The snow was crunchy, the air bracing and the herds of deer skittish. On the face of it, a run through the dips and hollows of Dyrham Park in the hills north of Bath seemed to win hands down over a slog in the city's municipal gym.
But what is better for you? Exercising in the great outdoors, or signing up for a gym and pounding away on running machines, as thousands will do as part of their new year resolutions to lose weight and get fit?
To try and find out, the Guardian was invited to spend a month working with fitness and sports psychology experts at Bath University and the National Trust. The concept was that a guinea pig – me – would spend alternate weeks exercising in a gym and on National Trust land.
The first week was spent on the exercise bikes, rowing machines and treadmills of the municipal gym at Bath sports and leisure centre.
Getting started at the gym was easy enough – with no insistence on a chat from a marketing person first. It was just a matter of turning up, pressing the start button on the machines and off you go.
There was a nice community too – office types in before work and a number of older people, all gently teasing and encouraging each other.
On the downside, it was hard to ignore the background noise of blaring dance and pop music. And all the machines faced screens showing music videos, rolling news and sports channels. Not a place to get away from it all.
So it was a relief in week two to head for the hills of Dyrham, a National Trust parkland full of flocks of over-wintering birds as well as those deer. If you stay away from the baroque mansion nestling in the valley and run around the park's higher contours (also a good idea because you may not get back up the steep hill once you've run down it), you rarely see a soul.
Weeks three and four followed the same pattern. Pre-dawn sessions in the gym, running or cycling nowhere to the dance music beat, or picking a way through icy Dyrham Park and, by way of variety, along the Bath Skyline route: a walking or running uphill and down dale, with lovely views of the Georgian city. And only one accident: a fall resulting in a cut hand during a pre-sunrise run.
The diaries I had kept, questionnaires I had filled in, and heart monitors I had worn, were then analysed by scientists from Bath University.
I suspected that the steadier, more solid-feeling exercise undertaken at the gym would prove more effective than the rather more erratic, sometimes stumbling activity that took place on the frozen footpaths.
In fact, the heart monitors established I had expended a similar amount of energy whether exercising in the gym or outdoors. But Martyn Standage, an expert in motivation in health, exercise and sport, was most interested by the fact that on the days when my exercise had been done outside, I used more energy through the rest of the day.
Standage said this fitted with studies that suggest working out in the outdoors leads to a greater feeling of vitality – physical and mental energy. Some studies suggest that this vitality is primeval: human beings have inhabited urban rather than natural environments for a relatively small number of generations.
Jo Barton, a member of staff at the University of Essex who specialises in studying outdoor exercise, suggested that working out in the fresh air could be "life -changing".
"Mood is an integral component of daily life and strongly influences our feelings of happiness and how we cope with stressful situations," she said. "Exercising in nature lifts your mood and boosts your self-esteem.
"Research implies this is true regardless of the weather conditions, where you are, and how long you exercise outside. Even a five-minute walk outside to escape your work can re-energise you and restore your mental fatigue. This is even more important in winter months when daylight hours are reduced. A short walk on a crisp winter morning can really lift your spirits and set you up for the day."
Such results will please the National Trust, which this week launched the Outdoor Gym Challenge, inviting people to exercise outside (preferably on their land). The trust argues – as it would – that it is cheaper to exercise outdoors rather than spending hundreds of pounds on gym membership.
My verdict? It was more fun outside but sometimes more convenient to get to the gym – especially at this time of year, when there isn't much daylight (see cut hand for evidence). A bit of both may be the way forward.
