The art of armoured fencing is one of the more spectacular and unique combative methods used by our european ancestors, and one of the three primary general divisions of martial arts at the time (roughly 1350 to 1550 AD), the other two being unarmoured, or open fencing on foot, and mounted combat. As a whole, comprising the trinity of personal Medieval combat skills. These methods each encompassed a general category of method, with some overlap, holistically integrating all of the applicable arms and conditions within. It is also, as is known to those who understand it, one of the more violent and morbid arts as well. As opposed to the less vicious popular view of weapons theatrically splitting or piercing armour or beating the wearer senseless, one primarily has to go about armoured combat with the full intention of subdueing and killing his opponent by forceful grappling and working the point of his chosen weapon into vulnerable and unpleasant areas, perforating arteries and vital organs.

This goes hand in hand with the misconceptions of the contemporary weaponry, in that people commonly think that the wider cutting blades, including falchions, were the ones meant to face armours, plate armours and mail particularly, rather than the narrower thrusting blades, such as narrow, tapering blades on single hand swords, bastard swords, and estocs. On top of this, many think the weapons were designed to defeat the armour itself, by some means penetrating it, rather than to defeat flesh - such designs allowing them to bypass the armour more easily. These people erroneously say things like "falchions were wide so they could be heavy in order to strike armour," rather than being wider in order to have a thinner cross section for more devastating cuts against flesh and soft material, or "bastard swords were pointy because they were armour piercing weapons," rather than being acutely tapered for point control and penetrative ability between armoured areas. The idea of delivering blows against armour, or piercing it with the point, at least with the idea of injuring the wearer, is almost entirely absent in the fencing manuals (with few notable exceptions, such as the devastating mordschlag), and in fact Masters Lichtenaur and Sigmund Ringeck, for example, strictly advise against it. Trying to beat down (partially excepting specifically percussive weaponry, such as maces and flails, which were never recommended by any fencing Master that I am aware of), cut, or pierce the armour of the opponent would have obviously been a lethal waste of time if your opponent was trying to kill you directly, much like a theatrical fencer attacking the blade of a soldiers sword. Such mistaken beliefs undoubtedly gave rise to the myths of unskilled warriors trying to club each other with heavy, dull or chisel edged swords, leaving the strongest as the victor. It makes sense if you think swords were meant to face and penetrate or crush armour, not flesh, and, of course, that everyone back then in Europe wore complete armour, all the time.

The belief in heavy, armour piercing, chizel-edged or dull European weaponry is even more absurd due to the fact that most of the people who believe it are also the ones that believe the armour was so thick, heavy and restrictive that it hindered the warrior within it. This would in fact further limit it's ability to be compromised by cut, perforation or impact (due to the weight and thickness it supposedly had), while further increasing the ease of getting around it (due to the limited agility the wearer would've been subject to).

These pervasive misconceptions of the medieval european arms race are the root of the majority of the most detrimental, ignorant and annoying mistaken beliefs about european arms and armour, carried on by roleplaying games, hear-say, hype and second hand historians who study the work of historians, not history itself.

Conversely, when one is in unarmoured combat, he can spontaneously react by cut or thrust to the adversaries openings, and any strike that lands will likely injure, maim, or kill.

When one is in armoured combat however, one would more often have to take a concious second step in killing or mortally wounding his opponent in order to stop him. The effectiveness of armour and it's massive combat multiplicative capability almost ensure this.

Armoured martial arts are equally, if not more, misunderstood than any of the other categories of Renaissance martial art. So, the reality of weapons and armour is supported by common sense, a knowledge of what weapons will and won't accomplish, the fencing manuals, technique, and even the prominence of curved weapons in areas with less common and less developed armours than Europe, for example.

Historically, the fitness to actively move and fight in armour was an extremely important aspect of the training of any man-at-arms, and is not to be underestimated. Without the fitness, he would be a rather ineffective soldier, regardless of all skill.

A good amount of physical strength and high endurance allows active exercise and combat for far longer periods than an unconditioned or improperly conditioned individual could hope to manage. Ask any infantryman. A properly conditioned body with low body fat percentage will be able to process the heat generated in armour and gambeson far more efficiently than an unconditioned or higher body fat one, not to mention the necessary benefits of the extra endurance and strength needed to function and fight wearing the extra weight that comes side by side with the defensive and offensive benefits of any personal armour.

Also, being properly conditioned will cause you to lose measurably less water, and handle the water loss that does occur with less ill effect. Efficient muscle, heart and lungs will make any restricted breathing that much more bearable as well.

Due to the form fitting nature of late Medieval and Renaissance plate armour, a change in body shape can very well mean your horribly expensive harness is now horribly decorative. So if you're planning on buying a plate armour, get in shape first. If you've bought armour, stay in shape. Consider the expense motivation.

Obviously, one of the best ways to get in proper condition for armoured combat is to simulate armoured combat, I.E. flouryshing, technique practice, drilling and sparring, all while wearing the armour.

To quote Bruce Lee, If you want to learn to punch, punch, if you want to learn to kick, kick.

But ideally, just as with normal unarmoured martial arts training, armed or not, this should have a great deal of supplemental exercise to ensure the proper fitness and develop the endurance, strength and agility required to move in armour by a comfortable margin.

In the reviving arts of historical fencing, the authenticity of the equipment and the required athleticism, techniques, and footwork in particular, does not easily afford it's students the luxury of disregarding supplemental exercises or being out of shape as can many other-than-martial armoured reenactment, tournament or play fighting faux-chivalric sports.

Safety
Ensure that an ample supply of water is readily available whenever exercising or training in armour, and steps are taken to avoid heat casualties.
Any of these methods, with extra weight in particular, require concentration on proper form and great care in their use to avoid injury through extra momentum.
Start slow and light, and take it easy. If it hurts, don't do it. Do what you're comfortable with and work within your physical limits.
Note that you don't necessarily need to wear or even own armour to get in a decent shape for it. There is a good variety of weight equipment and resistance exercises that will assist you in training for it without the need or hassle of wearing it. In many cases, you will have to simulate armour rather than wear it. For example, you probably wouldn't want to be on the treadmill at the gym in harness, unless you really like the attention.

Stretching
Stretching is important due to possible dehydration or heat cramps, and for injury prevention. Being flexible isn't just for high kicking martial sports. The more flexible you are, the less likely you are to cramp or suffer injury, and the more agile you will be in any combat situation, which is not to be underestimated in grappling situations where you are bearing armour weight.
A fraction of an inch of muscular flexibility can mean the difference between a tap-out, injury or defeat, and a successful escape or counter attack. It can also mean the difference between a pulled muscle in a fall or overextension, or a quick recovery.
You should make sure you have completed your stretches and warm ups before you are armed. You may not be able to fully stretch once you are in arms, and even if you tried, it would waste extra water.

Excess weight
Extra weight meaning that you wear more weight than the actual armour would exert upon you.
This is the same as training with extra heavy weapon simulators to gain strength and agility with normal weight weapons, wrist and ankle weights to gain power and speed with natural weapons, or lead soled shoes to gain agile footwork as mentioned by Master George Silver.
Excess weight can be added to anything you are already doing at the armour weight.

Historical Methods
Here I have compiled a few exercise and training methods that we know were used historically, to both exercise and train in armour, and to practice and show off your individual dexterity while so armed. It is by no means complete.
o Vaulting: Vaulting onto horseback is probably one of the better known feats that was expected of a fully armed man at arms. Doubtless they practiced this on the wooden horses that were used for martial training preliminary to the actual animals, and various substitutes can be commonly found, from low walls, to logs, to playground equipment.
o Climbing a ladder, on the underside, using only the arms: This is easy enough if you have a ladder and somewhere to prop it up. A somewhat less difficult version is traversing the bars, which can be found on most playgrounds. It's about the same, but horizontal, so you won't actually be pulling yourself upwards.
o Cartwheels, rolls, handsprings and tumbling: This may seem like something you'd do to show off, but try it for 10 minutes in arms and think again. It's also vital for learning to move in your armour, and learning just what it will and won't do. Some armour may restrict rolls somewhat, particularly solid, one-piece body armour that doesn't allow you to curl up. Try these slowly first. Don't put your entire weight on anything all at once until you know what'll happen. This will also tell you where you're not padded well enough. Ever fallen on your keys?

Key muscle groups/applicable weight training and cardio combination exercises
Basically any resistance or weight training exercise can be applicable to armoured fencing, but I'll note a few particulars that most people should be able to do with little available equipment.
When cardio training for armoured fencing, as with the other exercises, start slow and with little additional weight. It's better to start low and work up to what you need, than to start high and hurt yourself.
Many of these exercises are really a combination of cardio and muscular workout.
These should help break someone into moving in armour and bearing the weight, but it should be noted that you'll likely need to do far more than this to gain the strength and endurance absolutely required for grappling in armour.
I've narrowed these key muscle groups to ones that tend to get consistently sore with people just getting "broken into" armoured fencing.
If you can, get an experienced individual or trainer to show you the proper performance of each exercise, and some related exercises. Remember, these are just tips, and should not replace a complete fitness program.
Legs
Knee raises and lunges (with weight, these will condition the leg muscled used in bearing and lifting, and the ones used in foot maneuvers), calf raises (calves should be strong and well defined, not only for foot maneuvers, but to support the weight of the upper leg defense).
Arms/shoulders
Lateral raises, military press (works delts, which are especailly worked in mail), shrugs (one of the primary suspension points for body armour), and dips (for the triceps).
Body
Stiff legged deadlifts (works the upper hamstrings, but for armoured fencing, this will strengthen the lower back and abs as well), crunches, lying leg raises (a strong midsection is important for bearing weight well).
Neck
If weightier helms are worn, the neck muscles will feel it. With practice, this will go away as your neck muscles adapt. It's probably best to simply allow your neck to adapt naturally to any head armour.
General
Casting the stone, or, medicine ball. These (stones, duh, and medicine balls) come in various weights, and with a medicine ball (sort of a heavy volley ball) this can be done as a partner exercise. Rather than being "crushed like a worm", they can toss it back. If done properly, casting it will work the shoulders and legs.
Squat/thrust pushups (with weight, for the agility to quickly rise).
One exercise done for modern armoured combat conditioning by the military, is to do various runs, jogs, and sprints with body armour worn. This will condition your body for the armour, and get you used to the heat produced within it. It is best done with armour simulators to cut down on lumps, noise, and funny looks.
Jumping rope is also one of the best. Do this with any combination of weight on the body, wrists, and ankles. Be sure to warm up first, as this can stress joints with weight.
Finally, hiking with weight, or walking/jogging/sprinting uphill. This can also be done with a weighted backpack.
Obstacle courses: These are probably the best overall workout you can get in armour, and not dissimilar from authentic methods.
Many of these, such as obstacle courses and hikes, can be fun group workouts in authentic gear if you have several people with armour.

Some equipment for simulating armour
Remember that generally, any concentrated weight will not move or feel like armour.
o Weight vests: These are available on line and at some fitness stores, but can be very expensive.
o Wrist/ankle weights: These can be found at most fitness stores, and can be found cheaply. Some types can be joined together, making a belt. I use these as a cheaper alternative to weight vests.
o Backpacks: These can be used for certain exercises. When you put weight in them, wether it's a medicine ball or weight plates, make sure it's secure and comfortable, not loose. If there isn't a secure pocket, wrap it and tie it up in towels or clothes.
o Pockets: If you have military style pants with cargo pockets, weights can be put into those, and held with suspenders. Mechanics suits are also good for this. Just make sure the weights aren't too loose if they're hard.
o Logs: Yep. You can find a big, heavy log or something similar that can be balanced over the shoulders. Taking an uphill walk with one of these should help quite a bit. It also works well as a group exercise.

Energy conservation techniques
Proper breathing is even more important within armour than without. Someone who does not breathe properly, or who has the common habit of compressing, stifling, or stopping their breathing when exerting, will more quickly be overtaken by it if they do it in harness.
Likewise, anyone who over-flexes his muscles or does not relax will be worn out that much sooner. It is important to stay relaxed and fluid, to work with and around your armour, rather than against or through it. Relax the shoulders.
When not actively engaged with your opponent, adopt a narrower stance so your muscles will bear less weight and your skeleton more. When fighting, adopt a stance that is more balanced, like the waage, as opposed to the common slightly forward stance used when unarmoured.
Related to that, it is important to keep a good centerline and balanced stance when wearing armour. Your body should not be leaning forward or back, this will help to unbalance you, and it will place more strain on certain muscle groups that could be avoided. Neither should your head lean forward, as this will tire out your neck.
Keep your arms closer to your body. Half-sword guards help with this. Do not stand in the long point as anything more than a quick transitory position. Keep the hilt near the hips or shoulders when using standard guards.
When not actively engaged, do not lie in a high guard. Consider them transitory. This will also help to avoid exposing targets.
Ensure that your harness fits and is properly suspended! If it isn't, it will neither distribute the weight properly nor move efficiently.

Weight goals
If you have armour, you should weigh it, and train at that weight or more. If you don't have armour, estimate the weight of your preferred or future armour, or train at an average weight.
Historically, most complete armours would be anywhere from 45 to 80 pounds in their entirety, from a 12th century harness primarily of mail to a 16th century tourney armour of plate with gussets, so picking a weight anywhere in that range should do it.

As we work towards making these arts once again formidable and exemplary, we should do the same to honor the armoured methods. I hope to work on or see accomplished more articles on other aspects of armoured fencing in the near future.

Bibliography
Most of this was gleaned from the wasteland that is my mind, which often, to my detriment, omits sources. As usual, it's been more of a rant than an article anyway.

Many of the exercise descriptions:
the Body Sculpting Bible for Men; James Villepigue & Hugo Rivera; Hatherleigh Press

Remember that they want long-form:

Title; Author; Publisher; Date

For the biblio-listings

I certainly look forward to any pictures you include in this.