RPG Science: Physical performance with armor and other loads

Just how tiring is heavy medieval armor? How much does a load slow down climbing? If you’re the type who appreciates a bit of realism in your RPG action, here’s what recent research and an anecdotal report have to say about those questions. 

Heavy metal: Walking in plate armor

Quite a few months back, a study published by The Royal Society B looked at the effects of medieval armor on physical performance (BBC summary here). No one should be surprised by its finding of “hey, heavy armor is tiring!”. But the researchers’ detailed approach of measuring actual energy consumption under controlled treadmill conditions yields some quantitative crunchiness for the consideration of simulation-happy gamers.

The four subjects were fair-sized males in their mid-thirties and experienced in wearing replica armor. For the research, they wore custom-made full suits of 15-century-style plate armor averaging 35kg, representing a big proportion – about 44% – of their body weight. Plenty of results came out of the tests, but here’s what’s of gaming interest: the energy cost of locomotion (i.e., energy cost above that of a normal resting state) was about 120% (walking) or 90% (running) higher than that of unarmored men. In short, the armor roughly doubled the energy expenditure for motion.

An additional finding was this: the added cost of locomotion was worse than that of carrying the equivalent weight in backpack form, with the latter increasing cost by only 70% (walking) or 50% (running). That was a surprise to me; I had guessed that armor would create less of a burden than equivalent weight in a compact bundle, as the armor is more evenly distributed and close to the body, whereas a bulky pack in motion might tend to pull the body in its direction (due to inertia), made worse by placement of mass further from the body (due to moment of inertia).

I allude to this assumption in Summary of ways to handle power-vs-weight in GURPS creatures, suggesting that armor might be treated as less encumbering than “generic” loads (though I didn’t suggest worrying about it, and haven’t done so in games). The above research suggests the opposite, and offers a reason as well: it may primarily be heavy leg armor, and thus the burden of lifting and swinging heavy legs, that greatly increases energy cost beyond that of supporting and moving a load higher up on the body. “Heavy leg syndrome” may not account for the entirety of the difference, however; the researchers suggest that restricted breathing caused by armor, and possibly even frictional losses in armor joints, may also play roles, though these were not isolated and measured.

So, setting aside the matter of armor vs non-armor loads, how do the armor findings match up with the rules in a notably simulation-friendly game, GURPS? We have to make guesses, of course, including the assumption that we can tie “cost of locomotion” directly to Fatigue cost. Doing so, let’s imagine a ST 11 character carrying 35kg, or 77 lbs. He’s got Heavy encumbrance, for a combat or hiking Fatigue cost four times (B426) that of an unarmored man. A ST 12 or ST 13 character would have Medium encumbrance, for a tripled Fatigue cost. It takes a hulking ST 14 character to achieve Light encumbrance, with a doubled Fatigue cost that’s right on the money where the research findings are concerned. 

These observations suggest that GURPS‘ Fatigue penalties for encumbrance are perhaps harsher than necessary, but aren’t terribly off the mark.

Climbing with a load

In a somber video on the response to the 9/11 World Trade Center attack, we’re told that “a firefighter in full gear, carrying sixty-something pounds of hose and equipment, takes about one minute to climb a flight of stairs”.

If true, that’s pretty slow. To compare unencumbered results, you can easily measure your own time on stairs. The comparison may not be too useful, though; the above sounds an awful lot like an off-the-top-of-the-head estimate, and we know neither how high a flight of stairs is involved nor whether the imagined firefighter in question is rushing or taking a sustainable pace.

But is there anything we can get out of it? Well, given that you can likely climb some easily-testable flight of stairs in only ten seconds, or even five at a fast pace, the anecdote does suggest that encumbrance has a big effect on climbing performance. Taking GURPS as a guide, sixty-some pounds leaves a fit ST 11 or ST 12 character at Medium encumbrance, cutting Move to 60% of unencumbered Move. That penalty is rough and may be quite reasonable on flat ground, but where stairs are concerned, it still doesn’t create the sort of slowness suggested above.

That’s the sort of thing I tried to address in old climbing rules for my GULLIVER house rules on physical performance. The detailed rules there essentially start with normal unencumbered Move, cut that Move down for the unusual and inefficient action of climbing itself, and greatly boost any encumbrance via an effective weight multiplier (the tougher the climb, the higher the multiplier). The increased encumbrance further affects climbing Move and fatigue, and, quite realistically, can remove any ability to perform a difficult climb even when the character can still lumber across flat ground.

Let’s see how it’d work with a ST 12 character (Basic Lift 29 lbs.) lugging 65 lbs., leaving him with Medium encumbrance and reasonably rapid stair-climbing performance under GURPS.

The GULLIVER rules suggest multiplying effective weight in a climb, such as x1.4 for a 30° climb and x1.6 for a 45° climb. The slope of a staircase might fall in between the two, for x1.5. However, my rules envisioned actual sloped and/or uneven surfaces, not the flat and even surfaces of stairs, which are designed to make the ascent as easy as possible. I neglected to consider stairs, so will have to make up something here. Let’s say that a perfect stair-like “climbing” surface cuts about 20% off the degree of multiplier over the base x1. As a result, the x1.5 multiplier for the slope of stairs becomes x1.4. (Likewise, the suggested x2 for a 90° surface would become only x1.8 for a ladder.)

Multiply the climber’s 65-lb burden by 1.4, and it’s as hampering as carrying 91 lbs on flat ground. That better matches the feel of hauling a load up steps, and kicks our climber into Heavy encumbrance with only 40% of his ground speed – definitely slow, if not wildly so.

However, my old GULLIVER rules incorporate body weight itself, not just carried weight, in their detailed encumbrance rules. That’s what I want to check here. Follow along with the rules’ Encumbrance Table as we put the full system to use:

Say our big and strong climber weights 185 lbs. The rules refer to “Load ST”, a sort of proto-Basic Lift hack I needed to work with GURPS 3e‘s handling of ST. For a 4e character, we can simply replace any mention of Load ST with Basic Lift /2 (14.5 lbs for our ST 12 climber); that works great.

Without a load, the character’s weight-to-strength ratio (WSR) = full weight / Load ST = 185 / 14.5 = 12.8, which my Encumbrance Table terms Negative 1 encumbrance. This odd name indicates a ratio of weight to power better than the default encumbrance of None, worthy of a small bonus to Move and athletic skills, which is appropriate for this muscled fellow.

Now we add the burden: Laden WSR = (185 + 65) / 14.5 = 17.2, which on my Table gives Light encumbrance. That slows the climber notably. (The result is still more generous than straight-up GURPS, as it accounts for the innate advantage this fellow has in hauling a body weight that’s light relative to his power.)

Time to hit the stairs! From my old rules, multiply everything by 1.4. Laden WSR goes from 17.2 to 24.1, pushing the climber into Heavy encumbrance. Again, that’s quite a reduction in speed, though still not as slow as that reported firefighter climb.

But it’s not hard to get to real slowness. Simply drop ST from 12 to a still-fit 11 (Basic Lift 24), and we get laden WSR = (185 + 65) / 12 = 20.8, or Medium encumbrance on flat ground, and laden WSR = (185 + 65) / 12 x 1.4 = 29.2 on stairs, which on my Table pushes into X-Heavy encumbrance. That cuts speed to 20%, meaning a 10-second staircase ascent takes 50 seconds. The result is squarely in the ballpark of speed in the firefighter anecdote, and emphasizes just what a difference the effective weight multiplier can make.

The takeaway

So, what’s in the above that’s both interesting and playable enough to inject into games? Here’s what I take away:

1. When designing or testing a set of rules, the armor research provides a good rule of thumb for how plate armor fatigues the wearer. Gamers already know that an armored man remains quite mobile; we don’t entertain the silliness of knights as overturned turtles when fallen, or as requiring cranes to mount their steeds. But we now have a good study to show that while full plate is indeed tiring, it’s not devastatingly so. Don’t worry about perfectly duplicating research results in your game, as we can never know the subjects’ “strength scores”, among other details. Just be happy knowing that if, during combat or other game action where you’d worry about fatigue, a reasonably fit warrior in plate armor gets tired at a rate of, say, between 1.5 to 3 times his unarmored self, then your game rules are likely in the ballpark of realism on this point.

2. Simulation lovers might want to play with other details from the study, accounting for the differing fatigue effects of backpacks vs armor, as well as body armor vs leg armor. Here’s a framework to whet the simulationist appetite:

  • Rig the overall encumbrance system to keep the effects of carried weight relatively modest. That lets characters lug backpacks and upper-body armor without undue difficulty.
  • When in motion, multiply the effective weight of leg armor (and any footwear) by some factor (x1.2? x1.5?) for purposes of encumbrance calculation, due to its proportionately large effect in slowing and fatiguing the wearer.
  • When in motion, consider multiplying the effective weight of all jointed armor by some small factor for purposes of encumbrance calculation, due to the exertion needed to overcome friction in joints. Also, consider multiplying fatigue costs by some small factor for the effect of restricted breathing in armor. Both of these factors should be increased for poorly-fitted and low-quality armor, and reduced for well-fitted and high-quality armor.
  • Carrying weight in backpack form appears efficient from a speed and fatigue standpoint, but the inertia in such a concentrated, bulky load would arguably have a bit more impact on agility. (This is my own assumption, and is not suggested by the above study.) To simulate this, consider multiplying the effective weight of such a load by some small factor for purposes of encumbrance calculation, but only for determination of agility-related effects (i.e., penalties on skills, dodging, etc.), not speed of movement and fatigue effects.

3. Whether or not you use any of that extra detail, I stand by my recommendation for gaming performance in climbs: multiply all effective weight (whatever weight your encumbrance rules use) by some factor (a small amount for easy climbs, a large amount for difficult climbs) for purposes of encumbrance calculation. The multipliers I use are sheer guesses and the above firefighter example is only anecdotal, so don’t worry about hitting “realistic” target results. Just know that some sort of multiplier is very realistic in making a load far more exhausting in a climb than on the ground.

There. For my own home-brew rules, I’ll be sure to keep 1 and 3 in mind. I may offer some suggestions from 2, too, but only as optional details (they’re pretty futzy stuff).

How about you? Anything of interest in the above?


  • Esteemed Visitor

    Hmmmm, I think when I get some free time I’m gonna have to go about tweaking the AP system I came up for a older version of a home brew I’m messing around with. With my current version I’m taking advantage of the power of Excel (.. errrr, well Open Office Calc, as well as huge burst of inspiration from your GURPS GULLIVER ebook) to try a more experimental action system that might be a bit much for most RPGer’s outside of those of use who like their games as crunchy as their breakfast cereals. I’ll post what I come up with in the comments section of your It’s about time article.

    • tbone

      Needless to say, I’d be interested to see what you come up with. And I fully understand the point about “might be too crunchy”, but don’t let that be a deterrent. I see RPGs, like any other creation, as requiring R&D. Even if the result of some crunch-heavy R&D work isn’t suitable for play, it might be simplifiable to a new and playable system, or offer some playable improvements for existing systems, or just point out new directions to explore. (If nothing else, R&D helps in confirming that some ideas are just plain bad. : )

      • TheRyujin

        Ugh, I need to stop procrastinating and get on that GURPS AP write up (though I might want to change the term “Actions Points” to something else to avoid confusion with how Mr. Cole uses them). I kinda got stuck on how to have them interact with the current GURPS Maneuver system and then let myself get distracted by a fan mod to Dark Heresy called Adeptus Evangelion which is based on my favorite anime series which in turn has inspired me to do GURPS version heh.

        Now as to the crunchy version I’m using for my home brew, basically rather then have a set of action points, different actions cost a number of seconds (or factions there of) to do and each character has two derived stats called Metal Affinity and Physical Affinity (obliviously one is used for mental actions, the other for physical actions) which then modifies how quickly or slowly the character does that action (of course other things such as encumbrance and skill level effects this as well) and since the crunch is handled via spread sheet all you have to do is enter how long a task is and the sheet spits out how fast your character is at it.

        Warning, long winded explanation ahoy! Read at your own risk.

        To give you an “for example” of how this works played out I first need to cover another derived stat called Reaction Time which pretty much does what it sounds like, that is this is how quickly can a character respond to new stimuli. It is also used to determine how long it before they being their turn after the last initiative.

        After initiative is determined “Player A” has the highest, “Player B” has the second, “Goons 1 and 2” roll the same initiative so they go at the same time and “Player C” rolled the lowest.

        “Player A” starts at time 0.0 and has a Reaction Time of 0.3. He tells the GM that he’s making a run full run towards the beefiest looking car for cover while pulling hist pistol from his quick draw holster and then bringing it to bare and keeping an eye what the “Goons” are doing. The GM tells him it’ll take 3 seconds to cross the distance to the nearest full steel frame car and that while it would normally only take 0.3 seconds to pull the gun clear (1second normally but reduced to 0.6secs do to it being a quick draw model, doped another 0.1 sec do to his skill and finally dropped to 0.3 do to his Physical Affinity) in this instance it’ll be doubled to 0.6sec unless he makes a roll at -2 since his attention if focused on the “Goons” rather pulling the gun. After his gun is clear it will take him another 0.3secs to bring his gun to bare (normally half a second do to it’s weight but brought down to 0.3 do to his Physical Affinity) Also do to having his focus on the “Goons” he’ll be at -2 to any Agility rolls to avoid any trip falls along the way.

        0.3 seconds in “Player A” is 10% of the way to the car and half way done bringing out his gun and is at his first “Reaction Time” but since the situation hasn’t change he decides to not change what he’s doing. At this time it is also “Player B”s turn. “Player B” also has a Reaction Time of 0.3 and is peeking out from a door frame of a building across from where “Player A” is. She tells the GM she’s going to try and hack the “Goons” transmitters so they can’t call for back up while trying to stay out of their sight. The GM rules that since she already had her deck open and ready it would normally take her half a second to start the program that will lock onto the “Goons” data links frequency (1sec to start the program, dropped to 0.7 do to skill and further dropped to 0.5 do to her Metal Affinity) but since she’s also focusing on keeping out of sight her time to do it is also doubled and will take her a full second instead.

        0.6 seconds in “Player A” is 20% of the way to the car and finished bringing out his gun and know is starting to bring it up to bare. He is also at his second “Reaction Time” but has no reason to change what he is doing. “Player B” is now 30% done readying the program and it is now her first “Reaction Time” but she also has no reason to change things up.

        0.7 seconds in “Player A” is 23% of the way to the car and is now 1/3rd of the way done bringing his gun to bare while “Player B” is 40% done readying the program. “Goons 1 and 2” also start their turn 0.7 seconds in, they both have a Reaction Time of 0.4 and since they both roll the same initiative they go at the same time. The GM rolls in secret to see if they notice “Player B” or “Player C” and they fail but they automatically see “Player A”. “Goon 1” “decides” to drop down to his knee while bringing to bear his PDW and take aim at “Player A”, it will take him 0.3sec to drop down to his knee (0.5sec normally, bumped down to 0.3 do to his Physical Affinity, normally there would be a chance to damage his knee from dropping down onto the hard sidewalk but the “Goons” are augmented cyborgs so they’re all good here) while it will also take him 0.3secs to bring his gun to bare (fro same reasons as it did for “Player A”) so he’ll be ready to aim once he gets to his knee. “Goon 2” also brings his gun up but stays standing and tries to keep his eyes open for the other two players he knows are somewhere in the area, it will also take him 0.3secs to bring up his weapon.

        0.9 seconds in “Player A” is now 30% of the way to the car and is done bringing his gun to bare. It is also his third “Reaction Time” and since he was paying attention to what the “Goons” were doing he now knows they are a threat and decides to to take a quick unaimed pot shot at “Goon 1”, it’ll take him 0.1sec to pull the trigger. “Player B” is 60% done readying the program and now is at her second “Reaction Time” and decides that she will ready her gun once the program starts to run. “Goons 1 and 2” are both 1/3rd of the way done with their actions.

        1 second in “Player A” is 33% of the way to the car and takes his shot but since it was rushed he just misses passing just an inch above “Goon 1”’s left shoulder. “Player B” is 80% done readying the program. “Goons 1 and 2” are both 2/3rd of the way done with their actions, since a bullet just whizzed by him “Goon 1” is going to have to pass a Will save or be forced to spend his next action diving for cover rather then aiming his weapon. “Player C”, who is down the block from the other two players and hunkered down behind a car, now starts his turn, he has a Reaction Time of 0.3 and tells the GM that he first curses himself for being so slow and then that he’s going to try and hack the car he’s next to so he can use it an impromptu get away car…

        Now of course this is just an extra detailed brake down for demonstrative proposes, in reality a lot of this would be skipped over until something important comes up.

        Hope this wasn’t too confusing to read.

        • tbone

          Hullo. I think I followed things all right in the example. I’m just wondering how you’d handle the bookkeeping in play. I assume with timelines marked in increments of 0.1 seeconds, one timeline per combatant, letting you mark off each action on that character’s timeline?

          I imagine it’s far too much to handle for a big bunch of combatants, but might be interesting for very tactical fights with small groups. I would suggest developing it for one-on-one fights, and once things are working well for two combatants, expand it to three and onward!

  • Esteemed Visitor

    This would have been quite interesting for me as I was writing The Last Gasp.

    Increasing “Action Point” penalties for actions while encumbered did occur to me, but I chose to simplify by only really taking account movement costs. Encumbrances lowers Move, and so it’s more expensive in AP to cover a distance quickly.

    This suggests that AP costs might need to be MULTPLIED by the encumbrance level. So regular cost at No or Light, double cost at Medium, triple at Heavy, quadruple at Ex-Heavy. That’s a lot, but apparently swinging a warhammer in armor at ST 12 might be twice as tiring, so there you go.

    • tbone

      I don’t know details of the AP workings you describe (forgive me if “The Last Gasp” is something that’s been mentioned to me before and I’m drawing a blank). But off-hand, assuming AP equates to time to perform an action, then your suggestion of letting encumbrance modify movement costs, not AP costs in general, sounds good to me.

      To expand on that for interested passers-by: Armor that halves movement would obviously double the time required to run up into position for a melee attack. But while it might also somewhat slow the more detailed footwork, readying, etc. that takes place once the fighter’s in place to attack, I don’t think it’d fully double the time required to, say, take a swing at the foe. The armor that halves overall speed of movement won’t necessarily double the time for the action of the arms (there may or may not not even be any armor on the arms), and of course the weight of the weapon itself hasn’t changed.

      So just speaking in general terms about general situations, I’d have the above armor double the time required for movement (i.e., halve movement), probably double fatigue from movement as well, and maybe even double fatigue from all combat actions for the sake of simplicity – but I’d have it increase the AP (or other time cost) of combat actions by some lesser amount (or not at all, if simplicity calls for it).

      • Esteemed Visitor

        The last Gasp was a Pyramid article written by the venerable Douglas Cole (Whom I expect is the one who wrote the opening post) that pretty works in a more detailed fatigue system for GURPS. Tthe AP he’s talking about aren’t action points in the way your thinking, they’re more like fatigue points, though I do think that GURPS could work well with an AP system in place since it makes sense that some people will be able to do more per round. I’d say give people AP equal to their dodge since that would give most characters a nice round 8AP per second and do away with everything needing to be done in one “round” increments by let characters who have left over AP in a round “make a down payment” for an action the next round with their remaining points in the current one with the down side of them being “flat footed” till their next action (in this way you shouldn’t look at it as getting a set of points per round but rather a measure of potential you have to do things per second, if something take more AP then you have it just takes you more then a second to do it).

        • tbone

          Thanks for the tip; I’ll have to look for The Last Gasp. That D.C. writes some good crunchy stuff.

          I haven’t seen anyone write up a detailed AP system for GURPS, but it’d be interesting to see something along the lines of what you suggest. I could write a lot more on the topic – ideas, potential pitfalls, etc. – but won’t, as I already have elsewhere. If you haven’t seen it, check the three-parter that starts here: http://www.gamesdiner.com/about_time_part1

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