"I couldn't handle the fact people were increasing their steps when I was asleep."
Swailes sets individual and group challenges on the Facebook page - such as the recent Winter Wonderland challenge in which three groups of 10 women around New Zealand competed.
For group challenges, team captains are appointed to keep the group motivated and each member's daily steps can be seen using an app.
The group with the highest combined number of steps wins.
North Shore mum Rosslie Somerville joined because she needed some new "Fitbit friends" and said the page provided a constant stream of motivation.
"The Fitbit is great, especially when you link up with friends, but a lot of people lose motivation after three months," she said.
"You need that long-term motivation."
Since joining the group in April the mum of 6-year-old Charlee and Jasper, nearly 2, has completed a one-day and a week-long challenge.
"There are mums that do 20,000 steps a day and I know I am never going to do that," she said.
"But I see other mums in the same situation as me and I think, if she can do it so can I."
Somerville said she wasn't motivated to take out top spot but instead was striving to improve each day. "I don't need to come first, I just need to do better than I have previously and you get a lot of encouragement when you achieve that."