Cunningham's unachieved goal was a four-minute mile, a goal attempted and unmet by many other runners. Several theorists proclaimed it was impossible physiologically for humans. Some athletes tried running steady and fast-paced the whole time. Others tried to go steady for the first half then give it all they had. Glenn worried about the strength of his legs burned in his youth, so he started slow – running in the pack. He would be fresher in the second half – and would almost be sprinting the last 100 yards to the finish.