On the Fourth of July, 1939, 61,808 New York Yankees fans crowded into the House that Ruth Built. But they weren’t there for the Bambino. Not that day.

Instead, the afternoon marked a moment of appreciation and fond farewell for Lou Gehrig, the “Iron Horse,” the first baseman who played in 2,130 consecutive games.

The tall, once-muscular ballplayer donned his flannel, pinstriped uniform one last time on that hot July day in the Bronx. Just two weeks earlier, on June 19, he had celebrated his 36th birthday.

On May 1, 1939, Gehrig gallantly took himself out of the lineup because he could no longer will his body to perform athletic miracles. On his back was the number 4, indicating his position in the batting order, right after Ruth (#3); it was the first number to be “retired” in major league baseball. Lou Gehrig approached the microphone, looked out at the vast crowd of fans, and said, “For the past two weeks, you’ve been reading about a bad break. Today, I consider myself the luckiest man on the face of the Earth…I may have had a tough break, but I have an awful lot to live for.”

Thanks to radio broadcasts, millions more heard what is, without doubt, the most famous speech ever delivered from the diamond. And, of course, it was reprised and immortalized for many millions more by Gary Cooper in the 1942 Hollywood motion picture, “The Pride of the Yankees.” The American Film Institute later ranked “the luckiest man” speech the 38th best on its list of the 100 Greatest Movie Quotes, but these were no scripted lines. Gehrig actually said them.

Virtually every American today, be they a baseball fan or not, knows Lou Gehrig’s “bad break” was his diagnosis with amyotrophic lateral sclerosis (ALS), a fierce neurodegenerative disorder that robs one of muscle control, swallowing, breathing, and ultimately, life.

Two months earlier, on May 1, 1939, Gehrig gallantly took himself out of the lineup because he could no longer will his body to perform the athletic miracles that made him, arguably, the best baseball player ever to play the game. The Hall of Famer won the Triple Crown in 1934 and was the American League’s Most Valuable Player twice, in 1927 and 1936. He was a member of six World Series Championship teams (1927, 1928, 1932, 1936, 1937, 1938) and during his 14-year career, he knocked out 493 homers and 2,721 hits, batted in 1,995 runs, and achieved a lifetime batting average of .340!

His history of so many head injuries may well have played a role in his rapid decline and death. Gehrig began experiencing his first neurological symptoms in 1938, right around the time of his 35th birthday. Desperate to find out the cause of his problems, he and his wife visited the famed Mayo Clinic, from June 13 to June 19, 1939. On the 19th, Gehrig’s 36th birthday, his internist, Dr. Harold Habein, certified his diagnosis of the poorly understood, rare and typically fatal ALS.

Today’s medical consumer would be shocked to learn that Gehrig’s doctors couched the prognosis in terms of a 50-50 chance of recovery, even though they knew this not to be so. Yet medical ethics and practice of this era often emboldened physicians to tell a patient partial truth about a lethal malady or, paternalistically, not to tell the patient at all, and, instead, only inform close relatives. Nevertheless, recovery was a belief Gehrig hung onto for the remaining two years of his life. In retirement, he took on an active role as a member of the New York City Parole Commission, but by spring 1941, he had lost too much strength to fulfill those duties. He died on June 3, 1941, just 16 days shy of 37 years of age.

Approximately 30,000 people living in the United States have the incurable and progressive ALS, most of them are men between the ages of 40 and 70 years. Many die within a few years of being diagnosed; others, such as the famed physicist Stephen Hawking, can live for years with their brains fully functioning even though their bodies and muscles have degenerated and wasted.

But was ALS the cause of Lou Gehrig’s death?

Maybe not, say a group of neurologists, physicians and pathologists at the Boston University School of Medicine Center for the Study of Traumatic Encephalopathy. These doctors are presently conducting landmark research on the brains of deceased former NFL players. In 2010, they presented convincing pathological evidence that “repetitive head trauma experienced in collision sports” may be associated with the development of motor-neuron disease. In other words, repetitive head trauma, or chronic traumatic encephalopathy (CTE) may result in a syndrome that mimics ALS. (Journal of Neuropathology and Experimental Neurology. 2010; 69 (9): 918-929)

Lou Gehrig was called the Iron Horse not only for his incredible strength and speed, but also because he was always in the line-up, no matter what injury he incurred the day before. On numerous occasions, he was “beaned” by an errant pitch or hit in the face by ground balls, suffered repeated concussions, episodes of loss of consciousness, and other forms of head trauma, without the slightest protection, beyond wearing a woolen baseball cap. Gehrig collided with rapidly moving objects unrelated to the batter’s box or first base, as well. In 1924, for example, during a post-game fight with the Detroit Tigers, Gehrig took a swing at Ty Cobb, missed, fell, and hit his head on concrete pavement, only to lose consciousness for a brief period of time.

Lou Gehrig was called the Iron Horse not only for his incredible strength and speed, but also because he was always in the line-up, no matter what injury he incurred the day before. It is unlikely that we will ever definitively prove whether Gehrig died of ALS or a trauma-related motor neuron disorder diagnosis. His remains were cremated and the Mayo Clinic has sealed his records. Without Gehrig’s patient chart, it is impossible to even know if an autopsy was conducted. Yet his history of so many head injuries may well have played a role in his rapid decline and death.

The irony, of course, is that ALS is widely known and referred to as “Lou Gehrig’s Disease.”

It is only over the past several years that doctors (and athletes) have focused on the long-term effects of brain injuries associated with contact sports. With each passing year, the risks and dangers of these repetitive brain injuries have become abundantly clear. Indeed, they demand a slate of safety measures, especially for youngsters who engage in such activities.

Whatever Lou Gehrig’s precise diagnosis was, what better way to celebrate his birthday than by fighting both amyotrophic lateral sclerosis and sports-related concussions? We can attack ALS by donating money to research about its cause and treatment; and we can begin to prevent chronic traumatic encephalopathy (CTE) by making certain the heads (and brains) of our children and loved ones are well protected whenever they engage in sporting events.