The start of January has become synonymous with lifestyle changes - many new-year's resolutions involve getting fit, losing weight and changing eating habits.

It is all down to the fresh-start effect - most people believe choosing a set point, such as a new year, will help motivate them to reach a particular goal.

But research suggests this does not always work, particularly for fitness.

And there are a few reasons why those thinking about getting into exercise should bring their 2024 resolutions forward a few weeks.

Why do people wait until January?

The first month of a new year is seen as a transition point and has been adopted as a time that marks a new beginning.

Psychology professor Dr John Norcross has been researching new-year's resolutions for more than 40 years. And his findings suggest the most popular concern physical health, with more than a third of the thousands of people he has examined saying their main goal is to improve it.

The second most popular category is weight loss, with 20% of participants saying they want to slim down and 13% they want to change their eating habits.

But when Dr Norcross followed those making these resolutions, he found a third had given up after a month - and after six, most had.

Health and diet expert Dr Duane Mellor tells BBC News: "It can feel harder to to start exercising in winter - and we artificially put in new-year's resolutions, which are set with the best intentions, at sort of that time of year, when we feel we should do better."

And a lot of this comes from trying to recover from the "excess food and alcohol" consumed over the Christmas period, which, when coupled with less movement during colder days, leaves some feeling sluggish and in need of change.

Why might it be better to start in December?

"From a behavioural point of view, it's more sensible to start doing exercise earlier in winter or later in autumn, as our natural habitats, our environment and our way of living, tends to slow down this type of time of year," Dr Mellor says.

"With the darkening nights, our minds push away from [thinking about being active] so going against that can be a real strong positive."

Dr Mellor advises finding a routine that works in the late autumn and early winter period, while also "trying to maintain a healthy way of eating", so when the new year rolls around, healthier habits are already in place.

Many choose, running, the gym or group exercise classes as the place to kickstart a health journey - 12.5 million people took part in this type of activity last year, according to Sport England.

But typically, workout spaces are a lot busier in January than December, thanks to resolutions.

Pure Gym, which has 327 branches in the UK, and more than a million members, tells BBC News January is their busiest month, with November and December the quietest. And in January 2023, their gyms were nearly 40% busier than November and December 2022.

Parkrun, which puts on free outdoor running events, tells BBC News they "usually see a strong upturn in January, particularly in the first Saturday of the new year". And in January 2023, they had more than 50,000 registrations in the UK, compared with 26,000 in December 2022.

Personal trainer and fitness coach Morgan Brazier tells BBC News January fitness goals put too much pressure on people to achieve.

"If someone says they are going to start in January and make this massive change, if for whatever reason that doesn't work out, they can feel a sense of guilt and think the year has already started off badly," she says.

New starters can be put off by regular or experienced users - but with gyms so much quieter around Christmas, they can "feel more comfortable", with the time and space to build confidence by learning how to use machines or develop techniques.

Ms Brazier's other tips include:

• Have an induction when joining a gym - most offer them and it will help work out where everything is
• Go in with a plan - lots of free resources are available online to help structure a workout
• Bring a friend to a workout - it will increase confidence, especially if they are more advanced
• Try out a class and turn up early to speak to the instructor