Theodore Roosevelt’s childhood was marred by perpetual illness, namely severe asthma that made breathing a terrible strain on his heart. A countless number of nights were suffered in a state of panic, his chest squeezing tight and smothering him to near death.
Nearing the age of 12, Teedie (as his family was wont to call him) was weak and lanky and worse off than ever. His father had to take him across the state of New York no less than three times for a "change of air" over that summer before his twelfth birthday. This eventually led to a meeting with Dr. A.D. Rockwell.
The doctor’s suggested treatment seemed obvious, even redundant for the already active Teedie. Plenty of air and exercise. But what Rockwell meant specifically was the need for the boy to transform the frail, narrow cavity that was his chest into a thick muscular barrel that could reduce the strain on heart and lungs.
His father, Theodore Sr., presented his son with a challenge:
"Theodore," the big man said, eschewing boyish nicknames, "you have the mind but you have not the body, and without the help of the body the mind cannot go as far as it should. You must make your body. It is hard drudgery to make one’s body, but I know you will do it." (Edmund Morris, The Rise of Theodore Roosevelt)
Theodore’s mother, present at this very moment, recalled her son’s reaction. With a half-grin, half-snarl, he jerked his head back, clenched his teeth, and proudly said, "I’ll make my body." And then he set about doing just that.
He swung chest weights at Wood’s Gymnasium, or went about lifting, pushing, or pulling the athletic equipment set up at home by his father. He acquired the focus of a serious bodybuilder, dedicating himself to, as his sister Corinne remembered, "widening his chest by regular, monotonous motion—drudgery indeed."
This routine carried on for years. Changes to his appearance were negligible at first, certainly only visible to Theodore himself, but the effect on his health was noticed by all.
As Edmund Morris notes in The Rise of Theodore Roosevelt:
There is not a single mention of illness in his diary throughout August of 1871—his longest spell of health in years.
This is the very beginning of Roosevelt’s metamorphosis into the beacon of manliness we recognize him as today. His incredible resoluteness as a boy followed him into adulthood, into his vocation. It allowed him to thrive in the Badlands, participating in roundups that involved five thousand cattle and five hundred horses, that required of him several 24-hour days on horseback (which he described as "great fun"). It’s the resoluteness that drove him and his Rough Riders up San Juan Hill, that carried him into the presidency, that allowed him to drop elephants and white rhinos in Africa, and to navigate his way through the Amazon and down the River of Doubt.
All of this began with the simple act of a small boy picking up and swinging a chest weight while declaring adamantly, "I will make my body."