Saturday, July 17, 2010

Bench Press - Part Three

Figure 1. Typical Vertical Bar Movement with identification of Instants Used in Quantifying Bench Press. See text for further description of these instants.

Click Pics to ENLARGE

Figure 2.Geometry of the Lowering Phase. (1) = STRT, (2) = MXVL, (3) = MXAL, (4) = CHST; see text for further description of these characteristic instants. Angles are with respect to horizontal, where 1 (circled) is from STRT to MXVL, 2 (circled) is from MXVL to CHST.

Figure 3. Geometry of the Raising Phase. (4) = CHST, (5) = MXAR, (6) = MXVR, (7) = MNAR, (8) = MNVR, (9) - END. See text for further description of these characteristic instants. Angles are with respect to horizontal, where 3 (circled) is from CHEST to MXVR, 4 (circled) is from MXVR to MNVR, and 5 (circled) is from MNVR to END.

Table 2.

Table 3.

Table 4.

Figure 4. Bench press comparitive bar acceleration during two lifts by L. Pacifico (1978 injury with 523 pounds, and 1979 lift of 529 pounds.

Bench Press, Part Three

Chapter Two: Biomechanics of the Bench Press, or
“Technique is Everything”

2-1 – The Rules of Bench Pressing

No matter whether you are a powerlifter, an Olympic lifter, an athlete in another sport, a bodybuilder or general weight trainer, the rules for correct bench pressing are valuable. Years of experience have gone into their formulation. Some of the rules are actually designed to help prevent injury (for example, the no “bridging” rule helps protect against low back hyperextension injuries, the no “bouncing” rule helps protect against chest impact and shoulder injuries, etc.). What follows are the rules for bench pressing of the International Powerlifting Federation.

Bench Press Rules

1. The lifter must assume the following position on the bench, which must be maintained during the lift: with head and trunk (including buttocks) extended on the bench, lifting shoes flat on the floor.
2. The referee’s signal shall be given when the bar is absolutely motionless on the chest.
3. After the referee’s signal, the bar is pressed vertically to straight-arm’s length and held motionless for the referee’s signal to replace the bar.
4. The width of the bench shall be 30 cm. The height shall be 45 cm. The length shall not be less than 1 meter 22 cm. and shall be flat and level. The height of the bench uprights on nonadjustable benches shall be 87-92 cm. from the floor to the bar rest positions.
5. The spacing of the hands shall not exceed 81 cm., measuring between the forefingers.
6. If the lifter’s costume and bench top are not of a sufficient color contrast to enable the officials to detect a possible raising of the buttocks, the bench top may be covered accordingly.
7. For those lifters whose feet do not touch the floor, the platform may be built up to provide firm footing.
8. A maximum of four and minimum of two spotter-loaders shall be mandatory; however, the lifter may enlist one or more of the spotter-loaders to assist him in removing the bar from the racks. The lift-off may only be given to the lifter at arm’s length and not down at the chest.
9. In the event of a spotter error, a new attempt may be given the lifter.

Causes for Disqualification in the Bench Press

1. During the uplifting, any change of the elected position.
2. Any raising or shifting of the lifter’s head, shoulders, buttocks, or legs from the bench or movement of the feet.
3. Any heaving or bouncing of the bar from the chest.
4. Allowing the bar to sink after the referee’s signal.
5. Any uneven extension of the arms.
6. Stopping of the bar during the press proper.
7. Any touching of the bar by the spotters before the referee’s signal to replace the bar.
8. Failure to wait for the referee’s signal.
9. Touching against the uprights of the bench with the feet.
10. Touching the shoulders against the uprights of the bench.
11. Allowing the bar to touch the uprights of the bench during the lift.

2.2 – Typical Bar Velocity and Acceleration Patterns

The bench press is a quasi-static exercise. The accelerations and velocities are quite small, especially when compared to most human movements. A bar velocity of .4 m/s (which is less than 1 mph!) was discovered to be typical of the bench press (references 7 and 9, section 1.4). Also, bar accelerations for skilled bench pressers are typically less than 1.2 m/s/s (with even gravity at 9.8 m/s/s!). Always interesting to note the interest and excitement each individual derives from a subject which very well may mean nothing to another. And always fun to remember this when considering the ‘importance’ of our chosen interests. The collection of pre-World War Two matchbook covers with misprints that keeps me from losing all hope in living may not mean the same to others. But I highly doubt that! The corresponding rates of muscle extension associated with bench pressing are most probably also small as well. Consequently, due to the small velocities and accelerations involved in the bench press, the force that an individual exerts involved in the bench press, the force that an individual exerts on the bar would seem to be determined primarily by the positions of the bar and the body. (Note: velocity is the “speed” the bar is moving at, and acceleration is how fast that velocity is increasing (if positive) or decreasing (if negative).

Since the horizontal velocities and accelerations of the bar during bench presses are so small that they are essentially negligible, only the vertical velocity and acceleration patterns of the bar will be discussed. Using the techniques described elsewhere (reference 7 and 9, section 1.4) nine “instants” (or common points) in each bench press were selected in order to help in comparison of bench press performances between different skill groups. For example, one such instant chosen was the point during the lowering of the bar where the bar’s vertical velocity was greatest. The nine instants in the sequence in which they occur, as well as the number and name by which they are identified in the figures and tables that follow were:

1. STRT – the start of the lift, when the arms are fully extended and the bar is at rest.
2. MXVL – the instant at which the bar achieves its largest downward velocity.
3. MXAL – the instant at which the bar achieves it s largest upward acceleration while it is being lowered.
4. CHST – the instant at which the bar reaches the chest.
5. MXAR – the first local maximum of the upward acceleration after it leaves the chest.
6. MXVE – the first local maximum of the upward velocity of the bar after it leaves the chest.
7. MNAR – the first local minimum of the vertical acceleration of the bar after it leaves the chest.
8. MNVR – the first local minimum of the upward velocity of the bar after it leaves the chest.
9. END – the end of the lift, when the arms are again fully expended and the bar is at rest.

To get a better feeling for these nine “instants”, as well as to see the typical time histories of the vertical bar velocity and acceleration for a representative subject, please look carefully at Figure 1 and go through the list of instants again.

From a slightly different perspective, Figure 2 shows approximate where the first four instants occur during the lowering phase of the bar during a bench press. Also included in this figure are two angles, taken with respect to the horizontal, which help describe the geometry of the bar path during the lowering phase of the bench press. The first angle, 1 (circled) is the angle made with the horizontal between instant (1) – STRT and instant (2) – MXVL. The second angle, 2 (circled) is similarly taken between instant (2) – MXVL and (4) – CHST. It may help to picture each instant in Figure 2 as the position of the end of the bar as seen from a side view during the lift.

Figure 3 is a similar representation of where the second five instants occur during the raising phase of a bench press. Also included in this figure are three angles, taken with the horizontal as before, which help describe the geometry of the bar path during the raising portion of bench pressing. 3 (circled) is a key angle describing the angle from where the bar leaves the chest ( (4) – CHST) to where the bar reaches its maximum vertical velocity ( (6) – MXVR). 4 (circled) is from this point of maximum vertical velocity to the instant where the bar’s vertical velocity reaches its minimum on the way up ( (8) – MNVR). The final angle, 5 (circled), is similarly from this point of minimum bar velocity to the END – (9) of the lift. Of particular interest later on are 3 circled and 4 circled, so keep these in mind. By the way, you’ll no doubt notice in Figures 2 and 3 that the shoulder is the origin of the coordinate system used here (reference 7 and 9, section 1.4).

It is important to note that although the nature of the bench press (down, pause, and back up again) guarantees the existence of instants (1) to (6) and also (9), instants (7) and (8) need not be distinct from the end of the lift. The existence of distinct minimums of upward bar velocity and acceleration while the bar was being raised was proposed based on my earlier studies of the squat exercise. The proposed existence of these definite low points in upward bar velocity and acceleration during the raising phase in the bench press was verified by the results of the studies on novice and expert bench pressers (references 7 and 9, Section 1.4)

If one combines the results of those two studies, then the typical average values for the bar accelerations at key instants in the bench press are as displayed in Table 2.

Please note in Table 2 how similar the accelerations are for the two expert groups of powerlifters, and how much more peak acceleration the novices have both on the way down and on the way up. Also, note that the novices had a greater negative acceleration (indicating that the bar was slowing in velocity more) on the way up at instant (7). More later on these points.

To finish off this section, it is of interest to note both the total time for lowering the bar to the chest as well as the time it took to raise the bar from the chest to completion. Again, combining the data (from references 7 and 9, section 1.4) the results appear in Table 3.

Note also in Table 3 that both groups of expert powerlifters took more time both in lowering and in raising the bar during the bench press compared to the novices. Of particular interest is how much more time it took both the expert groups to LOWER the bar to the chest compared to the novices. This will be discussed in more detail in the next section.

2.3 – The Degree of Control Used in Lowering the Bar

In this section, I will (hopefully) prove to you that by controlling the bar’s descent better during the bench press (by mainly reducing the bar’s vertical acceleration on the way down to the chest), you can reduce the total force required to bring the bar to rest at the chest and thus dramatically reduce the potential for possible injuries to your shoulder joint.

Back in 1980, in a pilot experiment for a grant proposal to study the bench press, the author (along with Dr. N. Madsen and Dr. McLeod) decided to do a two-dimensional analysis to determine the total vertical force acting on the shoulders during a single maximal bench press using intermediate and world class subjects. Utilizing a high speed LoCam camera and standard two-dimensional biomechanics techniques in our laboratory at Auburn, the peak vertical acceleration of the bar was determined for each subject from the digitized film records. Table 4 lists the results for both groups. The Intermediate group were Auburn athletes with one to two years lifting experience who were filmed in our laboratory, and the World Class group were champion bench pressers whose lifts were analyzed from high-speed films that the author had recorded at the 1974, 1978 and 1979 U.S. Senior National Powerlifting Championships.

In Table 4, it is first obvious that the peak vertical acceleration of the bar on the way down is uniformly greater (by about three to four times) for the less skilled bench pressers during the lift. The total weight supported by the two arms is simply given by application of Newton’s Second Law, i.e.

Total weight = Bar Weight + (Bar Mass + Peak Vertical Bar Acceleration)

Thus, the total force acting on the two arms was calculated for each subject. As shown in Table 4, the actual total loading is uniformly greater for the less skilled bench pressers. For example, Subject 1, although lifting a bar weight of only 235 pounds has a peak loading during the descent on the upper body during the lift of 363 pounds. In contrast, the current World Superheavyweight Bench Press Champion, Subject 16 (Kazmaier), filmed in 1978 before coming to Auburn, only exerted 584 pounds total force (with 528 pounds on the bar).

If one were to construct a ratio of total weight to the bar weight (Table 4) it can be seen that there is a clear trend for the world class lifter to have total weights only ten to thirteen percent over bar weight, versus thirty to sixty percent over bar weight for the less skilled lifters. This simple experiment illustrates that loading on the glenohumeral (shoulder) joint in less skilled lifters is considerably greater than bar weight alone, and the implications for injury (especially posterior shoulder subluxation) are clear. Indeed, it is routinely noted that beginner and intermediate bench pressers, particularly when tired or sloppily trying to “squeeze” out one more repetition bench press, will let the bar accelerate on the way down even more dramatically. While it is not possible to infer particular structural loadings from this simple two-dimensional study, it is probable that such bench pressing can be a causative factor in shoulder and upper body injuries. The obvious point here is to not let the bar accelerate too much on the way down (especially in an uncontrolled fashion) during your bench presses – even during high repetition “light” sets! It is important to realize that doing fast sets of repetitions with lighter weights may in fact be more stressful to your body than doing heavier bar weights with more controlled technique (and lower acceleration). Think about it (the neo-Nazi behind Michael Douglas in Falling Down) . . . most of the top bench pressers do this in a meet! By the way, have you considered that the squat is another example of this concept? Ever try dropping down with a lot of acceleration in a squat? I heartily recommend it to all those I compete against . . . only kidding.

Subsequent studies (references 7 and 9, section 1.4) also verified the results of this pilot study. In general, the group of 17 novices used in these two later studies developed peak downward bar accelerations that were approximately 5-6 times larger than the expert groups (see Table 2). Thus, the best bench pressers seem to have clearly learned to minimize the bar’s acceleration during the bar’s descent. In fact, the later data (to be discussed in section 2.11) indicates that there is a trend for successful lifters to progressively reduce their peak vertical bar acceleration during the descent over the years. For example, multiple world record holder Mike Bridges decreased his peak downward bar acceleration by over four-fold between 1978 and 1980, while his lift jumped significantly. Bridges is a clear example of “smooth” form, since low acceleration type bench presses visually appear as being smooth and effortless. Watching Mike bench, it is clear that he has mastered this aspect of the lift.

When someone does allow acceleration to jump during the descent, he can expect very high loading of his muscular system and his shoulder joint. An example of this was the great bench press and powerlifting world champion Larry Pacifico’s bench press injury in the 1978 Seniors. As shown in Figure 4, a comparison of his 523 at that meet with his 529 at the 1979 Seniors showed that the bar’s vertical acceleration on the way down was about eight times greater than in 1979 when the bar reached his chest in his injury in 1978. The loading on his body in 1978 in this lift was effectively about 950 pounds. Ouch! It is incredible that some lifters with high descent acceleration, likes Lars Hedlund, for example, can stay injury free very long.

The obvious conclusion here is that the novice lifter could reduce the maximum force on his shoulder joints by lowering the bar more slowly. Hopefully, this will lead to a reduced chance of injury, particularly acute injuries. However, the question of whether the novice lifter can make this change in technique remains. Recall from Table 3 that the lowering phase is considerably longer for the competitive lifters. The average times of the lowering phase were 1.16 seconds for the novice group versus 1.72 and 2.34 seconds for competitive groups. The reduction in ability to generate force associated with time changes of this magnitude is certainly small. Each lifter has at his disposal the ability to reduce the maximum joint forces experienced during the lowering phase of the bench press. All we need to do is concentrate on not letting the bar achieve too large a velocity during the lowering phase of the lift . . .