Ankle joint moment-angle relationship in the frontal plane during the push phase of elite bobsleigh

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INTRODUCTION: The push phase in bobsleigh is positively correlated with final race times [1] and the performance in this phase is limited by the athlete’s ability to generate mechanical power with the ankle joint in the sagittal plane (SP) [2]. Therefore, the aim was to elaborate the understanding of the ankle’s function by investigating the moment-angle relationship in the frontal plane (FP). METHODS: Infrared cameras (250 Hz, Vicon, Oxford, UK) and force plates (1250 Hz, Kistler, Winterthur, Suisse) were used to conduct a 3D analysis of the ankle joint during the push start of the brakeman. Therefore, a rail system was installed on an athletics track, providing mechanical guidance of a sleigh (85 kg). 17 elite athletes (98,9 ± 6,9 kg; 185,8 ± 5,3 cm) of the german national squad were tested as follows: (1) initial acceleration (first and second step), (2) acceleration phase after 10 m and (3) 30 m. Statistics: four-level ANOVA. RESULTS: Each condition showed a resulting external eversion moment (EM) during the entire stance phase, reaching its maximum at around 60-70 %. The peak moments ranged from (1) 42.3 ± 12.5 Nm to (3) 35.1 ± 10.2 Nm and declined with increasing speed ((2) and (3) significantly lower than (1), (p < 0.05)). The mean inversion angles at touchdown (TD) ranged from (1) -1.6 ± 3.0° to (3) -5.3 ± 3.4°. The eversion after TD and the subsequent inversion was highest for (3) 1.7 ± 1.9° and (3) -5.9 ± 2.5°. After maximum inversion a slight eversion until toe off was present. CONCLUSION: Since the GRF increases with higher speed, the decline in peak EM must be due to a reduction in the moment arm of the GRF in the FP. This could be caused by an altered foot placement of the athlete. A wider step and an external rotation of the foot during the first and second step could enlarge the moment arm of the GRF in the FP while reducing the moment arm in the SP. A smaller external rotation after 10 and 30 m acceleration could explain the reduction in the moment arm in the FP and therefore the resulting decreased EM despite higher GRF. This pattern is consistent with elite sprinters who reduce their step width with increasing velocity [3]. Since a wide step is correlated with greater lateral impulse [4], it is still argued why this kinematic pattern could be advantageous for acceleration in anterior direction. Aside from greater muscle activation of adductor muscles during hip extension [5], a possible resulting reduction of the moment arm of the GRF in the SP could benefit the generation of mechanical power of the plantar flexors and therefore maximize propulsion. Strengthening the toe flexors and the m. tibialis posterior of the ankle joint complex could enhance the power contribution of the ankle joint and therefore lead to shorter push and final race times. [1] Brüggemann et al. JAB, 13, 1997. [2] Goldmann et al. Proceedings WCB Dublin, 2018. [3] Nagahara et al. Int J Sports Medicine, 7, 2017. [4] McClay et al. Clin Biomech, 9, 1994. [5] Wiemann et al. N stud Athletics, 10,1995.
Original languageEnglish
Title of host publicationBook of abstracts : 24th Annual Congress of the European College of Sport Science, 3-6 July 2019, Prague - Czech Republic
EditorsV. Bunc, E. Tsolakidis
Number of pages1
Place of PublicationKöln
PublisherECSS
Publication date04.07.2019
Pages318
ISBN (Print)978-3-9818414-2-8
Publication statusPublished - 04.07.2019
EventAnnual Congress of the European College of Sport Science: Uniting the World through Sport Science - Conference Center, Prague, Czech Republic
Duration: 03.07.201906.07.2019
Conference number: 24

ID: 4344254

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