On Mondays, his manager would come in with a sheet for employees to sign that listed their names next to their average picking times and order fulfillment rates.

“I would go a little faster sometimes after that,” said Mr. Fraser, who worked at the store from September to December before leaving to study computer science. “At first I wanted to do good, and I’m kind of competitive. But the more I started doing it, it was like, they’re asking me to go faster, faster and faster, and where does it end?”

The pandemic prompted millions of Americans to buy their groceries online and pick them up curbside or have them delivered, fueling new demand for so-called pickers like Mr. Fraser. Grocery companies are using tools that promise to map workers’ routes through stores and track their speed and accuracy, bringing metrics typically associated with warehouse jobs into local grocery aisles. Pickers, in turn, find themselves doing work that can be physically taxing, mentally stifling and increasingly guided by automation and technology.

“The guinea pig for this is warehouse workers,” said Chris Tilly, a professor and the department chair of Urban Planning at the University of California Los Angeles, who has studied how technology is changing retail jobs. “Warehouses are much more controlled environments — you don’t have customers wandering around the aisles and abandoned carts and so on. But that’s where a lot of these technologies are adapted from.”

In 2020, online grocery sales rose 54 percent to $96 billion, or 7.4 percent of all grocery sales, according to data from eMarketer. While many consumers will likely return to stores as the pandemic abates, more than a third of online grocery shoppers said in a recent survey from Coresight Research that they expected to continue shopping that way.

Online orders are costly for grocers, which already have incredibly thin profit margins and now find themselves building infrastructure to perform a task previously done by customers. Many customers expect the service to be cheap and fast, which requires labor. A growing number of chains are taking on at least some portion of the picking that they once outsourced to third-party companies like Instacart, which has been criticized for holding its in-store shoppers accountable for factors out of their control, like out-of-stock items.

Grocery stores are also designed for browsing, meaning an order that sends a picker to the bakery or in search of flowers can derail their attempts to be efficient.

“As you start to think about the tens of millions of orders that are being created each week now in retail, this ability to become a little quicker is going to be important,” said Steve Henig, chief customer officer of Wakefern Food Corp., whose chains include ShopRite. “A couple seconds here and there starts to add up to a lot.”

While grocery companies are expanding micro-fulfillment centers and massive automated warehouses, a cottage industry of companies is focused on tools designed to make human pickers in stores faster and more efficient, typically through software loaded onto hand-held devices.

Mercatus, a company in Charlotte, N.C., says that it can cut labor costs by 30 percent with its software. It can help workers pick multiple orders simultaneously by using what it calls zone paths that guide them through specific sections like produce. It has also made broader recommendations, such as encouraging grocers to price produce by bags rather than weight, and advising stores to put birthday-related products in one easily accessible area because of the “time burn” on such orders.

One company, Ox, is promoting smart glasses with “head-mounted displays” for pickers to wear, saying eliminating hand-held devices will save money. Its website says the average picker spends 705.6 hours per year touching a screen, adding, “Which means, you spend about $12,750 per associate per year to touch buttons on a scanner or tablet.”

AWM, in Aliso Viejo, Calif., offers retailers sophisticated overhead cameras that are able to track employees and customers as they walk around stores and recognize products, even down to Red Delicious versus Gala apples. Kevin Howard, its chief executive, said that the company could cut stores’ fulfillment costs by 60 percent through methods like flagging out-of-stock wares right away and directing pickers to the right items even if they were moved or misplaced.

“We dictate each aisle they should be going to because we know what product is in what aisle, then we dictate in real time, visually, the actual gondola, the shelf and the zone on the shelf of where that product lives,” Mr. Howard said.

AWM also helps retailers track “exactly who’s productive and who’s not,” Mr. Howard said. “If they went down the confection aisle and it took 12 minutes and the average picker takes four, how do we ensure we help them get to the four number? Sometimes it’s not knowing what the product is — with us, it’s usually personal time on their cellphones.”

The monitoring attached to grocery picking concerns some labor experts.

“Any of these systems saying ‘pick this now, pick this next,’ is by default tracking you,” Mr. Tilly said. “They all have clocks associated with them, and so it’s tracking you, monitoring your pace. It means if there turns out to be an error with the order, they know who did it.”

Even if the technology weren’t designed primarily for surveillance, “it’s not hard to then be tempted towards monitoring and using it for disciplining purposes,” said Françoise Carré, research director of the Center for Social Policy at the University of Massachusetts-Boston McCormack Graduate School, who has also studied how technology is changing retail jobs.

Noell Marion, an employee at Mariano’s, another Kroger-owned grocery chain, first started working at the Skokie, Ill., store through Instacart in 2019. Ms. Marion, 53, said that as a designated “veteran shopper,” she had 72 seconds for each item.

“That includes walking the store, getting the item, getting it scanned, getting through checkout and getting it staged and ready for delivery,” she said, adding, “It never took into consideration if you had to stand in line for something if the store was busy.”

Ms. Marion was also penalized when an item was out of stock and the customer did not approve the replacement she selected. If she refunded an item like a 20-ounce bottle of Heinz ketchup after a customer refused any other size or brand of ketchup, that also counted against her.

“There was always someone telling you, you’re not shopping fast enough, your time’s not where it should be, we’ve seen them fire people for not meeting their times so you just need to go faster,” she said. Instacart said the metrics Ms. Marion described were now outdated. She worked for Instacart until earlier this year.

Ms. Marion, who is 5-foot-3, added that the job was physically demanding as she bent for some shelves and reached for others. “I could not do more than a six-hour shift because you’re walking on a concrete floor and that’s very jarring on the body,” she said.

Natalia Montalvo, a spokesperson for Instacart, said that the company had “implemented new resources, policies and guidelines to help support in-store shoppers” over the past few years. The company is also “constantly exploring new tools and technologies that support the needs of the 600 retailers we partner with and further enable their businesses to grow and scale over the long-term,” she said.

Travis Gardin, 37, has worked for Kroger in downtown Dallas for almost nine years but only started picking in the past year and likes the physical activity. He said that his picking goal was 40 seconds per item and that Kroger had “done a lot on the back end” to make it easy to retrieve items. “They know where all the items are in the store, and they give us a route, like, ‘Hey, you’re going to go in this snaking motion up and down the aisles, you shouldn’t ever have to go back,’” Mr. Gardin said.

Pickers at his store push trolleys that are much bigger than shopping carts, with nine “totes” for multiple orders. “The way that our hand-held system works is that it just says, here’s the next item that you need, then you scan it, and it tells you OK, put it in Tote 5,” he said.

Mr. Tilly anticipated that eventually, grocers would expand facilities designed specifically for online orders. Takeoff Technologies, which puts micro-fulfillment centers in grocery stores, said people can typically pick 60 items per hour in stores. But with the help of robotics, they can pick 700 items per hour at its sites.

“We’re in the business of making humans and robots work together but making the humans much more productive and much more accurate,” said Max Pedró, its co-founder.

“Nobody thinks having people pick from stores in the long run is workable — it adds a bunch of expense and so far, grocers have not been able to figure out how to get consumers to shoulder that expense,” Mr. Tilly said. “So that’s an important piece of context and that’s why there is this constant search for how do we make this cheaper, more efficient, and in many cases, seeing this as a transition to something longer term.”