Matthew C. Miller

Performance and physiological effects of different descending strategies for cross-country mountain biking

Abstract This study investigated the performance-related feasibility and physiological benefits of purposefully eliminating propulsive work while descending in mountain biking and compared values to those measured during road descending. Participants cycled uphill on a road at race pace before descending over three conditions (off-road pedalling; off-road coasting; road coasting). Relatively low power output during off-road pedalling was associated with a greater oxygen uptake (p < .01) when compared with off-road coasting despite no difference in vibration exposure (p > .05). Importantly, pedalling did not invoke a performance benefit (p > .05) on the descent used in this study. Significantly greater heart rate and oxygen uptake (both p < .01) were observed between road and off-road descending, likely caused by the increase in terrain-induced vibrations (p < .01) experienced between the bicycle and rider. Results indicate that reducing propulsive work during descending can improve recovery without being disadvantageous to performance. Similarly, the vibrations experienced during road descending are relatively low, and further reduce oxygen cost. In an effort to increase efficiency, it is recommended that mountain bike athletes focus on skills to increase descending speed without the addition of pedalling, and that equipment be used to decrease vibrations nearer to those seen on the road.

Validity of a device designed to measure braking power in bicycle disc brakes.

Abstract Real-world cycling performance depends not only on exercise capacities, but also on efficiently traversing the bicycle through the terrain. The aim of this study was to determine if it was possible to quantify the braking done by a cyclist in the field. One cyclist performed 408 braking trials (348 on a flat road; 60 on a flat dirt path) over 5 days on a bicycle fitted with brake torque and angular velocity sensors to measure brake power. Based on Newtonian physics, the sum of brake work, aerodynamic drag and rolling resistance was compared with the change in kinetic energy in each braking event. Strong linear relationships between the total energy removed from the bicycle-rider system through braking and the change in kinetic energy were observed on the tar-sealed road (r2 = 0.989; p < 0.0001) and the dirt path (r2 = 0.952; p < 0.0001). T-tests revealed no difference between the total energy removed and the change in kinetic energy on the road (p = 0.715) or dirt (p = 0.128). This study highlights that brake torque and angular velocity sensors are valid for calculating brake power on the disc brakes of a bicycle in field conditions. Such a device may be useful for investigating cyclists’ ability to traverse through various terrains.

The impact of uphill cycling and bicycle suspension on downhill performance during cross-country mountain biking

ABSTRACT Non-propulsive work demand has been linked to reduced energetic economy of cross-country mountain biking. The purpose of this study was to determine mechanical, physiological and performance differences and observe economy while riding a downhill section of a cross-country course prior to and following the metabolic “load” of a climb at race pace under two conditions (hardtail and full suspension) expected to alter vibration damping mechanics. Participants completed 1 lap of the track incorporating the same downhill section twice, under two conditions (hardtail and full suspension). Performance was determined by time to complete overall lap and specific terrain sections. Power, cadence, heart rate and oxygen consumption were sampled and logged every second while triaxial accelerometers recorded accelerations (128 Hz) to quantify vibration. No differences between performance times (P = 0.65) or power outputs (P = 0.61) were observed while physiological demand of loaded downhill riding was significantly greater (P < 0.0001) than unloaded. Full suspension decreased total vibrations experienced (P < 0.01) but had no effect on performance (P = 0.97) or physiological (P > 0.05) measures. This study showed minimal advantage of a full suspension bike in our trial, with further investigations over a full race distance warranted.

Agreement between Powertap, Quarq and Stages power meters for cross-country mountain biking

Abstract Advances in technology have made the use of a variety of power meters ubiquitous in road cycling along with an ever-increasing popularity during mountain biking. This study compared data from one bicycle using three power meters: Stages (non-driveside crank arm); Quarq (chainring spider); and Powertap (rear-wheel hub). While no differences (p > .05) between power meters were present during treadmill riding at high or low cadences, dissimilarities for both power (W) and cadence (rpm) were apparent during actual cross-country mountain bike riding. Frequency distribution and analysis of coasting indicate that the Stages records more time (p < .001) at zero watts (6.9 ± 3.3 s) and zero cadence (6.9 ± 3.3 s) compared with Quarq (W = 3.3 ± 1.5 s, rpm = .8 ± .7 s) and Powertap (W = 1.1 ± .8 s, rpm = 3.0 ± 1.2 s). Consequently, significant interactions (power meter × terrain, p = .0351) and main effects (power meter p < .0001, and terrain p < .0001) for power output were present and included: uphill (317.5 ± 50.7, 340.8 ± 52.6, 327.3 ± 48.6 W); downhill (127.6 ± 12.3, 147.4 ± 23.8, 160.1 ± 24.0 W); and flat (201.1 ± 21.6, 225.2 ± 27.2, 224.0 ± 29.6 W) for the Stages, Quarq and Powertap, respectively. It is likely that accelerometry (Stages) compared with reed switch (Powertap and Quarq) technology to determine cadence, resulted in the discrepancies between power meters. However, while the reliability of the different methods appears acceptable for intermittent exercise such as cross-country mountain biking, the validity of each in such a situation requires confirming.

Tyre Volume and Pressure Effects on Impact Attenuation during Mountain Bike Riding

Exposure to impacts and vibrations has been shown to be detrimental to cross country mountain bike performance and health. Therefore, any strategy aimed at attenuating such exposure is useful to participants and/or industry. The purpose of this study was to assess the influence of tyre size and tyre inflation pressure on exposure to impacts. Participants completed nine trials of a technical section (controlled for initial speed and route taken) including nine separate conditions involving three tyre sizes and three tyre inflation pressures normalised per tyre. Performance was determined by time to negotiate the technical section while triaxial accelerometers recorded accelerations (128 Hz) to quantify impact exposure and the subsequent effects on soft tissue response. Increases in tyre size within the range used improved performance while changes to tyre inflation pressure had no effect on performance. Larger tyre sizes and lower tyre inflation pressures significantly reduced exposure to impacts which could be augmented or negated due to an interaction between tyre size and inflation pressure . It is recommended that mountain bikers use larger tyres, inflated to the moderate pressures used within this study, in order to increase performance and reduce the risk of overuse injuries.

Quantification of brake data acquired with a brake power meter during simulated cross-country mountain bike racing

Abstract There is currently a dearth of information describing cycling performance outside of propulsive and physiological variables. The aim of the present study was to utilise a brake power meter to quantify braking during a multi-lap cross-country mountain bike time trial and to determine how braking affects performance. A significant negative association was determined between lap time and brake power (800.8 ± 216.4 W, mean ± SD; r = −0.446; p < 0.05), while the time spent braking (28.0 ± 6.4 s) was positively associated with lap time (314.3 ± 37.9 s; r = 0.477; p < 0.05). Despite propulsive power decreasing after the first lap (p < 0.05), lap time remained unchanged (p > 0.05) which was attributed to decreased brake work (p < 0.05) and brake time (p < 0.05) in both the front and rear brakes by the final lap. A multiple regression model incorporating braking and propulsion was able to explain more of the variance in lap time (r2 = 0.935) than propulsion alone (r2 = 0.826). The present study highlights that riders’ braking contributes to mountain bike performance. As riders repeat a cross-country mountain bike track, they are able to change braking, which in turn can counterbalance a reduction in power output. Further research is required to understand braking better.

Predictive Validity of Critical Power, The Onset of Blood Lactate and Anaerobic Capacity for Cross-Country Mountain Bike Race Performance

Critical power is emerging as an important indicator of high intensity endurance exer- cise capability. Little is known regarding its ability to predict performance during high intensity intermittent events such as Olympic format cross country mountain bike racing. Therefore, the purpose of this pilot study was to assess the validity of critical power and anaerobic capacity compared to the more traditional measure of power at physiological thresholds previously re- lated to race performance. Five nationally competitive athletes (mean±s: age:31.4±9.3 years; mass: 70.8±9.5 kg; VO 2max : 63.8±7.0 mlkg -1 •min) volunteered for this study. Participants com- pleted a cycle ergometry step test to exhaustion in order to determine the anaerobic threshold. On a separate occasion participants completed a 3-minute all-out test against a fixed resistance to determine critical power and anaerobic capacity. Laboratory data showed no differences (P=0.057) between the power output at the onset of blood lactate or critical power and neither related to anaerobic capacity (p=0.499 and p=0.344, respectively). Performance was measured via race data analysis gathered from a USA Cycling sanctioned race. Linear regression was used to assess the prediction of performance. Critical power predicts Olympic format cross country mountain bike performance (r 2 =0.943, p=0.006) to a greater degree of accuracy than anaerobic threshold (r 2 =0.785, p=0.046) or anaerobic capacity (r 2 =0.477, p=0.197) with less error (39.413; 76.526; 118.9 s, respectively). Therefore, the ability to sustain a high intensity effort for the race duration, determined via critical power rather than the onset of blood lactate, is likely more valuable to cross country mountain bike athletes than anaerobic capacity.

Braking and performance characteristics of experienced and inexperienced mountain bikers navigating an isolated off-road turn using a brake power meter

ABSTRACT Using a brake power meter, experienced and inexperienced mountain bikers were tested on an isolated, controlled off-road cycling descent with a turn to determine how riding experience affects the pattern of braking behaviour. Overall braking measurements such as absolute and relative brake work and brake power, as well as brake time, were significantly related to performance time on the track used in this study. Inexperienced mountain bikers displayed greater absolute and relative brake work and brake time, but had lower absolute and relative brake power when compared with experienced mountain bikers, which resulted in a significant performance decrement for inexperienced riders. Experienced mountain bikers concentrated braking efforts to later in the track, which meant that they spent less time at lower speeds. Inexperienced riders displayed a greater reliance on the rear brake, which likely contributed to their overall increased braking variables. The results of this study highlight that differences in braking magnitude and behaviour are attributable to reduced performance on an isolated off-road track with a corner. Inexperienced mountain bike riders may be able to improve their performance by learning braking patterns similar to those of experienced mountain bikers.

The effectiveness of front fork systems at damping accelerations during isolated aspects specific to cross-country mountain biking

Abstract Cross-country mountain bike suspension reportedly enhances comfort and performance through reduced vibration and impact exposure. This study analysed the effectiveness of three different front fork systems at damping accelerations during the crossing of three isolated obstacles (stairs, drop, and root). One participant completed three trials on six separate occasions in a randomised order using rigid, air-sprung, and carbon leaf-sprung forks. Performance was determined by time to cross obstacles, while triaxial accelerometers quantified impact exposure and damping response. Results identified significant main effect of fork type for performance time (p < 0.05). The air-sprung and leaf-sprung forks were significantly slower than the rigid forks for the stairs (p < 0.05), while air-sprung suspension was slower than the rigid for the root protocol (p < 0.05). There were no differences for the drop protocol (p < 0.05). Rigid forks reduced overall exposure (p < 0.05), specifically at the handlebars for the stairs and drop trials. More detailed analysis presented smaller vertical accelerations at the handlebar for air-sprung and leaf-sprung forks on the stairs (p < 0.05), and drop (p < 0.05) but not the root. As such, it appears that the suspension systems tested were ineffective at reducing overall impact exposure at the handlebar during isolated aspects of cross-country terrain features which may be influenced to a larger extent by rider technique.