Sounds rather bizarre that volunteers would agree to get literally nailed to crosses in the name of science. I guess they drew the line at getting their legs broken eh. Anyhow this truly was a Miracle Man who if He had wanted to keep from shedding blood at all, He easily could have willed it. And so any suffering He suffered, was suffered by His humble choice.
In line with your thoughts, consider the many experts who have described the face of Christ on the Shroud, as “peaceful”.
“I guess they drew the line at getting their legs broken.” The volunteers were bound at the wrist, not nailed. And the situation of broken legs was simulated by the volunteers by hanging only by the wrists — they could still breathe just fine.
His tests that explored a volunteer's reactions to being on a cross assumed a pedulum, a foot rest, which allowed a much easier time on the cross, not an actual nailing to the stapes without a footrest, a much more common form of crucifixion. Earlier experiments assuming no pedulum (the position of the feet on the Shroud suggest this) found early exhaustion from having to choose between the pain of hanging on the nails through the arms (Zugibe's volunteer had a leather padded strap) and an inability to inhale completely complicated by fluid on the lungs from a severe scourging, to trying to get a deeper breath by pushing up against the nail driven through one's feet and that agony. Zugibe's allowed his volunteers frequent rest breaks. I discount his findings discounting asphyxiation as a mode of death.