Tonic immobility during sexual assault - a common reaction predicting post-traumatic stress disorder and severe depression

Acta Obstet Gynecol Scand. 2017 Aug;96(8):932-938. doi: 10.1111/aogs.13174. Epub 2017 Jun 22.


Introduction: Active resistance is considered to be the 'normal' reaction during rape. However, studies have indicated that similar to animals, humans exposed to extreme threat may react with a state of involuntary, temporary motor inhibition known as tonic immobility. The aim of the present study was to assess the occurrence of tonic immobility during rape and subsequent post-traumatic stress disorder and severe depression.

Material and methods: Tonic immobility at the time of the assault was assessed using the Tonic Immobility Scale in 298 women who had visited the Emergency clinic for raped women within 1 month of a sexual assault. Information about the assault and the victim characteristics were taken from the structured clinical data files. After 6 months, 189 women were assessed regarding the development of post-traumatic stress disorder and depression.

Results: Of the 298 women, 70% reported significant tonic immobility and 48% reported extreme tonic immobility during the assault. Tonic immobility was associated with the development of post-traumatic stress disorder (OR 2.75; 95% CI 1.50-5.03, p = 0.001) and severe depression (OR 3.42; 95% CI 1.51-7.72, p = 0.003) at 6 months. Further, previous trauma history (OR 2.36; 95% CI 1.48-3.77, p < 0.001) and psychiatric treatment history (OR 2.00; 95% CI 1.26-3.19, p = 0.003) were associated with the tonic immobility response.

Conclusions: Tonic immobility during rape is a common reaction associated with subsequent post-traumatic stress disorder and severe depression. Knowledge of this reaction in sexual assault victims is important in legal matters and for healthcare follow up.

Keywords: Depression; Tonic Immobility Scale; peritraumatic reactions; post-traumatic stress disorder; rape; sexual assault.

MeSH terms

  • Adolescent
  • Adult
  • Depressive Disorder / psychology*
  • Female
  • Humans
  • Immobility Response, Tonic*
  • Middle Aged
  • Predictive Value of Tests
  • Psychiatric Status Rating Scales
  • Rape*
  • Stress Disorders, Post-Traumatic / psychology*
  • Surveys and Questionnaires
  • Young Adult