Both can lay claim to having the quickest hands in heavyweight boxing and it is likely to be a crucial factor as they battle for the WBO belt.
Ruiz's promoter Bob Arum reckons his Mexican fighter has the ability to beat Kiwi Parker to the punch, but Parker is having none of that.
"He has great hand speed and I respect his hand speed a lot," Parker said yesterday. "But I'm the fastest heavyweight in the world and I back myself on my speed.
"I believe it's just a gift that I have, to be able to let my hands go fast, and I feel like it's improving all the time."
Not surprisingly, trainer Kevin Barry agrees with Parker while Ruiz's coach Abel Sanchez is backing the speed of his own man. Arum, the founder and chief executive of Top Rank, meanwhile, goes further, saying Ruiz is the quickest he has seen since the late, great, Muhammad Ali.
"Andy has the fastest hands, that I have seen, on any heavyweight since Muhammad Ali, who I promoted over 50 years ago," Arum said. "I am stunned to see Andy Ruiz look as good as he does, and he better look as good as he does because he's in with a heavy-handed kid in Joseph Parker.
"The truth is, we wouldn't have allowed this fight to happen, or for Andy to go to New Zealand to fight, if we didn't think he had a really big, big chance to win the fight."
Ruiz looked fast when the New Zealand Herald watched him shadow boxing at Sanchez's famous Summit Gym, in Big Bear Lake, California, recently, but so did Parker at his Las Vegas base.
Another factor of course is power and Parker appeared to possess plenty of that when hitting the heavy bag and Barry's pads in the ring at their suburban Las Vegas gym.
The 24-year-old South Aucklander puts his increased power down to linking with new strength and conditioning coach Elliott Kleven.
"Ruiz is a fighter who I have a lot of respect for. In the past he had a lot of weight on and you can tell he is taking it seriously because he has dropped a lot of weight. He has moved away from home, he's training at altitude with a good trainer, so it's not a surprise to me because it is a big occasion. We both want to win, we both want to make history."
Parker's increased power was evident against his most recent opponent, Alexander Dimitrenko, whom he dominated from the start in the knockout victory in Manukau in October. The fact that he has such a busy schedule - fighting five or six times a year - and has a stable weight is likely to be another bonus for Parker. "I came into camp in good shape," he said. "I only had a week off, just working on different techniques and approaches to fight a fighter like Andy.
"With Andy I think even when he was big and had the weight, he was fit, strong and fast, so with this taking off the weight, it will increase his fitness and make him a lot better fighter. "
