The aim of the present project was to quantify and compare differences in impact performance and damping effectiveness among various off-road bicycle suspension systems. Two experiments were conducted to compare suspensions. Fork impact performance was tested by measuring peak antero-posterior braking forces and impulses during impact with bumps of 6- and 10-cm height for five mountain bike suspension systems. These results were compared to a rigid fork condition. Comparisons among suspension systems showed small but significant differences in performance. While only marginal differences in peak force were found for the suspension conditions, more substantial differences in braking impulse were observed. Air-Oil design forks had the lowest braking impulse for the range of speeds and impact characteristics of this experiment. In another setting, an analysis of acceleration signals over a range of frequencies on two surface conditions (gravel and trail) was conducted to assess the damping effectiveness of the five suspension systems. The mountain bike was equipped with accelerometers mounted at the axle and frame. A spectral analysis of the signal was performed for each signal to provide a measure of fork effectiveness. Results showed that accelerations ranged from -33 to +40 g at the axle and from -13 to +13 g at the frame, while spectral analyses of the acceleration signals revealed two distinct frequency regions from 0 to 100 Hz and from 300 to 400 Hz. The various suspension systems were all effective in attenuating vibration over the first region. Vibration amplitudes at the frame were considerably less than at the axle for the suspension conditions while similar axle-frame vibrations were observed with the rigid fork. Lower frequency vibration amplitudes were typically greater on the trail than on gravel. In the frequency region between 300-400 Hz, the signal was attenuated at the frame for all conditions including the rigid fork. The quantification and comparison process of the various suspension forks using impulse provided an objective marker for performance, and allowed differentiation between various suspension conditions. Moreover, the effectiveness analysis through the use of accelerometers provided insight into the range of frequencies dampened by a suspension. The lower frequency range dampening suggested that effectiveness of a suspension fork can be quantified even though the experiment did not conclusively differentiate between the forks. / Graduation date: 2001

Mountain bike suspension forks have been developed to reduce the accelerations transmitted to the rider. However, the effectiveness of suspension forks has not been systematically investigated. It was the goal of this project to quantify the amount of impact acceleration damping afforded by three stiffness settings of suspension forks compared to rigid mountain bike forks. Seven experienced mountain bike riders gave their informed consent to participate in the study. The subjects coasted down a ramp and impacted a bump at 5.4 m/s located about 2.3 m past the ramp end. Accelerometers were placed on the axle and frame of the bicycle which was fitted with either a rigid fork (FR) or suspension forks set on soft (F1), medium (F3), or firm (F6) stiffness. Bumps were either small (B1), medium (B2) or large (B3). Accelerometer data were telemetered to a computer, sampled at 1000 Hz and smoothed with Butterworth filter with 50 Hz cutoff. Peak acceleration during impact (P1) and landing (P2) as well as the slope of the impact acceleration peak (jerk, J) were extracted from the data and analyzed using a 2 x 3 x 4 repeated measures ANOVA for each of the dependent variables (P1, P2, J), and with linear contrasts as follow-up tests. A significance level of p<.01 was chosen. All forks were found to produce similar impact acceleration (P1) at the axle and frame on the small bump (B1). On larger bumps (B2 and B3), softer suspension forks (F1 and F3) significantly reduced acceleration transmitted to the rider during bump impact (P1), while maintaining significantly higher axle acceleration than other forks (p<.001); Jerk was significantly reduced at the frame compared to the axle for each suspension fork with the larger bumps. Landing impacts (P2) were of similar magnitude for most fork conditions at both the axle and frame. It appears from these data that suspension forks with moderate stiffness may provide the best impact acceleration damping for mountain bikes encountering impacts with characteristics similar to the bumps and velocity used in this study. It is unclear how these results generalize to other conditions encountered while riding. / Graduation date: 1997

Made available in DSpace on 2016-12-06T17:07:11Z (GMT). No. of bitstreams: 1 Dissertacao - Vitor.pdf: 1297842 bytes, checksum: d4368ad562c4950f8963c90332222304 (MD5) Previous issue date: 2006-06-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The purpose of this paper is to identify morphophysiological characteristics of Brazilian mountain bike (MTB) athletes , and determine the physiologic demand imposed on organism during cross-country competitions (XC) and variables associated to performance. Fourteen mountain bikers that dispute local and national championships were selected (26,1 6,5 years; 68,4 5,7kg; 175,3 4,3cm; 5,8 1,7 %F; 8,6 4,6 years of training), in different categories: elite (n=6), junior (n=1), sub 23 (n=3), sub 30 (n=1) and master (n=3). Firstly, the participants were submitted to Wingate test (WT), with fixed load corresponding to 10% of body mass (CEFISE®, 1800). After a minimum interval of 30 min., the incremental progressive exercise (IPE) was accomplished in the cycle-simulator (CompuTrainer TM RacerMate® 8000, Seattle WA), with initial load of 100 W and additional load of 30 W every 3 min. until exhaustion. During IPE, HR (Polar® Vantage NV and S610i), VO2 (Aerosport® KB1-C), [La] (Yellow Springs 1500) and EPE - 10 points (Borg et al, 1982). LL1 were identified starting from the relation between the smallest equivalent value [La].W-1 and for LL2, the fixed value of 1,5 mmol.l-1 is included (Berg et al., 1990). The physiologic domains were identified from the theoretical model of Gaesser and Poole, (1996): below LL1 (moderate), between LL1 and LL2 (intense), above LL2 (severe). After a minimum interval of four days, the athletes of the category elite were monitored through the HR registration, during the Brazilian stage of the World Cup of XC. After two weeks, all participants were evaluated in the Brazilian Championship of XC. The results indicate that the athletes present morphologic characteristics similar to those of international athletes, although physiologic variables are smaller, except for VO2máx and VO2máx.kg-1. The behavior of HR during XC competitions indicates that the average HR ranges from 91 to 92% of HRmax, provided that great part of the tests is predominantly disputed in the severe physiologic domain (~ 90% of the total time). Wmax.kg-1 and Wmáx.kg-0,79 were significantly associated with the performance in both competitions and only WLL2.kg-0,79 in the World Cup of XC. Therefore, it is noted that XC competitions require high physiologic demand, and are disputed predominantly in physiologic severe domain, close to the maximum aerobic power. In addition, the physiologic variables associated with performance stand out when normalized by algometric scale. In this regard, in order to have good performance during XC competitions, athletes should emphasize of power and capacity, aerobic and anaerobic. / O objetivo deste estudo foi identificar as características morfofisiológicas dos atletas brasileiros de mountain bike (MTB), com determinação da demanda fisiológica imposta ao organismo durante as competições de cross-country (XC) e variáveis associadas à performance. Foram selecionados 14 mountain bikers que disputam campeonatos estaduais e nacionais (26,1 ± 6,5 anos; 68,4 ± 5,7 kg; 175,3 ± 4,3 cm; 5,8 ± 1,7 %G; 8,6 ± 4,6 anos de treinamento), que competem em diferentes categorias: elite (n=6), júnior (n=1), sub 23 (n=3), sub 30 (n=1) e máster (n=3). Primeiramente, os participantes foram submetidos ao teste de Wingate (TW), com carga fixa correspondente a 10% da massa corporal (CEFISE®, 1800). Após intervalo mínimo de 30 min., foi realizado o protocolo de cargas progressivas (PCP) no ciclo-simulador (CompuTrainer TM RacerMate® 8000, Seattle WA), com carga inicial de 100 W e incremento de 30 W a cada 3 min. até a exaustão. Durante o PCP, foram identificadas a FC (Polar® Vantage NV e S610i), o VO2 (Aerosport KB1-C), [La] (Yellow Springs ®1500) e PSE 10 pontos (Borg et al, 1982). LL1 foi identificado a partir da relação entre o menor valor equivalente [La]/W e para LL2, acrescenta-se o valor fixo de 1,5 mmol.l-1 (Berg et al., 1990). Os domínios fisiológicos foram identificados a partir do modelo teórico de Gaesser e Poole, (1996): abaixo de LL1 (moderado), entre LL1 e LL2 (intenso), acima de LL2 (severo). Após intervalo mínimo de quatro dias, os atletas da categoria elite, foram monitorados através do registro da FC, durante a etapa brasileira da Copa do Mundo de XC. Após duas semanas, todos os participantes foram avaliados no Campeonato Brasileiro de XC. Os resultados indicam que os atletas apresentam características morfológicas semelhantes aos atletas internacionais, sendo que as variáveis fisiológicas são menores, exceto o VO2máx e VO2máx.kg-1. O comportamento da FC durante as competições de XC, indica que os valores médios da FC estão entre 91 e 92 % de FCmáx, sendo que grande parte das provas é predominantemente disputada no domínio fisiológico severo (~ 90% do tempo total). A Wmáx.kg-1 e Wmáx.kg-0,79 foram associadas significativamente com a performance nas duas competições e apenas a WLL2.kg-0,79 na Copa do Mundo de XC. Assim, percebe-se que as competições de XC exigem demanda fisiológica elevada, sendo disputadas predominantemente no domínio fisiológico severo, próximo à potência aeróbia máxima. Em adição, as variáveis fisiológicas associadas com a performance destacam-se quando normalizadas por alometria. Desta forma, para que os atletas tenham um bom desempenho durante as competições de XC, sugere-se o treinamento da potência e capacidade, aeróbia e anaeróbia.