Science and cycling: current knowledge and future directions for research

Abstract

In this holistic review of cycling science, the objectives are: (1) to identify the various human and environmental factors that influence cycling power output and velocity; (2) to discuss, with the aid of a schematic model, the often complex interrelationships between these factors; and (3) to suggest future directions for research to help clarify how cycling performance can be optimized, given different race disciplines, environments and riders. Most successful cyclists, irrespective of the race discipline, have a high maximal aerobic power output measured from an incremental test, and an ability to work at relatively high power outputs for long periods. The relationship between these characteristics and inherent physiological factors such as muscle capilliarization and muscle fibre type is complicated by inter-individual differences in selecting cadence for different race conditions. More research is needed on high-class professional riders, since they probably represent the pinnacle of natural selection for, and physiological adaptation to, endurance exercise. Recent advances in mathematical modelling and bicycle-mounted strain gauges, which can measure power directly in races, are starting to help unravel the interrelationships between the various resistive forces on the bicycle (e.g. air and rolling resistance, gravity). Interventions on rider position to optimize aerodynamics should also consider the impact on power output of the rider. All-terrain bicycle (ATB) racing is a neglected discipline in terms of the characterization of power outputs in race conditions and the modelling of the effects of the different design of bicycle frame and components on the magnitude of resistive forces. A direct application of mathematical models of cycling velocity has been in identifying optimal pacing strategies for different race conditions. Such data should, nevertheless, be considered alongside physiological optimization of power output in a race. An even distribution of power output is both physiologically and biophysically optimal for longer ( >4km) time-trials held in conditions of unvarying wind and gradient. For shorter races (e.g. a 1km time-trial), an‘all out’ effort from the start is advised to‘save’ time during the initial phase that contributes most to total race time and to optimize the contribution of kinetic energy to race velocity. From a biophysical standpoint, the optimum pacing strategy for road time-trials may involve increasing power in headwinds and uphill sections and decreasing power in tailwinds and when travelling downhill. More research, using models and direct power measurement, is needed to elucidate fully how much such a pacing strategy might save time in a real race and how much a variable power output can be tolerated by a rider. The cyclist's diet is a multifactorial issue in itself and many researchers have tried to examine aspects of cycling nutrition (e.g. timing, amount, composition) in isolation. Only recently have researchers attempted to analyse interrelationships between dietary factors (e.g. the link between pre-race and in-race dietary effects on performance). The thermal environment is a mediating factor in choice of diet, since there may be competing interests of replacing lost fluid and depleted glycogen during and after a race. Given the prevalence of stage racing in professional cycling, more research into the influence of nutrition on repeated bouts of exercise performance and training is required.     

Nutritional strategies to influence adaptations to training

This article highlights new nutritional concerns or practices that may influence the adaptation to training. The discussion is based on the assumption that the adaptation to repeated bouts of training occurs during recovery periods and that if one can train harder, the adaptation will be greater. The goal is to maximize with nutrition the recovery/adaptation that occurs in all rest periods, such that recovery before the next training session is complete. Four issues have been identified where recent scientific information will force sports nutritionists to embrace new issues and reassess old issues and, ultimately, alter the nutritional recommendations they give to athletes. These are: (1) caffeine ingestion; (2) creatine ingestion; (3) the use of intramuscular triacylglycerol (IMTG) as a fuel during exercise and the nutritional effects on IMTG repletion following exercise; and (4) the role nutrition may play in regulating the expression of genes during and after exercise training sessions. Recent findings suggest that low doses of caffeine exert significant ergogenic effects by directly affecting the central nervous system during exercise. Caffeine can cross the blood–brain barrier and antagonize the effects of adenosine, resulting in higher concentrations of stimulatory neurotransmitters. These new data strengthen the case for using low doses of caffeine during training. On the other hand, the data on the role that supplemental creatine ingestion plays in augmenting the increase in skeletal muscle mass and strength during resistance training remain equivocal. Some studies are able to demonstrate increases in muscle fibre size with creatine ingestion and some are not. The final two nutritional topics are new and have not progressed to the point that we can specifically identify strategies to enhance the adaptation to training. However, it is likely that nutritional strategies will be needed to replenish the IMTG that is used during endurance exercise. It is not presently clear whether the IMTG store is chronically reduced when engaging in daily sessions of endurance training or if this impacts negatively on the ability to train. It is also likely that the increased interest in gene and protein expression measurements will lead to nutritional strategies to optimize the adaptations that occur in skeletal muscle during and after exercise training sessions. Research in these areas in the coming years will lead to strategies designed to improve the adaptive response to training.     

Dietary supplements

For the athlete training hard, nutritional supplements are often seen as promoting adaptations to training, allowing more consistent and intensive training by promoting recovery between training sessions, reducing interruptions to training because of illness or injury, and enhancing competitive performance. Surveys show that the prevalence of supplement use is widespread among sportsmen and women, but the use of few of these products is supported by a sound research base and some may even be harmful to the athlete. Special sports foods, including energy bars and sports drinks, have a real role to play, and some protein supplements and meal replacements may also be useful in some circumstances. Where there is a demonstrated deficiency of an essential nutrient, an increased intake from food or from supplementation may help, but many athletes ignore the need for caution in supplement use and take supplements in doses that are not necessary or may even be harmful. Some supplements do offer the prospect of improved performance; these include creatine, caffeine, bicarbonate and, perhaps, a very few others. There is no evidence that prohormones such as androstenedione are effective in enhancing muscle mass or strength, and these prohormones may result in negative health consequences, as well as positive drug tests. Contamination of supplements that may cause an athlete to fail a doping test is widespread.     

Energy expenditure and dietary intake in professional football players in the Dutch Premier League: Implications for nutritional counselling

ABSTRACT

Selecting effective dietary strategies for professional football players requires comprehensive information on their energy expenditure (EE) and dietary intake. This observational study aimed to assess EE and dietary intake over a 14-day period in a representative group (n = 41) of professional football players playing in the Dutch Premier League (Eredivisie). Daily EE, as assessed by doubly labelled water, was 13.8 ± 1.5 MJ/day, representing a physical activity level (PAL) of 1.75 ± 0.13. Weighted mean energy intake (EI), as assessed by three face-to-face 24-h recalls, was 11.1 ± 2.9 MJ/day, indicating 18 ± 15% underreporting of EI. Daily EI was higher on match days (13.1 ± 4.1 MJ) compared with training (11.1 ± 3.4 MJ; P < 0.01) and rest days (10.5 ± 3.1 MJ; P < 0.001). Daily carbohydrate intake was significantly higher during match days (5.1 ± 1.7 g/kg body mass (BM)) compared with training (3.9 ± 1.5 g/kg BM; P < 0.001) and rest days (3.7 ± 1.4 g/kg BM; P < 0.001). Weighted mean protein intake was 1.7 ± 0.5 g/kg BM. Daytime distribution of protein intake was skewed, with lowest intakes at breakfast and highest at dinner. In conclusion, daily EE and PAL of professional football players are modest. Daily carbohydrate intake should be increased to maximize performance and recovery. Daily protein intake seems more than adequate, but could be distributed more evenly throughout the day.     

Effect of Including Parents in a School-Based Exercise and Nutrition Program for Children

Abstract

The purpose of this study was to examine the effect of parental involvement in a school-based program about exercise and nutrition. One fifth grade and one sixth grade class were randomly assigned to each of the three different treatment conditions, a school-and-home condition (n = 45), a school-only condition (n = 43), and a control condition (n = 44). In the school-and-home condition, the children's parents were also asked to participate in nutritional and exercise activities at home as a family “home team.” A multivariate analysis of variance on change scores was completed on the following variables: height, weight, skinfold, sit-and-reach, sit-ups, mile run, exercise knowledge, saturated fat, cholesterol, percent calories from fat, percent calories from carbohydrates, and nutrition knowledge. There was a significant difference among groups. The school-and-home and school-only groups showed significantly greater improvement than the control group but were not significantly different from each other. Univariate analyses on posttest scores indicated that the school-and-home children scored significantly higher than the control group on sit-and-reach flexibility and nutrition knowledge. The results indicate that including the family was primarily effective in facilitating children's improvements in flexibility and nutrition knowledge rather than in diet and exercise behaviors.     

施肥处理对黄瓜营养品质的影响

本试验以露地栽培的黄瓜为试材，探讨了施肥对黄瓜营养品质的影响．结果表明五种施肥处理中最佳施肥处理为半量虫粪(3750Kg／hm2)与50％NPK配施，可显著提高黄瓜中Vc、可溶性糖、可溶性Pr、果胶质含量，降低硝酸盐含量及纤维素含量，从而提高蔬菜营养品质和产量．与单施尿素处理比较，黄瓜中糖酸比增加41．09％，硝酸盐含量降低9％．     

Comparison of three instructional strategies in food and nutrition education: developing a diet plan for a diabetic case

This study examines the performance of dietitians-in-training on developing a diet plan for a diabetic patient either independently or after peer discussion. Participants (n?=?58) from an undergraduate program in food and nutrition were divided into two groups based on their prior knowledge before being randomly assigned into three conditions: (1) peer discussion with just-in-time information (JIT information), (2) peer discussion without JIT information), and (3) independent performers. The learners’ performance in the three conditions was analyzed. The results presented here describe the role of prior knowledge and JIT information across the conditions and the interaction of the two factors as well as the instructional implications of the findings.     

同老年教师谈营养与健康

本文分析老教师保健方面的薄弱环节 ,并提出针对性的有力措施 ,力求在高校师生保健方面减少盲区 ,实现全民健身     

土壤吸收力问题的提出及其在农业化学的理论与实践中的价值

土壤吸收力问题是我们近十多年来在农业化学理论与实践上注意到的一个新的问题。本文汇报我们在土壤吸收力比较研究方法与某些水稻土吸收力比较研究上所做的工作。目前这方面的工作国内外开展均不多,研究表明,土壤吸收力问题如得到充分的研究与应用,必将能够大大地丰富我们因地制宜的施肥理论和实践,在农业化学的教学、科研、生产上均有重要的理论价值和实践意义。是化学工作者服务于农学的一个重要方面。