Determining the importance of ramp performance during BMX Supercross: Use of predictive assessments and strategies to improve performance outcomes.

The development of bicycle motocross (BMX) racing originated in the early 1970s to become a popular action sport with participation across the world. With similarity to other sprint-based and short duration cycling sports, BMX racing consists of a number of qualification races in order to make the final, with the number of races dependent upon the number of entries. The inclusion of BMX in the Olympics led the governing body, the Union Cyclist International (UCI), to develop specific criteria to showcase BMX racing at the Olympics, including qualification processes and BMX track specifications. BMX Supercross was then a series developed over the time from the Olympic inclusion announcement to the 2008 Olympic Games in Beijing, China. Further, UCI created a series of events including the World Cup series, completed around the world in order to attain Olympic selection for countries wishing to participate.

BMX Supercross includes an explosive and technical start, followed by a full lap of the track of approximately 36 to 42 s. The common contributors to performance outcomes observed during the start and throughout the race are peak power output (PPO), racing competencies, and bicycle technique (Cowell, McGuigan & Cronin, 2012a). As such, observations highlight that BMX racing requires a high level of coordination and skill to successfully complete the course (Cowell et al., 2012a; Rylands, Hurst, Roberts & Graydon, 2017b). It is also believed that successful athletes produce higher PPO in comparison to the less successful competitors (Campillo, Doremus & Hespel, 2007; Martin & Brown, 2009; Tomas, Ross & Martin, 2010; Rylands & Roberts, 2014; Rylands, Roberts & Hurst, 2016) theoretically contributing to faster finish line times (Herman , McGregor, Allen & Bollt, 2009; Cowell et al., 2012a; Cowell et al., 2012b; Rylands & Roberts, 2014). There has been a strong coaching emphasis on the starting phase, given the technical and physical components, strength and conditioning techniques, and practices to improve PPO (Zabala, Sanchez-Munoz & Mateo, 2009) and achieving the fastest acceleration down the BMX Supercross ramp (Milasius, Dandeliene, Tubelis & Skernevicius, 2012).

Therefore, the first study of the thesis investigated the importance of the starting ramp time (RT) to finish line time (FT) for BMX Supercross athletes. The aim was to determine the relationship between the RT and FT from 236 participants from the Australian National and Oceania Championships. The categories included: elite (19+ years) male; elite female; junior elite (17–18 years) male; junior elite female; 16-year male; and 16-year female. RT and FT times were recorded by individual transponders and linear regressions were performed to explore statistical associations and explanations of variance between RT and FT. Results revealed strong correlations between RT and FT (r = 0.686, Syx = 2.688 s; P<0.001). Correlations were significant for all categories, despite variability in statistical association (elite men: r = 0.524, Syx = 1.102; P< 0.001, junior elite men: r = 0.554, Syx = 0.908; P< 0.001, elite female: r = 0.953, Syx = 0.805; P< 0.001 and junior elite female: r = 0.883, Syx = 0.843; p < 0.001). In conclusion, RT is strongly correlated to FT for BMX athletes across a range of competition levels and ages suggesting that RT performance is a vital part of BMX performance across the competition spectrum.

The second study of the thesis examined the contributions from various athletic assessments in determining start ramp and finish line performances in BMX Supercross athletes. Twenty-seven highly-trained and elite participants volunteered for the study (19 male and eight female). All participants attended testing over a two-day period and completed: an unloaded peak cadence test, squat jump, counter-movement jump, 20m block sprint, 5 s sprint to determine peak power on a Wattbike at fan 1 (F1), fan 10 (F10) resistance settings and repeated sprint fatigue test (recording PPO and percentage decline), and lap of a BMX Supercross track to determine fastest RT and FT. Male and female data combined concluded the total variance of dependant variables, to determine RT, was 94.3% F(13,133) = 169.9, P = 0.005, with the largest contributor being Wattbike peak cadence at fan 1 with at 96% (P = 0.005). For the males, the largest contribution to RT was CMJ peak concentric force with 96% contribution from males (P = 0.0005), while the largest contributor for the females was Wattbike peak cadence at fan 1 with 76.4% contribution (P = 0.0005). These results show that the athletic assessments used in this study were useful in determining RT and FT performances and differences between sexes were apparent, suggesting future consideration in test selection, conditioning practices and coaching strategies when determining RT and FT performance outcomes.

Extending from knowledge gained during the initial two studies, the final study examined the effect of post-activation potentiation (PAP) on BMX Supercross RT and FT and the potential neuromuscular contributions. Thirteen sub elite and elite BMX athletes were recruited and completed 3 x 2-day experimental trials including laboratory testing (Day 1) and track-based testing (Day 2). Laboratory testing included neuromuscular assessments of five superimposed maximal voluntary contractions (MVC) pre and 5 min post the PAP protocols for determination of MVC, voluntary activation (VA), MVC electromyography (EMG) M-wave amplitude, and potentiated twitch responses. The PAP protocol included a Wattbike maximal cycling sprint on either fan 1 (F1), fan 10 (F10) or control (CONT). Day 2 track-based testing included the replicated PAP protocol, followed by 5 min recovery and completing the track-based time trial to determine RT and FT. Results showed peak power output (PPO) was higher in F10 compared to F1 (P=0.03), peak cadence (CAD) was also significantly lower (P <0.05). There were no differences between conditions for Day 2 RT and FT (P= 0.42-0.95). There were also no significant differences between conditions or effect of time for MVC (P >0.05) over all conditions; however, VA was significantly higher post-PAP compared to pre for F10 (P=0.03). The results demonstrate that PAP had an effect on centrally-mediated and peripheral neuromuscular properties primarily following the higher resistance (F10); however, these benefits did not translate to benefits for improving BMX Supercross performance with no significant findings for improved RT and FT.

The findings of the thesis demonstrate the need for an optimal starting (ramp) performance in BMX Supercross, where higher PPO and maximal cadence offer higher likelihoods of improved RT and FT. Further, athletic assessments which measure PPO, SJ, CMJ and peak cadence indicate performance likelihood of RT and FT. The findings from the first two studies support previous works, however, this thesis expands on previous works to identify training status and sex considerations, which are key contributors in determining performance outcomes. It may be suggested from these findings that improvements in strength and power (as evidenced in Study 2) should create higher PPO and acceleration on the track. Furthermore, the inclusion of an intervention-based study provided early work in this sport to determine strategies that may be useful in the field when competing. While study 3 findings indicate that a short-duration (5 s) PAP protocol did not improve a BMX Supercross RT or FT, the neuromuscular responses seen in laboratory testing suggest further work may be required to improve the clinical significance of the protocol. Collectively, the findings of this thesis recognise the strong relationship between RT and FT and the requirement for peak power and peak cadence for BMX Supercross athletes; however, would also suggest future research incorporates other pre-training strategies, in order to better understand BMX Supercross starting performance.