Sarah Robles and the Mechanics of Weightlifting

U.S. weightlifter Sarah Robles will rely on an athletic mix of strength, speed and timing to help create explosive power when she competes at the 2012 Summer Olympics. Robotics engineer Brian Zenowich compares Robles' movements to those made by the WAM Arm, one of the world's most advanced robotic arms. ʺScience of the Summer Olympicsʺ is a 10-part video series produced in partnership with the National Science Foundation.

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LIAM McHUGH, reporting: Pound for pound, Sarah Robles is one of the strongest women in the world. At the 2012 Olympic team trials she lifted 114 kilograms in the snatch and 144 kilograms in the clean and jerk for a total combined weight of 258 kilograms, or 568 pounds, which placed her first among women in the super heavyweight division.

SARAH ROBLES (U.S. Weightlifting Team): Most of the time when people watch weightlifting in the Olympics, they have this idea, oh, this big strong guy. That's big muscles and you're just going to lift a lot of weight.

McHUGH: While fans may marvel at her size and strength, it takes a robotics engineer like Brian Zenowich to appreciate the way Robles uses her body to create explosive power.

BRIAN ZENOWICH (Barrett Technology, Inc.): I watched what she's doing and it blows me away. Watching a person accomplish so many tasks, the balance, the speed, the agility, the posture, everything that goes into her lifts, it blows my mind.

McHUGH: Zenowich works in a field called biomimetics that uses nature as a model for engineering, materials, and medical technologies. With funding from the National Science Foundation, Zenowich and his collaborators at Barrett Technology have developed one of the most advanced robotic arms in the world, the Whole Arm Manipulator, or WAM Arm.

ZENOWICH: We designed our robot basically around how a human’s arm is put together. We wanted to be able to address problems and tasks that humans can address in a very natural way.

McHUGH: The WAM Arm has the same degrees of freedom as Robles' arm. The wrist, shoulder, and elbow have pitch, or up and down movement. The wrist and shoulder also have yaw, or side-to-side movement, and roll, circular movement. The WAM Arm is also a haptic device, meaning that it gets feedback from the things it touches, letting it know how hard to grip something, such as this foam block. This sense of touch and flexibility allows the WAM Arm to do tasks much like a real person can.

ZENOWICH: It's very important to be flexible with the robot if you're going to be working in a human environment. And having a dexterous, agile robot that can reach around things, reach behind things, that's really important in dealing with everyday situations.

McHUGH: To see if the WAM Arm can mimic Robles' craft, we first filmed Robles completing the two Olympic lifts with a high speed Phantom Camera. The clean and jerk is a two-part lift where she raises the weight to her shoulders before lifting it overhead. The snatch is a one-part movement where she raises the weight from the floor straight to an overhead position. While analyzing the lift, Zenowich pinpoints the key part of Robles' exercise.

ZENOWICH: She's pulling up. She's pulling up. She's pulling up. She's pulling up. Here. She stops pulling up.

McHUGH: Her lifting force actually throws the bar upwards a bit.

ZENOWICH: She was counting on that to continue upwards without her having to lift anymore. And in that moment she had just a fraction of a second where she had to get her entire body back underneath that bar.

McHUGH: Robles agrees that this is the key moment of the lift.

ROBLES: A lot of people just think it's moving the bar, but most of it is moving your body around the bar. So you're moving your body more than you're moving the bar.

McHUGH: To simulate what Robles did during the lift, Zenowich attempts to get the WAM arm to lift a five-pound weight using a method he calls "master-master" that allows him to control the WAM arm with another robot, but still feel the forces the WAM Arm is encountering.

ZENOWICH: First bringing the mass up to the middle of the robot, up to here, now if I try to just lift the mass above the robot, the robot's not strong enough to lift the mass all the way above. So I'm going to move the robot forward, and begin to impart enough momentum to the mass to get it flipped up above the robot. And it's balanced on top.

McHUGH: While Zenowich is able to get the WAM Arm to lift the weight, it requires hours of set up time to program it. The WAM Arm also has trouble compensating for unforeseen circumstances during the lift.

ZENOWICH: Seeing things, vision processing, identifying objects, identifying the locations of objects and where you should grab the bar. Those are pretty complex tasks for a robot to perform.

McHUGH: For Robles, these moves may look instinctual, but she had to perform the lift countless times before it became second nature.

ROBLES: You have to be able to put the right amount of effort into the appropriate amount of weight that you're lifting. So you don't have to know what the bar is doing, but you have to know what you're doing.

ZENOWICH: As an Olympian she is at the top of her game, so, you know, best of luck to her. She is an amazing athlete.

McHUGH: At the 2012 Summer Olympics, Robles will try to raise the bar of athletic achievement, something that may just inspire an engineer like Brian Zenowich to raise his robot's game too.

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