Sharing smug gym selfies on Instagram is all well and good, but if you really think you're fit, why not put your money where your mouth is and sign up to one of these epic fitness challenges?
From mud-soaked obstacle courses to invigorating open water swimming races, prepare to have your physical and mental limits tested as you battle to the finish line.
1. Tough Mudder
Endurance events don't come much more testing than Tough Mudder.
The team-based events, which happen at various times of the year all across the UK, involve scaling walls, jumping into icy water, climbing ropes, sliding over fire and running through lots and lots of mud.
There are hardcore eight to 10-mile obstacle courses for regular gym bunnies or faster 5km options for beginners.
Either way, it's sure to be a good story to tell the grandkids.
Events at various times through the year, toughmudder.co.uk
2. The Great North Swim
This iconic cold water swim needs no introduction. Europe's biggest open water swimming event caters to all fitness levels and sees 10,000 competitors make a splash in the breathtaking Lake Windermere - a huge body of water in the Lake District that stretches from Ambleside to Newby Bridge.
With distances from 250 metres to a whopping 10k, enjoy a bracing dip or challenge yourself to a full-throttle endurance swim.
June 5-7, greatrun.org/great-swim
3. Ironman UK
The Ironman concept is notoriously brutal. It involves taking on a savage 2.4-mile swim, 112-mile cycle, 26-mile run, and with no breaks in between.
It takes place in Bolton, which race organisers have dubbed Britain's 'friendliest town', so you're sure to make a few new mates along the way.
In the pursuit of Ironman glory, you'll swim in Pennington Flash, climb some tough hills on the bike and finish the run in Bolton town centre - where you can treat yourself to a well deserved pint.
July 12, ironman.com