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of the pull – using the moment arm along the back – is what actually starts the acceleration of the load, and this occurs well below the knees, not at the top as in a vertical jump for height. The knees re-bend as the bar passes them to allow the quadriceps to extend the knees a second time, but this occurs during the process of building velocity from the acceleration which started lower in the pull. Velocity builds during the whole acceleration phase, from the floor to the top of the pull, not just at the top. But during this shift from hips to knees it is typical that the increase in velocity slows, giving many people the impression that the only fast part of the pull is the top. The drop in bar velocity is due to the sudden reduction in work being done on the bar as the shift occurs – for a brief instant to acquire a better position to continue the pull, you are moving your body instead of the bar (Figure 6-34).

Figure 6-34. The change in moment arm length between the bar and the hips and the bar and the knees during the pull. As the knees rebend, the moment arm along the femur becomes a function of the knee extensors. (M.A.= moment arm)

As the hip angle opens, the hip extensors’ ability to accelerate the load along both the back and the femur diminishes as the moment arm from the hip shortens. The hips lose their ability to effective operate the “tool” we’re using to accelerate the bar, and to continue to increase the bar velocity we have to re-configure the levers. The knees re-bend and create leverage against the bar from the knee backwards, now powered by the quadriceps and adding to the velocity acquired during the middle of the pull. This “second pull” makes use of the fact that the moment arm along the femurs can be operated by both the knee and the hip extensors. So in some sense, it is still a jump – “jumping” keeps the bar from swinging into a loop. (The deadlift does not make use of this shift in leverage because the slow velocity at which a heavy deadlift is pulled will not allow a further loss of bar speed without actually stopping the pull and creating an illegal “hitch.”)

If this re-bend is excessive, as it will be if you try to stand up too vertically too soon, it will greatly reduce your ability to use the angular acceleration of the back through the middle of the pull. Excessive knee flexion slacks the hamstrings distally, removing much of their contractile potential from the pull and removing the posterior chain from the most critical part of the pull. A deliberate attempt to shorten the moment arm between bar and hips by coming into a vertical position before acceleration reveals a misunderstanding of the leverage system used in the clean. By keeping your shoulders out over the bar, you enable your back to whip the load up quickly. So the acceleration of the pull actually starts before the place we earlier identified as the jumping position. As the back loses its horizontal angle, the knees shift into position to continue the acceleration of the bar through to the top of the pull. This is why you can clean more from the floor than from the hang position.

So there are actually two periods of acceleration during the clean pull: the first through the middle of the pull as the back angle whips from more horizontal to more vertical, and the second after the knees re-bend to allow the knee extensors to add to the bar velocity. If the first phase is performed correctly, there will be little loss of velocity as the second phase begins. This entails the proper understanding of the acceleration function of the first part of the pull.

The bar needs to be in contact with your legs during this phase, touching the skin all the way up, as you maintain straight elbows. The path is vertical because the knees and hips extend in a coordinated way that results in the load’s moving up in a straight line, with as little forward or backward deviation (seen as horizontal movement in the bar path) as possible. During this section of the pull, forward movement of the bar is usually due to an incorrect start, as