Twitch and Tetanus Timing
A muscle twitch is the mechanical response to a single stimulus, while tetanus develops when repeated stimuli arrive so close together that force from one contraction is still present when the next one begins. A twitch and tetanus timing calculator focuses on the timing relationship between the latent period, contraction period, relaxation period, stimulus interval, and the resulting force pattern.
Core timing idea
One full twitch cycle is the sum of the three main phases:
\[
\begin{aligned}
T_{\text{cycle}} &= T_{\text{latent}} + T_{\text{contraction}} + T_{\text{relaxation}}
\end{aligned}
\]
Here, \(T_{\text{cycle}}\) is the total duration of one twitch, \(T_{\text{latent}}\) is the delay before measurable force appears, \(T_{\text{contraction}}\) is the force-rising phase, and \(T_{\text{relaxation}}\) is the force-falling phase. The key comparison is between the time between stimuli, \(\Delta t\), and the full twitch cycle.
\[
\begin{aligned}
\Delta t &= \frac{1000}{f}
\end{aligned}
\]
In this expression, \(f\) is the stimulus frequency in hertz and \(\Delta t\) is the interval in milliseconds between successive stimuli. As frequency rises, the interval becomes shorter, which increases the chance that contractions will overlap.
How to interpret the result
If the next stimulus arrives after full relaxation, the response remains an isolated twitch. If it arrives during relaxation, force from successive contractions adds and wave summation appears. If only partial relaxation remains between contractions, the pattern is incomplete tetanus. If stimuli are frequent enough that relaxation nearly disappears, the muscle enters complete tetanus and the force trace becomes strongly fused.
- A larger stimulus interval means more time for relaxation and less summation.
- A smaller stimulus interval means greater overlap and stronger force buildup.
- The force-time graph shows both timing and fusion, not just a final label.
- Fast-twitch and slow-twitch muscle presets shift the timing ranges for these patterns.
Example: if \(T_{\text{cycle}} = 100\,\text{ms}\) and \(\Delta t = 60\,\text{ms}\), the next stimulus arrives before the twitch has finished, so the expected response is summation or incomplete tetanus rather than an isolated twitch.
This tool is best used for studying contraction timing, force summation, and stimulus-frequency effects in skeletal muscle. It is not meant to replace deeper models of calcium handling, cross-bridge kinetics, or whole-muscle mechanics, which are the next step when a more advanced physiological analysis is needed.