The purpose of this study was to measure the dynamic tension force between the apparatus and the hanging equipment of five aerial circus apparatuses and to recommend minimal loading requirements in rigging and design. The forces generated by different acrobatic movements were measured and synchronized with video recordings. Sixteen students of the National Circus School of Montréal (Canada) participated in the study. The maximal forces were analyzed and characterized with respect to the discipline, the type of movement and the schooling level of the student. The maximal force measured was 5.3 kN performed in the discipline of aerial straps, equivalent to 7.9 times the bodyweight of the performer. A minimal breaking strength of 22 kN for the hanging point and all the equipments holding the rig is recommended. A minimal breaking strength of 22 kN for straps, 17 kN for rope and 12 kN for silk, aerial hoop and dance trapeze is recommended.

Human adaptive behavior in sensorimotor control is aimed to increase the confidence in feedforward mechanisms when sensory afferents are uncertain. It is thought that these feedforward mechanisms rely on predictions from internal models. We investigate whether the brain uses an internal model of physical laws (gravitational and inertial forces) to help estimate body equilibrium when tactile inputs from the foot sole are depressed by carrying extra weight. As direct experimental evidence for such a model is limited, we used Judoka athletes thought to have built up internal models of external loads (i.e., opponent weight management) as compared with Non-Athlete participants and Dancers (highly skilled in balance control). Using electroencephalography, we first (experiment 1) tested the hypothesis that the influence of tactile inputs was amplified by descending cortical efferent signals. We compared the amplitude of P1N1 somatosensory cortical potential evoked by electrical stimulation of the foot sole in participants standing still with their eyes closed. We showed smaller P1N1 amplitudes in the Load compared to No Load conditions in both Non-Athletes and Dancers. This decrease neural response to tactile stimulation was associated with greater postural oscillations. By contrast in the Judoka’s group, the neural early response to tactile stimulation was unregulated in the Load condition. This suggests that the brain can selectively increase the functional gain of sensory inputs, during challenging equilibrium tasks when tactile inputs were mechanically depressed by wearing a weighted vest. In Judokas, the activation of regions such as the right posterior inferior parietal cortex (PPC) as early as the P1N1 is likely the source of the neural responses being maintained similar in both Load and No Load conditions. An overweight internal model stored in the right PPC known to be involved in maintaining a coherent representation of one’s body in space can optimize predictive mechanisms in situations with high balance constraints (Experiment 2). This hypothesis has been confirmed by showing that postural reaction evoked by a translation of the support surface on which participants were standing wearing extra-weight was improved in Judokas.

Korean teeterboard is one of the most physically and technically demanding circus disciplines. Two performers take turns jumping vertically and land with high impact. The aims of this study were to (1) compare the stiffness across three different teeterboards, and (2) compare Peak Landing Force (PLF) and Maximal Loading Rate (MLR) of four acrobats performing jumps from three teeterboards using four landing techniques (normal, smooth, straight legs, and empty board). Pressure sensors were used to determine recorded forces under the feet, while Boosted Regression Trees (BRT) was used to analyze factors contributing to PLF and MLR. Standard static loading protocol was used to estimate teeterboard stiffness. PLF and MLR increased with jump height. PLF and MLR were reached when landing on the teeterboard with the highest stiffness. The “normal” and “straight legs” landing techniques were associated with higher PLF and MLR. The BRT model was able to associate both PLF and MLR with jump height, participant, teeterboard, and landing technique factors. PLF reached 13.5 times the body weight when landing on the stiffer teeterboard using the straight legs technique. Trainers should be aware of the injury risk to teeterboard acrobats during landing.

Circus practice is a very popular activity that has had minimal engineering research published. The purpose of this study was to measure peak cable tension in nine circus disciplines: aerial hoop, rope, aerial silk, flying pole, tightwire, Chinese pole, swinging trapeze, solo and duo fixed trapeze. Cables in these disciplines were instrumented with load cells and tension force was recorded. Thirty-four acrobats, professionals, and students from professional circus schools participated in the study and performed a total of 118 acrobatic movements. An analysis of variance (ANOVA) determined differences in participants. Almost all movements and disciplines showed a statistically significant difference between participants. Maximal forces were found to be 4.8 BW (bodyweight) in aerial hoop, 7.3 BW in aerial rope, 5.6 BW in aerial silk, 4.0 BW in flying pole, 5.6 BW in swinging trapeze, 6.8 BW in solo fixed trapeze, 2.5 BW in duo fixed trapeze, and maximal tension in cable were found to be 15 kN in tightwire and 2.8 kN in Chinese pole. These findings may provide substantial implications for acrobatic design and rigging to improve safety of circus equipment. La pratique du cirque est une activité très populaire pour laquelle peu de recherches en ingénierie ont été publiées. L’objectif de cette étude était de mesurer la tension maximale des câbles dans neuf disciplines de cirque: cerceau aérien, corde lisse, tissu aérien, mât pendulaire, fil de fer, mât chinois, trapèze ballant, trapèze fixe solo et duo. Les câbles de ces disciplines ont été instrumentés avec des cellules de charge et la tension a été enregistrée. Trente-quatre acrobates, professionnels et élèves d'écoles de cirque professionnelles, ont participé à l'étude et ont exécuté un total de 118 mouvements acrobatiques. Une analyse de la variance (ANOVA) a déterminé les différences entre participants. Presque tous les mouvements et disciplines ont montré une différence statistiquement significative entre les participants. Les forces maximales ont été trouvées à 4.8 poids corporel en cerceau aérien, 7.3 fois le poids du corps en corde lisse, 5.6 fois le poids du corps en tissu aérien, 4.0 fois le poids du corps en mât pendulaire, 5.6 fois le poids du corps en trapèze ballant, 6.8 fois le poids du corps en trapèze fixe solo et 2.5 fois le poids du corps en trapèze fixe duo, et la tension maximale dans le câble a été trouvée à 15 kN dans le fil de fer et 2.8 kN dans le mât chinois. Ces résultats peuvent avoir des implications importantes pour la conception et le gréage acrobatique afin d'améliorer la sécurité des équipements de cirque.

The aim of this study is to develop a method for assessing movement variability of circus acrobats. An analysis of the repeatability of force signals is used to quantify variability. Six students from the National Circus School of Montréal performed 5-10 trials of an acrobatic movement called dislock in aerial circus straps while tension force was measured at the hanging point of the aerial apparatus. The repeatability of force signals was calculated with three statistical methods: time-averaged standard deviation, intraclass correlation and root mean square error. These methods were compared with the ratings of a circus coach who ranked each acrobat's trial with regard to the movement variability. The standard deviation and the intraclass correlation methods are commonly used to quantify the agreement between measurements in biomechanics, while the root mean square error method is regularly employed to quantify the agreement between measurements and a model. All participants performed the movement with little variability (intraclass correlation 5 0.8). The results of the three methods were in good agreement with the coach's assessment. The root mean square error method, in particular, showed perfect agreement and is therefore considered the best measure of repeatability. In the future, the proposed method could be used by coaches or artists training alone, allowing a new form of feedback.