After graduating, McKenzie gained experience as a physician and surgeon, opening his own practice and teaching anatomy at McGill University.[14] He soon became convinced of the need for preventive medicine. He believed that training and preparation would prevent illness, physical deterioration and accidents, so he developed a physical exercise program.[15] In 1894, in an article on the role of physical education in universities, he was firmly convinced that the benefits of training not only benefited athletes, but also extended to those who had physical or health problems that kept them away from sports such as football or hockey. Individual differences had to be taken into account and physical activity programs had to meet the needs of all students, regardless of their grade or skill level for a specific sport.[12]​[13]​.

In 1894, he worked as the personal family physician of the Governor General of Canada, John Hamilton-Gordon.[16] He stayed for fifteen months at the governor's residence, where he met several political figures of the time.[4]

At that time, McKenzie proposed to the University the creation of a department and faculty of physical education, but McGill denied the request, citing lack of money. Later, in 1898, the University appointed him Medical Director of Physical Training, being the first in history with such a position at a Canadian university.[17]​ He established specific programs for three categories of students: athletic, sedentary and "bookworms",[18]​ and the faculty allowed him to perform physical examinations on new students.[17]​.

In addition to fulfilling his obligations at the University and attending to his practice in Montreal, McKenzie still had time to dedicate himself to art. He became fond of watercolors and always carried a small notebook in his pocket in which to scribble the outline of what caught his attention.[19]​ His interest in sculpture was the result of his extensive knowledge of human anatomy, his desire to represent athletics artistically, and the need to overcome the limitations that two-dimensional artistic forms imposed on the faithful reproduction of musculature.[20]​.

He began with a series of expressive masks that he called Violent Effort, Breathlessness, Fatigue and Exhaustion.[17] To make them, he studied the behavior of facial muscles in situations of physical effort and emotional tension.[21] With the result of this research he published the article The Facial Expression of Violent Effort, Breathlessness and Fatigue in the magazine in 1905. London scientist Journal of Anatomy and Physiology in London.[21][22]​.

His first complete sculpture was The Sprinter ('The Sprinter'). For its execution, he measured and studied in detail the limbs and torsos of numerous athletes. The Sprinter was the second in a series of more than two hundred sculptural works of athletic figures, martial figures, busts, masks, friezes and medallions spread throughout Canada, the United States, England and Scotland.[20]​ His work as a sculptor opened the doors of the Royal Canadian Academy of Arts.[23]​.

In 1890, his childhood friend James Naismith took the position of director of physical education that had become vacant at McGill after the death of Frederick Barnjum. Naismith appointed McKenzie his assistant during that course and, the following year, due to his move to the United States, McKenzie replaced him as director.[12]​[13]​.

After graduating, McKenzie gained experience as a physician and surgeon, opening his own practice and teaching anatomy at McGill University.[14] He soon became convinced of the need for preventive medicine. He believed that training and preparation would prevent illness, physical deterioration and accidents, so he developed a physical exercise program.[15] In 1894, in an article on the role of physical education in universities, he was firmly convinced that the benefits of training not only benefited athletes, but also extended to those who had physical or health problems that kept them away from sports such as football or hockey. Individual differences had to be taken into account and physical activity programs had to meet the needs of all students, regardless of their grade or skill level for a specific sport.[12]​[13]​.

In 1894, he worked as the personal family physician of the Governor General of Canada, John Hamilton-Gordon.[16] He stayed for fifteen months at the governor's residence, where he met several political figures of the time.[4]

At that time, McKenzie proposed to the University the creation of a department and faculty of physical education, but McGill denied the request, citing lack of money. Later, in 1898, the University appointed him Medical Director of Physical Training, being the first in history with such a position at a Canadian university.[17]​ He established specific programs for three categories of students: athletic, sedentary and "bookworms",[18]​ and the faculty allowed him to perform physical examinations on new students.[17]​.

In addition to fulfilling his obligations at the University and attending to his practice in Montreal, McKenzie still had time to dedicate himself to art. He became fond of watercolors and always carried a small notebook in his pocket in which to scribble the outline of what caught his attention.[19]​ His interest in sculpture was the result of his extensive knowledge of human anatomy, his desire to represent athletics artistically, and the need to overcome the limitations that two-dimensional artistic forms imposed on the faithful reproduction of musculature.[20]​.

He began with a series of expressive masks that he called Violent Effort, Breathlessness, Fatigue and Exhaustion.[17] To make them, he studied the behavior of facial muscles in situations of physical effort and emotional tension.[21] With the result of this research he published the article The Facial Expression of Violent Effort, Breathlessness and Fatigue in the magazine in 1905. London scientist Journal of Anatomy and Physiology in London.[21][22]​.

His first complete sculpture was The Sprinter ('The Sprinter'). For its execution, he measured and studied in detail the limbs and torsos of numerous athletes. The Sprinter was the second in a series of more than two hundred sculptural works of athletic figures, martial figures, busts, masks, friezes and medallions spread throughout Canada, the United States, England and Scotland.[20]​ His work as a sculptor opened the doors of the Royal Canadian Academy of Arts.[23]​.