After scientists studied a number of people having sex in an MRI scanner there’s one thing that has left them stumped about the human body – providing them with useful insights
06:30, 17 Jan 2026Updated 07:18, 17 Jan 2026
There was one thing that the scientists couldn’t figure out during sex(Image: BMJ)
A couple decided to get intimate during an MRI scan, all in the name of science.
Ida Sabelis and her boyfriend Jupp gave scientists an insight into exactly what happens to the body during sex – and there’s one thing the experts can’t quite figure out. The experiment, which featured in the British Medical Journal 1999 entry, concluded that “taking magnetic resonance images of the male and female genitals during coitus is feasible and contributes to understanding of anatomy” – but there was one element of the experiment that they weren’t expecting.
The astonishing study said: “The images obtained showed that during intercourse in the ‘missionary position’ the penis has the shape of a boomerang and 1/3 of its length consists of the root of the penis. During female sexual arousal without intercourse the uterus was raised and the anterior vaginal wall lengthened. The size of the uterus did not increase during sexual arousal.”
The MRI scan gave scientists a real insight into how bodies react during sex(Image: BMJ)
But while this was insightful, there was something else the experts couldn’t work out. There were a total of eight couples, and three single women taking part in the experiment. The experts found that during all 13 instances of sex in an MRI machine, the woman’s bladder would rapidly fill up.
The reason for this has stumped scientists, with expert Menko Victor ‘Pek’ van Andel suggesting it could be ‘evolution’s way to force women to urinate after sex’ and potentially ‘avoid urinary tract infections’. While this theory has not been confirmed, the expert said: “In every final scan we could see a big, full bladder, even though most of the women went to the toilet before they went inside the MRI.”
Ida said that sex in the MRI scanner wasn’t romantic but they didn’t need Viagra to get them going. She has previously spoken out about why she did it, noting that she is a big campaigner of women’s rights and was keen to broaden the understanding of the female body in science and medicine. Ida said the whole experience was an ‘act of love and a performance’.
While the scientific experiment was a safe success, others haven’t been so lucky. One woman was left with horrific injuries after a sex toy she left inside herself was dragged through her body during an MRI scan. The 22-year-old is said to have inserted a “butt plug” before the procedure – apparently mistakenly believing it was entirely made of silicon.
However, it contained metal at its core and, as a result, the item reacted dangerously with the machine, causing the toy to be dragged from her rectum and up into her body. An image was later circulated online and led to warnings about wearing metal objects during the scan.
A socia media user known as DreadPirateZero took to X, formerly Twitter, to share the picture along with the caption: “Never wear a butt plug to your MRI appointment. My God.” Their post further claimed that the sex toy had been pulled through the patient’s body and into their chest cavity, and that the woman managed to survive but with “major injuries”.
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