Evaluating and developing the key determinants of push-start performance in bobsleigh

Abstract

It is a common belief in bobsleigh that the push-start is a vital aspect of successful performance. Therefore, British Bobsleigh places a heavy emphasis on the use of field-based performance testing to assist with both athlete monitoring and talent identification. There is a general lack of published academic literature in bobsleigh. Thus, limited evidence exists confirming the importance of the push-start, as well as validating the field-based performance tests used by British Bobsleigh. The aim of this thesis was to validate and develop the core principles and scientific underpinnings of squad monitoring and talent identification specific to ‘brake-men’/’brake-women’ push-start performance in bobsleigh. Study 1 examined the relationship between the push-start and finish time across elite bobsleigh competitions for 2-man, 4-man and female event formats, across multiple tracks and over multiple on-ice seasons. The study demonstrated most tracks on the elite bobsleigh circuit to be either push-start dominant or moderately influenced by the push-start (common variance ≥ 10%). Thus, it highlighted the value of evaluating and developing push-start performance in British Bobsleigh athletes. Studies 2 and 3 investigated the current performance testing practices of British Bobsleigh, used in both talent identification and squad monitoring. Study 2 investigated the predictive validity of the ‘evaluation test’ used by British Bobsleigh to assess whether the whole test battery, as well as individual tests included within it relate to the bobsleigh push-start. Although this study confirmed the predictive validity of ‘evaluation test’ total points to assess athletes push-start capabilities (r = -0.86 to -0.94), completion of the entire testing battery proved somewhat unnecessary. This largely manifested from the major finding of this study that confirmed that the roll-bob push test could be used as a reliable (CV = 0.7 to 1.7%) and valid (r = 0.83 to 0.98) predictor of push-start performance. Subsequent attempts to explain push-start performance using only the general performance tests included within the 4 ‘evaluation test’, highlighted the importance of body mass and 30 m sprint time. However, the explained variance in male push-start performance (55 %), highlighted a clear need to examine other performance qualities beyond those in the current British Bobsleigh ‘evaluation test’. Study 3 explored the reliability, discriminative validity and predictive validity of the British Bobsleigh ‘Keiser Squat Test’. The findings of the study confirmed the reliability of the test protocol (CV = 6 to 10 %), as well as reporting very large to near perfect predictive ability for the female push-start (r = -0.86 to -0.96). Despite this, the strength of the prediction was only moderate in male athletes (r = -0.30 to - 0.47) and the test could only distinguish between world class performance (WCP) and national development (ND) male athletes at a moderate load. Subsequently, other performance tests outside the current practices of British Bobsleigh but identified from the winter sliding sport, strength and power diagnostic and sprinting literature were explored. Study 4 investigated the validity of vertical and horizontal jump test metrics, completed under both bilateral and unilateral conditions, to predict push-start performance. The major findings were that horizontally oriented tests (e.g. standing long jump (SLJ)) may represent better push-start predictive ability than vertically oriented tests (e.g. the countermovement jump (CMJ) and ‘Keiser Squat Test’). Also, maximising an athlete’s unilateral facilitation, as well as minimising any between limb asymmetries appears to be beneficial for push-start performance (r = 0.67 to 0.88). Thus, the addition of unilateral SLJ peak horizontal force, bilateral index and asymmetry index to the British Bobsleigh ‘evaluation test’, may help to account for some of the unexplained variance in push-start performance identified in study 2. Study 5 explored the discriminative validity and predictive validity of sprint force-velocity profiling for the bobsleigh push-start. Also, the study investigated the influence of a 16-week pre-season training phase on bobsleigh athlete’s sprint force-velocity mechanical profiles and associated changes in push-start performance. The sprint force-velocity mechanical variables Pmax, relative Pmax, V0 and Vopt were all shown to provide discriminative validity for the bobsleigh push-start. However, of these variables, Pmax demonstrated the strongest correlation with push-start performance (r = 0.80). At a group level, 5 the findings of the study detected training induced improvements in push-start performance, sprint speed and Pmax (absolute & relative), with the largest group-based improvements observed in absolute Pmax. This was reflected with all athletes making worthwhile gains in Pmax, however this did not always translate to improvements in push-start performance on an individual level. Thus, there may be other factors important for push-start performance beyond those measured in this study. To conclude, the push-start has a moderate to large influence on performance at most tracks on the elite bobsleigh circuit. The roll-bob push test provides a reliable and valid measure to quantify the push-start capabilities of bobsleigh athletes. When considering the key underpinning determinants of push-start performance in bobsleigh, this thesis highlighted the importance of body mass, sprinting speed (30 m sprint time), sprinting maximal mechanical power (sprint force-velocity profiling), unilateral horizontal force production (unilateral SLJ) and power production under moderate external loads (‘Keiser Squat Test’). Thus, practitioners working in bobsleigh should consider these key qualities when designing future squad monitoring and talent identification performance testing batteries and designing training programmes.