Understanding the Pull Trajectory

Comparison of Pull Trajectories in the Snatch

Figure 1: Comparison of Pull Trajectories in the Snatch

For those of us who have been around in the sport of weightlifting for 40 years or more, it is incredible to consider that digital video only arrived in the 1990’s and what a profound effect it has had on our ability to investigate and understand the movement patterns of athletes in Weightlifting.

These days coaches and athletes in Weightlifting should take every advantage of easily accessible technology to obtain a bar path (trajectory). All is needed is to capture some video from the side and then to import the video file into software such as Kinovea and use the ‘Cross Marker’ tool to trace the bar path. Some familiarity and practice with the software is needed but the task is quite simple.

The ability to interpret the bar path obtained, however, is dependent on the individual’s understanding of what is an ideal path, and the associated body positions and movement that give rise to bar trajectories, good and not so good. The knowledge needed for such interpretive analysis is gained by self-study not only be viewing countless hundreds of lifts but also by getting to grips with the physics (biomechanics) involved. This article seeks to assist in this regard.

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Snatch Technique – The Key Concepts Fully Explained

In the early stages of learning, it is exceptionally important for the coach to provide a conceptual picture of the snatch. The task for the coach is to help the beginner unravel the complexities of snatch technique, to simplify and make more understandable what the snatch is, and what it isn’t. If insufficient attention is paid to explaining the fundamental concepts of snatch technique, it is highly likely that the beginner will suffer considerable learning difficulties and may accumulate errors of technique that may be intractable. It is, of course, a truth that coaches will differ very considerably in their own understanding of the snatch. These differences among coaches emerge as a result of the passing on of knowledge, beliefs and attitudes from one generation of coaches to the next. Inevitably, the most powerful influence is when an athlete learns from their own coach, and largely adopts the same view of snatch technique. Some differences between coaches will be merely superficial and the end result of coaching will be athletes with broadly similar styles and consistent performance ability. On the other hand, some coaching beliefs result in athletes developing a style of snatch that has has a pronounced eccentricities and a great deal of performance unpredictability.

Kiana Elliott - Excellence in Snatch Technique - displaying a great Receiving Position

Kiana Elliott – Snatch Receiving Position

Therefore it is greatly important for athletes and coaches alike to investigate the key biomechanical concepts upon which snatch technique is built and avoid the trap of passed on beliefs systems.

Key concepts of snatch technique

CONCEPT 1: TWO BASIC SKILLS

Excellence in snatch technique depends broadly on two entirely different skills. Firstly, the skill to lift the bar and secondly the skill to move rapidly under the bar and stabilize the weight overhead. No matter how good the athlete’s capability is in the first skill, their performance will be limited by the second skill. In other words, no matter how strong an athlete is in the pull, if they cannot stabilise the weight overhead, their pull strength comes to no avail. It is critically important therefore to set about developing these two skills in tandem from the very first lesson. It is often the case, that far more attention is paid to the first skill (the pull) in the early stages of learning and not enough on the second skill (excellence in achieving a low, stable receiving position), and as a result athletes develop a lack of confidence with the bar overhead.

CONCEPT 2: CRITICAL HEIGHT

Good snatch technique is NOT a throwing action i.e. the bar is not catapulted or thrown overhead. Instead, the athlete’s task is to extend the body powerfully upwards to complete the pull as shown in Figure 2 below, and then to complete a fast drop into the receiving position and stabilise the bar overhead. The term “critical height” denotes the need for the bar to reach sufficient height so that the athlete has time and space to drop under it, and lockout.

Critical height to which the bar must be raised in order to be successful with the snatch

Figure 2: The simplicity of the snatch is that it is a pull to full extension followed by a fast drop.

The critical height to which the bar must be elevated depends on two factors:

  1. The depth of the athlete’s receiving position. The ability of the athlete to sit very low in the receiving position is an obvious advantage. The critical height that the athlete must achieve in the pull will be lower if they can sit deeper.
  2. The quickness of the athlete to move under the bar into the receiving position. This factor is often not worked on sufficiently. If an athlete is slow in their movement under the bar, the bar must be pulled higher to compensate. The longer the athlete takes to move under the bar, the more the bar falls in height.

Therefore, athletes who develop a low receiving position and are fast under the bar will tend to excel at the Snatch.

Concept 3: Final velocity

It is common for beginning athletes to think that it is necessary to pull the bar as fast as possible immediately at the start of the lift. However, the important concept that the coach must enable the athlete to grasp is that the velocity at the end of the pull is much more important. The velocity of the bar achieved at the end of the pull is termed the ‘final velocity’ and it is final velocity that determines the upward momentum of the bar. The larger the final velocity, the larger the momentum. This is illustrated in Figure 3 below, which depicts that the faster the car goes the greater the stopping distance.

The faster the car the greater the momentum

Figure 3: Momentum is a product of mass and velocity

Athletes should therefore focus on obtaining a strong pull finish rather than trying to gain as much velocity at the start of the lift.

Concept 4: Direction of Force

In Weightlifting, the task is to maximise the force applied in vertical direction and to minimise force applied in a horizontal direction. Movement of the bar horizontally is a major problem for the athlete for two reasons:

  • The athlete must keep the barbell over the base of support to remain in balance. If the bar moves too far horizontally,  it will move outside of the base of support.
  • Horizontal movement results in horizontal momentum, that is the bar has a tendency to keep moving in the same direction (horizontally). In the receiving position for the snatch, for example, if the bar is moving horizontally forwards or backwards the athlete will have extreme difficulty, or it becomes impossible to arrest the movement of the bar.

The problem is that the human body is not a machine built to lift weights in straight lines but is comprised of many parts that move in circular fashion. For this reason, it is very hard for the beginner to learn to minimise horizontal movement, nevertheless that is what good snatch technique demands.

Concept 5: Time

In general, when coaches and athletes think about the snatch technique, they think about good body positions at various stages of the lift, and about the trajectory or path of the bar. This is normal and useful. However, there is often little consideration of the time component of the lift and this is largely because coaches and athletes do not have easy access to tools that accurately measure the time dimension.

For athletes and coaches alike, the brevity of the snatch makes it very hard to appreciate the exquisite timing involved. It its is necessary to observe and compare a great many lifts of excellent and average performers alike, before it becomes possible to distinguish the small fragments of time that are critical to the success of the lift.

Table 1 below provides data obtained by video recording of a snatch by Kiana Elliott (Aus) at 25 frames per second (at 0.04 second intervals). The data illustrates two critical phases of the lift where excellence of performance is demonstrated. Firstly, Elliott is able to continue the pull for 0.16 seconds after the bar has reached the top of the thigh. This time component takes place between position A and position C in Figure 4 below:

Snatch Technique: Finish of the pull in the snatch

Figure 4: Kiana Elliott (Aus) demonstrating the finish of the pull in the snatch. From position A to position B takes just 0.16 seconds.

The time duration of the whole of the pull is 0.88 seconds (see Table 1 below) and therefore the phase of the pull from the top of the thigh to full extension is 18% of the total duration of the pull. If for example this phase where just 1/20th of a second (0.05 sec) less in duration, the athlete would lose nearly 6% of the time duration of the pull. This amount of time is virtually imperceptible to the human eye, yet the consequences of losing 6% of the pull is dramatic, sufficient to cause the difference between success and failure at the elite level.

Table 1: Time components of the Snatch Technique of Kiana Elliott (Aus)

Time Elapsed Event
0:00:00:00 Start of Pull
0:00:00:40 Knee Height
0:00:00:56 Mid-Thigh
0:00:00:68 Top-Thigh (see position A in Figure 4 below)
0:00:00:84 Full-Extension (see position C in Figure 4 below)
0:00:00:88 Toes still touching floor but body beginning to descend – end of pull
0:00:00:92 Feet airborne
0:00:01:00 Feet landing
0:00:01:16 Elbows locked
0:00:01:36 Attaining receiving position
0:00:01:44 Full compression in receiving position

The temporal data in Table 1 also indicates a second aspect of performance in which Elliott displays excellence. The quickness of movement under the bar into a full receiving position is an obvious attribute of success in Weightlifting. The faster the movement, the lower the critical height of the bar needed to achieve success and this means that effectively an athlete can succeed with a heavier weight. The data in Table 1 illustrates that the lifter’s feet are airborne after 0.92 seconds duration of the lift, and that the full receiving position is attained at 1.36 seconds, that is 0.44 seconds later. The height and mass of the athlete will be factors that influence this time component but in general a duration of 0.4 seconds for this phase of the lift might be considered fast, whereas 0.5 sec is average and 0.6 seconds slow. There needs to be much more investigation of this with much higher video frame rate before such a statement should be adopted as a truth.

The above data is presented to demonstrate the importance of time values as a key concept in understanding Weightlifting performance. There is a reason why coaches cue athletes to “finish the pull”. It may help the athlete to think in terms of the “finish of the pull’ being not only a body position imperative but also a time imperative. To “finish the pull” means to hang on to pull just 1/20th second longer, and while the human brain will not likely be able to interpret such a small time interval, the concept of time does help the build understanding of key differences between average and excellent performance.

The Jerk Balance

Purpose of the Jerk Balance

The Jerk Balance is a useful exercise that assists the athlete to master the receiving position for the Jerk. However, it is recommended that the Jerk Balance exercise is included in the beginner training program only after a measure of proficiency has been achieved in the Split Squat exercise.

Figure 1: The Jerk Balance

Figure 1: The Jerk Balance

 Benefit for Beginners/Novices

A good reason to include the Jerk Balance in the beginner program is that it simplifies the problem of learning the difficult receiving position for the Jerk. This simplification is necessary because it is hard for the beginner to learn the precise movement of the feet to achieve the Split Jerk position, while at the same time trying to concentrate on keeping the torso straight, keeping the rear knee bent and moving the bar overhead.

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Learning the Technique of the Jerk – Key Objectives

Take a long term approach

It is important to take a long-term approach, from the very first moment that training begins, toward achieving positional correctness, speed of movement and total confidence in the Jerk. Coaches and athletes should understand that learning the technique of the Jerk is a process that should not be rushed. If technical errors accumulate early in the learning process, they are hard to correct later. For example, a beginner athlete may miss crucial steps that teach pelvic alignment in the Jerk. As a result the athlete acquires a receiving position with a straight back leg and significant hyper-extension in the lumbar spine. Any such deficiencies in the technique of the Jerk will significantly diminish the athlete’s long-term performance potential.

It is therefore recommended that coaches and athletes pursue the following teaching/learning objectives:

Step #1: Teach/learn the Split Squat

Split Squats (see Figure 1 below) are a crucial exercise that should be implemented at the first instance that there is any intention to learn the technique of the Jerk.

Illustration of the Split Squats exercise

Figure 1: Split Squats

There are three key learning objectives in performing the Split Squat:

Objective 1:The athlete develops strength and confidence to take weight on their ‘back leg’ while the knee is bent. In the initial stages of learning, it is often easier for the beginner to jerk with a straight back leg but if this is not corrected, it usually leads to significant issues in performing the good technique of the Jerk with limit weights.

Objective 2: The athlete learns to maintain pelvis in normal alignment (without forward tilt of the pelvis). This is greatly important in avoiding an awkward hyper-extension in the lumbar spine. Not only is the hyper-extension an injury risk but also it usually results in the hips being behind the bar, rather than directly beneath the bar. This make it hard to stabilise limit weight overhead.

Objective 3: The athlete learns to keep front shin completely vertical at all times in the split position. It is often necessary for a coach to use hands on coaching to physically prevent the knee going forward during the split squat movement. The athlete must be able to sense their shin being vertical and that is why the coach must assist.

The actual amount of downward movement of the body while performing the split squat need only be 10-15cm. There is no need to touch the back knee on the ground. However, as can be seen in Figure 1 above, the back knee should move vertical downwards. Importantly, the athlete should practise holding the low position for 2 seconds before rising. This is an important strategy for preparing athletes for limit weights in the years to come.

Step 2: Teach/learn the Jerk Balance

After the Split Squat has been practised for around 3 sessions and the learner is achieving the above objectives, the next step is to incorporate the Jerk Balance. This exercise is a progression of the Split Squat.

The Jerk Balance Exercise illustrated

Figure 2: Jerk Balance

The main difference is that instead of practising the split position with the bar on the shoulders, the learner raises the bar overhead with arms fully locked out. The starting position in the Jerk Balance is the same as the starting position for the Split Squat. To facilitate the movement of the bar from the shoulders to above the head, the athlete uses an upward push from the legs while the feet are in the split position. During the action of raising the bar from the shoulders to overhead, the athlete purposefully drives their front foot forwards 10-15 cm. After a 2 second pause in the receiving position, the bar is lowered again tom the shoulders and the front foot is retracted back to it starting point.

This exercise has the same learning objectives as the Split Squat but also two more:

Objective 4: The athlete demonstrates the ability to hold the bar directly above the head, and furthermore the bar, head, shoulders and hips should be in vertical alignment.

Objective 5: The athlete demonstrates the ability to rapidly move their front forwards, keeping the foot very close to the ground. A common error is that in moving their foot forwards, the athlete substantially raises the foot  (see Figure 3 below) and it travels in an arc instead of a straight line. This is detrimental to fast foot speed. In the example below (Figure 3), the athlete’s heel raises 17 cm which is is nearly as much as the foot moves forwards (18.5 cm).

High foot lift in moving the foot forward in the Jerk, is not good technique.

Figure 3: High foot lift in moving the foot forward in the Jerk, is not good technique.

Step #3: Teach/learn a smooth and vertical ‘dip and drive’

This step is about teaching the following two objectives:

Objective 6: The athlete learns to “dip” with a vertical torso. This can only be achieved if the knees travel forwards during the dip. It is unfortunately very common for athletes to demonstrate a forward ‘lean’ of the trunk during the dip and this results in forward movement of the bar which is very hard, if not impossible to deal with when the bar is a near limit weight.

Objective 7: The athlete learns to control the speed of the dip, keeping the chest up and spine braced. If the athlete dips too fast it is likely that at the instant there is a change of direction of the bar (from downward movement to upward movement), the athlete will lose postural control, the chest and elbows drop and the athlete ‘buckles”. If this happens, it would be usual for the Jerk to be unsuccessful. It is often the case that perceptions of barbell heaviness tend to cause athletes to lose composure in the dip, drop too fast and buckle.

The Dip and Drive phase of the Jerk

Figure 6: The upper body must stay perfectly upright (vertical) in the dip.

Step #4: Teach/learn rapid movement under the bar

This step is about ensuring that the athlete learns to rapidly move into the ‘split’ receiving position in a fast and efficient manner. This is a significant aspect of acquiring good technique of the Jerk. There should be a focus on moving feet very fast into the split position and it is necessary for the trajectory of the foot movement to be as close to the floor as possible. To achieve the learning of fast foot movement, it is necessary for the beginner athlete to practise with light weights.

Objective 8: The athlete understands the need to practise speed of movement, particularly foot movement, into the receiving position for the Jerk. The athlete should also be guided to appreciate that this speed of movement under the bar is a key factor for success in the jerk.

Step #5: Teach control and balance in the receiving position

Many, many Clean and Jerks are lost at the very last moment. The athlete appears to have succeeded only to rush the recovery and lose control of the weight. It should be appreciated that a maximally heavy weight overhead is a very difficult balance issue and athletes must practise control and balance in the receiving position at all training intensities.

Objective 9: The athlete practises a slow and controlled recovery from the receiving position to the finish position, moving their front foot first. This is a very important, often overlooked aspect of the technique of the jerk.

The Dip Phase of the Jerk

Not all aspects of the Dip and Drive are well understood. Easy to understand, but not easily achieved, is the need to elevate the bar in one direction only – vertically upwards. This directional control requires an absolute avoidance of any rotation of the upper body during the dip, in other words the body must stay totally vertical as displayed in Figure 5. It is critical for the athlete to ‘bear down’ through the heels in the Dip to prevent forward movement of weight distribution to the front of the foot.

The Dip and Drive phase of the Jerk

Figure 6: The upper body must stay perfectly upright (vertical) in the dip.

A common fault in the dip is an inability to “dip straight” (keep the torso vertical). This incorrect action, displayed in Figure 6,  will send the barbell forwards. Even a slight rotation of the body will have an undesirable effect. Once the barbell is moving forwards it gains momentum and becomes very hard, and often impossible, to stop. In Figure 6 it can also be seen that the forward movement of barbell is so dramatic that even at the bottom of the dip the barbell is no longer over the base of support.

Forward rotation of the upper body in the dip

Figure 6: A common error in the Jerk Dip – forward rotation of the torso with centre of pressure moving forwards to the toes.

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Key Issues in the Jerk

anko Rusev (Bulgaria) performs the Clean & Jerk

Figure 1: The Jerk performed by Yanko Rusev (Bulgaria).

The Jerk is a highly complex movement that many athletes in Weightlifting find harder to master than the Snatch. In the Jerk, athletes must overcome several key issues if they are to become good exponents of the lift. These key issues are as follows:

Issue #1: The extreme heaviness of the barbell

Although Weightlifters are masters of ‘heaviness’, an exceptional performer in the Clean and Jerk will lift in excess of 80% of their best Back Squat. In addition to excellence of technique, the athlete will need great courage, will power and tenacity to complete a Clean and Jerk that is near to the limit of their strength capacity.

Issue #2: Achieving and maintaining a lockout of the elbows with the weight overhead

If an athlete, for anatomical reasons, has a difficulty in maintaining an elbow lockout, then the likelihood of reduced performance potential in the Jerk increases significantly.

Issue #3: Maintaining balance and control of the weight overhead

Even when both elbows are locked out, the athlete will experience significant difficulty in maintaining balance and control of the weight overhead. This is a matter of physics. In the situation where the athlete has a barbell of twice bodyweight overhead, the combined centre of mass (of the barbell and lifter) will be situated at approximately neck height or higher (see figure 2 below). The higher the combined centre of mass, the greater the balance problem.

Jerk Combined Centre of Mass

Figure 2: The heavier the barbell the higher the combined centre of mass rises

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