Strength and Conditioning for Skeleton : Strength & Conditioning Journal

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Strength and Conditioning for Skeleton

Mosey, Tim MExSci

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Strength and Conditioning Journal 36(6):p 62-70, December 2014. | DOI: 10.1519/SSC.0000000000000101

Abstract

INTRODUCTION

Skeleton is a Winter Olympic sport in which athletes slide head first down a bobsleigh track on a sled (the skeleton). Athletes complete the push start (PS) by accelerating their sled away from the start block before loading the sled with a forward diving motion. The PS requires a combination of speed and power so that the athlete can accelerate to maximum velocity before loading at around the 30-m mark (29). Ideally, the athlete will load by diving onto the sled with a velocity equal to or greater than the actual sled, resulting in—if possible—an increase in sled velocity (15). The PS has a technical component in which the competitor must run bent over while maintaining their sled in a straight line, within ice grooves, down the track (Figure 1). Once loaded, the athlete “drives” the sled down the track with the aim of completing the track in the quickest possible time.

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Figure 1:
Skeleton push start.

Early evidence suggested that the PS time was an important factor in determining overall performance (29); however, further research suggested that push times may not correlate with finish times and may only correlate with times over the first third of the track (4). Further research into enhancing the PS has looked at basic kinematics (14) and optimal warm-up methods (6). Sands et al. (22) identified correlations between stronger, more powerful athletes (as measured with loaded countermovement jump) and sprint and push time. They noted that sprint and push times tended to be faster in the athletes who produced higher power outputs in the loaded countermovement jump and subsequently concluded that athletes should consider undertaking strength and power training to enhance their ability to sprint and related actions involved in the PS.

The purpose of this article is to review the research on skeleton and subsequently provide evidence-based training recommendations to improve athletic performance.

ANALYSIS OF SKELETON PUSH START

A skeleton race consists of 2 heats or “runs” where the athlete has 2 chances to slide on the track. The accumulated time of both runs is the athlete's final time. A strength and conditioning (S&C) intervention aimed at improving the physical qualities during the PS may be optimal because the ability to accelerate the sled to maximum velocity before loading lays the foundation to build momentum down the track. Bullock et al. (4) analyzed start velocities and emphasized the finding that a fast acceleration over the first 15 m was essential to attaining fast 15 m and 45 m velocities, which held very large correlations with split times over the first third of the track. Therefore, speed and acceleration seem to be important qualities in maximizing start performance. In support of this finding, Sands et al. (22) showed that international skeleton athletes were able to reach 75 and 85% of their upright sprint times during a dry land push at the 15- and 30-m marks, respectively. This knowledge gives the S&C coach a platform from which to launch a training intervention.

One article was found that analyzed the PS from a kinematic perspective (14). Kivi et al. (14) showed that there are similarities between the initial starting position and that of a track athlete from blocks. Their results highlighted that single- and double-foot take offs were equally as good in attaining fast start times. The athlete never raises their torso during the PS—unlike a typical sprinter—therefore trunk angle does not change. Angles at the knee and thigh remain similar until the athlete loads onto the sled (14). The trunk angle remains the same, which is a consideration the S&C coach needs to make when thinking about exercise selection.

SKELETON “ON-SLED” KINEMATICS

A skeleton competitor may feel the effect of gravitational forces between 5 and 6 times applied to them travelling through corners at speeds over 135 km/h (16). The ability of the athlete to maintain control of their sled during these periods of the race is important. However, if athletes apply forces through adjustments on the sled, steering with shoulders or toes, or making adjustments to directly control the direction of the sled, the momentum built is potentially lost and potential energy gained depletes (16). The intention of the athlete outside of steering requirements needs to be that of complete stillness and relaxation—compared with rigid and stiff body positions. When steering is necessary, the athlete needs to make subtle adjustments—particularly with their trunk—to place force at the appropriate location on the sled. Away from actual sliding, this component of the race can be directly addressed in an S&C program (Figure 2). Neck strengthening and specific endurance is necessary to withstand the applied gravitational force through corners and throughout the duration of the race (Figure 3).

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Figure 2:
Prone stability ball stabilization.
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Figure 3:
Elastic band neck extension.

KINEMATICS OF SPRINTING

During the stance phase of maximal velocity sprinting (MVS) to produce propulsion in the forward direction, the primary catalyst is the gluteus maximus (24,27). During the stance phase, the knee extensors—particularly the vastus medialis—are responsible for stabilizing the knee joint throughout contact time. The gluteus medius and the oblique abdominals are responsible for stabilizing the trunk and pelvis (17). Wiemann and Tidow report that from toe off contact through to the flight phase, the primary movers are the knee flexors (semitendinosus, semimembranosus, and biceps femoris) (24). The authors found that the knee extensors, in particular, the vastus medialis, could not be considered muscles that produced forward acceleration in upright sprinting. The main propulsion for forward acceleration in upright sprinting during contact comes from a combination of the gluteus maximus and adductor magnus, which combine to control outward rotation and abduction of the pelvis. The hamstring muscle group, being knee flexors, has a hip extension function and knee extension function in the support phase (24). Frick et al. (10) found that knee extensor activity was very high in sprint acceleration (AS) compared with MVS and therefore suggested that the knee extensors were more important in AS than MVS (Table 1) (10,28).

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Table 1:
Contribution of muscle groups in sprint acceleration and sprint maximum velocity (10,28)

COMPARISON BETWEEN SPRINTING AND PUSH START

Similarities and differences can be seen between the kinematic variables in the AS, MVS, and PS (Table 2). Kivi et al. (14) showed there to be similarities between the different PS options (1 and 2 foot take off), in maximum trunk flexion, stance time, flight time, and stride length. The similarities between the AS and PS are closer than between the MVS and PS (Table 2) (14). These similarities and differences can then be used in a rationale for training methods in skeleton athletes.

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Table 2:
Kinematic variables between push start, sprint acceleration, and sprint maximum velocity (14)

TESTING BATTERY

When looking to adopt a testing battery, the S&C professional can identify the key performance indicators relevant to the sport or individual they are working with and subsequently come up with valid and reliable tests to assess these indicators (13). Because the qualities of strength, power, and speed are key indicators related to PS performance, a testing battery can be developed to measure these qualities. If equipment and facility access were extensive and a testing laboratory available, the S&C professional may use methods to determine power outputs through a direct measure, such as a force platform (Table 3).

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Table 3:
Lab-based strength, power, and speed testing protocol example

TRAINING INTERVENTIONS

After assessing the athlete's needs and analyzing the kinematics of the sport, methods to improve the physical qualities of performance can be recommended. Trunk and leg angles over the initial strides in the PS are similar to those in the acceleration phase of sprinting. It is therefore suggested that skeleton athletes undertake strength and acceleration training programs directed primarily toward developing strength, power and their rate of force development (RFD) in the weight room, and acceleration and speed on the track. For direct training application and applied specificity of speed generation, the athlete can perform bent over sprinting in conjunction with upright sprinting, to gain some ancillary speed adaptation in a sport-specific position. This can be achieved on a dry land sled away from the actual race venue.

Strength and power programs may be designed for internal physiological adaptations, coupled with external movement quality improvements. Strength training exercises to improve the specific phases of sprinting (Table 4) have been recommended in the literature (27). The exercises recommended by Young et al. (27) have been suggested because of the differing qualities displayed between acceleration and MVS. Exercise selection that targets movement improvement (1,8,25) combined with loading varying plyometric exercises across the force-velocity spectrum (8,12,19,20,25,27) have shown correlations with acceleration improvement and speed measures, such as RFD. Considering these exercise recommendations (27), and the relationship between strength, power, and speed shown by previous researchers (1,18,25,26), resistance training programs for skeleton athletes may be best directed at developing the needs of the PS (i.e., the acceleration equivalent of sprinting).

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Table 4:
Resistance training and plyometric exercises and their specificity to sprinting (27)

PRACTICAL APPLICATIONS

A resistance training program that addresses the development of power, the athlete's RFD, and their reactive strength is recommended. Exercises that address developments in the physiological qualities associated with optimal sprint performance combined with “sport-specific” type exercises (Figures 2–6) can be implemented within a program. Exercises, performed at high velocities with loads of ≤30% of (1RM) have been suggested to be effective in improving explosive power and RFD (23). The results of studies vary when recommending which loads to use for maximal gains in explosive power (3,8,9). Comparisons are difficult to draw between studies, with variations in subject population and methodology. Training programs, which address a range of loads across the force-velocity spectrum, are recommended at different stages of the yearly program (Tables 5, 6). The S&C professional can therefore make educated judgments based on the evidence.

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Table 5:
Sample resistance training program—General preparation phase (off season)
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Table 6:
Sample resistance training program–specific preparation period (in season)

When considering program planning methods and combining strength training with speed and acceleration work, it has been suggested that combining high-intensity (% of 1RM) strength training methods with sprint speed training methods may be more beneficial compared with just strength or speed training methods alone in experienced athletes (2). Speed and acceleration training methods seem optimal when developing overall athletic qualities of high-velocity, explosive athletes. Speed and acceleration training (5), resisted acceleration training (17), uphill sprinting (21), and weighted vest sprinting (11) have all been postulated to improve speed and acceleration. Weighted vests, however, may benefit the maximal velocity phase of sprinting more because of the greater loading in the eccentric braking component at the beginning of the stance phase. Because braking forces are more significant in MVS, weighted vest sprinting may be more applicable in training for maximum velocity (7). A weighted vest could be implemented as a way of varying stimulus and exercise selection. When considering a skeleton athlete's physical development program, these methods (Table 7) may be used to illicit improvements in speed and acceleration. As alluded to earlier, these methods may be supplemented with a sport-specific bent over sprinting option to make the movement more sport specific. The S&C professional should ensure that this sport-specific method is not overdone in consequence of losing valuable training time directed at specific methodologies to develop acceleration and maximal velocity qualities.

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Table 7:
Example weekly speed session

When considering using exercises that may be considered “sport specific,” the following are some novel options that may develop strength and endurance in skeleton specific positions. During the prone stability ball stabilization exercise (Figure 2), the athlete attempts to balance on tandem stability balls by engaging their gluteal muscles and anterior core. They attempt to balance by reacting to the unstable environment beneath their body. The athlete makes subtle adjustments to the stability balls movement to maintain stability.

Prone neck strengthening (Figure 3) requires the athlete to place an elastic band over their head and attempt to maintain a neutral head position. The weight plate offers an anchor point for the band—not a movable resistance. Attempting to keep the chin up is also an alternative to a neutral head position.

In the single-leg bent over squat (Figure 4), the athlete assumes a bent over Borzov position with back leg anchored to a bench or box. They place their torso in a similar position to where they would be at the start of a race or practice run. The athlete then does a single-leg squat flexing the knee, with the hip joint angle remaining fairly constant because of the initial trunk flexion. The chest is lowered to the knee by flexing the knee. The athlete then returns to the initial start position by extending the knee.

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Figure 4:
Single-leg bent over squat.

The supine neck stabilization exercise (Figure 5) involves the athlete placing a stability ball on a box so they can maintain a 45° angle to the floor. In a supine position, they place their head on the ball and raise their hips so they form a straight line between shoulder and knee. The athlete then manages the movement of the ball by applying subtle balancing movements with their neck to maintain the still position of the ball. Placing space between the ball and the wall increases the ability of the ball to move and raises the difficulty of the exercise.

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Figure 5:
Supine neck stabilization.

Supine twisting crunch (Figure 6) is performed with the athlete supine on the ground, knees bent to 90°. The athlete then raises their torso from the ground and twists a shoulder toward the opposite knee. This is performed in a controlled manner with a small torso raise from the floor compared with a full crunch.

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Figure 6:
Supine twisting crunch.

CONCLUSION

The PS in skeleton seems to be an important factor for skeleton performance. There are similarities between AS and the PS. Athletes should incorporate strength, power, and speed training into their training programs to improve the PS. Testing protocols that are valid and reliable can measure changes in strength, power, and speed performance. The S&C programs should also aim to improve skeleton-specific core stability and control. Further research is needed to understand the relationships and effects between relevant qualities, training methods, and skeleton performance.

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Keywords:

strength and conditioning; training interventions; strength; power; speed

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