Enhancing BMX performance using a multidisciplinary sport science approach (2021)
Type of ContentTheses / Dissertations
Thesis DisciplineHealth Sciences
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
The sport of Bicycle Motocross (BMX) is an Olympic discipline. It is classified as off-road bicycle racing with an intermittent sprint nature due to the high number of repeated maximal efforts required. To improve riders’ performance, practitioners often seek to identify the most important factors that contribute to winning a race. Current research has mainly focused on explosive starting ability and methods to generate and sustain maximal power, which have been deemed critical factors in BMX. However, data describing the physical and physiological demands, as well as ways of improving riders’ performance, are still scarce. Using a multidisciplinary sport science approach, this thesis consists of five complimentary studies providing insight into the key performance factors of BMX racing and novel ways of enhancing riders’ race performance.
The first laboratory study of this thesis focused on investigating the physical attributes of 15 sub-elite BMX riders and subsequently predicted the key performance indicators using correlation and multiple linear regression analyses. This study identified a model in which power-to-weight ratio (PWR), combined relative back-leg-chest strength, and arm span explained ~87% of the variability in BMX finish time.
It is important to identify the key performance predictors in the laboratory condition and define the demands of a BMX rider (Study 1). However, measuring performance in the actual track, where riders usually race, would provide more details around the demands of a race and help coaches to design effective programmes. Therefore, due to the lack of scientific research on physiological characteristics of a BMX race, Study 2 was undertaken to analyse the physiological factors involved in a simulated race where riders perform multiple time trial in a day. Twelve male sub-elite BMX riders undertook a maximum aerobic capacity test in the laboratory and a week later, completed six laps on a BMX track, each interspersed with 15 min of passive recovery. This second study identified a significant correlation between PWR with lap time, however the strength of this association decreased with each subsequent lap. A strong contribution of the aerobic energy system during BMX racing was evident with mean V̇O2peak greater than 80% of the laboratory measured V̇ O2max. The mean blood lactate response (difference of pre and post value) was significantly associated with lap time and demonstrates the importance of the anaerobic glycolytic energy system contribution to BMX racing. Despite the relatively short period (30-40 % of time trial time) of pedalling during BMX racing, both aerobic and anaerobic energy systems are important contributors to lap performance. Given the importance of power output in BMX racing highlighted by the first two studies, Study 3 was undertaken to investigate power production profile across the whole track circuit and correlated the power output during different track sections with overall time trial time. Fourteen male sub-elite BMX riders participated in this study and performed two laps with 15 min passive recovery between each lap. Lap time was significantly associated with time cornering (from start to the end of first corner). Having zero power values included (zero values reflect non-pedalling periods); the average power was ~ 28% of the peak power, compared to 62% when zero values were excluded. Race power output analysis may help BMX cyclists recognize the need to apply certain cadence strategies to maximise power production in certain sections of the BMX track, especially during the start and the first corner.
Having highlighted the importance of muscular power in BMX performance, it is important to explore strategies that could potentially improve power production. With this in mind, Study 4 assessed the effectiveness of a BMX specific Motor Imagery (MI) training program on time trial performance. To date, the transfer of MI has not been adequately evaluated in cycling specific settings. Using a crossover study, 13 sub-elite BMX riders (11 male, 2 female) undertook four weeks (80 min / week) of MI training, in addition to their normal BMX training. Pre and post MI training, physical testing was conducted which included assessing participants’ vertical jump as well as, three BMX track time-trials. Despite no statistically significant improvement in riders’ finish time following MI training in any of the three time trials, relative peak power significantly improved (~4 %) following MI practice compared to the baseline and control condition.
In addition to psychology strategies, athletes also use nutritional interventions to improve performance. In the fifth and final Study, the effects of pre-time trial caffeine supplementation on riders’ performance was investigated. The effect of caffeine on anaerobic sprint performance, such as BMX racing is equivocal and requires further investigation. In a randomized, placebo-controlled, crossover design, 14 male BMX riders consumed either (300 mg; 4.2 ± 0.2 mg·kg-1) caffeinated or a placebo gum, and undertook three BMX laps. Administering caffeine by chewing gum significantly improved simulated BMX time-trial performance by 1.5 %. This was most likely through improving riders’ power production (3%) and/or reducing the perception of efforts (6.6 ± 1.3) compared to the placebo (7.2 ± 1.7) during laps.
Overall, using a multidisciplinary sport science approach, this thesis highlighted several physical and physiological factors that contribute to BMX performance. In particular, riders’ anthropometry, muscular strength and explosive power, as well as having a highly developed aerobic capacity are especially important for BMX race performance. In addition, using a BMX specific motor imagery training improved riders’ power production, but further research is required to identify its influence on race performance. Lastly, caffeine consumption has an ergogenic effect on BMX riders’ overall time trial performance. BMX coaches and riders can utilise the outcomes of the current thesis and should consider using a multidisciplinary performance strategy when planning training programmes and considering talent identification and development.
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