Starting Strength, 3rd Edition - Mark Rippetoe [9]
Figure 2-6. The mid-foot balance point is the position favored by the body for balance. The point of rotation at the bottom of the leg – the ankle – does not function as the last piece of the kinetic chain due to the stability provided by the anchoring system of the lower leg, calf muscles, and foot; this system maintains the tibial angle and transfers force to the sole of the foot. Considering the system this way allows us to calculate balance from the mid-foot position, the point of greatest stability against the floor.
Consider the unloaded lifter: if you stand up straight with your hands on your hips and lean forward, even a little, you can feel the weight shift to the balls of your feet and feel the increased tension in your calves as you apply some force to the mass of your body above your feet to keep from falling forward. If you lean back, you can feel the shift onto your heels – lean back far enough, and you will have to actually hold your arms out in front of you to change your center of mass so that you don’t fall back. (Our bodies have evolved to move forward, and forward imbalances are more naturally handled by our anatomy.) You settle into a position of balance when the greatest amount of force is needed to perturb the position, or when the least amount of force is needed to maintain the position. When you stand, this position is where your COM is over the mid-foot, and when you squat down and stand back up, your body’s COM is in balance when it travels in a vertical line directly over this point. Since you will do most barbell exercises (except the bench press) while standing on your feet, this mid-foot balance point becomes a critically important concept in the analysis of good exercise technique.
Let’s assume that the bar in Figure 2-5 weighs 315 pounds. Were the bar forward of this balance point, it would still weigh 315 pounds, but the effort required to move it through its range of motion would be greater. The eccentric and concentric work done on the 315 pounds would be harder due to the bad leverage position generated by the distance the bar was out of balance. And the isometric stress of stabilizing the load in the bad leverage position adds quite significantly to the effort. Keeping the 315-pound bar directly over the mid-foot through the complete range of motion (ROM) constitutes the most efficient way the work should be done during the lift. When the bar is off-balance, the added energy you must expend due to the leverage of the off-balance load makes 315 much harder to lift.
It doesn’t take much of an imbalance for the leverage to increase to the point where the rep is missed. Imagine the bar on your back in a position 12 inches in front of the mid-foot as you try to squat; this is an awkward position with even 30% of your 1RM (1 rep max), and the heavier the weight gets, the smaller the imbalance you can deal with. You can easily see that this continuum ends up with essentially zero amount of deviation tolerable at 1RM loads. This concept applies to every barbell exercise where the load must be balanced. So, “good technique” in barbell training is easily and understandably defined as the ability of the lifter to keep the bar vertically aligned with the balance point. The ability to maintain this balanced relationship between the bar and the ground is one of the many things trained with barbells that are not trained in other exercise methods. Since balance is an important characteristic of most human physical endeavors, this is one more reason to base your training on barbell exercises.
Figure 2-5 also shows the angles we use to analyze the movement of the body under the bar during the squat. The hip angle is the angle formed by the femur and the plane of the torso. Even though the spine is curved when