Biomechanics and the Olympics: Part VII

I was asking my wife what today's topic should be when I came across this video of weightlifter Matthis Stenier dropping 432 pounds directly onto his neck (video courtesy of Deadspin.com).  Before you read any further, watch the video (disclaimer: it looks worse than it really is, but if you have a weak stomach, you may not want to watch it).  This video itself contains numerous possibilities for discussion, but let's talk about Newton's second law of motion, since we have previously discussed the first law.

Newton's second law of motion is the law of acceleration, represented by the equation F=ma, where F is force, m is mass, and a is acceleration.  This equation tells us that an object's acceleration is directly proportional to the force applied to it and inversely proportional to the object's mass.  Steiner is attempting to perform a lift called the snatch, where he must lift the weight over his head, and then stand up.  During his failed attempt, he was attempting to lift 432 pounds.  This weight represents a force, since weight is the result of gravity acting on the mass of an object.  To calculate the weight of an object, you multiply the object's mass by the acceleration due to gravity (-9.81 m/s^2).  Pounds is the US unit of measuring force, in the metric system, a Newton is the unit used to measure force.  One pound is equal to -4.45 N, so in this example, the barbell had a weight of -1,922.4 N.  We can also calculate this weight by multiplying the mass of the barbell (195.95 kg) by the acceleration due to gravity (-9.81m/s^2), which also gives us approximately -1,922.4 N.  In this example, the negative sign indicates that the force is acting in the downward direction, which is the case with weight, which always pulls us or objects towards the ground.

For Steiner to lift the barbell off the ground, he must exert a force in the upward direction to the barbell greater than 1, 922.4 N, or 432 pounds.  If the force he exerts is less than or equal to the weight of the barbell, no movement will occur.  Steiner is clearly able to exert a force greater than this because he is able to move the barbell over his head.  The muscular force he generates is greater than the weight of the barbell, and the muscles shorten, allowing him to begin the movement.  This causes an acceleration of the barbell in the upward direction.  When Steiner gets the weight over his head, he pauses for a second, and the barbell does not move.  At this point, the force he is exerting is equal to the weight of the barbell, and the muscles develop tension while remaining at a constant length.  Since the forces are balanced, there is no acceleration.  After this short pause, Steiner begins to stand up, meaning he is exerting a force greater than the weight of the bar.  However, he is not able to complete the lift, and because he is now exerting less force than the weight of the bar, the bar is now moving in the downward direction right onto his neck.  Now, the barbell has an acceleration in the downward direction.  Normally, after we have lifted something and are attempting to lower it back down, we do so in a controlled manner, in order to avoid injury and slamming it on the ground.  The muscles gradually develop tension as they lengthen to control the movement.  Steiner was not able to do this (which is very difficult since he was lifting 432 pounds).  It is difficult to tell from this angle exactly what happened, but I have two theories.  1) He was lifting too heavy of a weight and simply could not continue to produce enough force to lift it over his head or 2) the barbell moved too far back behind his head, causing a tremendous amount of tension on his shoulders and elbows, to the point where if he did not drop the weight, he likely would have dislocated one of those joints.  It was probably a combination of these factors as well as fatigue.

I am happy to report that he was not seriously injured, and actually attempted another lift.  Weightlifting can be a very dangerous sport, especially when attempting to lift something this heavy.  My advice is to leave these kinds of lifts to the professionals, and if you are attempting to lift something over your head, be very careful.