I'm sitting on a rowing machine but instead of staring at a line of exercise bikes in the local gym I'm gazing at two squirrels frisking in the grass. Beyond them are ducks paddling on a lake fringed with willow trees. I'm at a free outdoor gym in North London's Broomfield Park and if there's a heaven for fitness junkies, this is it.
Anyone who's ever used an indoor treadmill knows there's a big difference between exercising indoors and doing it in a natural environment – the enhanced sense of wellbeing that comes with fresh air and a green space is huge. With an outdoor gym like this one you get the same effect.
Gyms like these are appearing in parks all over the world - in Europe, the US and South Africa, as well as Australia. A 2010 study of outdoor gyms found there were more than 60 in Sydney alone.
There are big advantages to fresh air gyms. Number one is they're free so lack of money for gym membership is no barrier to accessing equipment to improve muscle strength or cardiovascular fitness. They're also great for anyone who feels intimidated by regular gyms and that includes older people who can really benefit from getting stronger – the day I used the Broomfield Park gym the mix of ages included some over-70s. Thirdly, combining exercise with natural environments can be a mood-booster. We already know that exercise can improve mental health and there's also growing evidence that being in green spaces helps, too.
Are there downsides? Weather is the main one - outdoor rowing machines don't beckon on rainy days. Not all outdoor gyms are in shady spots, either, so it's smart to use them in the cooler parts of the day and cover up with hat and sunscreen. And although the equipment should have clear instructions showing you how to use it safely, there's no one to show you how to get the most out of it - so I got some tips from an expert, Dr Jarrod Meerkin, a spokesperson for Exercise and Sports Science Australia, the professional organisation of exercise physiologists.
His advice is to go for equipment that uses large muscle groups in the legs and upper body. If there's a step or a low bar, use it to do lunges to strengthen bottom and thigh muscles. Keeping your back straight, put one foot forward on the step and then lower your back leg until it's almost on the floor. Don't let your front leg go over your toe. Repeat six to 15 times (depending on how strong you are), and switch to the other leg.
A rowing machine will improve cardiovascular fitness as well as upper and lower body strength, while using a chin up bar will target the muscles of the upper back and biceps. Don't let the idea of chin ups daunt you, says Meerkin – you can begin with a modified version to get you started.
"Along with a high bar for doing regular chin ups, there's often a lower bar that you can reach without your feet dangling off the ground," he says. "You can grasp it with your palms facing you, shoulder width apart. Slide your body under the bar then pull yourself back up with your legs off the ground. As you get stronger you can progress to a full chin up."
With no trainer to urge you along, it's up to you to work harder as you improve - but there are ways to do that, Meerkin says.
"You can gradually increase the number of times you do a circuit of the equipment, you can combine a circuit with a jog around the park – and you can download a mobile app with an interval training program that can help you get fitter or stronger by alternating 'sprints' of intense exercise with working out at a slower pace."
Have you used an outdoor gym yet?