Because Target's offer is not mandatory, some—or many—workers may not accept the Fitbits.
And there is no guarantee that the workers who do accept the Fitbits will keep using them. One study, by Endeavour Partners, found that among more than 6,200 U.S. adults who had bought a wearable device, more than half stopped using it, and one-third of respondents said they ceased using the trackers before six months had elapsed.
Earlier this year, The Associated Press reported, the health-care investment fund Rock Health said that Fitbit's own financial filings suggest that out of almost 20 million registered users of the device, just half were still actively using it.
Patel told CNBC that one hurdle to widespread continued use among workers is presented by the devices themselves.
"They need to be charged up, synched up" to share their data about a user's activity level, he said. "Those little extra steps really end up to be high hurdles."
Patel said companies like Target can improve the level of adoption and continued use of activity trackers by designing programs that encourage both, and not just by assuming that people will utilize the devices to their advantage.
CNBC reached out to both Target and Fitbit for comment, but had not yet received a response.
However, Target has said it will design programs around the use of the Fitbits, the first of which will be a monthlong competition in which teams of Fitbit users will track their activity levels, with the winners naming a charity that will receive a $1 million donation from the retailer.
"The design of this competition is what's most important," Patel said, adding that in other cases of programs to promote Fitbit use the design often isn't given much thought.