I have written to Peter Tremayne through his publisher, seeking additional information on the martial art he attributes to Sister Fidelma, about which I have never been able to obtain any additional information. If you would, please ask him to elaborate on this and give a hint where a researcher might seek additional information.”
The author responds:
In Shroud for the Archbishop, Chapter 13, Sister Fidelma first resorts to an unarmed combat technique which she calls troid sciathagid or "battle through defence" and which, she explains to her companion, Brother Eadulf, that Irish missionaries learn as a means of defending themselves without having to resort to weapons.
There is no complete text, so far identified, that has explained in detail how this method of unarmed combat worked. But, from various passing references, I believe we can assume that it was a series of defensive kicks, blows and wrestling holds which are parallels to akido or a similar method.
Ruairi Ó Flaitheartaigh (1629-1718) in his work Ogygia seu Rerum Hibernicum Chronologia stated that Comrac Mac Airt founded three colleges at Tara, one of which was for teaching military science, as well as the use of weapons, strategy and so forth, wrestling and unarmed defence, were taught. Because no ancient reference was given by Ó Flaitheartaigh, Eugene O’Curry (1796-1862) in his three volume study Lectures on the manners and customs of the Ancient Irish was inclined to dismiss this reference as he did not think there were "regular professors and a regular system" of military instruction. But O’Curry contradicts himself when he talks about the military training warriors receive as part of a general education. If they received such training it must be that there were people who were qualified to instruct them and on a regular basis.
We can also see from many other references, particularly in the Red Branch Cycle, or Ulster Cycle, of Irish Myth, there is mention of such schools where warriors were so instructed and we find that sons of chiefs and children of the "higher classes" were sent to such schools where they were placed under the instruction of a warrior. Perhaps one of the most famous of these schools was that of Scáthach, a female warrior, who teaches the military arts to Cú Chulainn in the tale Tochmarc Emire. It was from Scáthach that the famous Ulster warrior learns the torann-chless (thunder feat) by which he could leap over the heads of his enemies when surrounded using no artificial aids. Reference to such tactics is made in Aided Oenfhir Aife (or, The Tragic Death of Aife’s Only Son) showing that Cú Chulainn relies not only on weapons to defend himself but on physical agility and using his opponent’s aggression to bring about their downfall.
In Cath Fionntrágha we have a reference to warriors fighting unarmed against one another. Prof. Kuno Meyer interprets this as "wrestling warriors" (1885) and in the version of the Rawlinson B487 manuscript of the 15th century the phrase tucadar trodchuir trena troid d’aroili is given also implying that they were fighting with their bare hands and had no weapons.
Certainly, wrestling was given high priority on the list of arts taught to Irish children not only as a recreation game and also introduced as a pastime at the fairs but as part of warrior training. And this form of wrestling was particular to the Celts. Indeed, there are countless references to a particular form of Celtic wrestling - even before Agincourt in 1415 it was reported that the Cornish fought under a banner showing two wrestlers in a "hitch" which was looked upon as their national symbol. Geoffrey of Monmouth, Layamon, Spenser and Milton all mention the prowess of Celtic wrestlers. Francois I of France and Henry VIII in 1520 sent Cornish, Welsh and Breton wrestlers to have a match at the Field of the Cloth of Gold. A particular form of wrestling survived in Cornwall, Brittany, Wales and Cumberland so that in the 10th century annual Pan Celtic Wrestling Tournaments were normal and Pan Celtic Gatherings such as those at Lorient & etc. There are references to a similar sort of wrestling surviving in some rural parts of Ireland and some contests taking place at the Donnybrook Fair in the 19th century.
When we find references to peregrinatio pro Christo using troid sciathagid to defend themselves from bandits (a mention I think, without checking, in Essai d’un catalogue de la littérature épique de l’Irlande, Paris, 1883, and talk of it being a defensive art, I think we can only interpret in way I have in the Fidelma books. Especially the references to Irish missionaries being taught to defend themselves "without inflicting violence" - a particular reference in the Mss of the former College of Irish Franciscans, Louvain (Fourth Report of the Royal Commission on Historical Manuscripts, 1874).
Of course, I admit that I have taken the few references that I have come upon and made an interpretation for the fiction of the Fidelma novels. It needs more time and more workers in the field to see if more information on this subject can be recovered. Alas, I now do not have time to undertake such a task. But one of the problems in finding dedicated workers in the field is the lack of funding and encouragement of researchers in the field of Celtic Studies.