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Why is there a sticking region in the bench press?
The bench press is perhaps one of the most beloved lifts in gyms all around the world. It is also probably the one that brings the most recreational lifters the greatest frustration with their lack of progress. These days, it is not widely studied, as sports scientists concentrate on exploring the squat and the deadlift, as well as the mechanics of sprinting, so that they can better help strength and conditioning coaches prepare their athletes for sports performance. However, if we dig back into the archives, there are some great studies on the biomechanics of the bench press that really get under the skin of this fascinating exercise. In this article, Chris Beardsley (@SandCResearch) reviews the literature.
The study: A biomechanical analysis of the sticking region in the bench press, by Elliott, Wilson and Kerr, in Medicine and science in sports and exercise, 1989
(Too much detail? Skip to the practical implications)
What’s the background?
Lifters often remark upon the existence of a “sticking region” in the bench press, where bar speed slows and the movement becomes much more difficult. Early research into the biomechanics of the bench press also noted this sticking region (e.g. Lander, 1985 and Madsen, 1984). However, what causes it remains unclear.
What did the researchers do?
The researchers set out to identify the reasons for the sticking region in the bench press. They recruited 10 elite powerlifters who were able to bench press between 150 – 245kg and who ranged in bodyweight from 75kg – 120kg+. The elite status of the powerlifters was such that they were all at least state champions and three of them were Australian national record holders. The subjects attended a single testing session in which they performed up to five lifts while the researchers videoed them. The video allowed the researchers to measure the length of time spent in the different phases of the lift (both absolute and relative). It also enabled the researchers to measure the external moment arms of the barbell at the shoulder and at the elbow.
The lifts were based on the lifters’ own estimates of their one-repetition maximum (1RM) for the day in question and comprised proposed lifts of an estimated 80%, 95%, 100%, 103% and 105% of 1RM. The final two lifts were only included if the preceding lift was successful. For each lift, the researchers enforced competition standards that the powerlifters were familiar with. Lifts that did not comply with the rules were repeated. Since the lifters were in training for the 1987 Australian State Powerlifting Championships, it is assumed that the rules applicable to that event were used. As well as the video, the researchers took surface EMG measurements of the triceps brachii, sternal head of the pectoralis major, anterior deltoid and biceps brachii.
What are the various phases of the bench press?
The researchers note that there are generally four clear phases to the bench press: the acceleration phase, the sticking region, the maximum strength phase and the deceleration phase.
Acceleration phase – the acceleration phase lasts from the start of the concentric phase of the lift with the bar on the chest until the bar stops accelerating, which is the same point as the point of peak velocity (called MAX-V in the charts below). In the middle of the acceleration phase is the point of maximum force (called MAX-F in the charts below).
Sticking region – the sticking region starts at the point of peak velocity and ends at the point of minimum velocity (called MIN-V in the charts below). In the middle of the sticking region is the point of minimum force (called MIN-F in the charts below).
Maximum strength phase – the maximum strength phase starts at the point of minimum velocity and ends slightly arbitrarily when the bar speed reaches the same velocity again. In the middle of the maximum strength phase is another point of maximum force (also called MAX-F in the charts below).
Deceleration phase – the deceleration phase starts at the second point of minimum velocity and ends with the completion of the lift.
The important thing to remember is that the points of maximum and minimum force are not identical to the points of maximum and minimum velocity. Although the points of maximum and minimum velocity are used to mark the starts and ends of phases, they in fact lag behind the points of maximum and minimum force, which are the true turning points within the lift where things start to get either easier or harder.
Distance at which each phase of the lift occurred
The researchers were pleased to discover that the distance of the bar from the chest at which each sticking point occurred was very similar to that seen in previous studies. The following chart shows the results of this study and compares it to the results of Lander, 1985.
Time spent in each phase of the lift
The following chart shows the average time spent by the elite powerlifters in each phase relative to the overall lift for two heavy loads.
We can see from the chart that the heavier lift spent relatively more time in the acceleration phase and sticking region and relatively less time in the maximum strength and deceleration phases. This makes good sense, as the heavier weight would have taken more time to accelerate initially, thereby increasing the time spent in that phase. Similarly, the time spent in the sticking region would be expected to be proportionately longer for the heavier weight.
External moment arms during the bench press
If you have read Hip Extension Torque, you will understand fully how external and internal moment arms affect a lift. If not, here’s a brief reminder. It’s important to recall that although muscles themselves produce force by contracting, it is torque or the turning force about the joint that causes the barbell to move. Very simply, torque is force multiplied by moment arm length. Moment arm lengths are the perpendicular distances between the pivots and the lines of action of the force. So larger forces and larger moment arms both produce greater torque. Instinctively, we know this, because when we need to turn a wrench we grasp it lower down the handle to make the job easier for ourselves. In this case, the wrench handle is the moment arm. In a barbell lift, we have two categories of torque acting: the external torque (i.e. the barbell and bodyweight loads acting on the joints) and the internal torque (i.e. the torque produced by the muscular actions on the joints in order to counteract the barbell and bodyweight loads).
So while it might sound like a long moment arm is always a good thing, there are two sides to every coin. With external moment arms, which are the perpendicular distances between the joint centers and the direction of force of the external weight (i.e. vertically downwards, in most cases where free weights are concerned), longer moment arms make the lift harder. This is why the deadlift and squat are really hard at the bottom and easier at the top. The external moment arms for the hip joint are much longer in the bottom position. On the other hand, with internal moment arms, which are the perpendicular distance from the muscle’s line of action to the joint’s center of rotation, longer moment arms make the lift easier to perform. So in a biceps curl, at 90 degrees of elbow angle, where the internal moment arm length is quite long, the torque that you can exert is greatest. Whether that means you will find the lift easiest at this point is another matter, because that will depend upon the relative difference between the internal and external moment arms. Again, if you read Hip Extension Torque, all of this will become clear…
Shoulder external moment arms
Anyway, back to the bench press. In this study, researchers used their video to calculate the external moment arms of the bench press about the shoulder joint at varying points during the lift. The chart shows the results:
The chart shows that the two loads were very similar in terms of the external moment arm about the shoulder that they produced. However, more importantly, the researchers found that the external shoulder moment arms decreased throughout the lift and were largest when the bar is on the chest. This would require the shoulder muscle to produce the most force at the start of the concentric phase, in order to generate a similar torque. It also implies that the lift might become steadily easier for the shoulder muscles from the beginning to the end.
In terms of understanding the sticking region, however, it would suggest that the sticking region is not caused by an adverse change in the external moment arm at the shoulder. In other words, the bench press does not become suddenly more difficult for the shoulder muscles in the sticking region as a result of changing leverages. It is worth noting that how easy the shoulder would find it to produce a greater force at that joint angle would also depend upon the length-tension relationship of the shoulder muscles, as well as the way in which neural drive alters with joint angle for those muscles. These variables are not always predictable and could lead to significant differences in the ability of the shoulder to generate force at different joint angles.
Elbow external moment arms
The researchers also used their video to calculate the external moment arms of the bench press about the elbow joint at varying points during the lift. The chart shows the results:
From the chart we can see that there is a slight trend for decreasing external moment arm lengths about the elbow from the start of the lift through to the point of minimum velocity, which marks the start of the maximum strength phase. At this point, the bar begins accelerating again. This tells us that the triceps find that the lift gets steadily easier the further the bar goes from the chest, at least up to the start of the maximum strength phase. So again, in terms of understanding the sticking region, it would suggest that the sticking region is not caused by an adverse change in the external moment arm at the elbow. In other words, the bench press does not become suddenly more difficult for the triceps brachii muscles in the sticking region as a result of changing leverages. Interestingly, there is a big spike in the external moment arm about the elbow around lockout, which suggests that the triceps suddenly find themselves mechanically disadvantaged. This may reflect the tendency of some lifters to struggle to lockout the last few inches of a lift, despite breaking through the sticking region.
The researchers noted that the three prime movers (triceps brachii, sternal head of the pectoralis major and anterior deltoid) all mostly displayed significant levels of EMG activity during the lift and did not differ markedly in the level of activity at any joint angle during the lift. They noted that the triceps brachii occasionally displayed a slight delay in activity in some lifters but this was not a strong trend across the whole group. However, Krol (2010) and Van Den Tillaar (2009) proposed that the co-ordination of the various prime movers was key to the creation of the sticking region. Krol noted that the activity of the triceps is delayed with increasing weight and Van Den Tillaar noted that failure does not always occur in the sticking region.
Angle of bar path
The researchers used the video recording to measure the exact angle of the bar path. They found that the bar did not travel completely vertically. The following chart shows the relative angle of the bar with respect to the horizontal at various points during the lift. The larger the angle, the steeper the bar path. A vertical bar path would be 90 degrees and a horizontal bar path would be 0 degrees.
The chart shows three different kinds of lift. The 81% lift occurred without any sticking region or maximum strength region and just had acceleration and deceleration phases. The angle of bar path became more horizontal as the lift progressed. However, in the 100% lift, the bar path stayed around the same angle the whole way through. Finally, in the 104% lift, which was a failed attempt, the bar suddenly starting moving almost entirely horizontally (towards the head) at the point of failure. The researchers suggested that the bar path became more horizontal because the lifter was trying to reduce the external moment arm about the shoulder by moving the bar to be positioned directly over the shoulder joint. This would theoretically increase the leverage of the shoulder at this point in the lift. However, it does not explain why the sticking point occurs where it does.
Further investigation into the sticking region
Another factor that might affect the sticking region that was not addressed by the researchers is the internal moment arm of each of the pectorals, triceps and shoulder muscles. Before we think about these moment arms, it’s probably helpful just to cover the joint angle terminology, as it is quite easy to get confused between degrees of joint angle and degrees of flexion and extension.
Shoulder: at the start of the bench press, the shoulder joint is at least in full extension in the sagittal plane and probably slightly hyperextended, which amounts to a shoulder angle of less than 0 degrees. At lockout, the shoulder joint is in around 90 degrees of shoulder angle in the sagittal plane. (I’m going to ignore the frontal and transverse planes because that this post is getting out of hand).
Elbow: in contrast, the elbow joint is probably at around 110 degrees of elbow angle the start of the bench press and finishes in 0 degrees, fully extended.
So, with those angle ranges in mind (shoulder: from 0 – 90 degrees; elbow: from 110 – 0 degrees), let’s take a look at how the internal moment arm changes during the bench press movement:
Shoulder: Ackland (2008) reported that the superior pectoralis major internal moment arm in the sagittal plane is maximal at 71 degrees (being 53.7mm) and minimal at 2.5 degrees (being 9.6mm). The researchers only tested between 2.5 – 120 degrees, so it is probable that 0 degrees of shoulder angle is in fact the smallest internal moment arm for the superior pectoralis major in the sagittal plane. So the internal moment arm for the superior pectoralis major is around 495% greater in 71 degrees of flexion than in 2.5 degrees flexion. They found that the anterior deltoid internal moment arm in the sagittal plane is maximal at 120 degrees (being 40.0mm) and minimal at 2.5 degrees (being 11.6mm). So the internal moment arm for the anterior deltoid is around 245% greater in 120 degrees of flexion than in 2.5 degrees flexion.
Elbow: Sugisaki (2010) reported that the triceps internal moment arm in the sagittal plane increased as the elbow angle decreased, from 17.4mm at 110 degrees to 23.9mm at 30 degrees. This means that the internal moment arm for the triceps is at least 37.3% greater when it is 30 degrees from full extension than when the elbow is fully flexed in a similar position to the start of the bench press.
So these internal moment arm differences suggest that the ratio of muscular force to torque produced by the prime movers (in the sagittal plane only) is greatest towards the end of the lift and least at the beginning of the lift. This is diametrically opposite to the external moment arms, suggesting that the bench press should always be hardest off the chest.
The existence of the sticking region mid-way through the lift therefore remains problematic. For completeness, it’s important to note that the moment arms in these studies were calculated in purely the sagittal plane. When actually performing the bench press in which there is also a degree of humeral movement in the transverse and frontal planes. So the moment arms during the bench press may be different from those in more controlled joint angle studies.
What did the researchers conclude?
The researchers concluded that the sticking region in the bench press is not caused by adverse changes in the external moment arms at either the shoulder or the elbow. They also concluded that the sticking region is not caused by changes in neural drive to the prime movers. In consequence, the researchers speculated that the sticking region is therefore caused by the gradual reduction in stored elastic energy as a result of the eccentric phase prior to the lift.
The researchers proposed that the sticking region is the phase between the release of the stored elastic energy and the onset of a more mechanically advantageous position for the movement. Whether this is the case, however, requires further investigation. It is possible that titin may provide very large amounts of passive elastic force contribution at the bottom of the lift. Because of the age of this study, this research wasn’t mentioned by the researchers. It could be that the sticking region starts at the point where titin contribution reduces significantly.
What are the limitations?
The study was limited as follows:
- The study included only elite powerlifters and they may have used very specific techniques in order to achieve their maximum lifts. Different results might be observed in athletes who are not bench press specialists.
- The study only covered the EMG activity of four muscles and did not record the activity of the trunk, back or leg muscles. While these muscles may not be prime movers, their importance is known to powerlifters and the elite status of these athletes indicates that any and all muscles may have been involved in the lift so far as was possible.
- The researchers did not normalize the EMG activity and did not formally calculate onset times for the muscles during the lifts. This may have led to them missing features of muscular activity.
- The study presented a number of factors that do not appear to be the cause of the sticking region in the bench press but they did not present a factor that could be taken as the cause. Their proposal of elastic energy being the cause was made on the basis of not finding any other reason, which is not quite the same thing as showing that it is the cause. To demonstrate the effect of elastic energy in the bench press on the sticking region, the researchers would have to compare a concentric-only bench press with an eccentric-concentric bench press and show that the concentric-only bench press failed at the chest rather than in the sticking region. Personally, I don’t think this would happen but I would be curious to hear other peoples’ views.
What are the practical implications?
The performance of the eccentric phase may be critical during the bench press. Care should therefore be taken to maximize the benefit of the elastic energy storage during this phase. Maintaining tightness in the bottom position to ensure maximum recoil may lead to improved performance.
The bottom position of the bench press is likely the most difficult, as it is the least mechanically advantageous for the shoulders and triceps. Lifts that increase the strength of these muscles in this position may be useful as assistance work.