Sports that need to lose weight can be basically divided into two categories: one is weightlifting and fighting, such as wrestling, boxing, judo, taekwondo, etc. Athletes lose weight in order to participate in the heavyweight that is conducive to their outstanding performance; The other is high-skilled events, such as gymnastics, rhythmic gymnastics, trampoline, acrobatics, diving, figure skating and so on. In order to gain biomechanical advantages, athletes lose weight by making movements more difficult, easier to complete and more elegant. The process of losing weight is generally carried out during the pre-competition training period. Pre-competition training is one of the important links in sports training, and a good pre-competition training plan can make athletes in the best competitive state during the competition. The sports that need to lose weight are different from other sports in the arrangement of pre-competition training plan. The biggest difference is that athletes in these sports must meet the requirements of losing weight during pre-competition training. Therefore, losing weight has become one of the important contents of athletes' pre-competition training plan. This kind of pre-competition training plan requires different time, training content and training means from the traditional pre-competition training, which is called pre-competition weight loss training. It is always a contradiction to lose weight and maintain good physical fitness before competition, and it is also a difficult problem in international competitive sports training. At present, both at home and abroad are discussing how to achieve the ideal weight in pre-competition training, and how to minimize the impact of weight loss on the maintenance of athletes' training volume and intensity and the best performance in the competition. However, in sports practice, there are many differences in the establishment of ideal weight, the appropriate weight loss range and the choice of weight loss methods. In addition, researchers have done a lot of research on the influence of weight loss on athletes' physiological function and sports ability, and the conclusions are not the same. This paper summarizes the establishment of athletes' ideal weight, the physiological and biochemical theories and methods of weight loss, the suitable range of weight loss and its influence on athletes' physiological function and sports ability, the problems existing in the process of weight loss, and the principles and measures of reasonable weight loss.
1 Physiological and biochemical theory of weight loss
1. 1 weight and body composition
Weight is an index reflecting the development of human bones and muscles and the degree of obesity, and it is also an index reflecting human body shape. Physiologically, weight refers to the total weight of all parts of the body. Body composition refers to the total composition of human tissues and organs, and its physiological composition model consists of body fat (fat weight) and fat-free weight (lean weight), that is, body weight = fat-free weight+body fat. Among them, the fat-free weight includes non-fat tissues such as muscles, bones, organs, body fluids and skin. Body composition is usually expressed by body fat percentage, that is, body fat percentage = body fat weight ×l00%. The chemical composition model of body composition consists of sugar, fat, protein, water, inorganic salts and vitamins. The change of human body weight must be expressed by the concept of body composition, which is objective and scientific.
Relationship between body composition and athletic ability.
Exercise ability is positively correlated with human body's fat-free weight, which is closely related to sports performance in many sports. Therefore, increasing the proportion of fat-free weight of athletes will improve and enhance their sports potential. Although adipose tissue has the functions of energy supply, heat preservation and buffering, the excess fat in the body is considered as "dead", which will affect the development of human strength, speed and endurance and increase the consumption of oxygen and energy during exercise. For most athletes who need to lose weight, they don't need to use body fat in the competition except the fat needed to ensure the normal physiological function of the body. So in most cases, fat will limit the competitive level of athletes. Li Yunxia and others investigated the body composition of the weightlifters who participated in the competition after losing weight quickly, and found that among the male athletes of the same level, the athletes with better performance in the competition had lower body fat percentage, heavier fat-free weight and higher body fluid content. Some athletes sometimes use unsafe measures to lose weight, such as diuretics, dehydrating laxatives, self-vomiting, appetite suppressants and complete fasting. However, judging from the influence on sports performance, it is advisable to restrict diet moderately. Zachwieja et al. found that moderate food restriction for two weeks made people lose weight, of which the fat-free weight accounted for 665,438+0%, but the maximum muscle strength remained unchanged or even increased, and muscle endurance and anaerobic working ability increased [8]. Fogelholm et al reported that when the slow weight loss is less than or equal to 5%, limiting energy intake has little effect on the athletic ability of experienced athletes [10].
2. 1.2 Increase the amount of exercise
The negative balance of heat energy not only reduces the intake of heat energy, but also increases the heat energy consumption of the body. Exercise provides a way to increase energy consumption, which can help to adjust the energy balance when losing weight. At least 30 minutes of moderate-intensity aerobic exercise every day is helpful to lose weight, and more exercise is better for losing weight. Resistance exercise has little effect on overall weight loss, but it has a good effect on improving body composition. Research shows that under the same energy deficit condition, limiting diet is more effective for losing weight, while increasing exercise is more effective for reducing body fat and maintaining fat-free weight. In addition, increasing exercise and restricting diet have a good effect on blood lipid components [1 1]. It is suggested that the part of increasing exercise should be included in the slow weight loss plan. Increasing exercise is an important part of slow weight loss. A large number of studies show that regular exercise is beneficial to lose weight. Aerobic exercise can directly affect energy balance, promote fat decomposition and energy supply, and reduce body fat; Resistance exercise stimulates neuroendocrine system, promotes muscle protein synthesis, and helps to maintain fat-free body weight. At the same time, by increasing basal metabolic rate and increasing fat oxidation, it has a certain effect on weight loss [12, 13]. Combining aerobic exercise with strength exercise, the overall effect is to improve body composition, reduce body fat percentage, and keep the fat-free weight unchanged or increase, which is the first choice for weight control and maintenance.
Athletes should pay attention to the following factors when carrying out slow weight loss exercise: 1) Choose suitable sports. First, aerobic exercise exercises physical strength and endurance, such as long-distance running, jogging, cycling, swimming, etc. Second, resistance training aimed at training muscle strength and endurance; Third, stretching exercises at the time of preparing and ending activities. 2) Exercise time, one day or one exercise time should reach more than 30min. 3) Exercise intensity. Generally speaking, the intensity of aerobic exercise is 60% ~ 70% v.o2max.. 4) Exercise frequency: Ideally, practice every day, at least 3~4 times a week.
When arranging slow weight-loss exercises, it is more important to deal with the relationship with pre-competition training so that slow weight-loss exercises do not affect the skills and tactics of pre-competition training. Reasonable arrangements are feasible, such as other forms of less intense exercise during training or competition, which can not only lose weight, but also help the body recover as soon as possible. If you do some technical decomposition exercises, relax skipping, empty hitting, jogging and so on. You will lose some weight without losing too much energy. In addition, it should be noted that too much low-intensity and long-term slow weight-loss exercise will easily cause mental fatigue of athletes, and will also affect their explosive power and speed of action, which will have side effects on special techniques. So as the competition approaches, we should gradually reduce this practice.
2. 1.3 Restrict diet and increase exercise
For all the best slow weight loss programs, it should be to selectively consume body fat while keeping the fat-free weight unchanged. For athletes, another problem is to maintain their athletic ability. Losing weight only through energy restriction usually leads to a considerable amount of fat-free weight loss, but aerobic exercise usually reduces this loss. In the case of limited energy intake, resistance exercise can prevent fat-free weight loss and even increase muscle weight. Research shows that during the period of limiting energy intake, athletes' aerobic capacity may be damaged and their muscle function may be poor. Increasing exercise while limiting energy intake can alleviate these negative effects on sports ability. Sufficient intensity and amount of aerobic exercise can improve aerobic exercise ability even in the period of strictly limiting energy intake, while resistance exercise can increase muscle volume and strength while losing weight [14]. The combination of increasing exercise and restricting diet can relax the restriction on dietary energy intake, avoid the adverse consequences of fat-free weight loss caused by simply restricting diet, and retain the advantages of exercise to lose weight. Combining the two, supplemented by reasonable diet and nutrition, is exercise.
The first choice for slow weight loss.
Bryner et al. reported that using a low-calorie diet to lose weight slowly led to fat-free weight loss. The weight loss effect of low-calorie diet plus aerobic exercise is obviously higher than that of low-calorie diet plus resistance exercise, but the fat-free weight loss effect of the former is obvious, while that of the latter is not obvious [9]. Kraemer et al reported that limiting diet combined with aerobic and resistance exercise during slow weight loss can prevent the decline of fat-free weight and muscle working ability, and increase the maximum strength and oxygen uptake. Compared with food restriction combined with aerobic exercise, food restriction combined with aerobic exercise and resistance exercise can prevent the loss of fat-free weight [15]. Increasing exercise combined with diet restriction and slow weight loss will also have a certain impact on sports ability. Maffulli reported that when the athletes lost about 8% of their weight after 22 days of strenuous exercise and eating low-calorie food, although the athletes maintained the maximum oxygen uptake, anaerobic threshold and maximum isometric intensity before slowly losing weight (these indicators were expressed by relative weight values, and they increased), the isometric endurance and short-time sprint ability decreased by 7% and 13%[ 16] respectively. Therefore, in most cases, slow weight loss should be done within a period of time before the competition (generally within 1~ 1.5 months according to the weight loss), by moderately restricting diet and moderately increasing exercise, including aerobic exercise and resistance exercise, and the weekly weight loss rate should not exceed one's own weight.
4%。
6 1 cooperate with exercise, sweat at high temperature, water loss, and the main component of loss is water. Some unsafe measures to lose weight quickly, such as using diuretics, dehydrating laxatives, self-vomiting, taking appetite suppressants, fasting completely, etc.
And so on are sometimes used to lose weight quickly [6]. Fast weight loss is generally a measure taken by athletes participating in the project according to their own weight level, but it is generally not suitable or necessary for athletes who do not have the weight level requirements after slow weight loss.
2.2. 1 Sweating and dehydration
Water occupies a considerable proportion in the human body. Sweating to excrete water from the body can quickly achieve the goal of losing weight. There are two main ways for athletes to sweat: 1) wearing airtight clothes made of rubber or plastic (that is, weight-loss clothes) for heavy exercise training (mainly physical training such as running) to sweat; 2) Sweating in high greenhouse, sauna and steam bath. Both of these sweating methods have a certain rapid weight loss effect, which is a remedy for athletes whose pre-competition weight is slightly higher than the specified heavyweight. Greiwe et al. reported that after losing weight in sauna for 3.5h, the maximum isometric strength and endurance of the body did not decrease [17]. However, sweating can only reduce water in the body, but not body fat. Losing weight is only urgent and temporary, and you can't sweat a lot in a short time, otherwise it will cause water shortage and electrolyte disorder in your body, affect your body's function and reduce your exercise ability. Webster et al. reported that athletes lost an average of 3.3kg (4.9% of their body weight) by wearing rubber weight-loss suits within 1.2 hours before the competition. Rapid weight loss reduces the strength of athletes' upper limbs, the working ability under anaerobic power and dehydration, the threshold speed and maximum speed of lactic acid, the maximum oxygen uptake and the time from exercise to fatigue [65,438+0.8]. Caldwell et al. reported that the adverse effect of sauna sweating and fast weight loss on aerobic capacity is more obvious than that of exercise, and the harm of fast weight loss is positively correlated with the rate of fast weight loss [19]. It is also reported that rapid weight loss through sweating and dehydration in sauna has an impact on athletes' sports ability.
There are gender differences, which have no effect on the anaerobic exercise ability of male athletes, but make the anaerobic exercise ability of female athletes decline [20].
2.2.2 Strictly restrict diet and drinking water.
Dramatically restricting diet and drinking water can quickly reduce weight. A person can lose weight 1.5kg by fasting completely for one day, in which water accounts for 1kg[2 1]. Chen et al. reported that weightlifters lose weight quickly mainly by strictly limiting their diet. Usually, the heat energy intake of athletes during the pre-competition weight loss period only accounts for 65,438+00% ~ 65,438+05% of the usual heat energy intake, and even the heat energy required for basic metabolism cannot be met [22]. Although some studies show that severe restriction of diet and drinking water does not always lead to the decline of athletes' athletic ability, compared with the restriction of diet when losing weight slowly, athletes who use severe restriction of diet and drinking water to lose weight quickly will bring many negative effects: fat-free weight loss, hormone disorder, decreased athletic ability and so on. Li Ning et al. reported that after athletes lost 3. 16kg by limiting calorie intake for five days, their back strength and leg strength decreased, and fatigue, dizziness, leg twitching and other phenomena appeared [23]. Filaire and others reported that judo athletes ate a low-calorie diet for 7 days in a row, and their weight dropped significantly, and their left arm strength and 30s jump test scores dropped significantly [24].
2.2.3 Restrict the combination of diet and drinking water for sweating and dehydration.
When an athlete's weight does not meet the requirements of the competition heavyweight a few days before the competition, moderate restriction of diet and drinking water combined with sweating and dehydration can lead to a rapid negative balance of energy and water in the body, thus losing weight faster. Fogelholm and others reported that experienced athletes quickly lost 6.0% 0.6% of their weight within 2.4 days by limiting their diet and drinking water and forcing them to sweat, and their scores in the 30m sprint and 1minWingate test did not change, nor did their vertical jump height with load [10].
2.2.4 Unsafe or prohibited measures to lose weight quickly.
Still exists in [6]. Although these measures can achieve the goal of losing weight quickly, they will do great harm to health. Vomiting drugs, laxatives and diuretics do great harm to the body. All three methods will lead to dehydration and electrolyte disorder, and diuretics are also listed as prohibited drugs. For the health of athletes, it is forbidden to take diuretics, dehydrating laxatives, spontaneous vomiting, appetite suppressants and complete fasting to lose weight quickly.
2.3 slow weight loss combined with rapid weight loss
For athletes who participate in sports according to their weight classes, their pre-competition weight loss usually includes a slow weight loss period and a rapid weight loss period. In the early period before the competition, they should try to reduce excess body fat as much as possible. If you still can't control your weight to meet the requirements of the heavyweight competition a few days before the competition, you can take rapid weight loss measures to further lose weight in order to meet the requirements of the heavyweight competition. Studies have shown that after slow weight loss, the anaerobic capacity of the body remains unchanged, but the strength may increase and the aerobic capacity may increase [7]. In most cases, weight loss should be achieved by moderately limiting diet and moderately increasing exercise. Losing weight faster and faster through fasting and dehydration will reduce strength and endurance. In addition, there are age and gender differences when athletes choose specific measures in the process of losing weight. Zhao reported that young athletes should focus on fat-reducing training and diet control in the process of slow weight loss; Old athletes focus on diet control, supplemented by fat-reducing training, to avoid consuming too much physical strength [25]. It is reported that judo athletes of different sexes adopt different methods to lose weight. Female athletes mainly adopt the method of restricting diet and drinking water, while male athletes mainly adopt the method of increasing exercise. In addition, athletes choose different specific weight-loss measures in different weight-loss periods. Zhao believes that because athletes need to reduce the amount of training and cultivate competitive state before the game, most athletes reduce low-intensity, long-term slow weight loss training and pay more attention to limiting diet to lose weight quickly [25]. 3. Establish an ideal weight and an appropriate weight loss range. Losing weight is widely used by many athletes in order to get the best results in the competition. In the event of competing according to weight level, it has become a tactic for athletes to lose weight artificially in order to participate in a certain level of competition. Recently, it was reported that a 5-year-old wrestler lost weight in order to participate in a smaller heavyweight competition. In what range can you control your weight to maximize your competitive level? How much can you lose on the premise of keeping the competitive level as far as possible and not damaging your health? These are difficult problems that have long plagued coaches and athletes at home and abroad.
3. 1 Establishment of ideal weight
A key problem for athletes to lose weight is to find the "ideal" competition weight, which is difficult to determine. But once the ideal weight or body fat is determined, it is of reference significance for whether and how much the current weight needs to be reduced.
At present, the ideal weight of athletes is often obtained by observing the weight and body composition of excellent athletes, and also by experience. Some people put forward the so-called ideal weight of athletes: 1) the weight of athletes at their best performance; 2) The weight of the athlete when he gains the maximum strength, speed and endurance; 3) The athlete's weight with the minimum body fat percentage when gaining the best ability. The ideal weight can not be determined only by subjective judgment, nor by the physiological index of height and weight. The determination of body fat is the key to determine the ideal weight standard, obtain and maintain the ideal weight. At present, it is considered that it is more appropriate to determine the ideal weight of athletes by the ideal body fat percentage. The National College Sports Association (NCAA) stipulates that the minimum body fat for wrestlers is 5%, while the National Association of High School Associations (NFHS) recommends the minimum body fat for male wrestlers in high schools.
It is 7%, and the NFHS Sports Medicine Committee recommends that the minimum body fat of female wrestlers in high schools be 12%. Studies have shown that,
A certain amount of body fat is necessary for the normal operation of the body. It is reported that sports scores are being evaluated. The coach must determine the weight loss goal reasonably according to the athlete's height, figure, body fat and the interval between weighing and competition.
Blind weight loss can not only improve sports performance, but even make it decline, even Feng et al.: Research status of athletes' weight loss In some projects, about 50% of world-class elite female athletes have eating disorders due to low body fat, accompanied by anorexia nervosa, menstrual disorder and bone mineral loss. Therefore, some scholars have suggested that an appropriate body fat percentage is beneficial to health, with a minimum of 5% for men and no less than12% for women [26]. The American Sports Medicine Association stipulates that athletes should stop competing when their body fat is less than 5%. When their body fat is less than 7%, they can't lose body fat any more, at best, they can only reduce water in their bodies to a limited extent.
The "ideal" weight can be determined by determining the "ideal" body fat percentage, and the "ideal" body fat is also obtained through repeated tests or repeated observations of elite athletes. The following formula can be used to estimate the athlete's allowable body fat loss: allowable body fat loss = athlete's current weight × (current body fat ratio-"ideal" body fat ratio) (1- lower limit of body fat ratio). To estimate the athlete's "ideal" weight, please refer to the following formula: "ideal" weight = 100× fat-free weight (kg) when weighing (100-"ideal" body fat%). When judging the appropriate weight, we must consider the level of body fat. Sometimes athletes weigh more than normal people of the same age, but their body fat level is low, which is related to high fat-free weight components such as muscles. However, the percentage of muscle is directly proportional to the muscle strength of athletes. Therefore, when the weight gain is caused by muscle growth, there is no need to lose weight, but when the weight is overweight and the body fat percentage is high, attention should be paid to losing weight.
3.2 Suitable weight loss range
There are some misunderstandings in the actual weight loss process. Some coaches and athletes don't know how much weight athletes can lose at most. When they choose the weight class, they only take 5% of body fat as the lower limit of weight loss. As we all know, athletes vary greatly. With the increase of height and weight, the lower limit of normal body fat also increases. The research shows that it will be difficult for athletes with medium and high figure to estimate the allowable weight loss with 5% body fat as the standard and then determine the competition level, and it will also be difficult to lose weight and damage the athletes' sports ability. For medium-sized athletes, the lower limit of body fat ratio is 8%, the body fat of athletes below medium-sized body can be slightly lower than 8%, and the body fat of tall athletes should be higher than 10%[27]. Fogelholm reported that if the interval between weighing and competition in the project is less than 5 hours according to the weight level, the rapid weight loss should not exceed 4% of the weight; If the interval is long, it is acceptable to lose weight quickly less than or equal to 8% [7]. It has been reported that many excellent athletes weigh more than the minimum weight (weight at 5% body fat) when their performance is particularly good. However, Wroble et al. reported that in the category of low-weight wrestling, many athletes weigh less than the minimum weight. However, the weight below the minimum weight is positively related to the victory of the competition. It has been suggested that the concept of wrestlers' minimum weight is largely based on the athletes' health status, rather than the competition results [28]. Therefore, adult athletes can determine the ideal weight needed for competition through experiments, not necessarily the minimum weight. Fogelholm reported that when weight loss is less than or equal to 5% of body weight, rapid weight loss and slow weight loss have little effect on the athletic ability of experienced athletes [10]. Yang's research on weightlifters shows that young athletes should not lose more than 6% of their weight, and adult athletes should not lose more than 8%. If you are thin, the decline in your grades will be small; If you lose more weight, your grades will drop significantly, and the adverse effects on your health and sports life will increase. The frequency of losing weight should not be too frequent [29]. Appropriate weight loss should vary from person to person in order to achieve athletes' goals.