Bar Path Analysis of an American Record Snatch

At the 2015 National Championships, Jared Fleming snatched 170 kg (~375 lbs) to set a new American record, and displayed one of the best celebrations in recent memory. Hookgrip posted a slo-motion video of the lift on YouTube, which is fortunately from an almost perfect side view (below), giving me the opportunity to track the barbell trajectory and run a full biomechanics analysis. I found the results interesting and I hope others might too so I wrote-up the some key findings from the analysis of the bar path below. The mechanical analysis of the snatch has the potential to be greatly expanded in the future but I think the bar path is a good place to start.

Video Credit: Hookgrip

full video: https://www.youtube.com/watch?v=UJia-S29bTI&t=14s

When analyzing the mechanics of Olympic lifting, the pull is generally broken down into four phases. The phases are determined based on the characteristic extension/flexion/extension pattern of the knee angle [1,3]. The four phases of the pull, for both the snatch and clean and jerk, are the 1st pull, transition phase, 2nd pull, and 3rd pull. I’m going to be referring to each phase throughout the analysis so I’ll start by giving a quick explanation of each one.

The 1st Pull:

The 1st pull is the interval from the initial lift-off to the end of the first period of knee extension. The end of the 1st pull usually occurs right after the bar passes the knee when the athlete begins to re-bend their knees to move their hips under the bar (Picture 1).

End_1PULL

Picture 1. End of the first pull

The Transition Between the 1st and 2nd Pulls:

The transition between the 1st and 2nd pulls occurs during the re-bending of the knees to position the athlete to execute the 2nd pull (Picture 2). It is this motion that gives weightlifting its characteristic “double knee bend” [1]. During this phase, the knees flex while the trunk rotates to reach nearly a vertical position. The transition phase ends when the knee begins to extend for the second time.

START_2PULL

Picture 2. End of the transition phase; Start of the second pull

The 2nd Pull:

The second pull starts at the beginning of the second knee extension. This generally occurs with the athlete in the “power position”, characterized by a vertical torso with the knees and ankles flexed. The key event of this phase is the violent extension of the hips, knees, and ankles, commonly referred to as “triple extension”. The 2nd pull ends when the bar reaches its maximum vertical velocity (Picture 3). This is the most explosive part of the lift with the maximum power production occurring during this phase.

END_2PULL

Picture 3. End of the second pull

The 3rd Pull:

The third pull is the pull under the bar. It occurs from the point of maximum vertical bar velocity to the athlete locking out their arms under the bar. The maximum height of the bar occurs during the 3rd pull (Picture 4).

MBH_FRAME

Picture 4. Maximum height of the barbell. Mid third pull

Bar Path:

The barbell reached a peak height of 1.25 m. This number is hard to put into context until you compare it to Jared’s 5’8” height (1.7272 m). This means that barbell was only lifted to 72.4% of his total height.

The total span of horizontal displacement of Fleming’s bar path from lift-off to maximum bar height is only 7.1 cm. The majority of this displacement was during the sweeping back of the bar into the hips. This accounted for 6.7 cm of the total displacement range. After making contact with the hips, the bar traveled over an arc peaking at 7.1 cm, or 2.8 in, away from the contact point. This also means that the bar only traveled less than a centimeter in front of its initial starting position on the floor. Fleming had a distinct jump backward after making contact with the bar and the ultimate catch position was 14.4 cm behind the initial bar position.

The tight barbell trajectory and minimal displacement away from his body after making contact at the hip were certainly key factors for the successful lift. Jared sweeps the bar aggressively back into his body throughout the pull allowing himself to get his hips underneath for the final extension when he creates the greatest amount of power. The backward motion of his body after bar contact is a direct result of the backward momentum of the barbell during the pull and the equal and opposite reaction force applied to his body from making contact with the bar.

Barbell Displacement Data

Maximum Bar Height 1.25 m
Maximum Backward Displacement -6.7 cm
Maximum Forward Displacement 0.4 cm
Catch Position -14.4 cm
Total Displacement Range 7.1 cm
Jared Fleming Height 1.7272 (5’ 8”)
Max Bar Height as % of Athlete Height 72.4%

Fleming Bar Path

Figure 1. Digitized Barbell Locations (Bar path)

Barbell Velocity and Acceleration:

The velocity and acceleration data of the barbell provide further evidence for the efficiency of the lift. The peak velocity of the barbell is 1.62 m/s with the max vertical max of 1.50 m/s indicating a predominately vertical trajectory. The peak vertical acceleration is 4.90 m/s2, occurring right after contact at the hips. One very important aspect of the bar acceleration profile is that there is no period of negative vertical acceleration. Often during the transition phase of the pull, the bar will decrease in upward velocity as the athlete positions themselves for the final extension [1,4]. Although this is sometimes necessary, it requires more energy to re-accelerate the bar [3]. The fact that Jared is able to continually accelerate the bar means that all of the energy he produces goes to increasing the height of the bar and not to overcoming losses [3,4]. The horizontal acceleration appears large compared to the vertical direction, however this is primarily due to the rapid change in direction as the bar meets the hips and only occurs for a very short period of time.

The peak power delivered to the bar was 4160 W or almost 5.6 hp! This is an interesting number to use to compare lifts at the same weight or for specific training purposes; however, it can be deceptive because peak power generally decreases as the lifter approaches their maximum, due to the subsequent decrease in bar velocity. Fortunately, we do have past data in published research to compare it to.

Dr. John Garhammer calculated the maximum power production of multiple athletes at the 1978 World Weightlifting Championships, including the overall champion in the 100 kg weight class who snatched the same 170 kg that was in this video [2]. The Soviet athlete studied produced a calculated power of 4700 W, which is higher than the power Jared produced. Why are the two values different? The Soviet lifted was a slightly larger athlete (100 kg) and most likely produced a greater bar velocity and pulled the bar higher. Additionally, Jared’s tremendous speed under the bar allows him to lift heavier weights with less upward power than most other athletes.

Velocity, Acceleration, and Power

Max Bar Velocity 1.62 m/s
Max Vertical Bar Velocity 1.50 m/s
Max Horizontal Bar Velocity 0.62 m/s
Max Bar Acceleration 13.47 m/s
Max Vertical Acceleration 4.90 m/s2
Min Vertical Acceleration 0.0087 m/s2
Max Horizontal Acceleration 12.77 m/s2
Peak Power Applied to Bar 4161 W

Energy and Work:

Mechanical Work is the amount of energy transferred into a system by outside forces. In the case of Olympic weightlifting, the lifter does Work on the bar to transfer energy into it, increasing its height and velocity [3]. The energy transferred to the bar during each phase of the lift is shown below. The relative energy produced during each phase of the pull, and the total energy produced, can provide insight to an athlete’s strengths and weaknesses, giving an indication to how they can improve. Simply put, more total energy transferred to the bar will result in a higher barbell height and the opportunity for more weight to be lifted.

Work, Energy, and Time

Phase Work on Bar (Joules) % of total Work Phase Duration (seconds)
1st Pull 600 35.1% 0.633
Transition 286 16.7% 0.167
2nd Pull 623 36.4% 0.233
3rd Pull 201 11.8%
Total 1710 1.33*

*Time to max bar height

One interesting take-away is that 11.8% of the energy transferred to the barbell occurred after the second pull as Jared was pulling under the bar during the 3rd pull. Even as he is moving under the bar, upward force is still being applied to the bar as the reaction force is used to aggressively pull himself under the bar.

The data from this analysis has value on its own but will be more meaningful when compared to the data from other lifts. From additional data, there is a great opportunity to see trends between lifters, differences between successful and unsuccessful lifts, as well as the progress of the same lifter over time.

I look forward to breaking down more lifts from this meet and others with similar camera angles.

Upcoming posts will include:

  • Comparing the differences between a successful and unsuccessful lift in competition.
  • A full biomechanics analysis of this lift and comparing Jared’s lifting style to other athletes.

Technical Notes: The location of the barbell was digitized at a rate of 60 frames per second using a program written in Matlab. The position data was filtered with a low-pass Butterworth filter at 6 hz. This was chosen based on similar methods utilized in scientific literature [4].

References:

  1. Enoka, Roger M. “The pull in Olympic weightlifting.”Med Sci Sports 2 (1979): 131-137.
  2. Garhammer, J. “Energy flow during Olympic weight lifting.”Med Sci Sports Exerc 5 (1982): 353-60.
  3. Gourgoulis, Vassilios, et al. “Unsuccessful vs. successful performance in snatch lifts: a kinematic approach.”The Journal of Strength & Conditioning Research 2 (2009): 486-494.
  4. Kipp, Kristof, and Chad Harris. “Patterns of barbell acceleration during the snatch in weightlifting competition.”Journal of sports sciences 14 (2015): 1467-1471.

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