The group were reaching the end of the activity when he stopped and fell to the ground and became unconscious.
He received immediate first aid assistance and an army medic started treatment within five minutes of his collapse.
The incident has sparked an inquiry into selection processes for the NZSAS.
Defence Force spokesman Major John Gordon said there was a robust medical plan in place for the training.
"When you have such rigorous and demanding selection processes there is going to be a risk of injury or medical issues," he said.
"The large proportion of issues would relate to physical injury as opposed to any sort of heat-related issues."
Army chief Major-General Tim Keating said the inquiry would review whether the selection process needed to change.
- HERALD ONLINE