The gate opens and about 100 children, and a handful of adults, fan out and start bouncing as if their tops were made out of rubber and their bottoms were made our of springs. Every day, the scene plays out up and down the country, from Inverness to Cornwall.

Three years ago, trampolining was confined to gymnastics clubs, schools and back gardens. Today, there are around 120 trampoline parks in the UK, which provide people with about 250,000 hours of exercise per week. That’s a lot of cardio, countless calories burned, many legs strengthened and, encouragingly for most jumpers, it even feels a little like exercise.

If you are - nominally at least - a grownup and have never released your inner Simone Biles by landing a forward somersault, the local trampoline park is the only game in town. There is a risk of injury but the adrenaline rush is powerful. Bounce forward, tuck, spin, stick your legs out, land on the airbag, throw your arms out then take a second to imagine the applause. This is clearly an activity that is not just for children. It is for childish adults too.

Roughly 20% of regular bouncers are over 18 – largely parents, some reluctant and some enthusiastic. On the enthusiastic side, there are the fun mums, confident in the resilience of their pelvic-floor muscles, and the over-excited dads. The latter are probably at the greatest risk of injury; the former probably better attuned to the health benefits.

Robert Smith of RS Sports Therapy, currently working with Premier League champions Leicester City, says: “Studies of both sedentary, middle-aged women and highly trained athletes show a modest but significant improvement in cardiovascular fitness with regular, 30-minute trampoline workouts.

“Because the trampoline pad is bouncy and soaks up a large amount of the impact of your landing, your bones and joints are protected and strengthened at the same time.

“Trampoline parks are offering aerobics on trampolines, dodgeball on trampolines, basketball on trampolines and endless bouncing, all of which are great workouts. And bouncing is a lot of fun.”

And for those who run or play football, netball, rugby or racket sports competitively, the risk of lower-limb injury is not that high, relatively speaking, unless you seriously overestimate your ability or lose concentration. For older muscles unused to bouncing it is worth getting warmed up. Looking like you’re taking yourself too seriously is better than risking a strain, pull or tear. Worryingly, a few trampoline parks are licensed to sell alcohol too.

Despite some operators claiming relatively low accident rates, there is no data on how many people get injured at UK trampoline parks. In the US, where the industry has a decade’s head start, there have been rare reports of paralysis but no such serious accidents have yet occurred in the UK.

According to the Royal Society for the Prevention of Accidents, most injuries are lower-level sprains from falls, acrobatic moves such as flips and from people hitting objects. There have also been reports of fractures but, so far, no serious life-limiting injuries have been reported.

Peter Brown is chairman of the UK branch of the International Trampoline Parks Association (ITPA) and managing director of Freedome Trampoline Parks. With input from environmental health officers, RoSPA, the HSE, constructors, operators and insurers, he is producing the technical specification manual for UK trampoline parks, due for publication this month.

He says: “There’s nothing you can do to get away from the fact that it is a high-risk activity. If you are bouncing on a trampoline, there is a risk of injury.

“When you get on a rollercoaster, you expect to get off the rollercoaster in the same condition that you got on it. At a trampoline park, the way you interact with the equipment has a direct effect on your safety, and that has to be managed.”

Inevitably, more accidents will occur as trampolining grows in popularity and one or two less diligent operators might get found out. If there’s no trampoline park near where you live, it is unlikely to be long before one opens. The ITPA and consultancy BDA estimate that there is room for at least another 100 in the UK. Chester and Derby each have two trampoline parks and they are big business. There are between 10 and 15 million visits annually, each one costing about £12 on average.

Calculus Capital, which usually works with life-sciences, healthcare or technology firms, has just invested £3m in Gloucester-based trampoline-park operator Jumptastic, believing that the trend has strong commercial legs.

Calculus chief executive John Glencross says: “Trampoline parks are a relatively new attraction in the UK but the sector has grown strongly in the US and the activity is quickly establishing itself here. Jumptastic is targeting the UK market but is also looking beyond the UK to continental Europe, including Scandinavia.

“In places where summers are short and the weather unreliable, parents will always want to take children somewhere relatively cheap, good fun and thoroughly exhausting.”