The latest in modern bicycle innovation takes some cues from the fictional mode of transportation used in the "Flintstones" cartoon.
A new bicycle designed by German engineers does away with pedals and instead requires the rider to run or walk to generate speed.
Dubbed the "Fliz Bike," it is actually based on the world's first bicycle, the "Laufrad," which also operated without pedals and was created by German inventor Karl Drais in 1817.
"The prior aim of developing FLIZ was to bring a completely new driving experience to everyone," designers Tom Hambrock and Juri Spetter write on their website. "Its laminated, innovative frame with 5 point belt system provides a comfortable, ergonomic ride between running and biking."
Riders of the Fliz must strap themselves into a harness (the "5 point belt system"). After building up enough speed, they lift their legs onto footrests located near the bike's rear wheel.
"The frame integrates the rider and due to its construction it works both like a suspension and like a top carrier whereas the belt replaces the saddle and adjusts your position," the designers write.
You can watch a video of the Fliz in action below:
Hambrock and Spetter explain that their goal is to create a more environmentally friendly transport for crowded urban settings. It's unclear how the prototype is an improvement over conventional bicycles, which also do not generate pollution and are less physically demanding than the Fliz. However, Hambrock and Spetter say creating a healthier mode of transportation is also part of their vision for the Fliz.
The Daily Mail reports that Hambrock and Spetter have entered their design into this year's James Dyson Award competition, which awards a £10,000 ($15,924) top prize to the winner.