- Science of Sport
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- Paris 2024
More than muscle: The hidden physics of javelin
The world’s best javelin throwers have started strutting their stuff on the runway at the Stade de France.
No other animal can throw a weighty object at high speed with accuracy, which means the winners can truly call themselves the skill’s greatest exponents on Earth (certainly, the fastest swimmers, runners and jumpers can’t make the same claim).
Australian Mackenzie Little at a competition in London last month. Credit: Getty Images
But raw power alone doesn’t secure victory. A mastery of the wind, aerodynamics and energy separates the best from the rest.
The javelin’s journey through the air begins long before it leaves the thrower’s hand.
It starts with the run-up, a crucial phase where kinetic energy – the energy of movement – is built up. This isn’t a simple sprint; each athlete must find their perfect speed, fast enough to generate substantial energy but controlled enough to precisely execute the complex throwing sequence.
As they approach the throw, athletes transform their bodies into coiled springs. Turning sideways and performing crossover steps, they set themselves up for a rapid rotation that injects additional energy into the throw.
This positioning is crucial because, surprisingly, the arm muscles used in throwing a javelin are relatively small. The majority of the javelin’s eventual flight energy comes from the run-up and rotation.
The delivery step is where physics takes centre stage. As the thrower slams their front leg into the ground, rapidly braking their forward momentum, they simultaneously rotate towards the throw direction.
This is where the first law of thermodynamics – the conservation of energy – comes into play. The energy from the run-up doesn’t disappear as they brake. Instead, much of it is transferred into the only part of the body still free to move: the throwing arm.
The human shoulder acts like a catapult. The muscles and tendons stretch, storing elastic energy, before recoiling to propel the javelin forward. This whip-like action generates immense power – about 10 times what our much larger leg muscles can produce in a maximal jump or bicycle sprint.
But the throw itself is half the battle. Once airborne, the javelin’s flight becomes a lesson in aerodynamics.
Unlike throwing a ball, the optimal launch angle for a javelin isn’t the textbook 45 degrees. Thanks to its ability to generate lift like an airplane wing, javelin throwers can aim for a flatter trajectory, typically between 32 and 38 degrees, depending on throw speed and the wind.
The orientation of the javelin at release is equally crucial. Throwers aim to align the javelin’s long axis with its flight path, often described as throwing “through the tip”. This minimises air resistance and sets up ideal flight conditions.
But the complexity doesn’t end there. Because the body rotates during the throw, spin is imparted on the javelin. This helps stabilise it in flight, much like the spin on a bullet or an American football.
It also causes the javelin to rotate towards the left for a right-handed thrower. So, the thrower has to release the javelin a little bit sideways, and it causes the nose to dive a little. Most throwers point the javelin tip about 5 degrees upwards, rather than throwing it perfectly through the tip.
The wind also plays a pivotal role in the javelin’s journey. A headwind requires a flatter throw to prevent the javelin from diving, while a tailwind allows for a slightly steeper angle. Crosswinds add a layer of complexity, demanding adjustments from the throwers as they race down the runway.
It’s all mindbogglingly complex, and both the athlete and their coach will need to make the right decisions for each throw and execute those plans perfectly.
In this arena, Australia’s javelin throwing women’s trio – two-time world champion and Tokyo Olympic bronze medallist Kelsey-Lee Barber, world championship bronze medallist Mackenzie Little, and Australian record holder Kathryn Mitchell – aren’t just athletes; they’re practical physicists, making real-time calculations and adjustments that would challenge even the most advanced computers.
They embody the unique human ability to master the art of throwing and the ability to change their technique based on the environment at the time – skills that set us apart in the animal kingdom.
As the competition unfolds under the Parisian night sky, keep an eye out for the throwers who seem to make their javelins defy gravity. Watch for the rhythmic run-ups, the explosive releases, and the graceful arcs of flight.
In these moments, you’ll see more than just sport – you’ll witness a beautiful interplay of skill and the laws of physics.
Tony Blazevich is a professor of biomechanics at Edith Cowan University and the author of Sports Biomechanics: The Basics: Optimising Human Performance.
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