I don't think physical labor is a big deal -- indeed us computer-and-desk workers think a lot about how to stay active -- and I don't take that to be the crux of the article at all.
In fact, I'm surprised that none of the comments here have yet mentioned what I see as the worst, and tangibly different aspect of Amazon warehouse work: the gamification of the tasks.
> blue bars on the scanner count down the amount of time they have left to complete the task
> the company constantly sends messages to workers’ scanners telling them to work faster
> without warning, Amazon changed the amount of time workers had to stow an item from six minutes to four minutes and 12 seconds
This sound absolutely terrible. This would make any normal task stressful. The randomized changes and constant oversight strike me as borderline abuse/interrogation techniques. And while the article doesn't dig into it, I assume this is driven by AMZL software systems, operating on a global scale (using all workers and all warehouses as inputs), with machine-learning algorithms constantly tweaking the timers and count-down bars, and possibly even suggesting to managers "hey, worker A has slowed down in the past 15 minutes, would you like to send this pre-written message X to A? Tap [Yes] [No]". This sort of thing might sound like a brilliant idea to some rockstar developer in Seattle, and to the data science team, and the management team signing off, when in reality it creates a Hunger Games race-to-the-bottom mentality in your actual workforce.
And this is materially different from how Stater Brothers across the street operates (or any other warehouse job), presumably.