Top speed

Usain Bolt is the fastest man on Earth. In 2009, the Jamaican sportsman broke the World Record for the 100-metre sprint, completing it in just 9.58 seconds. That’s an average speed of about 23 mph (miles per hour), faster than cars that drive past your school! But how fast can the human body go and is there anything that might stop us achieving superhuman speeds?

Bolt’s pace is impressive but is only a fraction of what some objects can achieve.

Lots of different factors control how fast humans can run. These include weight, stride length (how long your steps are), nutrition and muscle composition (what muscles are made of).

The speed of sound (known as Mach 1) is 761 mph. According to The Flash TV series, Barry Allen’s top speed is Mach 3.3 (2,532 mph) but researchers at the University of Leicester have calculated his maximum velocity (speed) to be roughly Mach 13 (almost 10,000 mph) based on his diet.

Physiologist (someone who studies how bodies work) Peter Weyand reckons humans could reach speeds of up to 40 mph. When we run, we contract our leg muscles to apply downward force which helps propel us forward. To increase speed, athletes need to generate force more quickly during the limited time their foot is on the ground. Weyand’s study discovered that the only thing currently holding humans back from achieving speeds of between 35 and 40 mph is how fast our leg muscles can contract.

But as athletes run, there are external forces acting upon their bodies. You might have felt the same when walking in a windy environment, like on top of a hill. When Usain Bolt broke his record, there was a tailwind (wind behind him) of 0.9 metres per second, making him marginally faster! The opposite can also happen; these are called headwinds.

Fast and furious

Not only is our physical composition a barrier to The Flash’s superhuman speeds but so are forces like headwinds that act on our bodies.

Acceleration is the change in velocity per second. We measure acceleration in terms of “g-force” where “g” refers to gravity. During shuttle launches, astronauts routinely endure 3g. Riders of Stealth at Thorpe Park – one of Europe’s fastest rollercoasters which propels riders to speeds of 80 mph in just 1.9 seconds – experience 4.5g. This means your body feels 4.5 times heavier than normal. Trained individuals like fighter pilots can withstand a maximum of 9g but only for a few seconds. If acceleration doesn’t decrease, you will pass out and eventually die. The g-force our bodies can withstand is one barrier to us achieving superhuman speed.

The fastest speed that a human body has ever endured was that of Austrian skydiver Felix Baumgartner. In 2012, he jumped from the edge of the stratosphere and reached a freefall speed of 843.6 mph (Mach 1.25) but did so in a pressurised suit designed to withstand the stunt. Felix spent 30 seconds supersonic (travelling at the speed of sound).

As well as super speed, Barry Allen also has lightning-fast reflexes. It’s unclear whether anything else helps him beat forces like g-force and resistance. Felix’s skydiving suit might be the closest thing we have to Barry Allen’s Flash suit which is designed to be breathable and fire-resistant.

Need for speed

There are some small ways we can increase our speed.

New Nike Vaporfly running shoes were banned from the 2021 Tokyo Olympics because organisers thought they helped athletes too much. Sports Scientist Dr Ross Tucker called them “the shoe that broke running”. Nike reckoned they made athletes run 4% more efficiently thanks to lightweight materials and the way the shoe supports runners. That’s very similar to what Peter Weyand said.

While we may dream of achieving superhuman speeds like The Flash, our physical abilities and external forces remind us of our limitations. But Felix shows us that with the right equipment, we can push the boundaries of what’s possible. The potential might still be there.

Also

Actiniaria (sea anemone) look like colourful plants but are actually organisms that live in the ocean. They’re related to coral and jellyfish.

As adults, anemones typically don’t move. They root themselves to solid objects using their adhesive foot (called a pedal disc). However, if their environment becomes inhospitable, sea anemones can slowly “walk”.

Time-lapse photography reveals they can move at the pace of around one centimetre per hour; that’s 0.000006 miles per hour! It would take one sea anemone almost half-a-million years to walk around the circumference of the planet…

Their leisurely pace makes them the slowest animals on Earth.

First published in The Week Junior Science+Nature, issue 63, July 2023.