We often make the assumption that the actual cause of death in a crucifixion is the asphyxiation resulting from the difficulty in breathing while the weight of the body is supported by the arms. Some research however, would appear to cast a degree of doubt on this;
(copied from wikipedia)
"
Cause of death
The length of time required to reach death could range from hours to days depending on method, the victim's health, and the environment. Death could result from any combination of causes, including blood loss resulting in
hypovolemic shock,
sepsis following infection due to the wounds caused by the nails or by the
scourging that sometimes preceded the crucifixion, or eventual
dehydration.
[40][41]
A theory attributed to
Pierre Barbet holds that, when the whole body weight was supported by the stretched arms, the typical cause of death was
asphyxiation.
[42] He conjectured that the condemned would have severe difficulty inhaling, due to hyper-expansion of the chest muscles and lungs. The condemned would therefore have to draw himself up by his arms, leading to
exhaustion, or have his feet supported by tying or by a wood block. When no longer able to lift himself, the condemned would die within a few minutes.
Experiments by
Frederick Zugibe have, however, revealed that, when suspended with arms at 60° to 70° from the vertical, test subjects had no difficulty breathing. Subjects did suffer rapidly increasing pain,
[43][44] which is consistent with the Roman use of crucifixion to achieve a prolonged, agonizing death. Legs were often broken to hasten death through severe traumatic shock and
fat embolism."
The full article can be found here;
http://en.wikipedia.org/wiki/Crucifixion
and makes for a very interesting read