The mechanics of pulling a heavy barbell off the floor is controlled by the interaction between the musculoskeletal anatomy of the human body and the weight on the bar. Briefly, the bar must be over the middle of the feet, and the shoulders must be slightly forward of the bar, with the hips high enough to facilitate this position, with the bar pulled vertically over the mid-foot off the floor, as discussed in detail in Starting Strength: Basic Barbell Training 3^rd edition. The heavier the weight, the more efficient the mechanics must be to finish the pull, and at 1-Rep-Max weight the configuration of the pulling mechanics will either be efficient as the bar comes off the floor, or the pull will not be completed.

A 1RM pull is a 1RM deadlift. A 1RM clean is a submaximal pull, since it is between 50-70% of the deadlift, depending on the lifter. It may be the most you can clean, but it's not the most you can pull. And since it is submaximal, a clean can tolerate deviation from these perfect mechanics. A 1RM snatch is even more submaximal, and can be pulled damn near any way you want to pull it. Add reps and you are taking weight off the bar: a 5RM deadlift is a submaximal pull, by definition. A set of 2 snatches is light compared to a 1 RM deadlift, even if you can't do a third rep. But whether a deadlift, clean, or snatch, even if technique is perfect (and it never is 100%), force production – strength – is the limiting factor for a limit attempt.

The deadlift stops at the mid-thigh, but the clean stops on the shoulders. A deadlift can take 10 seconds to lock out and still be a completed deadlift, whereas a clean must be racked in a little over 1 second, or it's a miss. A heavy clean cannot be rowed into position after the pull stops at the mid-thigh, because the rowing muscles are inadequate to the task. The lifter must get the bar moving fast enough to make it fly upward high enough to catch it after the pulling stops, and that must happen before the bar gets to the mid-thigh, where the lifter has already used all of the hip and knee extension available.

The difference between a deadlift and a clean or a snatch is acceleration: the rate of change in the velocity of a moving object. Acceleration is directly proportional to the force applied to the object but inversely proportional the mass of the object. If you want to accelerate the barbell to get it moving faster, you've got to pull it harder – with more force. If you want to accelerate a heavier barbell, you've got to pull it harder – with more force. And the higher you want the bar to travel, the harder you have to pull it so that it gets moving fast enough to travel the longer distance – again, more force.

A clean must be accelerated in order to be racked on the shoulders – it must be moving fast enough to attain sufficient momentum (the product of the mass of the bar and its velocity) to continue upward after the feet break contact with the floor as you drop into the catch position. The “fast-enough” part – the velocity-part – of the momentum is the result of acceleration, which is always and forever a function of force production – strength.

Getting under the bar quickly obviously improves the efficiency of the pull by reducing the distance the bar falls after its upward momentum is exhausted, but if the bar doesn't get pulled high enough, the quickness of 90 cats will not let you clean the bar. The bar gets pulled high enough because you were strong enough to accelerate it – get it moving fast enough to have sufficient momentum to fly up as you whipped it through the middle of the pull, so that it continues upward as you come down into the rack position.

Which means that force production is inherent in the clean, and the deadlift always contributes to a heavier clean. It should be obvious that a lifter with a 500 deadlift can clean more than the same lifter with a 200 deadlift, or a 300 deadlift. What is not obvious is how strength is converted into power, which is strength displayed quickly. The ability to produce a rapid efficient muscle contraction is largely controlled by genetic endowment, and the standing vertical jump test (SVJ) measures this capacity. Not everybody is explosive, and explosive capacity is not particularly trainable. But everybody can clean, and since cleans require acceleration, everybody can do a movement that requires and practices acceleration.

The way the acceleration is accomplished is with leverage – the use of moment force by the musculoskeletal system. This is discussed extensively in the Blue Book, so I'm not going to take the space here to explain it in that level of detail. But just to jump right in, probably the most familiar use of leverage is the crowbar. A long moment arm (or lever arm) multiplies the force applied against the short moment arm and allows you to pull the nail out of the board with the strength of just your arm. Less familiar is the opposite use of the leverage, as seen in the medieval siege engine called the trebuchet: a large amount of force applied through a short moment arm can accelerate a lighter load at the end of a long moment arm.

Both systems rely on the rigidity of the segment transmitting the force – rubber crowbars don't work, since they “leak” force. And both systems rely on the differences in linear arc length traveled by the ends of the long and short segments. Since the segments are rigid, they travel through the degrees of angle at the same angular speed, but the linear speed traveled through the linear distance at the ends of the segment are different. The short end of the crowbar may only move 2 inches, while the long end moves through 24 inches of arc in the same time. Thus, 12 times the distance at lower force concentrates into the same force expressed across 2 inches at the short end, enough to pull the nail. This is known as mechanical advantage.

The long arc was covered faster than the short arc, since 24 inches was covered on the long end in the same time 2 inches was covered on the short end. Therefore, if we apply sufficient force to the short end of a lever, it moves the long end much faster, since they cover the same angular distance while moving through different linear distances. Like stepping on a rake, the trebuchet works on this principle – look it up, it's easy to understand.

The human hip is a first-class lever, with the ischium the short segment, the spine up to the shoulders the long segment, and the hip joint the fulcrum. The short segment (high force) operates the long segment (high velocity). The clean is accelerated with the moment arm that is created between the hip joint and the bar – the horizontal distance between the fulcrum and the load. If you're strong enough, you can use the short moment arm to “whip” the long moment arm – and the bar – up through the pull, accelerating it until the point where your feet break contact with the floor, where the high momentum you created causes the bar to continue upward as you drop down and catch it on your shoulders.

An efficient clean holds the back as horizontal as possible – “shoulders out over the bar” – for as long as possible, so the bar can be accelerated for more of the pull. This is why the clean should start with high hips, because high hips is a more horizontal back with the bar over the mid-foot balance point, a longer portion of the pull spent with this longer moment arm accelerating the bar, and more bar speed as a result of the longer acceleration.

In contrast, the deadlift doesn't need to be accelerated, just lifted, and slowly is just fine. So the back in the deadlift becomes more vertical from the time it leaves the floor until it locks out at the top. At deadlift weights, the shorter the moment arm between bar and hip, the less moment force it takes to lever it up to lockout, so dumping the moment arm length by getting more vertical is efficient.

Both the clean and the deadlift must start with the bar directly over the mid-foot balance point and the shoulders forward of the bar, for reasons explained in the book. The difference is what happens after the bar leaves the ground: the back stays horizontal for a while in a clean, and immediately gets more vertical in a deadlift.

What we have discovered over the course of teaching the clean to thousands of people over the last 17 years is that lower hips in the start position of the clean – as is commonly taught by weightlifting coaches – results in a shorter ROM pull than the same weight pulled with higher hips. We have photographic evidence of this, and we demonstrate it at every seminar. It's merely the application of simple mechanics to the lifts, instead of mindlessly teaching it the way it's always been taught.

The bottom line is that if you want to clean big weights, you have to be strong enough to accelerate the bar. You have to generate enough force to get the bar moving fast enough, you have to be in the right position to accelerate the bar, and you have to be strong enough to hold your back flat while you're doing it. Technique is important, but correct technique only allows you to clean what you're strong enough to accelerate. There are a couple of different ways of getting strong, but heavy squats and deadlifts are legal.   

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