Sitting on the couch reading a slaying satire about exercise fanatics should be as satisfying as a chocolate chip cookie, but Lionel Shriver’s new novel is exhausting. I’ve never felt so worn out by the labor of wincing.

The Motion of the Body Through Space” tells the story of Serenata and Remington, a long-married couple in their early 60s living in Hudson, N.Y. A grim coincidence of professional and physical setbacks has recently halted the pleasant progress of their lives. Osteoarthritis in both knees has forced Serenata to stop running, a habit she had practiced for decades. And Remington has been forced out of his job at the Albany Department of Transportation, a dismissal that has unmanned him.

At a moment when they should be stewing together in stationary solidarity, Remington suddenly announces, “I’ve decided to run a marathon.” That declaration opens the novel and launches Serenata and Remington toward a crisis that will test their marriage and even threaten their lives. Having never seen her husband “run from here to the living room,” Serenata is dumbfounded by his new obsession. But her skepticism quickly curdles into bitterness. She takes it as a personal affront that Remington has decided to start running only now that she must stop. She imagines that running is her thing, a proprietary discipline begun and perfected by her long before the rest of America turned it into a fad.

Indeed, the fitness industry is a fat target for satire. And Shriver brings all her ferocious wit to bear to mock its hucksters and disciples. Readers who have endured condescending pity from well-toned gods and goddesses will initially relish Shriver’s merciless ridicule. Remington throws himself into daily practice with absurd enthusiasm — and humiliating running shorts. He spends thousands of dollars on specialized equipment, convinced that sufficiently expensive accoutrements will compensate for a lifetime of sedentary behavior. And finally, after tiring of exercise videos on YouTube, he hires a sexy personal trainer named Bambi Buffer.

Bambi Buffer — her nom de guerre in the war against flab — has a body honed to such perfection that it looks like “the diagrams of human musculature in anatomy textbooks.” She’s an obnoxious carnival barker for the glories of exercise, and she whips Remington into a froth of culty devotion to extreme fitness.

For Serenata, there is nothing worse than a fad. The exercise craze is just one example of that “lemming-like behavior that drove her wild.” She’s irritated by the overused phrase “bucket-list.” She’s irritated by the ubiquity of sushi bars. She’s irritated by the way everybody wears large men’s watches. She’s irritated by her daughter's faith in Jesus. She objects to all this and more with the confirmed superiority of someone convinced that she’s the smartest, bravest person in the room.

As a character, Serenata is a fascinating and daringly unsympathetic heroine, burdened with the loneliness of her greater insight. But she can also be a hectoring bore. Many pages of the novel are given over to acerbic arguments in which Serenata spars with her husband about his rabid training. She claims the two of them are engaged in Noël Coward-like repartee, but their interactions sound wholly mirthless. This is satire that moves, like Remington, with heavy weights strapped to its legs.

Unfortunately, beneath its parody of fitness fanatics, the plot is premised on whiny canards about the insidious effects of reverse racism. The novel’s most distasteful section is a flashback designed to illustrate administrative sensitivity gone amok. In a dramatic set-piece, we see Remington passed over for a promotion that goes, instead, to an incompetent young black woman who then badgers him out of the department. She’s an affirmative-action villainess who sounds like she was plucked from an alt-right fundraising letter. Remington notes that his nemesis is “African African-American, which confers extra points. She’s second-generation Nigerian, which means she nominally gets credit for being an immigrant, too.”

Similarly, poor Serenata finds that her career as a voice-over actress is snuffed out by zealots who insist that a white woman shouldn’t be “mimicking” minorities’ accents. Everywhere, the novel suggests, members of historically oppressed groups have latched onto the rhetoric of identity politics to accrue power that they can’t otherwise win with reason or their own skills.

A profile in this week’s New Yorker notes that Shriver once said the difference between fiction and nonfiction is that “fiction is much more subtle. . . . It’s more evasive, it’s more circuitous, it should be a little harder to discern what the message is.” All true — but contradicted by this novel. There is, after all, a complex and humble case to be made for an artist’s freedom to imagine the voices of any character she wants. And the question of how best to rectify the long history of employment discrimination does not lend itself to simple answers. But “The Motion of the Body Through Space” sets up Shriver’s arguments without any subtlety. For all Serenata’s ranting about the inanity of acquiescing to crowds, she never seems to acknowledge that complaints about the oppression of white people stem from another crowd with a very nasty history.

This is all tremendously disappointing because there’s a rich and sympathetic story here about how aging can disrupt a marriage in strange and surprising ways. Remington’s frantic efforts to run himself back into virility and purpose will resonate with anyone staring at the prospect of a long, useless retirement. And Serenata’s resentment toward her failing knees feels poignant and universal. But this is a novel more determined to make its point than to make us consider the profound mystery of what it means to tend a body for the long haul.

Ron Charles writes about books for The Washington Post and hosts TotallyHipVideoBookReview.com.

The Motion of the Body Through Space

By Lionel Shriver

Harper. 352 pp. $28.99