Their comments come after a survey from Southern Cross, which revealed that more than a quarter of the 2000 people surveyed exercised either "less than once a week" for 30 minutes, or, worse, "not at all".
Ministry of Health guidelines recommend adults do a minimum 30 minutes of moderate physical activity at least five days a week, but more than 60 per cent of those questioned were not achieving this.
Most of Timaru's gym operators said they had received the traditional influx of post-New Year arrivals, but Go Girl Physique director Stephan Heppleston said people should be wary of making resolutions.
"Too many people make these resolutions after a few drinks on New Year's and promptly forget about them."
Mr Heppleston said the gym had averaged 25 new entrants a week recently, but this was largely due to marketing and social networking.
Snap Fitness manager Mike Wrigley said there had been several dozen new members in the past month, but he found the busiest time was either in October, or near the end of the summer holidays.
"We find it's those who want to get in shape for the summer, or conversely, people who have put on a bit after the Christmas break," Mr Wrigley said.
"People also like to make the summer holiday last a little longer, and are probably just as active outdoors as indoors [at this time of year]."
According to the survey, Dunedin and Wellington were the country's most active cities, with nearly half of the respondents exercising at least four times a week. Aucklanders were the least active, with 45 per cent exercising once a week or less.
People aged under 30 or over 50 were the most frequently active.
Southern Cross chief executive Peter Tynan said the results were worrying as exercise could help save lives and tax dollars.
"Regular physical activity can help to reduce the risk of chronic conditions such as cardiovascular diseases, cancers, obesity and diabetes."
The survey was conducted by a research company, which asked people to rate their activity levels.
A Sport New Zealand study of more than 4000 Kiwis in 2007-08 found almost 50 per cent exercised five times a week or more, while only 12 per cent were active less than once a week