Posted On: 2021-04-05
A stamina system is a fairly simple design, but it can serve a wide variety of different purposes depending on how it is configured. Stamina is a resource that a player can spend that recovers over time. It has a few obvious parameters to tweak, such as the rate it recovers and the maximum amount available at any one time, but designers can create wildly different play experiences simply by adjusting those values. For today's post, I'd like to look at three different approaches - each of which is a cornerstone of a different genre.
In action games players can spend stamina to perform certain high-value actions (such as sprinting or dodging), and spent stamina quickly recovers when not used. Such stamina systems are often used to add tactical depth to combat, as wantonly spending stamina can quickly leave a character depleted and vulnerable. When both defensive and offensive actions share the same stamina resource, it creates a natural way for players to drive the tension of the game, as spending stamina to attack increases the risk of being unable to defend*.
Despite its benefits, a stamina system that is poorly configured can do more harm than good. If the maximum stamina available is too high, it will have no impact on player choice (as they will always have enough to do any action). If the recovery rate is too low, it can lead to player frustration, as waiting around is antithetical to the core appeal of an action game. Lastly, if too many actions are tied to stamina, it can lead to choice overload - thereby encouraging players to ignore some actions merely to keep their decision space manageable.
Stamina in "casual" games is a quasi-finite resource that players spend to play the game, and it recovers over a long time horizon (usually measured in hours). Such systems are nearly ubiquitous in mobile games - one often has to spend stamina to enter a dungeon or attempt a puzzle. Often, this system is used to influence player behavior, as the stamina recovery rate drives the rate at which content in the game may be consumed. In many cases, using stamina systems can enable games to launch earlier than they might otherwise: by limiting the rate players can progress, content can be patched in before players reach the end of what's available.
The downside of such stamina systems is that it is easy to use them unethically. Game designers generally have to balance influencing players' behavior against respecting player autonomy, but stamina systems affect player psychology in multiple ways simultaneously*, often tipping the balance too far. To make matters worse, stamina systems are often leveraged by the business side for monetization purposes, swiftly turning the (already questionable) practice of controlling players' play schedule into something downright predatory.
Many survival games feature a food clock: the player has a resource that decreases over time and they must use consumables (food) to restore it. What's interesting about this is that a stamina system with a negative recovery rate (that is, decreases over time) is effectively a food clock. Indeed, one could easily include consumables to allow players to instantly recover stamina in either of the two earlier examples - food clocks merely make such consumables more common (due to being the primary/only way to recover it.) . Interestingly, many survival games make activities associated with draining stamina (such as sprinting) also affect the food clock, giving players a means of strategically spending this (alternate) stamina system*.
A food clock often has an outsized impact on the game if it is misconfigured, as it is closely tied to the game's lose state*. Draining it too quickly can render the game impossible, while draining it too slowly can suck out the game's tension. Too many consumables can make the food clock irrelevant (often making it a different genre), while too few can prevent players from engaging with the game's other systems (ie. base building.) Thus, more than any other stamina system, the food clock must be carefully tuned, as poor configurations can make the game outright unplayable.
These three different kinds of stamina systems are not mutually exclusive. Developers can mix them together - either as multiple separate systems or even by combining them together. One example of the latter can be found in the multiplayer society simulator Eco*. The game uses a single, unified stamina system, Calories, to both determine long-term survival and influence play schedule.
Fundamentally, the Calories system is a food clock: over time calories are depleted, and food must be consumed to restore them. Unlike most food clocks, however, every in-game activity drains calories - from sprinting, to chopping wood, to placing an object. Additionally, there's no separate stamina system for any of these activities; players can sprint for hours on end (provided they have enough calories to do so.)
Importantly, calories also control access to long-term advancement: every food has certain "nutrition" points associated with it, and as calories are depleted over time, players are rewarded with progress towards skill points (the game's progression system) based on the average nutrition of the food consumed over the past 24 hours. Thus, the Calories system incentivizes playing at least once per day, while also demanding the player choose between seeking long-term progress (nutritious food) and indulging short-term play (high-calorie food). Lastly, and (for Eco's design goals) most importantly, food is a quasi-finite resource (ingredients take several real-world days to grow) that is shared between all players: players are effectively competing to get enough food to keep playing, but they need to collaborate in order to do so successfully (the food supply collapsing is a shared, de-facto lose-state*.)
As you can see, stamina systems can serve a variety of functions, depending on how they're configured and used. Additionally, while different genres typically use certain configurations, one can very easily mix those together to get something unique and more closely tailored to the needs of a particular game. I hope you've found this exploration interesting - and I hope the next time you play something with a stamina system, this inspires you to look a bit more closely at how it's configured.