 |
 |
 |
 |
 | |
| ||
 |
|
 |
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
 ResourcesNutritionResearchFuelling YOURSportHot TopicsSupplementsQ&A PageMore About UsNutritionHome
|
Peak
Performance: training and nutritional strategies for sport Chapter 11: Changing body size and
shape 11 Changing body size and shape
11
Changing body size and shape '"There is a huge difference between fifth and first." With the advice of his trainer Dr Cecchini, Riis has completely changed his approach. Dr Cecchini sent the cyclist to ride up a mountain near his home in Tuscany carrying five kilograms of lead, to illustrate the improvement he could expect if he lost weight. The lesson hit home: in the past 6 years Riis has lost 8.5 kg and is now just "skin and bone".'
'I feel good, and at my current weight, I feel I have never trained better . . . But, my coach wants me (to lose weight) . . . because that's what I weighed last year when I set the world record . . . He reminds me of my weight a lot, and I have to train differently than I would like . . . After our afternoon workout, which lasts about 2 hours, most people on the team work out in the weight room. This is what I feel I need. Instead, I have to run to lose the weight.'
'I ran in one Great Britain team which consisted of six runners and a reserve. Of these seven, I know that as many as five were suffering from some kind of eating disorder, including me.'
Athletes come in a range of sizes and shapes that almost define the boundaries of the human body. They range from the tallest basketball player, to the most petite gymnast, and the sheer bulk of the sumo wrestler. On the other hand, muscularity can stretch from the bursting definition of the body builder to the almost wasted upper body of the distance runner. Physique and body composition play a vital role in the performance of many sports. Elite athletes typically show the characteristics that are suited to performance in their sport. This is a result of inherited features that first directed the athlete to an activity that they could do well in, as well as changes achieved through the conditioning effect of training. Some athletes naturally arrive at a physique that is ideal for top performance. Others may need to work on the features that can be moulded—body fatness and muscle mass. HOW MUCH DOES BODY SIZE AND FATNESS AFFECT SPORTS PERFORMANCE? In some sports, particularly those based on skill (eg golf, archery and shooting), performance is largely independent of body fatness. Both selection and conditioning factors tend to allow higher body fat levels in these athletes. In fact, top performers in these sports may actually be overweight (or over-fat) by community standards. At the other end of the spectrum there are sports in which a low body mass, and in particular a low body fat level, are a distinct advantage to performance. The advantages of a low body fat level include physical and mechanical gains due to an increased power to mass ratio, or simply to a reduction in the 'dead weight' that must be moved by the athlete. This is a particular advantage where the athlete has to transport their own body mass over long distances (eg distance runners, triathletes, road cyclists) or to move vertically against greater gravity effects (gymnasts, jumpers, basketball players, or cyclists riding a hilly course). Higher body fat levels are seen in endurance athletes, most notably swimmers, who perform in a weight-supported sport. A high 'power to mass' ratio plays a role in 'stop–start' sports by increasing speed, agility and the ability to change direction quickly. In some team sports, players in mobile field positions or with a mobile playing style are often observed to have lower body fat levels than their team-mates. On the other hand, particularly in sports involving physical contact, a higher body fat level may be less problematic for 'set position' players. A certain level of body fat may help to protect body organs against injury from body contact, and to provide bulk against tackling. Nevertheless, a high body mass should be achieved principally through an increase in muscle mass. A small body size per se is an advantage in distance events, especially in hot conditions where a greater surface area to volume ratio enhances heat dissipation. It also helps in acrobatic sports such as diving and gymnastics to assist the athlete to rotate or spin their entire body over a smaller area or in a faster time. Finally, in some sports there is an aesthetic component to performance. A slim, petite figure is currently deemed de rigueur in gymnastics, diving, figure skating and other subjectively judged sports. Extreme leanness is an obsession in body building, to allow muscularity to be maximally defined. A number of studies of elite athletes have identified profiles of body fat and muscularity that confirm these principles. And in some sports, across a group of athletes of differing abilities or disciplines, there is a statistical relationship between performance and body fatness: a lower body fat level is related to better performance. These data help to promote the interest, and sometimes obsession, of various groups of athletes to achieve minimal body fat levels. But there are some limitations of these types of studies that are not taken into account by individual athletes. First, it is true that among heterogeneous groups of athletes, individual factors such as body fat levels or VO2max are predictive of performance. However, among a group of top performers or athletes with similar ability, the importance of these factors alone disappears. Instead, a combination of factors begin to play interconnected roles. Even when there is an association between body fat and performance, this does not hold true for individual cases. Among a group it is likely that some of the best performers do not conform to the stereotyped lean model, whereas some athletes with very low body fat levels are not highly gifted. Most importantly, these studies are cross-sectional rather than longitudinal. In other words, there are no good studies in which the performance of individual athletes have been monitored across a range of body fat levels. These studies would be necessary to confirm the absolute value of a certain, particularly low, level of body fatness. It is likely that if such studies were undertaken, they might confirm general tendencies towards benefits of size and body fat in some sports. But they might also confirm the observation of sports nutrition practitioners, that each athlete has a 'natural' body shape, and that they perform best within a range of this. Trying to achieve a stereotypical 'ideal' must always be balanced against the cost and disadvantages of fighting against their natural body fat levels. A separate story of size, shape and performance involves sports with specific weight limits for competition. In sports such as boxing, wrestling, judo, light-weight rowing and weight lifting, weight divisions (commonly ranging from two to ten) have been set with the intention of matching competitors or opponents of similar size and strength. This is proposed to allow fair and equal competition. In horse racing, the horse is similarly handicapped in that they carry a certain weight, which then sets an upper weight limit for the jockey. Of course, athletes in these sports all want to compete in a lower weight class than they really deserve to be in, believing that this will mean competing against a smaller, lighter opponent. 'Making weight', the practice of reducing body mass to meet the competition weight limit, will be discussed later. METHODS FOR ASSESSING BODY FAT AND MUSCLE LEVELS Most people have some interest in assessing or monitoring their size and shape, and the bathroom or gym scales are usually where they first turn for information. This is at best a crude assessment technique, and in the case of athletes especially irrelevant, since such measures do not distinguish between body fat and lean body mass. This distinction is important in determining sports performance, and the levels of each tissue vary considerably among athletes. Apart from those athletes who need to weigh-in to meet a competition limit, the only other justified use of scales in sport is to monitor acute changes in body mass over the duration of an exercise session, or from day to day, to reflect body fluid losses (see Chapters 13, 14 and 15). There are a number of techniques that attempt to assess body fat levels and muscle mass, or lean body mass. Some techniques use expensive equipment or require experts to make the measurements. These include underwater weighing (densitometry) and DEXA (dual X-ray absorptiometry). These are usually impractical for everyday use by athletes and are typically used for research purposes only. Techniques such as TOBEC (total body electrical conductivity), bioelectrical impedance (eg 'Futrex') and air displacement (eg 'Bod Pod') are also available. However, more work is needed to ensure that the results obtained by these methods are valid for athletic populations. Often mathematical equations are involved in the final calculations, or assumptions are made in the method that are valid for sedentary populations but may not apply to well-trained athletes. Kinanthropometry involves the measurement of body girths, circumferences and skinfold fat thicknesses to describe physique. It offers the advantage of being portable and cheap—a technique that can travel with the athlete into the field. However, accurate readings and interpretation of the results require considerable skill. Skinfold fat readings have been popular for many years as a method of estimating total body fat. There are many limitations to this technique, especially when percentage body fat is estimated using mathematical equations generated from general populations or even from general groups of athletes. Such equations are only accurate when they are derived from, and then used for, a specific group. This is important if accurate information is needed. An alternative to generating percentage body fat information is to work with the skinfold measurements themselves. In many countries, athletes have body fat measurements presented as a 'sum of skinfolds'. This represents the sum of the individual skinfold fat thicknesses from a number of specific sites (usually seven), taken according to a standardised procedure. Whatever method is used to generate information about body fatness or physique for use by an athlete, the following guidelines should be met:
SETTING IDEAL BODY FAT LEVELS An athlete's ideal body fat level is an individual characteristic. Generally, the 'norms' for a specific group of elite athletes can provide a guideline to the range of levels that are compatible with good performances. But this information should not be used for making strict prescriptions or setting narrow standards that one or all athletes must adhere to. Another mistake made by some athletes and coaches is to set their sights on the body fat levels of a certain elite performer, or on minimum body fat levels per se. For a start, this makes the assumption that the observed body fat levels of elite athletes or a certain athlete are optimal. In fact, they may not be. Secondly, it fails to account for individuality. An athlete's ideal level of body fat and body mass are specific to them, and can really only be judged by 'trial and error', over a period of time. They must encompass a range of health, nutrition and sporting issues. Or more specifically, they must achieve the following goals:
In practice, the concept of ideal may change over an athlete's career, and may vary according to the time of the year and the athlete's immediate goals. The clever athlete works within a range of 'ideal' and may fine-tune for important competitions. The dangers of very low body fat levels If all athletes complied with the simple laws of physics, it might be easy to calculate an ideal power to weight ratio, or body fat level, for a given sporting situation. And in some cases, the lower the 'dead weight', the better the performance. However, humans carry body fat for a number of reasons, including to carry on the inherited characteristics of their parents, to provide insulation and protection for their body and its important organs, to preserve body hormone levels, and to provide an energy reserve for the 'lean times'. This last issue is especially relevant to females, whose gender is programmed to carry 'hard to shift' body fat on their buttocks and legs. This may not suit sports coaches, but it is part of Mother Nature's plan to ensure that females can support the energy cost of pregnancy and breastfeeding, come what may. Some racial groups and individuals naturally carry low levels of body fat, or can achieve these without paying a substantial penalty. And some athletes vary their body fat over a season so that very low levels are achieved only for a specific and short time. However, in many cases where an athlete tries to adopt a very low body fat level, or a level that seems unnatural for their inherited body characteristics, problems occur. These problems remain mostly speculative, but include loss of body warmth and protection, as well as disturbances to hormonal balance and the immune system. Some of the disadvantages arise directly from the methods that the athlete used to try to lose body fat—severe energy or nutrient restriction, excessive training loads, or disordered eating behaviours. Typically, there is an immediate improvement in exercise performance accompanying the loss of body fat. However, after a honeymoon period, chronic problems gradually emerge. The athlete finds that they are often sick, or eventually suffers a consequence of disturbed menstrual status (see below). Unfortunately, it is hard to persuade many athletes to overturn what was initially a successful strategy. MAKING WEIGHT The typical practice in weight classification sports is to compete in a division that is substantially lower than normal training weight or the athlete's 'natural' level of body mass and body fat. Some of these athletes reduce their weight by minimising body fat levels through food restriction and extra training. Most athletes 'make weight' over the last days prior to their competition by dehydrating and restricting food. Some athletes need to use a combination of these methods in order to weigh in on target. In the case of body builders, similar techniques are used to 'cut up' so that the muscle and vascularity appear defined against minimum body fat levels and dehydrated skin tissue. The rapid weight-making techniques reduce the athlete's body mass principally by reducing the mass of body fluid levels, food in the gastrointestinal tract, and muscle fuel stores. Some loss of muscle protein may also occur. Techniques include:
Making weight has been studied extensively in college wrestlers in the United States, where these athletes compete over a season of weekly competitions, in teams with up to thirteen different weight classes. Dr Suzanne Nelson Steen and Professor Kelly Brownell are two of the researchers who have documented the pattern of weekly cycling of weight loss and regain, as the wrestlers cut to a lower weight division to gain a perceived advantage in strength and leverage over a smaller opponent. They observed among college wrestlers who were trying to qualify for the National Collegiate Athletic Association (NCAA) competition that 80% of the subjects were always dieting during the season and that they were often or always preoccupied with food. The typical (median) weight loss each week was 6.8 kg, and on average the wrestler was required to make weight fifteen times a season. Some wrestlers reported losing up to 20 kg in one cycle, and to having to make weight 60 times in that season. They reported using several practices from the list above among their rapid weight-loss techniques. Clearly none were striving for a natural body fat level, since their post-season weight gain was 7 kg, similar to the level that they were continually trying to shed. Similar practices have been observed in light-weight rowers, jockeys, weight lifters and other weight-making athletes, although the situations differ slightly. The frequency of making weight varies, from weekly in sports such as horse racing and wrestling, to once or twice a year as in the case of professional boxers who prepare only for specific fights. In most weight classification sports, athletes are required to weigh in at a specified time prior to their event, ranging from one hour to the day before. Jockeys are unusual in that they must certify their weight after their performance (i.e. after the ride) and may choose to ride at a number of weight handicaps on the same day's program. However, in all other sports there is a variable period between the weigh-in and competition during which the athlete can attempt to recover from the effects of their weight-making strategies. Unfortunately, most times, full or even significant recovery is not possible due to inadequate time, or due to the gastrointestinal limits on food and fluid intake immediately prior to exercise (see Chapter 14 for issues of recovery). Clearly there are a number of disadvantages associated with severe and rapid weight-loss techniques. In the short term, the athlete is challenged by moderate to severe levels of dehydration—on some occasions in the order of 5–10% of body mass. Depleted glycogen stores in the muscle and liver arise from low carbohydrate intake, as well as utilisation during the exercise undertaken to produce sweat loss. These factors provide a challenge to the performance of exercise (see Chapters 12 and 13). In the long term, the athlete faces issues of protein loss, inadequate nutrient intake due to erratic food patterns, and changes to hormonal and metabolic function. In some cases this may be superimposed on the problems associated with restricted energy intake and unnaturally low body fat levels. The effect on psychology cannot be underestimated. Many studies comment on the increased feelings of fatigue, anger, anxiety and depression associated with continued food stress and repeated cycles of making weight. Although in some combative sports this is rationalised as a positive factor in competition aggression, it is more likely to detract and distract from good performances. It is easy to condemn weight-making practices—even if only on the grounds that they try to 'cheat' the original goal of matching opponents of similar capability. But from the performance view, it is not as black and white as nutritionists and scientists outside these sports might first think. There are a number of arguments from the inside of these sports that must be noted:
Nevertheless, the extreme levels and techniques of current weight-making practices cannot be condoned. They persist despite the continued attention of medical, educational and research bodies, because they have been internalised and even romanticised within the cultures of the sports. The issues are too specific to the individual athlete and to their sport to provide general strategies that are of use. Instead, it is recommended that athletes in weight-making sports receive individual expert advice about determining their optimal competition weight division and achieving it with minimal compromise to their success or health. Meanwhile, the governing bodies and expert panels in these sports might consider that education strategies are ineffective without reinforcement from appropriate regulations and rule changes. For example, in wrestling, at least one state organisation in the United States has proposed or undertaken rule modifications to discourage severe weight-making practices. These include the certification of athletes at a weight division at the beginning of a season, measuring the level of hydration in competitors before the event, distributing weight divisions to better match the typical distribution of body mass in the sports population, and making the weigh-in closer to the event to prevent the notion of post-weigh-in recovery. Such strategies may be necessary to enforce safer athlete practice. LOSING BODY FAT Many people might think it strange that a book on sports nutrition needs to contain a section on fat loss. Shouldn't regular exercise keep an athlete in trim? However, being overfat, whether real or imaginary, is the major dietary concern of athletes. Female athletes suffer typical female fears and misconceptions about their body image, regardless of their sporting excellence. The issues of body fatness and performance that have been previously discussed are an additional angle, and occupational pressure, for both sexes. Athletes may have a number of valid reasons for intentionally promoting a loss of body fat. Sometimes this is to augment their genetics and training to arrive at a lower body fat level that may promote better performance. Athletes in 'aesthetic sports' experience a particular mismatch between their body fat goals and their energy expenditure. In these sports, low body fat levels are regarded as necessary for optimal performance, yet these athletes are not assisted to achieve these levels through their typical training activities. Although they are committed to long hours of training, these primarily involve skill, flexibility, strength and short bursts of high-intensity work. Another common case is the athlete who has gained body fat and may desire to regain their original ideal level. This can occur when there is a sudden change in the factors that determine an athlete's energy balance. For example, when an athlete suffers an injury or comes to the end of their season, they usually incur a dramatic reduction in activity levels. It is hard to respond immediately with an equal reduction in food energy intake. In fact, this is a time when many athletes are tempted to eat more. The result is a rapid gain of body fat. Athletes who are faced with a new or changing lifestyle often increase their food intake without realising the change in energy balance. This includes the travelling athlete who eats out of 'hotels and suitcases', the young athlete who leaves home to take up a sporting contract or scholarship, or the athlete who moves into an 'all you can eat' dining hall in an athletes village. Of course, some athletes in skill-based sports have reasons unrelated to sports for losing body fat—such as health, comfort or appearance. The key to loss of body fat is to achieve a long-term scenario where energy intake is lower than energy output. Guidelines are provided in the panel on the following pages. GAINING MUSCLE MASS In many sports, a high level of muscle mass and strength are important factors in performance. Methods to gain these have intrigued the sports nutrition world and muscle industry alike for most of this century. The key ingredients for success are:
Despite the interest in protein and muscle growth (see the panel on the following pages), the most important nutritional factor required for an increase in muscle mass is energy. Although protein is laid down to form muscle cells and other cells which support the new tissue, this accounts for only a small amount each day. It is the energy cost of building new tissue, and the cost of doing the exercise to stimulate its growth, that are most important. Inadequate amounts of carbohydrate to fuel the training, and inadequate energy intake, will both impair the rate of increase in lean body mass. Although it is understood that additional amounts of some minerals and other micronutrients are needed in the manufacture and support of new tissue, there are no systematic studies to quantify these additional requirements. It is generally deemed that a high-energy diet sufficient to promote the gain of lean body mass will contain additional levels of micronutrients. Further research is necessary to define the nutrient intakes that optimise gain of muscle mass. In the meantime, the most practical issue is to help athletes increase their total energy intake to a positive balance. This can be difficult for athletes who are already high energy consumers. The battle is against gastrointestinal comfort and finding time to consume kilojoules in an already overcommitted timetable. Guidelines are summarised in the panel on the following pages. EATING DISORDERS AND DISORDERED EATING There are many reports of athletes who set unrealistic fat loss goals; either seeking to achieve an unnecessarily low or harmful body weight or body fat level or trying to achieve it in an unacceptably rapid time. The pressure to set these goals comes from a number of sources. Athletes by nature are obsessive. The same personal characteristics that encourage good performance in athletes—perfectionism, dedication, 'tunnel vision', ability to deprive themselves—may lead them to overfocus on body fatness. Parents, peers, trainers and coaches are guilty of providing additional pressure and incorrect advice. In some cases of high-profile athletes, their physique (or perceived physique) may become public property via concentrated media attention. Simply being female carries a risk of being dissatisfied with one's body image. Although there is some criticism of the methodology used in making diagnoses of 'eating disorders', many studies report a high prevalence of disordered eating behaviour and body image among athletes. More specifically, they observe a higher prevalence of these problems in female athletes and those involved in sports in which weight and body fat is an issue, than in sedentary controls or among sports in which weight/fatness is not a performance issue. The exact extent of this is unknown, as is the nature of the link with sport. It is likely that sport provides a permissive environment for the development of disorders in those who are prone. While some individuals obsessed with body fat seem capable of stopping disordered food and exercise behaviours once they are removed from the environment (eg at the end of a season or when they retire from sport), for others these behaviours become the end, rather than a means to an end. In other words, they lose control. Equally, there may be cases where individuals with existing eating disorders turn to sport because it camouflages and supports behaviour such as food restriction, low body fat levels and high energy expenditure. In fact, for a while it may promote good athletic performance! Many sports are currently examining ways to reduce the pressured environment that may contribute to the development of eating disorders, and to develop effective and early treatment for athletes who develop disordered eating and body image problems. Eating disorders in male athletes are also recognised. The prevalence of cases that meet the full diagnostic criteria of anorexia nervosa or bulimia nervosa as set by psychiatric bodies remains low in sport. Instead there are a larger number of athletes who fit within the spectrum of eating behaviour between 'normal' and 'clinical eating disorder', but lie closer to the latter end. 'Anorexia athletica' or 'disordered eating' are terms sometimes given to describe these situations. The athlete is obsessed and dissatisfied with their body weight and fat levels, is driven to undertake unhealthy eating and exercise patterns while striving for an unhealthy or unnatural body fat level, and will persist with these behaviours despite the occurrence of obvious side-effects and problems. Indeed, this may be seen as an occupational hazard or a common personality trait of athletes competing at elite levels—in other words, it is 'normal' or necessary. However typical or common it appears, the side-effects must be recognised and minimised. More importantly, it is also a common occurrence at non-elite levels where it cannot be justified as one of the sacrifices that is undertaken for the reward and glory of excellence. A striking feature of many dietary surveys is that female athletes often report energy intakes that seem too low to be true. Their kilojoule intake would seem able to sustain only their basal metabolic requirements without the added energy cost of a heavy training program. Some people have suggested that this 'energy discrepancy' is due to metabolic efficiency—that these athletes have lower basal metabolic requirements or have somehow lowered the energy expenditure of their training and lifestyle activities. Maybe this is true for certain individuals. There is some evidence and a believable hypothesis that the body will try to defend its 'natural' or critical lower level of body fat, particularly the sensitive body fat stores on the thighs and buttocks of females, in this way. But the methodology of dietary survey work is famous for being inexact. It is well-known that people under-report their food intake when keeping food records. Either they underestimate the portions of food that they are eating and forget to record everything that was consumed, or they eat less than usual during the period of recording. Everyone does it, but it is possible that those who are more 'body conscious' do it to an even greater extent, thus exaggerating the extent of the energy discrepancy. A recent energy balance study on elite female runners by Dr Jeffrey Edwards and colleagues from Indiana University has provided data to support this. They measured the match between energy intake (estimated from seven-day food records) and energy expenditure over the same period (estimated using the double-labelled water technique). They found that mean daily intake only accounted for 70% of expenditure (8.5 MJ versus 12.5 MJ), yet none of the subjects lost body fat or weight over this time. This could indicate that the subjects were metabolically efficient and the double-labelled water technique overestimated their real expenditure. But an anomaly in the group data stood out. There was an inverse relationship between body mass and the size of the energy discrepancy. That is, the heavier the athlete, the less they ate compared to their estimated energy expenditure. These athletes also had the poorest body images. It seems that the more stressed an athlete is about their body fat and body size, the more they are likely to underreport their intake—sometimes by as much as 50% of their intake. Evidence of an 'energy drain' in an athlete may be important. The athlete who eats less than they 'deserve' or struggles to keep low body fat levels on a restricted intake may directly encounter some hormonal and metabolic side-effects from their efforts. But equally, this may be a warning sign that the athlete has a disturbed body image, poor recognition of their real dietary intake, and a tendency to cycle between dietary restriction and dietary excess. The combination of metabolic stress, nutritional stress and psychological stress can lead to real problems. The existence of the 'female athlete triad' has recently been proposed to publicise the cluster of medical/nutritional problems that are frequently found together in female athletes. These are:
These problems are of considerable consequence to the health and performance of the athlete. The development of strategic programs to minimise risk factors for their development, and to intervene with early and effective treatment, deserves support. However, there is some danger in turning the situation into a neat triangle, with the idea that simple solutions can be found. Each of these disorders is complex, with a multitude of causes that seem to vary in importance according to the individual athlete. And they can exist alone. One doesn't necessarily lead to another. Furthermore, male athletes may also suffer from two of the three elements of the triad. The issue of menstrual disturbances in female athletes has received much attention in the last decade. It is now realised that numerous factors predispose to this, including:
Each athlete seems to have a critical threshold for each of these factors. For example, some athletes continue to have regular periods while training hard and having very low body fat levels. It is important to recognise the individuality of the response to these factors. A common outcome of menstrual irregularity is the decrease in level of reproductive hormones, particularly estrogen. Since estrogen levels play an influential role in maintenance of bone health, it has been easy to demonstrate a general loss of bone density, or failure to gain optimal bone deposition, in female athletes with menstrual disturbances. This condition, called osteopaenia, is also multi-factorial with risk factors including race, small frame size, low calcium intake and inadequate bone loading. Interestingly, gymnasts are a group at high risk of impaired menstrual function—usually due to a failure to establish menses in the first place. However, their training appears to provide strong mechanical loading stress on the bone which compensates for a low estrogen environment. By contrast, amenorrhoeic female runners generally present with low bone density. Low bone density is of concern to athletes in that it may predispose them to the development of stress fractures. And in the long term it may dramatically increase the risk and the earlier development of osteoporosis—the condition of fragile bone density that occurs with the ageing process. Athletes are generally more concerned with the here and now of their bone health. Again, the picture of stress fractures is complex. Low bone density is a plausible risk factor, but it interacts with other factors directly related to the impact on the bone. These include the amount and the change in training, cushioning provided by shoes, the surface on which training is undertaken, and the biomechanics of footstrike. Clearly, the prevention and management of each of these issues is delicate and complicated. Individual attention from the appropriate experts is recommended. Calcium intake and healthy bones Bone is a living tissue that is continually breaking down and reforming. Sports science now recognises that hormonal status, particularly in females, plays a major role in the balance of bone remodelling. Nevertheless, a low calcium intake is one of the factors that may be involved in the development of osteopaenia. Adequate calcium intake helps to ensure gain in bone mass during adolescence and early adult life, and to minimise the bone loss that occurs with ageing. Recommended dietary intakes for calcium are set to provide additional calcium during times of increased need, such as growth, pregnancy and breastfeeding. It may be useful to provide higher calcium intakes to females with low estrogen levels to reduce the calcium drain. Therefore, an increased target is suggested for post-menopausal women and for athletes with absent or irregular periods. Recommended daily intakes for calcium are summarised in Table 11.1.
In a typical Western diet, dairy foods provide 60–75% of total calcium intake. Athletes who fail to consume enough or any dairy foods are at risk of inadequate calcium intake, unless alternative sources can be found. Low-energy consumers are one such group. Meanwhile, dairy products have received undeserved criticism and have been unnecessarily avoided by groups worried about fat and cholesterol intake, 'allergies' or 'mucous formation'. While some vegans avoid dairy products for ethical or cultural reasons, there are few other causes to delete these calcium-rich choices from their eating plans. Strategies for achieving a calcium intake target within the athlete's total nutritional goals are summarised in the panel on the following pages.
see our Resources - Books page for ordering details
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
 |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
The Department of Sports Nutrition is a program of the
Australian Institute of Sport General enquires can be emailed to: aisnutrition@ausport.gov.au Copyright
© Australian Sports Commission
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
