I'm looking for a short story, similar to H.G. Wells' "The New Accelerator," about a device that speeds up time for the person who goes through it. A promoter uses it to give a boxer super-fast reflexes and the boxer gives rise to suspicions by catching a dropped bottle too quickly. The protagonist is forced into the machine and accelerated to the point where he lives the entire remainder of his life in a single day and his body is found naked and elderly. While accelerated, he does things like taking a bite out of a stream of pouring whiskey and punching a pedestrian in the stomach to see what happens. Anybody out there have any idea what this story is?
This sounds like Half Past Eternity by John D. MacDonald, first published in the July 1950 edition of Super Science Stories. From what I remember of the story it matches your description exactly - though it is a few years since I read it. The story can be read here.
As I remember the story, the first part deals with the effects of the technology on athletes. People treated with the device basically live at a faster rate than those around them and can run or react faster. At one point a bottle gets knocked off a table and is easily caught by one of the treated athletes before it can hit the ground.
The second part of the story comes about because of conflict between the people using the device. I think one person is killed by being put into the device and having their time rate accelerated by a huge factor - they die of old age before they can open the door and escape. The protagonist of the story is destined for the same fate, but manages to force the door open before he starves to death. The remainder of the story is about him living out his life in a world where he can only interact with difficulty with the objects around him. The only food he can eat is what is currently being served - the time required to open a packet or a can is too great for him. I remember the punched pedestrian incident, and there was another where he finds a woman sunbathing on a roof top. He stays there so long (falling asleep while he watches her I think) that she perceives him, and he then sees her running from the roof in slow motion (seconds for her, days or weeks for him).
The first half of your description is "The Einstein Slugger" by Manly Wade Wellman
A boxer is sped up to incredible speeds (by his trainer and their professor friend) using unspecified electrical impulses from a radio set. He doesn't get caught out though, his freakish speed is immediately noticed by sports broadcasters. You can read the full version here
The second part of your description has nothing to do with this short story and is likely conflated from another story.