Question

despite the global popularity of skateboarding, little is known about the biomechanics of the sport. in this study, we aim to partially rectify this paucity of hard data by describing the kinetics of a common movement used by intermediate and 5 advanced skateboarders: the kickflip. a kickflip is a jumping maneuver used by skateboarders to hop onto, off of, and over obstacles. it is similar in motion to an ollie but differs slightly as it incorporates a kicking or flicking motion of the foot during the airborne phase of the jumping movement that 10 causes the board to rotate in the air underneath the skaters feet. as part of a larger study to develop a kickflip simulation machine, we were curious about how much force was generated by skateboarders in order to successfully take off and land while performing kickflips. 15 seven male and highly skilled skateboarders performed ten kickflips from a standing position on a large force plate. vertical ground reaction force (vgrf) data were measured using the force plate. high speed digital video was used to 20 visually aid in the analysis of these rapid movements using a jvc camera. results show typically the vgrf rose slightly above one bodyweight (bw) during the first 200 ms of the movement as 25 the subject initially plantarflexed their ankles on the skateboard before rapidly lowering their center of mass by flexing their ankles, knees, and hips. the vgrf then rose rapidly as the subjects jumped into the air off their back foot while their front foot controlled the motion and direction of 30 their skateboard. average peak to forces were found to be 2.05 ± 0.17 bws. average peak l vgrf forces were found to be 4.61 ± 1.19 bws during landings across all the subjects. the magnitudes of the vgrf during takeoff and landing were 35 similar to previous studies examining skateboarders performing ollies. in one study, take off forces were found to be 2.22 times normal body weight when their subjects first rolled onto a force plate and ollied up onto a platform. later when their subjects ollied off the platform down onto a force 10 plate at ground level landing forces ranging from 4.26 to 5.38 bws were recorded. given that our subjects were stationary and landed at the same height they took off from we would expect lower landing forces in our study, however this was not the case. landing forces in our study ranged from 2.9 to 6.4 15 bws. a closer look at the high speed video revealed a possible cause for this result. as the board rotated underneath the feet of the subjects and the riders reached the peak of their jump, they had to quickly stop the boards rotation and align it underneath their feet for landing. some of the skaters in our 50 study intentionally spiked their landings as soon as they stopped and aligned the board underneath their feet in order to stabilize themselves and ensure they would land on top of their skateboards. other subjects seemed to land more naturally after stopping their boards from rotating and let the 55 effects of gravity force themselves to land on top of their boards. it is not known at this time which landing method is more beneficial for consistently landing a kickflip. further analysis of the vgrf data also shows the magnitudes and shape of the force - time curve are similar to other studies 60 examining countermovement vertical jumps. a different study of vertical jumps in professional basketball athletes found average to forces to be 1.7 ± 0.52 bws and l forces to be 4.3 ± 1.16 bws, though no jump heights are reported. dowling and vamos (1993) examined vertical jumps of 97 65 young adults and found to forces ranging from 1.8 to 2.8 bws for jump heights similar to those recorded in our study. the fact that ollie and kickflip movements so closely mirror other jumping movement sports such as basketball and 70 volleyball, at least on a kinetic level, suggests that skateboarders may benefit from similar training exercises used in these more traditional sports to increase jump height ability. if skateboarders could increase their jumping ability they could theoretically be able to jump over higher objects with 75 their boards or increase the number of revolutions the board completes during kickflips. 1. the main purpose of this study was to: a. compare kickflip forces to ollie forces b. compare kickflip forces to other jumping movements c. gather data to build a kickflip simulation machine d. compare intermediate and advanced skateboarders forces 2. in line three, the word “paucity” most nearly means: a. scarcity b. uncommonality c. low quality d. important

Explanation:

1. Question 1:

• The text states “As part of a larger study to develop a kickflip simulation machine, we were curious about how much force was generated by skateboarders in order to successfully take off and land while performing kickflips.” This directly relates to option c.

1. Question 2:

• The context is about rectifying the lack of hard data. “Paucity” means a lack or scarcity. “Scarcity” (option a) fits this meaning as it implies there is not enough data (the opposite of abundance). “Uncommonality” (option b) is more about something not being common in terms of occurrence rather than quantity. “Low quality” (option c) is about quality, not quantity. “Important” (option d) is unrelated to the meaning of lack in this context.

Answer:

1. c. Gather data to build a kickflip simulation machine
2. a. Scarcity