Behind TIME’s Science of Exercise Cover

LIFE’s Gjon Mili was known for his stroboscopic images–a series of rapid flashes that allowed him to capture multiple movements in a single photograph. His background was extensive. He received a degree in electrical engineering from the Massachusetts Institute of Technology and worked as a lighting researcher with the Westinghouse Lamp Company in the late 1920s and 30s. The advancements made in the electronic flash at that time helped him hone his photography skills.

This newer method of capturing images allowed him to take thousands of photographs of various subjects including athletes and dancers through the course of his distinguished career. One of these pictures is featured on this week’s cover of TIME, dedicated to the science of exercise.

Colorized by Sanna Dullaway to make it appear as if it had been taken in the present day, Mili’s images were a new challenge for the artist. “It was something new,” she says. Used to colorizing photographs that captured only one moment, with Mili’s photographs she had to deal with several moments contained within one frame. “The longer I looked at the stroboscope photographs the more intricate details I discovered,” she says.

In each image, Mili carefully captured the ongoing motion of the subject, detailing in one instance, the process of a Yale basketball player making his one-handed hook shot and displaying the positions of a dancer’s arm movements in another. The challenge in colorizing Mili’s work was ensuring that the body parts of each subject did not cross over with the color of the subject’s outfit while not sacrificing the quality of lighting Mili achieved.

“It was more realizing what I was actually looking at when there were a lot going on in the same spot, like in the basketball and jump rope photographs there was a lot of crossover,” she says. “What I thought was a leg turned out to be an arm.”

Sanna Dullaway is a photo editor based in Sweden. See more of her work here.

Myles Little is a senior photo editor at TIME.

Bianca Silva is a contributor to TIME LightBox. Follow her on Twitter.