Physiological demands of downhill mountain biking

Abstract

Mountain biking is a popular recreational pursuit and the physiological demands of cross-country style riding have been well documented. However, little is known regarding the growing discipline of gravity-assisted downhill cycling. We characterised the physiological demands of downhill mountain biking under typical riding conditions. Riding oxygen consumption ([Vdot]O₂) and heart rate (HR) were measured on 11 male and eight female experienced downhill cyclists and compared with data during a standardised incremental to maximum ([Vdot]O_2max) exercise test. The mean [Vdot]O₂ while riding was 23.1 ± 6.9 ml · kg^?1 · min^?1 or 52 ± 14% of [Vdot]O_2max with corresponding heart rates of 146 ± 11 bpm (80 ± 6% HRmax). Over 65% of the ride was in a zone at or above an intensity level associated with improvements in health-related fitness. However, the participants’ heart rates and ratings of perceived exertion were artificially inflated in comparison with the actual metabolic demands of the downhill ride. Substantial muscular fatigue was evident in grip strength, which decreased 5.4 ± 9.4 kg (5.5 ± 11.2%, P = 0.03) post-ride. Participation in downhill mountain biking is associated with significant physiological demands, which are in a range associated with beneficial effects on health-related fitness.     

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.     

Influence of wheel rim width on rolling resistance and off-road speed in cross-country mountain biking

The rim width of cross-country mountain bike wheel sets has increased in recent years, but the effect of this increase on performance remains unknown. The aim of this study was to analyse the influence of rim width on rolling resistance and off-road speed. We compared 3 tubeless wheel sets: 25 mm inner width as baseline, 30 mm width with the same tyre stiffness, and 30 mm width with the same tyre pressure. Three riders conducted 75 rolling resistance tests for each wheel set on a cross-country course. We determined rolling resistance using the virtual elevation method and calculated off-road speeds for flat and uphill conditions using a mathematical model. Baseline rolling resistance (C_r) was 0.0298, 90% CI [0.0286, 0.0310], which decreased by 1.4%, [0.7, 2.2] with the wider rim and the same tyre stiffness and increased by 0.9%, [0.1, 1.6] with the wider rim and the same tyre pressure. The corresponding effects on off-road speed were most likely trivial (0.0% to 0.7% faster and 0.1% to 0.6% slower, respectively). Because the effect of rim width on off-road speed seems negligible, athletes should choose the rim width that offers the best bike handling and should experiment with low tyre pressures.     

Influence of wheel size on muscle activity and tri-axial accelerations during cross-country mountain biking

ABSTRACT

This study aimed to investigate the influence of different mountain bike wheel diameters on muscle activity and whether larger diameter wheels attenuate muscle vibrations during cross-country riding. Nine male competitive mountain bikers (age 34.7 ± 10.7 years; stature 177.7 ± 5.6 cm; body mass 73.2 ± 8.6 kg) participated in the study. Riders performed one lap at race pace on 26, 27.5 and 29 inch wheeled mountain bikes. sEMG and acceleration (RMS) were recorded for the full lap and during ascent and descent phases at the gastrocnemius, vastus lateralis, biceps brachii and triceps brachii. No significant main effects were found by wheel size for each of the four muscle groups for sEMG or acceleration during the full lap and for ascent and descent (P > .05). When data were analysed between muscle groups, significant differences were found between biceps brachii and triceps brachii (P < .05) for all wheel sizes and all phases of the lap with the exception of for the 26 inch wheel during the descent. Findings suggest wheel diameter has no influence on muscle activity and vibration during mountain biking. However, more activity was observed in the biceps brachii during 26 inch wheel descending. This is possibly due to an increased need to manoeuvre the front wheel over obstacles.     

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

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.     

The anaerobic power reserve and its applicability in professional road cycling

This study examined if short-duration record power outputs can be predicted with the Anaerobic Power Reserve (APR) model in professional cyclists using a field-based approach. Additionally, we evaluated if modified model parameters could improve predictive ability of the model. Twelve professional cyclists (V?O_2max 75 ± 6 ml?kg^?1?min^?1) participated in this investigation. Using the mean power output during the last stage of an incremental field test, sprint peak power output and an exponential constant describing the decrement in power output over time, a power-duration relationship was established for each participant. Record power outputs of different durations (5 to 180 s) were collected from training and competition data and compared to the predicted power output from the APR model. The originally proposed exponent (k = 0.026) predicted performance within an average of 43 W (Standard Error of Estimate (SEE) of 32 W) and 5.9%. Modified model parameters slightly improved predictive ability to a mean of 34–39 W (SEE of 29 – 35 W) and 4.1 – 5.3%. This study shows that a single exponent model generally fits well with the decrement in power output over time in professional cyclists. Modified model parameters may contribute to improving predictability of the model.     

Well-being of cycling tourists in Hainan,China

Abstract

Bicycles are now gradually losing their attraction for utilitarian use, but in recent years, cycling for tourism and recreation has gained in popularity. However, the experiences and well-being involved in cycling tourism from a theoretical perspective have received little attention. This article intends to explore the relationships between cycling tourism and well-being by studying cyclists on Hainan Island in China. Interviews and participation observations were used to collect data. The types of cycling tourists were firstly identified and classified, followed by analysis of how the tourists obtained well-being through physical and social activities and their contexts. The study finds that human–bicycle relationships and China’s collectivistic culture play important roles in how cycling tourists obtain well-being. This study provides a mobility perspective on cycling tourism and well-being.     

Tour de France,Giro, Vuelta,and classic European races show a unique progression of road cycling speed in the last 20 years

Abstract

Road cycling ranks among the most intense endurance exercises. Previous studies and mathematical models describing road cycling have not analysed performances per se. We describe the evolution of road cycling performance over the past 116 years. We studied the top ten cyclists' mean speeds in eight famous classic races and three European Grand Tours, using a previously published multi-exponential model that highlights the different progression periods of an event during the century. In addition, we measured an indicator of difficulty for the Tour de France by calculating the climbing index (i.e. the total altitude climbed over total distance). The eleven races' mean speed increased progressively from 23.13 km · h^?1 in 1892 to 41.19 ± 2.03 km · h^?1 in 2008. Road cycling development, like other quantifiable disciplines, fits a piecewise progression pattern that follows three periods: before, between, and after the two World Wars. However, a fourth period begins after 1993, providing a speed progression of 6.38% from the third one. The Tour de France's climbing index also provided insight into a recent paradoxical relationship with speeds: when the climbing index increased, the winner's speed also increased. Our results show a major improvement (6.38%) in road cycling performance in the last 20 years and question the role of extra-physiological parameters in this recent progression.     

体育舞蹈中常见运动损伤的原因及预防

近些年来,随着我国体育舞蹈的普及和竞技水平不断提升,体育舞蹈的教学和训练中舞者运动损伤时有发生,这不仅给舞者个人带来困扰,而且在一定程度上对体育舞蹈的整体发展产生消极影响。本文通过对陕西省8家体育舞蹈俱乐部的舞者们进行调查,找出了不同程度运动损伤的形成原因,并通过数据分析发现规律,最终提出解决的手段和方法。     

The effect of torsional shoe sole stiffness on knee moment and gross efficiency in cycling

Altering torsional stiffness of cycling shoe soles may be a novel approach to reducing knee joint moments and overuse injuries during cycling. We set out to determine if the magnitude of three-dimensional knee moments were different between cycling shoe soles with different torsional stiffnesses. Eight trained male cyclists cycled at 90% lactate threshold power output in one of two cycling shoe conditions in a randomized crossover design. The shoe sole was considered torsionally flexible (FLEX) compared to a relatively stiffer (STIFF) sole. Gross efficiency (GE) and knee joint moments were quantified. No significant effect of shoe condition was seen in GE (21.4 ± 1.1% and 20.9 ± 1.6% for FLEX and STIFF, respectively, P = 0.12), nor in three-dimensional knee moments. 4 of the 8 subjects had reduced knee moments in at least 2 of the 3 moment directions. These “responders” were significantly shorter (1.73 ± 0.02 m vs 1.81 ± 0.04 m, P = 0.017) and had a higher relative maximal aerobic power (MAP) (4.6 ± 0.3 W?kg-1 vs 3.9 ± 0.3 W?kg-1, P = 0.024) compared to non-responders. These results suggest that certain shoe characteristics may influence certain individuals differently because these participants belong to different “functional groups”; certain individuals may respond positively to FLEX, while others may not. Further studies should test this proposed hypothesis.     

Knowledge is power: Issues of measuring training and performance in cycling

ABSTRACT

Mobile power meters provide a valid means of measuring cyclists’ power output in the field. These field measurements can be performed with very good accuracy and reliability making the power meter a useful tool for monitoring and evaluating training and race demands. This review presents power meter data from a Grand Tour cyclist’s training and racing and explores the inherent complications created by its stochastic nature. Simple summary methods cannot reflect a session’s variable distribution of power output or indicate its likely metabolic stress. Binning power output data, into training zones for example, provides information on the detail but not the length of efforts within a session. An alternative approach is to track changes in cyclists’ modelled training and racing performances. Both critical power and record power profiles have been used for monitoring training-induced changes in this manner. Due to the inadequacy of current methods, the review highlights the need for new methods to be established which quantify the effects of training loads and models their implications for performance.     

浅淡体育学院篮球专项学生运动损伤原因及防治

高校体育院、系的篮球专项学生不论在篮球课堂教学,还是篮球比赛、课外活动中,运动损伤时有发生,这不仅给学生的健康带来损害,而且严重阻碍了学生对篮球运动技术的掌握和运动水平的提高,不同程度地影响了学生日常的学习生活。本文试图采用文献资料法、问卷调查法、数理统计法,通过对吉林体育学院2005一2008级篮球专项学生受伤情况的调查和分析,探讨篮球专项学生运动损伤发生的部位、性质、时间和原因等规律,针对性地提出必要的预防建议,旨在进一步改进教学方法,强化学生的自我保护意识,使学生在篮球运动中尽量减少或避免运动损伤的发生。     

Changes in substrate utilisation and protein catabolism during multiday cycling in well-trained cyclists

There is a paucity of studies that have evaluated substrate utilisation and protein catabolism during multiday strenuous exercise in athletes. Eleven well-trained male cyclists completed 3 h of race-simulated cycling on 4 consecutive days. Cyclist exercised 2 h postprandially and with carbohydrate supplementation (~50 g · h^?1) during exercise. Whole body substrate utilisation was measured by indirect calorimetry, protein catabolism from sweat and urine urea excretion, and blood metabolite concentration was evaluated. Protein catabolism during exercise was significantly greater on days 2–4 (29.9 ± 8.8; 34.0 ± 11.2; 32.0 ± 7.3 g for days 2, 3, and 4, respectively) compared to day 1 (23.3 ± 7.6 g), P < 0.05. Fat oxidation was greater at 21 km (~45 min) on days 2–4 (1.06 ± 0.23; 1.08 ± 0.25; 1.12 ± 0.29 g · min^?1) compared to day 1 (0.74 ± 0.23 g · min^?1, P < 0.05), but the rate of carbohydrate and fat oxidation was similar between days at 50 and 80 km. Whole body substrate utilisation is altered on subsequent days of multiday prolonged strenuous cycling that includes a quicker transition to greater fat utilisation from exercise onset and a 28–46% greater reliance on endogenous protein catabolism on all successive days.     

高校体育专业学生篮球运动中踝关节损伤的调查分析

踝关节损伤是篮球运动中常见的一种损伤。本文通过问卷调查对普通高校体育专业学生在篮球运动中踝关节损伤的类型、程度、原因等进行了调查,根据踝关节生理结构和篮球运动特点对损伤原因进行了研究,并对踝关节损伤的预防提出了合理的建议。     

Effects of magnitude and frequency of variations in external power output on simulated cycling time-trial performance

Abstract

Mechanical models of cycling time-trial performance have indicated adverse effects of variations in external power output on overall performance times. Nevertheless, the precise influences of the magnitude and number of these variations over different distances of time trial are unclear. A hypothetical cyclist (body mass 70 kg, bicycle mass 10 kg) was studied using a mathematical model of cycling, which included the effects of acceleration. Performance times were modelled over distances of 4–40 km, mean power outputs of 200–600 W, power variation amplitudes of 5–15% and variation frequencies of 2–32 per time-trial. Effects of a “fast-start” strategy were compared with those of a constant-power strategy. Varying power improved 4-km performance at all power outputs, with the greatest improvement being 0.90 s for ± 15% power variation. For distances of 16.1, 20 and 40 km, varying power by ± 15% increased times by 3.29, 4.46 and 10.43 s respectively, suggesting that in long-duration cycling in constant environmental conditions, cyclists should strive to reduce power variation to maximise performance. The novel finding of the present study is that these effects are augmented with increasing event distance, amplitude and period of variation. These two latter factors reflect a poor adherence to a constant speed.     

Cycling power output produced during flat and mountain stages in the Giro d'Italia: A case study

Abstract

Until recently, the physiological demands of cycling competitions were mostly reflected by the measurement of heart rate and the indirect estimation of exercise intensity. The purpose of this case study was to illustrate the varying power output of a professional cyclist during flat and mountain stages of a Grand Tour (Giro d'Italia). Nine stage recordings of a cyclist of the 2005 Giro d'Italia were monitored using a mobile power measurement device (SRM Trainingssystem, Julich, Germany), which recorded direct power output and heart rate. Stages were categorized into flat (n = 5) and mountain stages (n = 4). Data were processed electronically, and the overall mean power in flat and mountain stages and maximal mean power for various durations were calculated. Mean power output was 132 W ± 26 (2.0 W · kg^?1 ± 0.4) for the flat and 235 W ± 10 (3.5 W · kg^?1 ± 0.1) for the mountain stages. Mountain stages showed higher maximal mean power (367 W) for longer durations (1800 s) than flat stages (239 W). Flat stages are characterized by a large variability of power output with short bursts of high power and long periods with reduced intensity of exercise, whereas mountain stages mostly require submaximal, constant power output over longer periods.     

体育教学中常见伤病的预防和急救

体育教学过程中，由于教师和学生对预防伤病的意义认识不足，缺乏防范观念，缺乏正确的方法和组织，经验不足，造成学生的运动损伤和伤病，影响教学的正常进行。在总结多年教学实践经验的基础上，对体育教学中常见的几种伤病的产生原因、预防措施和急救方法进行了探讨，以期避免或减轻体育教学中常见伤病的发生。     

Radial bone size and strength indices in male road cyclists,mountain bikers and controls

Abstract

Mountain biking (MB), unlike road cycling (RC) involves exposure to ground impact bone strain and requires upper-body muscle forces to maintain stability over uneven terrain and therefore may have differential effects on radial bone structure and strength. This study aimed to compare serum bone turnover marker concentration, 1-repetition maximum muscle strength and the radial proximal (diaphysis) and distal (metaphysis) bone structure [bone mineral content, total and cortical area (CoA), density and thickness, diameter and circumference], strength strain indices and muscle cross-sectional area (MCSA) using peripheral quantitative computed tomography (pQCT) between 30 male cyclists (18–34 years) MB (n = 10), RC (n = 10) and non-athletes controls (CON, n = 10). Differences were assessed by ANOVA and an ANCOVA (adjusting for body mass and height) where appropriate. MB radii were characterised by significantly stronger (14–16%), denser (9–27%) and larger (10%) metaphyses and stronger (22–23%) and larger (11–13%) diaphyses compared to RC and CON. RC had significantly 7% higher strength indices and 4% greater CoA and thickness than CON at the diaphysis, with no differences for other bone measurements. Serum C-terminal telopeptides of type-1 collagen concentration (bone resorption marker) was higher in RC than MB (p < 0.05) and above the age-reference range. MCSA and strength were greater in MB than RC (p < 0.05). Muscle forces generated during RC appear to produce an osteogenic stimulus to increase radial bone strength indices with minimal improvement in bone structure. However greater resorptive activity in RC suggests inadequate loading to support bone maintenance. In conclusion, bone loading, muscle size and strength of MB are superior to RC.     

Performance differences when using 26- and 29-inch-wheel bikes in Swiss National Team cross-country mountain bikers

The purpose of this study was to analyse the effect of bike type – the 26-inch-wheel bike (26“ bike) and the 29-inch-wheel bike (29“ bike) – on performance in elite mountain bikers. Ten Swiss National Team athletes (seven males, three females) completed six trials with individual start on a simulated cross-country course with 35 min of active recovery between trials (three trials on a 26“ bike and three trials on a 29“ bike, alternate order, randomised start-bike). The course consisted of two separate sections expected to favour either the 29“ bike (section A) or the 26“ bike (section B). For each trial performance, power output, cadence and heart rate were recorded and athletes’ experiences were documented. Mean overall performance (time: 304 ± 27 s vs. 311 ± 29 s; P < 0.01) and performance in sections A (P < 0.001) and B (P < 0.05) were better when using the 29“ bike. No significant differences were observed for power output, cadence or heart rate. Athletes rated the 29“ bike as better for performance in general, passing obstacles and traction. The 29“ bike supports superior performance for elite mountain bikers, even on sections supposed to favour the 26“ bike.