whip it good
The type of bar matters when it comes to how it bends and recoils, but why is still a mystery.
Olympic weightlifting consists of three basic movements performed on a barbell: the snatch, the clean, and the jerk (with the latter two executed in combination). At such an elite level, athletes seek to exploit every possible advantage, including how a barbell bends and recoils in response to loaded weight and applied force—a property known as flexural bending in physics and dubbed the “whip” by Olympic athletes. Scientists are learning more about the underlying mechanisms of the whip, according to a presentation at this week’s meeting of the Acoustical Society of America in Philadelphia.
Joshua Langlois, a graduate student at Pennsylvania State University, competes in Strongman competitions as a hobby. He also has friends who compete at the national level in Olympic weight-lifting events. “They told me how they use the whip,” Langlois said during a media briefing. “When they dip down, they can feel when the bar flexes back up and use that to accelerate the movement upward to increase the amount they can lift.”
Langlois decided to conduct a modal analysis, i.e., how an object moves or vibrates, to quantify the whip and better understand the mechanics, as well as what makes for a good barbell at the elite level. He suspended four 20-kg men’s barbells (women use 15-kg barbells)—with 50 kg loaded on each end—from elastic resistance bands so that the bar was essentially floating in space. Then he attached accelerometers at each end of the bar where the vibrational mode patterns occur. Next, he tapped set locations across the bar with a small hammer, measuring the acceleration at the endpoints, which enabled him to map out how the bars moved in response. He compared the vibrations of different barbells, as well as a single barbell loaded with different weights.
Sleeves or no sleeves?
Langlois found that the standard motion of a bar floating freely in space has a higher frequency without sleeves—i.e., the outer, thicker area of the bar that holds the weights and can rotate independently of the central shaft—than with sleeves. This was an expected result, per Langlois, since adding mass to the ends of a bar will typically decrease the rate of oscillation and also shift the nodes (the points where the bar is stationary).
The surprise came when he looked more closely at the higher bending (flexural) modes: in that case, the frequency increased at higher loads. “The bar becomes more fixed so the actual wavelength of the bar is less,” Langlois explained. “With a set wave speed, wavelength is inversely proportional to the rate of oscillation, so we get a higher frequency. This is something we did not foresee happening. So the barbell is likely to matter.”
The experimental setup used to determine the vibrations of barbells used in Olympic weightlifting.
Credit: Joshua Langlois
The experimental setup used to determine the vibrations of barbells used in Olympic weightlifting. Credit: Joshua Langlois
Granted, it’s a small effect, in the range of a single percent, per Langlois. “But for elite sports, a single percent makes all the difference,” he said. “I am not an expert Olympic weightlifter. I have a hard time timing the whip, it’s hard for me to feel it exactly. There’s a similar thing with golfers. The best golfers in the world can actually feel how the golf club bends as they swing, and they can use that to change how the balls hit. So I don’t expect casual lifters to be able to use this very well. It’s just for the very elite level.”
Precisely which features make for the best barbell is still a puzzle. Olympic barbells have the same weight, diameter, and length, but other aspects can differ from brand to brand, such as the materials used. Most are made of some sort of steel, with stainless and chrome-coated being the most common, and the respective mechanical properties can make a small difference to a given bar’s whip, according to Langlois. Specifically, the stiffness of the bar (the Young’s modulus) can vary quite a bit. “We don’t have a good feel for this because no barbell manufacturers will tell you exactly how they make the bar,” he said. “It’s all proprietary.”
There can also be variation in the coupling mechanism between the shaft (where you hold onto the bar) and the sleeve (where you load the plates), which can affect how much the bar bends. Sleeves can be bearing (with moving bearings inside for faster rotation), bushing (a solid piece with no moving parts), a hybrid of the two, or just bare steel. Barbell manufacturers typically recommend bushing sleeves for slower, heavy lifts and bearing sleeves for faster Olympic lifting. “The coupling mechanism varies between bushings, bearings, or bare steel,” said Langlois. “Bearings seem to have the best coupling, and that’s what most expensive barbells use.”
So what’s next? “We know that the bar matters,” said Langlois. “We know that it changes shape, changes frequency, with load. So now we’re going to take data with real Olympic weightlifters [men and women] so we can see exactly how they use the whip and how the bar matters for them.”
Jennifer is a senior writer at Ars Technica with a particular focus on where science meets culture, covering everything from physics and related interdisciplinary topics to her favorite films and TV series. Jennifer lives in Baltimore with her spouse, physicist Sean M. Carroll, and their two cats, Ariel and Caliban.
