Variables of a Fast Skeleton Push-Start

graybill skeleton push-start

USA Skeleton Athlete practicing Push-Starts on the Push Track

Here is an excerpt from my Master’s Thesis on the Skeleton Push-Start on the variables of a fast push-start.

Skeleton athletes have 60 seconds from when their name is called to when they must start. There is a 2-inch high block they are able to push off of with their feet at the start. This is referred to as the starting block. The technique of the start varies from athlete to athlete between foot placement, hand placement, and if they rock the sled back and forth prior to driving off the starting block.

Each athlete has the opportunity to choose a foot placement during the setup for the start that incorporates the block in order to maximize acceleration of the sled. There are several variations of two general techniques, the one-footed, or track start, and the two-footed start. Details of foot placement will be described in the next section.

Once the feet are set, the athlete grabs the sled. There are two variations of how to hold the sled – with athletes utilizing a one-handed grip or a two-handed grip. The one-handed grip allows the athlete to use their free hand to swing forward, assisting in the generation of momentum from the first push off the block. When using the two-handed grip, athletes place two hands on the handle of the sled until they take their second or third step off the block. The understanding is that this type of hold allows for better control of the sled.

For every track, skeleton athletes have 15-meters from the starting block until they hit the first photo-electric timing cell. Each course’s start ramp must have an average slope of 2% up to 15-meters. From there, the athletes have an additional 50-meters until the second photo-electric timing cell, which gives them their start time for each course (“International Skeleton Rules”, 2015). After this, each courses’ slopes differ, making them unique. Bullock, Martin, Ross, Rosemond, Holland, and Marino (2008) found that quick acceleration to get to a high velocity at the 15-meter mark explained 89% of the variation for a fast start, making this variable one of the best indicators for a fast overall start time when compared to the other variables such as time to 15-meters, time to load, steps to load, and velocity at 45-meters. This highlights that there are different phases of the start (skeleton: Roberts, 2013; swimming: Vantorre, Chollet, and Seifert, (2014) that an athlete must smoothly transition from one to the next for a fast overall start. The skeleton push-start has several four phrases – drive, acceleration, load, and slide.

The start in skeleton accounts for 7.5-10.2% and 7.0-9.6 % of the total time for the top 4 individuals at the 2011, 2012, and 2013 FIBT Skeleton World Championships for women and men respectively (author’s unpublished data). This is roughly similar to other sports, such as swimming. Here, the start, classified as from the takeoff from the starting block to 15-meters, accounts for 0.8% to 26.1% of total race time with the latter percentage being sprint events (Vantorre et al., 2014). In skeleton, this variable will be dependent on the length and type of the course (i.e., technicality of turns, number of turns, etc.). However, this variable may signify what courses are more dependent on a good push rather than superior driving techniques in order to place on the podium. Zanoletti, La Torre, Merati, Rampini, and Impellizzeri (2006) found that a good push phase is necessary for a good placing during skeleton events, although it does not guarantee a medal. There are differences between females and males with regards to push start rank for each run for those athletes who placed in the top four at a World Championship or Olympic Games from 2010/2011-2013/2014, however, having a fast start provides one with a better opportunity to win a medal. This can be observed more clearly in Table 1 for the Men at the 2014 Sochi Olympic Games, where men who placed in the top four never had a start time that fell outside of the top six (authors unpublished data).

Table 1. The calculated mean for the top four athletes’ push-start rank for each run at each major World Championships leading up to and including the 2014 Sochi Olympic Games (unpublished data).
2010/2011 8.8 7.2
2011/2012 7.5 7.4
2012/2013 8.8 3.9
2013/2014 6.4 3.9

In order to have a fast start, coaches and athletes must take into account the start ramp profile and starting grooves. Each course has two grooves cut out of the ice in which the athlete will place one of the runners, or the blades, into. The groove helps guide the athlete and sled down the start in a straight line so that the athlete can focus on accelerating the sled. Coaches and athletes both inspect the quality of each groove, taking into account how each groove sets up the athlete into the first turn and the athletes preferential side of the sled from which to push and from which to load onto. Degrading grooves (i.e., increased friction, more ice fractures, etc.), improper push start mechanics, and hand position (i.e., one vs. two-handed start) on the sled can lead to or influence the athlete to “pop a groove”, which happens when the runner dislodges from the groove. This often results in a slower start time and will almost always send that athlete back several places and out of medal contention.

For Track & Field, the end goal of a great start is to get into a position(s) that allow(s) for the best mechanical advantage for horizontal displacement (Eikenberry, McAuliffe, Welsh, Zerpa, McPherson, and Newhouse, 2008; Fortier, Basset, Mbourou, Faverial, and Teasdale, 2005; Menely & Rosemire, 1966; Mero, 1988; Mero & Gregor 1992; Murrell & Dragunas, 2012; Schot & Knutzen, 1992; Shinohara & Maeda, 2011; Slawinski Bonnefoy, Leveque, Ontanon, Riquet, Dumas, and Cheze, 2010), and the same goal applies to skeleton. These positions generally are arranged within the parameters of the muscle force-length principle, which states that muscles produce the most amount of force at their middle range of length (Knudson, 2007; Murrell & Dragunas, 2012). That is, if the start position places the muscle in a position of excess shortening or excess lengthening, then it would be considered less efficient and effective based on this principle. An understanding of physics is necessary to fully understand this principle and objectively quantify an effective start.

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