BURLINGTON -- ''Thwack!"
My longsword slashes through my enemy's helmet.
''Ow!" he cries. His eyes gleam through his visor. ''Good!"
Yet still he stands. My foe -- this ''Sir David of Chelmsford" -- is worthy, indeed. I strike another death-dealing blow, this between his neck and shoulders.
''Excellent!" he replies, still grinning. ''Try again."
A third lethal blow, an ''oberhau," straight down and double-handed with all my might, and my blade cleaves his brain in two. I wait for the torrent of blood to pour down his face, the involuntary twitching of his nervous system.
Nothing. Shouldn't he be at least a wee bit stunned?
I pummel him again and again. Despite my ruthless attack, Sir David is in fine fettle. He's not even angry.
''Nice work," he says. Now he wants to smite me.
Whereupon Sir David unleashes a whirlwind of sword blows. I should be dead, I think, as my head falls to the floor and rolls away.
Of course, the blood and gore exist only in my imagination. Our longswords, made of a nylon bushing stock and polyethylene core, could leave a sharp sting on an unprotected face, but otherwise they are fairly harmless. My nemesis, David Martelli, 22, of Chelmsford, is in fact not an enemy knight, just my sparring partner, and an instructor at Guard Up!, a martial arts facility whose Sport Weapon classes let you live the sword-fighting fantasy -- with padded weapons and protective armor.
''I think everyone is born wanting to pick up a sword and swing it in the defense of a righteous cause," Meghan Gardner, 37, director of Guard Up!, tells me later. ''Whether that is to defend your friends, slay the dragon, or whack your boss upside the head in class after a hard day of work. We let you live the fantasy and be the hero."
Tall, slender, and buff, Gardner, of Bedford, began her martial arts training at age 12. She is also an avid rugby player, snowboarder, motorcycle racer -- and mother of two girls. I wouldn't want to be on the wrong end of her rapier.
Gardner explains that while her facility still teaches traditional martial arts, she saw a market for those who wanted to fight like J.R.R. Tolkien's Aragorn or George Lucas's Anakin Skywalker. Fencing was too limited; other programs made would-be swordsmen wait months before they handled a weapon.
So she and her instructors began playing with padded swords and ''armor" cobbled together from motocross, ice hockey, and lacrosse gear. They studied medieval sword-fighting and adapted the techniques to the nonlethal world of injection-molded plastic, Velcro, and spandex. They created a series of Sport Weapon programs, such as Sport Sword and Sport Armor, as well as kids' classes like Little Knights. In a stroke of brilliance, Gardner demonstrated swordplay for schools and movie patrons waiting in line to see swashbuckling epics like ''Star Wars" and ''The Lord of the Rings." Guard Up! now has more than 300 believers.
Of all the Sport Weapon classes, Sport Armor offers the most hard-core action. Unlike Sport Sword, or fencing's courtly culture of ''touché," Sport Armor allows full-force hitting and head shots. Nor is Sport Armor limited to one-to-one combat. Suspend your disbelief, and some multi-person melees can feel like all-out war.
It's clearly an improvement on my previous dueling experience; my childhood buddy J.P. and I would arm ourselves with duct-taped broomsticks and garbage can lids and wreak havoc. We played this until, yes, someone almost lost an eye.
''Much of the art of medieval swordsmanship was lost with the advent of gunpowder," Gardner says. ''The goal of Sport Armor isn't necessarily to be historically 'authentic' as it is to provide the sense of a full-contact activity that develops a great deal of stamina and lightning reflexes."
Before I'm allowed to face Sir David, I need a private tutorial. My Sport Armor teacher is Jeff De Biase, 27, of Quincy, a stocky but lithe Kendo champion and fight choreographer for History Channel shows. Kendo is the art of Japanese samurai swordsmanship.
As I select my 46-inch longsword and slip on my gauntlets, De Biase explains the fundamentals. ''Sport Armor is based on the historical, two-handed German longsword," he tells me. ''We're trying to build a sport based on a system that's hundreds of years old." He says present-day knowledge of the technique stems largely from a 15th-century how-to manual, ''Sigmund Ringeck's Knightly Art of the Longsword" (itself based on teachings of the 14th-century German grand master, Johannes Lichtenauer).
First things first. De Biase shows me the grip. The German longsword was held somewhat like a baseball bat. ''A real longsword would have been a few pounds," De Biase reminds me. I'm not allowed to flick it around like a foil. I'm to strike with sweeping blows that use my whole arms. The nylon and polyethylene may be only a few ounces, but I pretend my sword is as heavy as a maul for splitting wood. Or heads.
Next, ''Footwork, footwork, footwork": how to be poised and balanced, how to distribute my weight, how to step toward my opponent with each sword cut and retreat without exposing my back. Then he whips me through the nine basic sword blows. We move in unison across the room, practicing cuts from above called ''oberhau," ''zornhau" diagonals (''zorn" means wrathful), cuts from below known as ''unterhau" and horizontal blows, or ''das redel" (wheel cuts). After three reps, the awkward-seeming moves start to sink in. The sword and my body begin to work as one. But the crash course is over. The seasoned Sport Armor students, men and women of all body shapes, arrive and don their armor. We pair off -- Sir David and I -- and begin parrying drills, then practice the ''half-sword," a close-combat technique to thrust the blade into the armpits or throat. Ouch.
''This is our couples therapy," admits Aya Jameson, 25, of Chelmsford. She and Matt Ridge, 31, of Billerica, met here. ''We come here and beat the [stuffing] out of each other."
From across the room, someone shouts, ''Who wants to warm up?" then laughs, maniacally, like a villain.
No need to hold back.
The ''Lord of the Rings" soundtrack swells in my head -- along with my head itself. Like Aragorn, I pause for a moment. Psych up my inner warrior. Then, meeting my foe's fiery eyes, I charge into battle.
Contact Ethan Gilsdorf, a Somerville freelance writer, at email@example.com.