Under 50 per cent of over-16s complete at least 150 minutes of physical activity per week, according to a public health report.
However, a county health chief says projects offering free exercise classes and advice on healthy living are helping to improve the outlook for residents.
As part of a health overview for Preston, the Public Health England statistics say 47.5 per cent of adults are estimated to be meeting the activity target, compared with the national average of 57.
Sakthi Karunanithi, Director of Public Health for Lancashire, said progress was being made with targeted schemes to encourage behaviour change.
He added: “We have been working very hard to tackle this issue in recent years in collaboration with partners including Preston City Council and Lancashire Sports Partnership, and have seen improvements.
“We commission Active Lives and Healthy Weight programmes across Lancashire, run by ABL Ltd.
“The scheme provides a range of support to help people become more active and manage their weight, which individuals can refer themselves on to, including free exercise classes and groups for people who want to raise their levels of activity.”
The 150-minute per week target for exercise is based on guidelines set out for healthy living by the Chief Medical Officer.
Activities categorised as physical exercise are those performed at “moderate intensity”, which means the raising of heart rates and participants getting “a little out of breath.”
Those who take part in 30 to 149 minutes of exercise per week are said to be “fairly active” with anyone exercising for fewer than 30 minutes are said to be inactive.