Spring Weight and Fatigue Across a Long Session

Two people can type on the same keyboard for the same hour and report completely different levels of tiredness. One finds it comfortable throughout, the other notices their hands fading halfway through. The difference is usually spring weight interacting with how each person presses, and it is one of the few ergonomic variables that is straightforward to measure.

We logged force curves and session comfort across several spring weights and the pattern was clear. Heavier springs are not simply worse, and lighter ones are not simply better. What matters is the relationship between the spring and the way the individual bottom outs.

What does spring weight actually specify?

Usually the force required at the bottom of the travel, or sometimes at the actuation point. That is a single number describing a curve that is not linear in how it feels, because the hand experiences the whole stroke rather than one point on it.

Two springs with the same rated weight can have different curves, with one rising steeply at the end and the other more gradually. The first feels heavier than its number suggests, which is why rated weight alone predicts comfort poorly.

Why does fatigue appear partway through?

Because it accumulates. Each press costs a small amount of effort, and the total load over thousands of presses is what produces tiredness rather than any single press. A spring that costs slightly more per press becomes significant across a long session.

The effect is not linear with weight either. Below a certain point the finger is doing work just to move the key, and above it the work becomes noticeable quickly. There is a comfortable middle that varies by person and by how hard they naturally press.

Does bottoming out change the calculation?

Enormously, because the impact at the bottom of the stroke is a separate load from the spring resistance. Someone who bottoms out hard experiences the end of the curve as a collision, and that contributes to fatigue more than the spring weight itself.

That is why a heavier spring can actually feel better for someone who bottoms out. A firmer spring decelerates the key before it reaches the bottom, which reduces the impact, and the total load can end up lower than with a lighter spring.

How do you measure your own press?

Record how often you bottom out, which you can do by listening, or by typing on a board with a very soft landing and noticing the difference. Then consider whether your fingers feel tired in the muscles that lift or the joints that absorb impact. Those two complaints point to different fixes.

A more objective version is to type a fixed passage and rate your comfort at intervals, comparing two boards in the same session. It is subjective, but doing it side by side within one sitting makes the comparison far more reliable than memory.

Does typing speed matter?

Yes, because faster typing means more presses per minute and therefore more accumulated load. Someone who types quickly will notice a spring that is slightly too heavy much sooner than someone who types slowly, on identical hardware.

Speed also changes how much of the bottom-out energy is absorbed. A fast press arrives at the bottom with more momentum, so the impact component grows with speed, which shifts the ideal spring weight upward for fast typists.

Are lighter springs always better for gaming?

Not necessarily. Lighter springs reduce the effort per press, which helps with repeated actuation, but they also make it easier to rest a finger on a key and trigger it accidentally. The right value depends on how much contact you have with the keys when you are not pressing.

Some people also find very light springs harder to control, because the lack of resistance removes the feedback that tells them where the key is in its travel. That is a genuine control issue rather than a strength one.

How consistent are springs within a batch?

Reasonably consistent but not perfectly so, and the variation is enough to matter on a board where every key should feel the same. We measured differences between nominally identical springs that a careful hand can detect, particularly across a full keyboard.

Mixing weights across a board is a deliberate technique for exactly this reason: heavier springs on keys that are pressed accidentally and lighter ones on keys used constantly. It works, and it is easier to justify than a single compromise value.

Does the spring change with use?

Slightly. Springs relax a little under repeated compression, which reduces the force marginally over a long period. The change is small, but it is in the direction of making the board feel lighter with age, which most people do not notice consciously.

Most of the perceived change in an ageing board comes from other sources: lubricant migration, housing wear, and keycap shine. The spring contributes the least of those, which is worth knowing before attributing a change in feel to it.

Can you swap springs without new switches?

Yes, on most designs, though it means opening each switch. It is a slow job and it introduces the risk of damaging the housing or losing the tiny parts. Whether it is worth it depends on how much the current weight bothers you.

The alternative is buying switches with the weight you want, which is simpler and often barely more expensive. Given the effort involved, swapping springs makes most sense when you already have switches you otherwise like.

What role does the keycap play here?

A small one, mostly through mass. A heavier cap increases the total moving mass, which changes how much force is needed to accelerate it and how much energy arrives at the bottom. The effect is real but much smaller than the spring’s contribution.

It is worth knowing because it explains why the same springs can feel slightly different under two cap sets. If you have already chosen your caps, evaluate spring weight with those caps fitted rather than in isolation.

How should you choose a weight?

Start from how you press rather than from a recommendation. If you bottom out hard, a firmer spring may reduce fatigue by softening the landing. If you type lightly and rarely bottom out, a lighter spring reduces the work per press with no downside.

Then test over a full session rather than a few minutes, because the effect you are managing is cumulative. A board that feels fine for five minutes tells you very little about how it will feel at the end of a working day.

What is worth measuring after this?

Does key height and layout affect fatigue?

Yes, through reach. A layout that requires frequent stretching adds load that has nothing to do with spring weight, and the effect accumulates over a session in the same way. Reach is often the larger contributor to end-of-day tiredness.

Adjusting the board position is free and it addresses the cause directly. Changing spring weight to compensate for a badly placed keyboard treats the symptom instead.

Is fatigue measurable?

Loosely, through timed tasks and reported comfort, and it is inherently subjective. What is measurable is the work done, which is the product of force and distance across the number of presses. That figure predicts fatigue better than any single specification.

Reducing either factor helps. A lighter spring reduces force, a shorter travel reduces distance, and fewer presses reduces the count. Most people only think about the first of those three.

Does rest position matter?

Yes. Resting fingers on keys adds a small constant load and risks accidental presses, and a spring light enough to be comfortable for active typing may be too light to resist that. The right value depends on your habits.

Someone who lifts their hands between words can use a lighter spring than someone who rests. That is a genuine difference rather than a preference, and it explains a lot of disagreement.

Should different rows use different springs?

Some people do this, with lighter springs on the keys used most and firmer ones on the edges. It works, and it reflects the fact that different fingers apply different force.

The cost is complexity and the risk of an uneven feel between neighbouring keys. Done carefully it is an improvement, and done casually it is worse than a uniform board.

Does grip change which weight feels right?

Yes, because different grips apply force through different parts of the hand. A grip that uses larger muscles tolerates a heavier spring, and one that relies on fine finger movement does not.

Testing with your own grip rather than someone else’s recommendation is the only reliable method. The difference is large enough that general advice has limited value.

Does the same spring feel different on two boards?

Yes, because the plate and the case change how the bottom of the stroke feels. A spring that is comfortable on one board can be harsh on another through no fault of the spring.

Evaluating springs on the board you will use is therefore the only valid test. A switch tester gives a rough idea and nothing more.

The force curve at both ends of the stroke, which captures bottom-out behaviour that a single weight figure misses. Comparing curves rather than weights is the natural next step, and it explains most disagreements about how heavy a switch feels.