Biomechanical analysis of lumbar spine loading in Russian bar porters
Bibliographic record
Abstract
Russian bar, an acrobatic circus discipline involving dynamic loading on one shoulder, is associated with porters’ low back pain. The aim of this study was to compare lumbar forces and moments generated on porters during typical maneuvers including saltos, candle jumps and consecutive jumps. A biomechanical model previously validated for lifting tasks was used to estimate L4-L5 intervertebral forces and moments. A Russian bar trio was recruited to participate in data collection, including motion capture and electromyographic measurement. Considering artists safety, external forces were indirectly estimated using a mechanical characterization of the bar and an actuator-based ground reaction force estimation. The model’s validation involved assessing the agreement and the peak-cross correlation between EMG-recorded muscle activity and the model-predicted muscle activity. Results showed no significant differences between salto and candle jumps (p>0.05) for compressive force and moments but showed significant differences between the propulsion and landing phases (p<0.05), with the propulsion phase exerting the highest lumbar forces (12,571.7 ± 1,714.5 N) and frontal moments (68.9 ± 10.8 Nm). It appears that porters’ technique enables low shearing stress (961.6 ± 419.5 N). Artists and coaches should be aware of the high compressive forces, emphasizing the need for caution, especially for young and unexperienced artists. La barre russe est une discipline de cirque acrobatique. Le rôle du porteur consiste à soutenir une charge dynamique sur une épaule. Cette pratique peut engendrer des douleurs lombaires. La présente étude vise à comparer des forces et des moments appliqués sur la colonne lombaire des artistes lors de plusieurs mouvements type, notamment les saltos, les sauts droits et les sauts enchaînés. Un modèle biomécanique précédemment validé pour des activités de levage a permis d’estimer les forces et les moments entre les vertèbres L4-L5. Un trio d’artistes de barre russe a été recruté pour participer à une collecte de données intégrant la capture de mouvement et des mesures électromyographiques. En matière de sécurité des artistes, les forces externes ont été estimées indirectement grâce à une caractérisation mécanique de la barre et à une estimation des forces de réaction au sol sur la base d’actuateurs. Pour valider le modèle, il a fallu estimer la correspondance et la corrélation croisée maximum entre l’activité musculaire enregistrée par les capteurs électromyographiques et celle pronostiquée par le modèle. Les résultats ne montrent aucune différence majeure entre le salto et les sauts droits (p > 0,05) pour la force et les moments de compression. En revanche, il existe des écarts importants entre les phases de propulsion et de réception (p < 0,05). En effet, la phase de propulsion développe le plus de forces sur les lombaires (12571,7 ±1714,5 N) et le plus de moments dans le plan frontal (68,9 ± 10,8 Nm). Il apparaît que la technique des porteurs assure des forces de cisaillement réduites (961,6 ± 419,5 N). Les artistes et les équipes d’encadrement doivent avoir conscience de la sévérité des forces en jeu. Il est notamment crucial d’adapter les entraînements selon le niveau des artistes et leur forme physique.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".