Bipedal in-shoe kinetics of skateboarding – the ollie

Introduction Skateboarding is a globally participated and popular sport with a reported participation of over 11 million in the United States alone (SGMA, 2007). Published epidemiological studies have stated the significant incidence of musculoskeletal injuries associated with skateboarding (Frederick, Determan, Whittlesey, & Hamill, 2006). The inherent nature of skateboarding makes it difficult to quantify using standard laboratory methods. In-field protocols have been attempted to quantify the metabolic demands of the activity, while only partial segments of a given movement have been quantified from a biomechanics perspective (Frederick et al., 2006; Hetzler, Hunt, Stickley, & Kimura, 2011). Therefore, unique methods of testing are necessary to develop a complete understanding behind the basic movements of skateboarding. Purpose of the study The purpose of this pilot study was to quantify the basic skateboarding manoeuvre of the ollie using novel methods and technology in the athlete’s own environment. Methods Four experienced male skateboarders participated in this pilot study. Each subject wore identical Vans Authentic footwear, but used their own skateboard throughout thedata collection. Each subject was tasked with performing an ollie under three randomized conditions: (1) standing ollie (SO); (2) rolling ollie (RO); (3) ollie down (OD). The OD manoeuvre was performed utilizing a 36.0-cm platform. OpenGo (Moticon GmbH, Munich, Germany) wireless sensor insoles were utilized to continuously record underfoot forces at 50 Hz. Each insole contains 13 pressure sensors with a specified load range of 0–40 N cm¡2 along with an accelerometer. To ensure a similar fit in the footwear, the production insoles were replaced with the OpenGo insoles during the data collection. Statistical comparisons were made using a single-factor ANOVA (a D 0.05). Results The average peak take-off forces during an SO, RO and OD were 2.47 § 0.38 BWs, 2.55 § 0.51 BWs and 2.34 § 0.32 BWs, respectively. Average peak landing forces of the SO, RO and OD were 2.40 § 0.33 BWs, 2.71 § 0.23 BWs and 3.15 § 0.51 BWs, respectively. Pressure distribution during take-off and landing was centred around the medial forefoot in sensors 0, 2 and 3 shown in Figure 1. Discussion and conclusion The measured take-off forces were similar to previous studies that evaluated the impact forces from an ollie movement (Frederick et al., 2006; Nevitt, Determan, Cox, & Frederick, 2008). The landing forces in our findings were different when compared to previous literature (Nevitt et al., 2008). Nevitt et al. compared landing forces from various platform heights for the OD manoeuvre, while forces of 3.15 § 0.51 BWs when landing from a height of 36.0 cm we found in this pilot study, they do not compare to the 4.61 § 0.80 BWs from a platform of 22.9 cm. Previous literature on skateboarding forces utilized force plates to determine the force measurements for the whole system. It is critical to keep in mind that the board, bushings and wheels of the skateboard, as well as the footwear may provide for shock attenuation. As shown in Figure 2, the OpenGo system differentiates itself by providing for force measurements underneath each foot without the need for a tethered data logger on either the distal limb or waist of the subject (St€oggl & Mariner, 2016) The unique methods of data collection in this pilot study allow the subject to perform in his or her given environment without external influence from testing equipment. This pilot study reveals that skaters experience significant forces underfoot while having the various factors of shock attenuation. Future investigation in the roleof shock attenuation of the skateboard and footwear would be useful to footwear and skateboard manufacturers. Disclosure statement No potential conflict of interest was reported by the authors.