Britons are being urged to shed the estimated 80,000 tonnes of weight they put on over Christmas by using "outdoor gyms".
The National Trust has launched a month-long challenge to encourage people to get fitter and lose excess pounds. Starting on New Year's Day, people can sign up for a 31-day plan which includes exercises such as lunges, power walking, tree press ups and 'spotty dogs' (on the spot step backs).
With the average gym membership standing at 442 a year, the National Trust wants to inspire people to see outdoor exercise as fun rather than a chore.
Research has suggested that exercising outdoors rather than inside boosts wellbeing.
Dr Jo Barton, an exercise specialist with the University of Essex, which has carried out such research, said: "The effects of exercising outdoors in natural surroundings can be life-changing.
"This is because of the effect it has on your mood and levels of self-esteem.
"Mood is an integral component of daily life and strongly influences our feelings of happiness and how we cope with stressful situations. Exercising in nature lifts your mood and boosts your self-esteem.
"It also has immunising properties which helps you deal with future challenges more effectively.
"Even a five-minute walk outside to escape your work can re-energise you."
The Outdoor Gym Challenge, which can be done anywhere, has been devised for the National Trust by the firm Eco Fitness.
The British Dietetic Association says Britons gain 5lb on average in the four-week Christmas party period.
Jo Burgon, outdoors programme director at the National Trust, said: "Enabling everyone to enjoy the outdoors is one of the core reasons why the Trust exists."
To follow the day-by-day plan visit: www.nationaltrust.org.uk/outdoorgym