And, perhaps not surprisingly, he has the scars to match the lifetime he has spent weightlifting at the highest level for Great Britain, earning 52 world records and a torn bicep and dislocated elbow along the way.
Yet the diminutive Mr McKenzie - who now lives in Auckland - had a surprising message when he visited Dunedin yesterday in his more recent role as a back injury prevention consultant.
Mr McKenzie was in the city to offer advice to a group of nine workers at the Emerson Brewing Co plant, and was happy to take on all challenges - lifting beer kegs and bags of malt to demonstrate correct technique, and even hoisting Emerson's owner, Richard Emerson.
However, speaking to the Otago Daily Times, he said it was not the big lifts that people had to be wary of.
Rather, it was the smaller efforts, combined with bad technique, that often did the damage.
"It's the smaller things people take totally for granted. It's not really the heavy objects because you are too smart with the heavy objects. You respect it," he said.
Mr McKenzie should know, after a long and distinguished career in weightlifting since leaving his homeland of South Africa for Great Britain to pursue his sport.
He represented Great Britain at three Olympics - 1968, 1972 and 1976 - and won four Commonwealth Games gold medals, numerous other open and masters titles, and was presented with an MBE by Queen Elizabeth II.
He injured his elbow and bicep just three months before the 1972 Munich Olympics, but recovered in time to compete.
He has lived in New Zealand for the past 34 years, and travels from his home in Auckland to offer consultation services to companies around the country, including Fulton Hogan, and others in Britain, Europe and the United States.
He trained "almost every day" and could still bench press 100kg - equalling a world record he set at the Nevada World Masters Power Lifting Championships in 2004, he said.
People were generally "very poor" at looking after their backs, and stressed that prevention was better than a cure.
"Once you get a back injury it will always be there," he said.
