Starting Strength, 3rd Edition - Mark Rippetoe [129]
Your elbows might bend because you are trying to curl or upright-row the bar with your arms. Your elbows can rotate very fast – blindingly fast, in fact – if the muscles of your arms are relaxed and provide no resistance to the rotation. The very second you tighten the forearms, biceps, and triceps as you attempt to use these muscles to move the bar, you slow the movement down. After you rack the bar, this tightness causes the elbows to stop at the point where these muscles reach the end of their range of motion in contraction, which leaves the elbows pointing down and the bar sitting on your sternum. (This is another good reason to use the hook grip. The hook makes for a secure grip without the need to squeeze the bar with the fingers, thus contracting the forearm muscles.)
The same force transmission analysis can be applied to the low back. The back is the transmission attached to the hips/legs engine, and force generated against the ground travels up the back, across the scapulas, and down the arms to the bar. If the low back is not locked in hard, absolute extension, it is not as tight as it could be. A round back is a deformable component in the same way that bent elbows are, and it will result in the same unpredictable bar path that is the inevitable consequence of unpredictable force transfer. If form problems are occurring without any set pattern, this might indicate that your low back is not as tight as it could be. Both straight elbows and a solid back position are the basic mechanical requirements of a technically perfect clean.
Figure 6-28. The spine during the pull should be in absolute thoracic and lumbar extension. Any softness in the chest-up position or lower-back arch reduces the effectiveness of the back as the transmitter of force from the hips and legs to the shoulder blades and on down to the bar.
As the bar approaches the jumping position, the most important part of the movement occurs. If you are correctly pulling the bar, it is accelerating as it moves up the shins, sliding up your skin or your sweats. As it gets to the middle of the thighs, the trigger trips as the bar touches the jumping position, and you try to jump off the ground with the bar. The reaction with the ground during this explosion produces the impulse that imparts momentum to the bar. The knees, hips, and ankles extend simultaneously, with the knees and hips being the primary contributors to force production. But it is important to understand that the acceleration of the load starts BEFORE the jump actually occurs, and this acceleration results in peak velocity at the jump.
The leverage produced by the moment arm of the back can be thought of in two ways. (Remember that the moment arm along the back is the horizontal distance between the load and the hips, not the length of the back itself.) The pessimist will view the load hanging from the arms as moment force against the hips that would be better configured as a shorter moment arm with a more vertical back angle in order to take the “load” off the hips and low back. The effective lifter will see the moment arm of the back as a tool with which to accelerate the barbell more effectively. The same way a pitcher throws a ball by using the moment arm provided by the length of his forearm (no one would argue that a short arm is an advantage to a pitcher), the lifter accelerates the bar through the middle of the pull by using the length of the moment arm along the back as a tool. Back strength makes this possible and is one of the ways the deadlift is useful for heavy cleans.
The wrench analogy was used to illustrate the concept of moment force, with the bar on the shoulders being the force that turns the bolt, the back being the wrench handle, and the hips being the bolt.
Figure 6-29. The important mechanical concept of the moment arm, as illustrated