This project was conducted as part of the 'Motor Control' class during the 2023-1 academic term
In weightlifting competitions, athletes compete in the snatch and clean and jerk events, with the highest combined total from three attempts determining the final rankings. The basic principle of weightlifting is for the athlete to exert maximum force against the resistance of the barbell, overcoming that resistance and successfully executing the prescribed movements. In weightlifting, even the slightest, imperceptible changes in posture can significantly impact an athlete's performance. Therefore, in addition to strength, athletes must acquire highly refined techniques to achieve optimal results.
The clean and jerk consists of two consecutive technical movements: the clean, where the barbell is lifted to the chest, and the jerk, where the barbell is lifted overhead from the chest. 윤정환 & 이석구 (2004) classified the clean into six events and five phases. Similarly, 박태민 et al. (2009) classified the jerk into five events and four phases.
However, in this experiment, the difficulty of the movements was reduced by starting with the hang clean instead of the power clean and modifying the split jerk to a push jerk, considering that the participants were not elite athletes specializing in weightlifting but rather the general population and undergraduate students majoring in physical education. Consequently, the clean was classified into three events and two phases, while the jerk was classified into four events and three phases for the purpose of this experiment.
This experiment measured how well participants performed the modified clean and jerk movements after three weeks of practice. Pre-assessment, mid-assessment, and final assessment were conducted weekly, with both quantitative and qualitative evaluations. All assessments were recorded using a camera. Quantitative evaluation measured changes in the participant's stride length and time between phases, while qualitative evaluation was based on the subjective judgment of the demonstrator.
The experiment participants were members of Group 8 enrolled in the 'Motor Control' class: A, B, and C. The participants had no musculoskeletal disorders and regularly engaged in weight training.
| Participant | Age | Height (cm) | Weight (kg) | Skeletal Muscle Mass (kg) | Prior Weightlifting Experience |
|---|---|---|---|---|---|
| A | 23 | 177 | 70.2 | 36.1 | Yes |
| B | 23 | 180 | 88 | 44.5 | No |
| C | 22 | 178 | 78.2 | 40.6 | No |
- Evaluations were conducted three times: pre-assessment, mid-assessment, and final assessment. Goals were categorized into three types: outcome, performance, and process.
- The outcome goal for the mid and final assessments was to master the Clean & Jerk posture, while the performance goal was to maintain a stride length as close as possible to that of the pre-assessment.
- Process goals:
- Mid-assessment: Improve on the common issues identified among participants in the pre-assessment.
- Final assessment: In addition to improving on the common issues identified in the pre-assessment, address individual issues noted in the mid-assessment.
When expressing the technical characteristics of the Clean & Jerk in terms of organization and complexity, the task was found to have high complexity and low organization. Therefore, it was analyzed to be similar to dance and floor exercises in gymnastics. As the participants were beginners with no prior experience in Clean & Jerk technique and the experiment aimed to improve posture accuracy, the focus was on qualitative practice. In summary, considering the high complexity and low organization of the Clean & Jerk, the participants' skill level, and the experiment's objectives, a progressive part-practice method was employed. To reduce contextual interference effects during practice, block practice was implemented for each Event and Phase. Participants practiced twice a week at their usual gyms and supplemented their learning with YouTube videos for areas needing improvement.
-
Clean Events:
- Event 1 (Clean_E1): The moment when the barbell reaches its lowest point for momentum
- Event 2 (Clean_E2): The moment when the knee joint is fully extended and the elbows are raised
- Event 3 (Clean_E3): The moment when the half-squat position is completed with the elbows tucked in and the barbell resting on the shoulders at its highest point
- Event 4 (Clean_E4): The moment of full standing from the squat position
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Clean Phases:
- Phase 1 (Clean_P1: Clean_E1–E2)
- Phase 2 (Clean_P2: Clean_E2–E3)
- Phase 3 (Clean_P3: Clean_E3–E4)
-
Jerk Events:
- Event 1 (Jerk_E1): The moment when the barbell is stationary on the chest
- Event 2 (Jerk_E2): The moment when the knees are bent and the barbell reaches its lowest point before being lifted
- Event 3 (Jerk_E3): The moment when the feet are spread laterally, the barbell is quickly fixed overhead, and foot movement stops
- Event 4 (Jerk_E4): The moment when the feet are brought back together, knees are extended, and the barbell is fixed overhead
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Jerk Phases:
- Phase 1 (Jerk_P1: Jerk_E1–E2)
- Phase 2 (Jerk_P2: Jerk_E2–E3)
- Phase 3 (Jerk_P3: Jerk_E3–E4)
Evaluations were conducted three times: pre-assessment on May 16, mid-assessment on May 25, and final assessment on June 1. All evaluations were video recorded.
Quantitative evaluation measured the lateral width between the feet during the clean and jerk, as well as the time for each phase. Foot width was measured between the inner sides of the heels, and phase timing was analyzed by examining the recorded video frame by frame.
Qualitative evaluation was conducted for each event and phase. It was based on the demonstrator's subjective judgment and occurred in three stages. First, the participant practiced the Clean & Jerk by event, phase, or as a complete movement. The demonstrator then provided feedback. Next, the participant performed the Clean & Jerk movement continuously, followed by feedback. Finally, a post-evaluation was conducted using the recorded video. During the practice portion, only common problems among participants were recorded. However, in the final evaluation, instead of assessing the participant's practice, the continuous performance was evaluated, and all videos from the pre-, mid-, and final assessments were compared for evaluation.
The mean and standard deviation of the lateral foot width for each participant across all assessments were as follows: Participant A (hereafter A) showed 11±2.9 cm for clean and 15.7±2.9 cm for jerk. Participant B (hereafter B) showed 40±2.5 cm for clean and 35±3.7 cm for jerk. Participant C (hereafter C) showed 23±5.1 cm for clean and 30±10 cm for jerk. While B had the widest average stance in the clean, the standard deviation was the lowest, indicating the most stable stance during the clean. For the jerk, A had the lowest standard deviation at 2.9, suggesting the most stable performance among participants. C showed higher variability than A and B in both clean and jerk.
The phase timing evaluation focused on the combined time of Clean_P1 and Clean_P2, which involve the fastest and most difficult-to-control movements, and the time for Jerk_P2. A's Clean_P1-P2 time averaged 1.157±0.201 seconds, and Jerk_P2 averaged 0.723±0.203 seconds. B's Clean_P1-P2 was 0.844±0.137 seconds, and Jerk_P2 was 0.687±0.033 seconds. C's Clean_P1-P2 was 0.89±0.069 seconds, and Jerk_P2 was 0.589±0.104 seconds. A's Jerk_P2 time was 0.436 seconds in the pre-assessment but remained consistent at 0.867 seconds in both the mid and final assessments, indicating stability in Jerk_P2 performance.
Assessment
| Evaluation Criteria | A | B | C |
|---|---|---|---|
| Clean - Lateral foot width (cm) | 7 | 37 | 18 |
| Clean_P1 (sec) | 1.002 | 0.567 | 0.634 |
| Clean_P2 (sec) | 0.434 | 0.3 | 0.167 |
| Clean_P3 (sec) | 1.333 | 0.767 | 0.632 |
| Jerk - Lateral foot width (cm) | 16 | 36 | 28 |
| Jerk_P1 (sec) | 0.534 | 0.33 | 0.333 |
| Jerk_P2 (sec) | 0.436 | 0.67 | 0.5 |
| Jerk_P3 (sec) | 0.432 | 0.6 | 0.767 |
| Evaluation Criteria | A | B | C |
|---|---|---|---|
| Clean - Lateral foot width (cm) | 12 | 43 | 30 |
| Clean_P1 (sec) | 0.735 | 0.601 | 0.567 |
| Clean_P2 (sec) | 0.233 | 0.065 | 0.333 |
| Clean_P3 (sec) | 2.001 | 1.135 | 0.633 |
| Jerk - Lateral foot width (cm) | 19 | 30 | 43 |
| Jerk_P1 (sec) | 0.833 | 0.274 | 0.235 |
| Jerk_P2 (sec) | 0.867 | 0.734 | 0.532 |
| Jerk_P3 (sec) | 1.468 | 0.834 | 0.869 |
| Evaluation Criteria | A | B | C |
|---|---|---|---|
| Clean - Lateral foot width (cm) | 14 | 39 | 21 |
| Clean_P1 (sec) | 0.567 | 0.701 | 0.603 |
| Clean_P2 (sec) | 0.5 | 0.299 | 0.365 |
| Clean_P3 (sec) | 1.901 | 1.068 | 0.567 |
| Jerk - Lateral foot width (cm) | 12 | 39 | 19 |
| Jerk_P1 (sec) | 0.5 | 0.368 | 0.534 |
| Jerk_P2 (sec) | 0.867 | 0.658 | 0.734 |
| Jerk_P3 (sec) | 2.034 | 1.344 | 0.833 |
Common issues were identified among the test participants. In Clean_P1, criticisms related to the posture of lifting the barbell were common. In Clean_E3, the main issues were the position of the upper body and the angle of the elbows. In Jerk_P3, participants showed simultaneous rather than sequential movement in standing up and lifting the feet from the ground. Therefore, the plan was to focus on practicing these common issues until the mid-assessment. As B regularly exercised with the demonstrator D, it was decided that B would receive feedback from D during practice.
Details
| Issue | A | B | C |
|---|---|---|---|
| Clean_E1 | · Gaze should not be directed straight ahead. Keep gaze natural, straighten thoracic spine | · Gaze should not be directed straight ahead. Keep gaze natural · Straighten thoracic spine | |
| Clean_P1 | · No upward movement from E1. · Pulling the barbell is too fast | · When lifting the barbell, need to pull more · Maximum height of the barbell is too high | · When lifting the barbell, need to pull more · Maximum height of the barbell is too high |
| Clean_E2 | · Elbows should go up. Feel like throwing upwards. · Hips not engaged when lifting barbell. · Don't lift heels, throw barbell with force | ||
| Clean_P2 | · Heels come up too much. · At landing moment, when barbell reaches highest point, elbows should move forward | · When barbell reaches highest point, elbows should move forward | · When barbell reaches highest point, elbows should move forward |
| Clean_E3 | · Upper body leaning back. Upper body should be more forward. Elbows should be more forward. Demonstrator touched elbows to bring them forward | · Head tilted back. Keep head neutral. Upper body leaning back. Upper body should be more forward. Elbows should be more forward. Demonstrator touched elbows to bring them forward | · Head tilted back. Keep head neutral. Upper body leaning back. Upper body should be more forward. Elbows should be more forward. Demonstrator touched elbows to bring them forward |
| Jerk_E1 | · Reduce foot width slightly | · Reduce foot width slightly | |
| Jerk_P2 | · Heels come up too much | ||
| Jerk_E3 | · Lean head forward slightly and lower. Gaze straight ahead | · Wrists are bent too much | · Wrists are bent too much |
| Jerk_P3 | · Lift feet after standing up. Jerk_E3 and Jerk_P3 phases occur simultaneously instead of sequentially | · Lift feet after standing up. Jerk_E3 and Jerk_P3 phases occur simultaneously instead of sequentially | · Lift feet after standing up. Jerk_E3 and Jerk_P3 phases occur simultaneously instead of sequentially |
| Jerk_E4 | · Maintain same foot width as in E1 when feet are brought together |
The goal of the mid-assessment qualitative evaluation was to improve on the common issues identified in the pre-assessment. For Clean_P1, improvement was minimal for A and C, except for B. In Clean_E3, B received the same criticism as in the pre-assessment, while C improved upper body angle but not elbow angle. A showed improvement but a new issue of excessive outward foot angle emerged. The Jerk_P3 issues were improved for all except B. Although none of the participants lifted their feet after standing up, B was noted for a more severe simultaneous occurrence of Jerk_E3 and Jerk_P3.
For the final assessment, all participants aimed to improve the common issues from the pre-assessment. Additionally, individual goals were set: A focused on improving heel lift during jumps in Clean_P1 and Jerk_P2, and correcting foot angle; B aimed to address wrist bending in Jerk_E1; and C worked on gaze direction in Clean_E1, wrist bending throughout the jerk phase, and issues identified in Jerk_P2.
Details
| Issue | A | B | C |
|---|---|---|---|
| Clean_E1 | Gaze control. Head is tilted slightly back | ||
| Clean_P1 | · Heels lift during jump. Pulling barbell too fast. Hips should thrust forward. Don't land too quickly after jump | · No hip drive. Hips should thrust forward | · When lifting barbell, need to pull more. Hips should thrust forward |
| Clean_E3 | · Feet angled too wide | · Upper body leaning back. Upper body should be more forward. Elbows should be more forward | · Upper body angle is good, but elbows need to be more forward |
| Jerk_E1 | · Wrists are bent | · Wrists are bent throughout entire jerk phase | |
| Jerk_P2 | · Heels lift during jump | · Don't land on toes. Entire foot should contact ground | · Should land with barbell pushed up. Elbows should be fully extended |
| Jerk_E3 | · Feet angled too wide. Bend knees less | · Head should be more forward | |
| Jerk_P3 | · Lift feet after standing up. Jerk_E3 and Jerk_P3 phases occur simultaneously instead of sequentially |
| Improvement | A | B | C |
|---|---|---|---|
| Clean_E1 | · Body's center of gravity correctly positioned | ||
| Clean_P1 | · Hips thrust slightly more forward | ||
| Clean_P2 | · Timing of upper/lower body and elbows improved | ||
| Clean_E3 | · Upper body angle improved | · Upper body angle improved | |
| Jerk_E3 | · Knee depth increased |
In the final assessment, common issues from the pre-assessment showed improvement in all participants, except for B's Jerk_P3. Individual goals were also largely achieved. However, A exhibited excessive jumping attempts in Clean_P1 and Jerk_P2, resulting in dropping the barbell in Clean_P2. Overall, participants' postures improved, but compared to demonstrator D's Clean & Jerk, B and C still showed deficiencies in areas such as pulling the barbell in Clean_P1 and elbow angle in Clean_E3.
Details
| Issues & Improvements | A | B | C |
|---|---|---|---|
| Clean_E1 | |||
| Clean_P1 | · Heel lift improved. Jumping excessively | · Barbell pull improved but still insufficient | · Barbell pull improved but still insufficient |
| Clean_P2 | · Excessive jump causing barbell to be dropped occasionally | ||
| Clean_E3 | · Foot angle improved | · Foot angle improved. Upper body angle much better. · Elbow angle needs improvement | · Elbow angle needs improvement |
| Jerk_E1 | · Wrist bend improved | · Wrist bend improved | |
| Jerk_P2 | · Jumping excessively |
The present experiment focused on the extent to which learning the Clean & Jerk technique could improve the participants' form, targeting beginners. The common issues exhibited by all participants during the pre-assessment were largely resolved in the final assessment. Setting specific goals based on the assessment results and providing supplementary learning through video materials can be said to have had a significant impact on improving the participants' form.
However, while the participants' form clearly showed significant improvement in the final assessment compared to the pre-assessment, the limitations of the experiment include the need for more quantitative measurements and the lack of a standardized scale for qualitative measurements.
Furthermore, as the participants practiced only the Clean & Jerk movement without training in supplementary exercises or stretching, the degree of improvement in the participants' form could have been further enhanced if supplementary exercises and stretching were included.
박태민, 류지선 and 윤석훈. (2009). 역도 용상 Jerk 기술 동작의 성공·실패에 대한 운동학적 분석 -사례연구-. 한국운동역학회지, 19(4), 739-748.
윤정환 and 이석구. (2004). 역도 용상 Clean 동작에 관한 연구. 한국 스포츠 리서치, 15(4), 1829-1836.