"Stationary Bike" is a 34-page short story originally published in the fifth edition of From the Borderlands in 2003, and later included in King's own 2008 collection, Just After Sunset. An audiobook version, narrated by Ron McLarty, was released in June of 2006.
The story opens with Richard Sifkitz, a commercial artist and widower, visiting his doctor, and staring at the results of his physical. Richard's cholesterol is dangerously high, largely due to his high fast food intake. The doctor tells him an interesting anecdote in relation to the number. He likens Richard's metabolism to a team of workmen who clear the various junk foods that Richard ingests. As Richard ages, these metabolic workmen tire out and begin to slow down, resulting in heart trouble. This metaphor strikes Richard, and he ultimately becomes somewhat obsessed with the idea.
Determined to lose weight, Richard sets up a stationary bike in his basement. At first, he hangs a map of the United States on the wall, imagining himself traveling to a foreign destination with each mile. As time passes, though, the notion of the metabolic workmen enters his mind again, and he paints a bizarre landscape on a mural, depicting four tired workers clearing a fat-laden road. Richard's exercise soon produces results: he loses weight, and his cholesterol plummets. Some time later, he has a horrible nightmare about one of the workmen committing suicide. He is driven to put the imagery of his dream to paper, but that is not to give him peace. These events cause the mural Richard has painted to transform, warping into a more nightmarish appearance with every passing day. Despite these warning signs, though, Richard cannot stop exercising; he enters a trance when he rides, and seems to enter the mysterious landscape as he does.
Desperate with fear, Richard even goes so far as to try taking the machine apart, but he suddenly finds himself riding on the bike "one last time". Suddenly, he is run off the road by a pickup truck, and finds himself face to face with the three remaining workmen on the crew. They pass from the alternate reality of the road to Richard's world, where they deftly disassemble the stationary bike, then return to speak to him. They angrily accuse him of ruining their lives; without a stream of fatty foods, they have stopped receiving income for their work. The workmen list their expenses, and explain that loss of income drove their fellow member was driven to suicide. Richard realizes that the men are conglomerations of people he has met before in life, and tries to tell them that they are nothing but imaginary figures, but they are not fazed in the least. Still unnerved by this strange experience, Richard agrees to relax his diet. On impulse, he makes one request - he wants a cap that the workmen wear (blood red, with the word "LIPID" written on it. Before departing, the workmen admonish him to take care of himself... but not too much. As he steps back into reality, he begins to wonder when he will convince himself that the strange experience was all a dream.
The story jumps forward to a few weeks later. Richard has forgotten much of the experience, but it has affected him. For instance, he still eats mostly healthy foods, but allows himself a few indulgences (like apple pie a la mode), and obviously no longer rides the bike. When his mail comes one afternoon, he sees a package which contains a baseball cap just like the one worn by the workers. He smiles as he dons the cap and prepares to go to work painting.