This site is a measuring instrument, and the thing being measured is a hand. That is worth saying plainly once.
What the fatigue threshold is
Sustained rapid clicking loads the forearm flexors and extensors in a static contraction — the muscles hold tension continuously while small movements repeat inside it. For most people the threshold arrives within twenty seconds of continuous clicking, and it announces itself as a dull ache in the forearm rather than in the fingers.
The per-second profile shows it before you feel it. When the last third of an interval reads consistently lower than the first third, and rest between attempts stops restoring the opening rate, the limiter has moved from technique to tissue.
The techniques are not equal here
- Single clicking loads the least. It is the only method most switches were designed for, and the only one that is comfortable at length.
- Butterfly shares the work across two fingers, which is easier on any one of them.
- Jitter is the hardest on the arm by a wide margin, because the rate comes from sustained tension rather than from movement. Treat it as a sprint.
- Drag clicking loads the fingertip and the switch rather than the muscle, and mostly damages the mouse.
Practical limits
Three ten-second sets, twice a day, with a full minute of rest between sets. Stop at the first ache rather than the second. A gain of 40 to 80 CPM over two weeks is a normal outcome from that, and pushing harder does not accelerate it — the adaptation is neural, and neural adaptation runs on rest.
When to stop entirely
Ache during a set is ordinary. Sharp pain, tingling, numbness, or anything that persists after the session is not, and is a reason to stop for a week rather than to change technique. If it recurs after that week, it is worth raising with a doctor, who will be considerably more use than a click test.
None of this makes the measurement less interesting. It just means the instrument has a subject, and the subject is the part that does not have a replacement switch.