• Warehouse work is physically taxing, with employees moving thousands of pounds per day.
• As Walmart automates distribution centers, new robots and forklifts are lightening the load.
• CFO John David Rainey says Walmart's labor-saving automation may add a decade to workers' careers.

Warehouse work is one of the most physically taxing jobs in the digital age.

That intensity has been well documented at Amazon, and now increasingly at Walmart as the world's largest retailer beefs up its e-commerce operation.

"So you take a distribution center today, one of our associates is walking up to 10 miles a day, lifting thousands of pounds, moving pallets and things like that," Walmart CFO John David Rainey said Tuesday at Bank of America's London Investor Conference.

And all that distance and weight really adds up over the course of a person's career, potentially forcing them to leave the workforce earlier than they might otherwise prefer.

Walmart typically employs about 1,000 workers at each of its 42 regional distribution centers, which are sprawling warehouses of up to 1.5 million square feet that support its 4,600 US stores.

Walmart is now adding automation to that fleet of facilities, and though some workers may worry about losing their jobs to machines, Rainey says retrieval robots and forklifts are actually lightening the load in a meaningful way for workers.

"The feedback that we get from many of our associates is that we add as much as 10 years to their career because of the less manual-intensive nature of this work," he said.

Now, instead of a worker jogging a 5K before lunch, picking orders across 26 football fields worth of shelves, a robot can make the trip.

Not only that, the retrieval robots learn how to navigate the route more efficiently, saving time on the next loop, Rainey said.

Taken together, these automations are driving a fourfold increase in how much stuff a distribution center can process with the same number of workers, Rainey said previously.

Walmart's situation closely resembles that of Amazon, which has doubled the number of robots deployed in its fulfillment centers and warehouses in the last three years, including a humanoid robot named Digit.

Walmart's Rainey would likely agree with Amazon's director of global robotics, Stefano La Rovere, who told CNBC that "robots and technology help our employees … by reducing walking distance between assignments, by taking away repetitive motions, or helping them to lift heavy weights."

"That's something that we're very focused on," Rainey said, "doing this automation in a very associate-friendly way that becomes a complement to what they're doing and actually enhances their overall job experience."

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