There's two extremes I notice when it comes to armour. There is the one extreme where armour is portrayed as being bulky and hard to move in such as the knights armour. And there is the other extreme where since armour was made to fit person for persona and to be distributed evenly so that even a 100lb armour would not feel heavy and be so light that you can do cartwheels, hand stands, jumps, run, and even fancy acrobatics. That armour is so light that someone who's not conditioned would feel its like wearing a T-Shirt.

So when I found my sister's weighted vest that totals to about 20 lbs, I decided to test it out. At first it did not feel heavy at all and it felt so light I can jump around it and even walk 2 miles without feeling exhausted. So I thought real armour must be as light as the other extreme is, so l thought plate armour was lighter than a shirt.

However once I started crouching and doing other prone movements to test swordsmanship and aerobics I began to feel pressure. In fact I was surprised as hell how tired I got just doing squats and practising low level attacks. In addition when I tested running, it suddenly felt so heavy. Not as heavy as Hollywood portrays mind you but I began to wonder if some of the tests such as the link below had validity.

http://www.bbc.com/news/science-environment-14204717

As I was finishing my first mile and I reread the above article while I was resting, everything was so spot on.

Also trying to do high level acrobatics such as jumping over hurdles in a track field and some of those fancy gymnastics was almost impossible.

So it makes me wonder how wearing an armour would be like. I know its a running vest I used that had pockets filled with metal bars that totaled 20lbs, far less than a typical breastplate so its a different tool. In addition I'm not exactly a nerdy waste as I lift weights enough that I can curl 2 sets of 50 lbs dumbells casually and benchpressing a barbell with 50 extra weights on both side for 100 reps ain't hard. So does that explain why wearing the vest was initially not difficult?

I am so curious how armour felt like but don't have money right now to buy it so I ask people with experience here!

It really depends on the armour and how much of the body it covers. Armour that only covers your chest is not inhibiting at all. Armour that covers your entire body is more restrictive. IMO it largely depends on how well the armour fits your limbs and articulates at the joints.

Others far more knowledgeable than I will chime in soon enough, but just my thoughts:
There is a big difference between middle/long distance running and the "difficulty" of moving in armour. Armour was designed to protect people engaging in combat from the weapons of their opponents, not to give marathon runners a bit of extra protection against mountain lions. Sure it will be more restrictive than a t-shirt, but the types of movements you want to be able to do, that the armour is designed to impede as little as possible are those involved in combat from the time period the armour is from.
Also, 100 pounds for a full harness and 20 pounds for a breastplate are both ridiculously heavy for "standard" armours. Maybe specialised jousting harnesses for heads of state that didn't have male heirs, but not normal armours.

At the peak of my training in my full suit of armor, I could run for a good distance, do pushups, tuck and rolls, and had good mobility (even did a swimming test). If the armor is made for you and is suspended correctly you should be able to move well in it especially if you train and wear it a lot. I've clocked 14 hours staight strapped in and have hiked in the mountains in full kit.

There are indeed two extremes:

Badly made armour that film makers want to have some drawback, ie lesser maneuverability.

People that have well fitted armour, are trained in its use and want to show mobility is not that much impacted.

but both these cases do not matter for your case, your case is about strength and stamina.

You found yourself with very little limits in how you could move but you're still heavier, and have not yet trained the muscle neccesary to compensate. Training or not, it will tire you faster than not wearing armour, you simply have to move more weight. Running with a mail shirt on (closest equivalent) is also different from running without one. I try to keep my center of mass much more level when running with the weight on.

... look at this:

https://www.youtube.com/watch?v=pAzI1UvlQqw

Great video, thanks for sharing! It does should how much a heavy load affects speed in difficult terrain. I can see why 16th-century arquebusiers, expected to skirmish in rough terrain, often tried to travel light, apparently sometimes even declining to wear swords.

A lot depends on the type of armor as well. I do medieval reenactment and wear a chain hauberk, up to 8 hours a day. If properly belted, it isn't terrible--my helmet is the worst part. But the weight does sap your energy. I can mount a horse, fight, etc. But getting up from prone and seated is tougher. In properly fitted plate, those activities are much easier.

Most of the mail today isn't fitted to the wearer. In the past it often was. You'll find that it would be a lot easier to move in if it was tailored for you, Properly-fitted mail feels like a second skin made from steel.

I agree with that totally, Dan. I lucked out and got a haubergon that looks(and feels) like it was painted on me, except a bit of slack in the lower sleeves. Total mobility. ;) All of my plate armor is 'off the shelf', but was all selected very carefully to the closest possible sizes for my particular frame---much to the annoyance of some sellers customer service people. :lol: I find it to be about as close to custom-made as I can get on my budget. As far as the question---"How much more difficult is it......"---I plan on wearing it to Scarborough Fair Ren-Fest...in Texas heat...this weekend. I'll tell y'all when/if I make it back alive. :lol: ....McM

Daniel Jaquet is pretty much the leading source on this these days. Apart from the Obstacle Run in Armour video ( https://www.youtube.com/watch?v=pAzI1UvlQqw ), there are a couple more where he addresses mobility or the lack thereof in armour:

https://www.youtube.com/watch?v=zvCvOC2VwDc

https://www.youtube.com/watch?v=q-bnM5SuQkI

And a detailed interview with him by Rob Runacres and Hans Jornlind: https://www.youtube.com/watch?v=bnI_nfb4HyY