I won't bore you with the math details, but I learned in freshman physics that if you hang an object, say with two strings; if the strings are straight up and down, each one carries half the weight of the object. If you move the strings so the tops are farther apart, the tension on each string becomes more than half the weight; and the farther apart the tops of the strings get, the more the tension on them increases.This means that when our Lord was hanging from the Cross, each of His arms was carrying much more than half His weight, and considering how far apart His wrists were nailed, the tension on His arms may have been enough to dislocate His shoulder joints.
Worse than that: IF (don't try it alone!) you go to a gym or playground and jump up and hang from the high bar so your feet are unsupported, you will find that you can inhale but you cannot exhale. So when Jesus wanted to breathe, He had to push His body upwards on the Cross against the nail going through His feet. Which must have hurt incredibly, and He could stand it only so long, so He would sag back down again, and found Himself unable to breathe, and the whole process would start all over again.
The object of crucifixion was to cause death by asphyxiation, coupled with agonizing pain and increased weakness. Jesus had had nothing to eat since supper the night before, and He very likely had had nothing to drink either, which contributed to His physical weakness.
But He made Himself stay alive long enough to ask His Father to forgive everyone;
promise Paradise to the repentant thief;
give Mary to John and all of us as our mother;
utter a cry of seeming despair (actually quoting Psalm 22 which ends as praise to God, and note well this is the only place in Scripture where Jesus refers to God other than as "Father");
say that He was thirsty (some spiritual writers imply spiritual thirst for souls as well as His physical thirst);
announce the completion of our salvation;
and commend His Spirit to God.
Then He willed Himself to die, which is what He came to us for.
Pilate was surprised that Jesus died so soon (see Mark 15:42ff) and sent a centurion (commander of a hundred men) to see if Jesus was really dead. When the centurion reported that Jesus was dead, Pilate released the body to Joseph of Arimathea. (When a Roman army centurion said someone was dead, you can bet that one was really dead.)
