History is replete with experiments that are, shall we say, a little on the ethically dubious side. Up there with the winners of the "this would not be allowed today" category for science are the baffling number of medically trained professionals who crucified people to figure out how exactly Jesus died.

First out to bat was Dr Pierre Barbet, who took the trouble to experiment on people who were already dead. Barbet was intrigued by the "shroud of Turin", a large piece of cloth supposedly wrapped around Jesus Christ after his crucifixion or someone else who was executed in this manner. The shroud has been carbon-dated to 1260-1390 CE, making it almost certainly a forgery, with the only other option being it was a dirty cloth mistaken for Jesus's death blanket.

However, Barbet was not aware of this and believed that the blood from the person's hand wounds depicted in the shroud appeared to flow in two different directions. He believed that the bloodstains could be caused by Jesus shifting his position, lifting himself up in order to breathe.

Naturally, Barbet wanted to test this by finding himself a corpse to nail to a cross he had built himself. The experiment appeared to confirm what Barbet believed: the body slumped into a similar position to that on the shroud, suggesting that this position made it difficult to breathe, and it was from this position that the occupant of the shroud attempted to pull himself up.

This was not good enough for others interested in crucifixion. So, in the 1940s, German radiologist Hermann Mödder began crucifying medical students. Thankfully opting for leather straps instead of nails, Mödder hung his students on crosses in positions designed to mimick crucifixion. If you think your college experience was bad, imagine if one of your lecturers asked if they could try out a well-known method of execution on you.

He monitored their vital signs during their crucifixion, taking them off the cross at around the six-minute mark when their blood pressure began to drop and breathing became difficult.

“What will set in after the end of the sixth minute can be foreseen by the physician: unconsciousness, intense pallor, sweating," he wrote of his experiments. "In short: collapse due to insufficient blood supply to the heart and brain.”

Now you'd think that people would be satisfied with this explanation. The position during crucifixion causes difficulty breathing. If the victim doesn't die of blood loss (from the nails or whipping before execution) they will die of exposure or difficulty breathing. However, there's one more man who began crucifying people, in fact going on to possibly crucify the most people since Roman times: Frederick Zugibe.

Zugibe, as well as being a medical examiner, was pretty religious and wanted to give people the experience of being Jesus – for some reason not opting for one of Jesus's less painful days, or maybe one of his days off. At his home, he set up medical monitoring equipment, and staffed with volunteers he began allowing people to dangle themselves from a cross for as long as they wanted.

Some lasted up to an hour, before being taken down. Unlike the medical students, he found that they suffered no difficulty breathing, which he attributed to how he had bound his subjects' feet, whereas Mödder had not. 

However, he also found that the subjects, when prompted, were unable to pull themselves up to positions better for breathing, finding it pretty much impossible.

Thanks to far too much experimentation, and our knowledge of the human body, we now know that victims of crucifixion did die through difficulty breathing.

"The weight of the body pulling down on the arms makes breathing extremely difficult,"  Jeremy Ward, a physiologist at King's College London told the Guardian. Those who don't suffocate could die as "the resultant lack of oxygen in the blood would cause damage to tissues and blood vessels, allowing fluid to diffuse out of the blood into tissues, including the lungs and the sac around the heart."

As bad as these experiments were, evidence for this hypothesis comes from a much worse source. During World War II, the Nazis conducted crucifixions as a method of torture. At Dachau, one Father G Delorey witnessed the Nazis suspending inmates by their wrists on a horizontal bar.

"After their hanging for one hour," Delorey wrote, "the victims could no longer exhale the air that filled their chest.”

They could only breathe when they were able to pull themselves up high enough to take the weight off their chests.