Learning More: Tonic Immobility Part 2

Part 2 of our series on Learning More about Tonic Immobility:

“I felt paralyzed”: breaking down a sexual assault reaction (Part 2)

Welcome back! Last time, we talked about a reaction that can happen during sexual assault called tonic immobility. Basically, this is a state of temporary paralysis where you’re fully conscious but you can’t move, yell, or feel pain. It’s induced by two things: extreme fear and either physical restraint or just the perception of being trapped. Today, we’ll get into more detail on what scientists know about tonic immobility during sexual assault.


Originally, tonic immobility was researched in animals, which is what initially led to the list of characteristics and conditions associated with tonic immobility. Since the realization that this also occurs in humans, not just animals, researchers have learned much more about how this phenomenon affects people. Research on human tonic immobility happens differently than animal tonic immobility, however. With animals, experimenters induce this reaction to observe it happening in real time since we can’t ask animals about their experience with tonic immobility. With people, it would be very unethical to put a person through this reaction when we have the option of asking them about it instead. Experts have put together a survey to retroactively figure out how many tonic immobility symptoms someone had—without putting them through tonic immobility all over again. Getting a certain score or above on the survey indicates that the respondent did, in fact, have a tonic immobility reaction. These survey results can then be compared with other factors, like type of trauma or PTSD survey scores, to then draw conclusions.

A great deal of this research focuses on tonic immobility during sexual assault, which is the main focus of this post. One of the earliest human tonic immobility studies in 1993 showed that there was an immobility response in 37% of the sexual assault survivors who took the survey2. Later, in a 2005 study, researchers found that 52% of respondents who had been through childhood sexual assault experienced tonic immobility3. Furthermore, a 2017 study in Brazil found that tonic immobility survey scores were two times higher for sexual trauma than any other type of trauma4

Ultimately: this trauma response is VERY common in both adult and childhood sexual assault.

There are a few notable post-assault outcomes linked to tonic immobility. One study showed a stronger association between tonic immobility and the female gender, and tonic immobility and PTSD (as compared to respondents of the male gender and without PTSD)5. Expanding the latter association, another study linked tonic immobility to more negative PTSD diagnoses and worse responses to PTSD treatment6. The link between tonic immobility and poorer PTSD outcomes is considered to be a result of the perception of being trapped, one of the two necessary cues to turn this reaction on7. Tonic immobility is also connected to stronger feelings of guilt and self-blame after an assault, which can further worsen PTSD and negatively impact a survivor’s healing process4, 8. Finally, just going through tonic immobility may be traumatic in and of itself 9. The bottom line?

There’s a complex relationship between tonic immobility during a sexual assault and what negative consequences a survivor faces as a result of this reaction.

Knowing how drastic the characteristics of tonic immobility are, how frequently it occurs in sexual assault, and how it can lead to many negative consequences for survivors, there are steps we can all take to help out survivors. Next time, we’ll talk about what to do with all of this tonic immobility information and how to navigate conversations about sexual assault reactions. Stay tuned!

ABOUT THE AUTHOR: Britta Koenen is a senior at St. Olaf College studying biology and women’s and gender studies. Her senior project involved researching, writing, and creating educational programs focused on tonic immobility. Contact her at britta.koenen@hotmail.com.