CHANPER 7 PHYSICAL PERFORMANCE AND EVALUATION

1. CHANPER 7 PHYSICAL PERFORMANCE AND EVALUATION

2. Athletic competition represents the classic test of physical fitness or performance capacity. Competitive performance can be measured objectively in centimeters or seconds,or it can be judged subjectively as in gymnastics figure skating or diving. The individual’s performance is the combined result of the coordinated exertion and integration of a variety of functions. The purpose of this chapter is to discuss the importance of some of these functions • The demands of the event must be perfectly matched by the individual’s capabilities to achieve top performance and championship. It is impossible to present one formula that takes into account all aspects of a person’s maximal performance, because the demands set by different types of activities vary greatly. • Natural endowment (genetic factors) undoubtedly plays a major role in a person’s performance capacity,at least for those aspiring to the levels required for the attainment of Olympic media. The individual’s response to training also is associated with an endowed fenotype. Thus,it appears that up to 70% of an individual’s maximal force power,or capacity is a matter of genetics

3. Athletes are mainly concerned with improving their ability to cut off seconds or add centimeters to their records. The scientist is interested in analyzing why the results improve or vary from time to time. Therefore, the scientific objective is(1) to evaluate quantitatively the influence of the various factors on the performance capacity in different tasks (performance requirements);(2)to examine how these factors vary with sex, age, and body size (capacity profile);and(3)to study the effect of such factors as training and environment. • We therefore begin the more detailed analysis of physical performance with a discussion of the oxygen uptake during submaximal and maximal exercise and the maximal aerobic power (the individual’s maximal oxygen uptake).

4. Click to edit title style 1 Intensity and Duration of Exercise 2 Recovery Section1 Aerobic processes 3 Exercise Styles 4 Muscular Mass Involved in Exercise 5 Muscular Mass involved in Exercise

5. Section 1 Aerobic processes • For each liter of oxygen xinsumed ,about 20 KJ(range 19.7-21.1KJ;or 5 Kcal,range 4.7-5.05 Kcal)will be delivered;hence,the higher the oxygen uptake,the higher the aerobic energy output.The oxygen uptake during exercise can be measured with an accuracy of +or- 0.04 ml·min-1(VO2>1 ml·min-1).

6. 1 Intensity and Duration of Exercise • The slow increase in oxygen uptake at the beginning of exercise is explained by the sluggish adjustment of respiration and circulation,that is,the sluggish adjustment of the oxygen-transporting systems to exercise.Consequently,during the first 2 to 3 min there is an oxygen deficit.The attainment of the steady state conincides roughly with the adaptation of cardiac output,heart rate,and pulmonary ventilation.A steady-state condition denotes a work situation where oxygen uptake equals the oxygen requirement of the tissues.Consequently,lactic acid does not accumulate in the body.At steady state,heart rate,cardiac output,and pulmonary ventilation have attained fairly constant levels. • In light exercise,the energy output during the first minrtes of exercise can be delivered aerobically,because oxygen is stored in the muscles bound to myoglobin and in the blood perfusing the muscles.During more severe exercise,anaerobic processes must supply part of the energy during the early phase of exercise.

7. 1 Intensity and Duration of Exercise • The breakdown of energy-rich phosphate compounds,adenosine triphosphate(ATP) and phosphocreatine,is certainly anaerobic and essential,but their quantitative role is limited.Therefore, the anaerobic breakdown of glycogen and glucose to lactic acid has an important potential to support the aerobic processes when they cannot provide enough energy for ATP production. In exercise that engages large muscle groups and that is performed for some minutes,lactate produced in the activated muscles escapes and appears in the blood.The well-trained person can exercise at a higher intensity without an increase in blood lactate concentration than an untrained individual.The heavier the exercise,the more important the anaerobic energy yield and the higher the muscle and blood lactate concentrations.As the exercise becomes more strenuous,a decrease in the body’s pH affects muscular tissues,respiration,and other functions.

8. 1 Intensity and Duration of Exercise • From a methodological viewpoint, maximal oxygen uptake is attained at rates of exercise that are not necessarily maximal. Thus, an all-out test is not necessary to assess an individual’s maximal aerobic power. On the condition that large muscle groups are involved in the exercise and that the exercise time is 4 to 5 minutes, three main criteria are used to show that the subject’s maximal aerobic power is uptake despite further increase in the rate of exercise, and second, post exercise blood lactate concentration exceeds 8 to 9 mM.(In children and old subjects, it can be difficult to attain such high values, however) the third criterion is that the respiratory exchange ratio, or respiratory quotient should be above 1.15.(The R value has been shown to vary with the subjects’ training status and age.) Thus, subjects should not be expected to meet all the criteria on any single test.

9. 2 Recovery • It may take 60 min or more before the oxygen uptake and rate of aerobic metabolism return to the preexercise level. After relatively heavy exercise, one may identify three phases: • （1）First is a fast exponential component in the decline in oxygen uptake with a half-time of about 30 s. Most likely this rapid phase is associated with aerobic replenishment of the ATP and PC stores and a refilling of the oxygen stores. During the first minutes of recovery, there is a rapid synthesis of the energy-rich phosphates. There is a close relationship between the reduction in ATP and PC on the one hand and both oxygen deficit and the fast component of the “oxygen debt” on the other . A realistic figure for refilling depleted oxygen stores is about 0.5 L, and the oxygen cost for the ATP and PC production is up to 1.5 L .

10. 2 Recovery • （2）Then comes a more complex slow component, which,after supramaximal exercise, has a half-time of about 15 min. In the classic literature,this component has been attributed to the energy cost of the elimination of the lactate produced, that is, a payment of a lactic oxygen debt. This concept has been criticized by Brooks and his group, who suggested that the term should be replaced by excess postexercise oxygen consumption (EPOC), a term that is commonly used today • Inevitably, most of the energy yielded in the metabolism is converted to heat and the tissue temperature increases, which in turn elevates the metabolic rate by about 13% per degree centigrade. The increase in sympathetic nerve activity will also stimulate the metabolism, via adrenaline and noradrenaline. An elevated oxygen demand of the activated respiratory muscles and heart also contributes to the increased metabolism.

11. As mentioned, when the oxygen demand during exercise exceeds the oxygen supply, the vreakdown of glycogen to lactate will support the metabolism. In very heavy exercise lasting for minutes or more substantial amounts of glycogen are used.. During recovery, some of that lactate is reconverted to glycogen, a process that demands energy. • Altogether, the oxygen uptake during recovery from maximal exercise of some 5 min duration can, in extreme cases, amount to almost 40 L during the following 60 min. At rest, during the same period of time, the individual would consume about 18 L of oxygen. • （3）After sustained exercise there is a slightly elevated metabolism lasting for several hours, eventually for at least 24 h. It has been suggested that the oxygen consumption during this ultra-slow phase is attributable to a stimulation of substrate cycles.

12. 3 Exercise Styles • （1）Interminttent Exercise • Balsom(1995) attempted to evaluate how the different energy systems are used in this type of intermittent exercise with short periods(up to 10 s)of very high intensity and which metabolic factors limit performance in a group of highly motivated,physically active males.The ability to maintain a high target power output during consecutive work perilds was found to be greatly influenced by small changes in the exercise duration and intensity and in the duration of the intervening recovery periods.

13. Nest some of the most important principles are discussed on the basis of a few classic experiments concerning intermittent exercise 1 A subject whose maximal oxygen uptake was 4.6 ml·min-1 could exercise at 350 W for about 8 min.Because the oxygen need was approximately 5.2 ml·min-1 ,the anaerobic processes had to proveide part of the energy. 2 In another experiment with the same subject, the rate of exercise was again 350W,but now exercise periods of 3 min were alternated with 3-min rest periods .The subject could proceed with great difficulty for 1 hr,and the same total amount of work was performed as in experiment 1.The oxygen uptake and heart rate were now maximal,as was the peak blood lactate concentration(13.2 mM). 3 When the heavy exercise periods were shortened by introducing more frequent rest periods ,the total oxygen uptake over the hour was not markedly reduced.The subjective feeling of strain was less severe, however,and peak oxygen uptake, heart rate, and blood lactate concentration were lower, Hence, with intermittent exercise and rest for 30 s, the heart rate did not exceed 150,the blood lactate was only 2.2 mM, and the total oxygen uptake was 154 L during the hour.The subject’s maximal heart rate was 190.

14. 3 Exercise Styles • Apparently,during intermittent exercise with short exercise periods,one can endure very high rates of exercise aerobically and therefore experiencce little lactate production.However,it is essential that the exercise periods are kept sufficiently brief(around 15 s) to prevent the oxygen supply from being exhausted and the anaerobic lactate production from being too great. • Dynamic exercise is certainly an intermittent type of activity, and its superiority over static exerciser as an endurance exercise can be explained partly on the basis of the muscle pump and the alternating emptying and filling of the oxygen stores during alternating muscle contraction and relaxation.

15. Summary • The buffering effect of an oxygen store means that a great amount of exercise can be performed at an extremely heavy rate ,with a relatively low peak demand on the circulation and respiration, by the introduction of properly spaced, short exercise and rest periods. The heavier the work rate , the shorter should be the exercise periods. This physiological concept has at least two important applications: • 1. It may explain why older or physically disabled individuals, despite a reduced maximal aerobic power, can remain in jobs involving heavy manual labor such as forestry, farming, and construction, or can enjoy physically demanding hobbies. As long as they are free to choose the optimal length of the exercise and rest periods ,the acute loads on the respiration and circulation do not exceed the limits of their reduced capacity. However, if the pace is determined by a machine, even a less heavy peak load, but with relatively long activity periods, can overtax the capacity of the worker whose physical performance capacity is limited.

16. Summary • 2. If the aim of a training program is to increase muscle strength,the highest load on the muscle fibers will be obtained within a given period of time if periods of rest are frequently interspersed between activity periods of 5 to 10 s.On the other hand,training the oxygentransporting system will be easier if the exercise periods are prolonged to at least 2 to 3 min.This typw of exercise also adapts the tissues to high lactate concentrations provided the exercise is severe.

17. Summary • （2）Prolonged Exercise • Moderately well-trained individuals may walk or run for about 1 h with an oxygen uptake around 50% of the VO2max,maintaining the oxygen uptake, heart rate, and cardiac output at approximately the same level as attained after about 5min of exercise. • The well-trained individual can maintain steady state at a higher relative work rate than 50% ,indicating more efficient oxygen transport and oxygen and substrate utilization in the active muscles. Elite cross-country skiers can exercise at 85% of their maximal aerobic power at least for 1 h. • Well-trained athletes, including marathon runners, can exercise for hours with an oxygen uptake around 75%-85% of their maximum with little or no increase in blood lactate concentration.

18. Summary • The limiting factors in prolonged exercise may vary from individual to individual. It is conceivable that the electrolyte balance, the ratios of potassium and sodium ions, for example, across the muscular cell membrane are disturbed during prolonged exercise, and that the activity of key enzyme systems is hampered by the decreased PH and\or accumulation of metabolites. In fact, in some experiments involving prolonged severe exercise, none of the physiological parameters studied. • Motivation is undoubtedly an important factor determining endurance during heavy exercise. Well-trained, highly motivated subjects can maintain their oxygen uptake at a maximal level for at least 15 min, although most individuals feel an urge to stop after 4 to 5 min at a work rate that taxes the oxygen-transporting systems to a maximum.

19. Summary • It is obvious that an individual’s maximal aerobic power plays a decisive role in his or her physical performance. If a given task demands an oxygen uptake of 2.0 ml·min-1 ,the person with a maximal oxygen uptake of 4.0 ml·min-1 has a satisfactory safety margin, but the 2.5 ml·min-1 individual must exercise close to his or her maximum, and consequently the internal equilibrium becomes much mote disturbed. In prolonged exercise, motivation, state of training, water balance, and depots of available energy are important for performance capacity. A technique and efficiency factor is of decisive importance for the energy cost of a given task, more so in activities that demand skill, such as swimming and cross-country skiing.

20. 4 Muscular Mass Involved in Exercise • The demand on the oxygen-transporting functions varies with the size of the active muscles. Since isometric contractions hinder the local blood flow and dynamic exercise facilitates the circulation, it follows that a greater oxygen uptake can be obtained during dynamic exercise. Usually,exercise involves both static and dynamic muscle contractions. Static exercise produces a relatively high heart rate and arterial blood pressure. This may complicate a task evaluation based on the measurements of heart rate and blood pressure. • In maximal work on a cycle ergometer in the wupine position, the oxygen uptake is only about 85% of the value obtained in the sitting position. But, if the subject exercise with both legs and arms simultaneously in the supine position, the oxygen uptake, cardiac output, and heart rate increase to the values typical for maximal exercise in the upright position. One plausible explanation for the lower aerobic power for maximal cycling in the supine position, despite an optimal venous return to the heart, is the less favorable position, because the body weight cannot be used during the critical stages of pedaling. Second, the blood perfusion of the activated leg muscles is enhanced when a person exercises in the upright position.

21. 5 Evaluation of physical performance on the basis of tests • In this chapter，we shall deal with an important aspect of work physiology，namely testing physical performance ability. This includes both the actual measurement of parameters reflecting basic physiological functions and the prediction of performance on the basis of data obtained at rest or sub-maximal exercise. Physical performance ability commonly is referred to as physical fitness，which is an umbrella concept covering a series of qualities related to how well an individual performs physical activity. Because most of the so called fitness tests，including evaluation of flexibility，agility speed，power balance ,and skill ,are related to special gymnastic or athletic performance ,they are not really suitable for an analysis of basic physiological functions. Practice and training in the performance of the actual test greatly influence the results.

22. Section 2 Anaerobic Processes Power and Capacity for High-Energy Phosphate Breakdown 1 Power and Capacity for lactate Breakdown 2 Evaluation of anaerobic power 3 Interaction Between Aerobic and Anaerobic Energy Yield 4 Anaerobic Threshold 5

23. Section 2 Anaerobic Processes • During light exercise,the required energy is provided almost exclusively by aerobic processes,but during more severe exercise,anaerobic processes are brought into play as well.Anaerobic,energy-yielding metabolic processes play an increasingly greater role as the severity of the exercise increases.As discussed previously,the aerobic power during exercise can be followed quite accurately by measuring the oxygen uptake.Because we lack a similar tool for directly measuring the anaerobic power,indirect methods have to be applied when studying the kinetics,power,and capacity of these processes. • The energy yield from the breakdown of ATP and PC is indispensable,but,quantitatively,the available stores of these high-energy phosphates alone can only cover the energy requirement for less than 10s during maximal effort.Theseprocesses of breakdown and resynthesis occur very quickly.Acurally,processes of key importance in the anaerobic energy yield occur within fractions of a second,but with the available methods in human experiments,seconds may elapse between sampling and stopping the biochemical events in the sample.The

24. Section 2 Anaerobic Processes • rate of turnover of ATP in a sprinting human is approximately 2.7 mmol·s-1 per kilogram of muscle in a high jump it may be as high as 7 mmol·s-1·kg-1.With only 5 mmol·kg-1 of ATP available, it obviously has to be quickly resynthesized as in the case of a 100-m race. PC is the initial source of energy in this process. For an analysis of anaerobic biochemistry, it may be convenient to discuss the breakdown of high-energy phosphate separately from the anaerobic glycogen breakdown to lactate. There is an overlap in these processes as well as in the kinetics of the aerobic energy yield, but with an exercise period of about 5 s the lactic power will dominate .Reports indicate that there is a delay of up to 6 s before glycogenolysis sets in.

25. 1 Power and Capacity for High-Energy Phosphate Breakdown • In some activities ,the developedpower can be measured. C.T.M.Davies and Rennie(1968) had their subjects perform a high jump from a force platform. From the time course of the vertical velocity of the center of gravity of the body, the researchers could calculate the average peak power output to be 3900 W for their male and 2350 W for their female subjects. This peak power, developed during 0.2s in the jump, is actually 15 times larger than the subject’s maximal aerobic power, developed for 5 to 8 min during cycling. However, the mechanical efficiency in a jump is not known, and therefore its metabolic cost cannot be estimated. • A method by which one can estimate the maximal anaerobic power output has been developed. The subjects climb a normal flight of stairs at maximal speed taking two to three steps at a time. The peak speed is attained within 2 to 3s and can be maintained up to the 6th second; from then on it declines. From speed, vertical distance climbed, and body weight, the power output can be calculated.

26. Text Text Text Text 1 2 Power and Capacity for lactate Breakdown How Does Continued Light Exercise Influence the lactate removal? Lactate Production, Distribution, and Disappearance Effects fo Metabolism on Tissue and Blood pH Time Course of the Blood Lactate Concentration What is the Fate of the Lactate Produced?

27. （1）Lactate Production, Distribution,and Disappearance • It has been known for a long time that skeletal muscle is a major producer of lactic acid in the body, but the way we regard lactate changed dramatically during the last quarter of the 20th century. We used to see it as a dead-end waste product during anaerobic conditions, responsible for such unwanted effects as muscle soreness and fatigue. Today, lactate has emerged as a normal metabolic intermediate, even under aerobic conditions. In fact ,as much as 50% of the glucose metabolized under fully oxygenated conditions is converted to lactate .

28. （1）Lactate Production, Distribution,and Disappearance • Even our view of how lactate is transported across cell membranes has changed. We used to believe that it was by simple diffusion, but it has turned out to be facilitated diffusion by means of specific transporter molecules in the cell membrane. As previously mentioned, these lactate transporter molecules belong to a family of proton-linked monocarboxylate transporters that plays an important role in the pH regulation of skeletal muscle. Skeletal muscle contains both the MCT 1 and MCT4 is forms. The amount of MCT1 is correlated with the aerobic capacity of the muscle fiber, possibly because MCT1 has been found in mitochondrial membranes. Consequently,there is more MCT1 IN TYPE I than in type II muscle fibers.MCT4,on the other hand, is found in all fiber types. These monocarboxylate transporters are bidirectional, meaning that they are able to transporter lactate out of or into muscle cells depending on the hydrogen ion(H+) and lactate gradient. This makes them ideal for energy transfer between cells as described by the “lactate shuttle” hypotheses.

29. （2）Time Course of the Blood Lactate Concentration • Blood lactate concentration is relatively simple to determine. Understandably, this has made it a frequently measured parameter. Even the salivary lactate concentration serves as a relevant indicator of blood lactate concentration. A semantic piece of warning is appropriate at this point. The terms lactate concentration and lactate production are often used synonymously. As will be evident in the following, they are not the same. The lactate concentration, wherever it is measured, reflects the difference between lactate’s rate of appearance and its rate of removal.

30. （2）Time Course of the Blood Lactate Concentration • The events can be summarized as follows: • ①During light exercise, the demand for ATP is small and the oxidative removal of pyruvate keeps pace with its production. Most ordinary daily activities belong to this category. • ②During exercise of moderate intensity, the demand for ATP initially surpasses the supply by oxidative metabolism, and the glycolytic rate is increased temporatily to cover the demand until the aerobic oxidation can take over and completely cover the energy demand. Produced lactate diffuses out of the muscle fibers by means of lactate transporters in the cell membrane and can be traced in the venous blood draining the muscle. As the exercise proceeds, the blood lactate concentration decreases again, and the exercise can be continued for hours.

31. （2）Time Course of the Blood Lactate Concentration • ③During heavier exercise, the imbalance between pyruvate producion by glycolysis and its removal by the mitochondria is more prolonged but eventually can reach a steady state, depending on the intensity of the exercise. In such cases, the blood lactate concentration can remain constant and high throughout the exercise period. The length of time that the work rate can be endured will depend, to some extent, on the subject’s motivation. • ④During very high-intensity exercise, there is a continuously increasing imbalance and a corresponding increase in the lactate content of the blood .As a rule, the exercise cannot be continued for more than a few minutes, because the subject’s muscles can no longer function. The work rate has exceeded some sort of a threshold, and the condition is no longer one of a steady state.

32. （3）What is the Fate of the Lactate Produced? • In an aerobic metabolism of glycogen down to carbon dioxide and water, the energy yield for ATP production is 2813 KJ per six carbon unit. Of this potential, only about 8% is available in the anaerobic breakdown to lactate. However, the produced lactate is not wasted. In addition to being an important metabolic intermediate for the muscle cell itself, it is a very important molecule for the transfer of energy substrates from one muscle cell to another. Once phosphorylated, a glucose molecule is trapped inside the muscle cell, and it is not liberated from the cell until it is converted to pyruvate or lactate. Without any loss of energy, the process of putuvate transformation to lactate can be operated in reverse. From that point, there are two alternative routes; ①The pyruvate can be oxidized, or②it can be a substrate for a synthesis of glucose and glycogen. When oxidized, it yields the remaining 92% as energy, and the heart muscle, kidney cortex ,and skeletal muscles can use lactate as a substrate.

33. （3）What is the Fate of the Lactate Produced? • From what we know about differences between muscle fiber types ,the fate of lactate produced during a bout of exercise depends on several factors,the more important of which appear to be the muscle fiber type pattern of the muscles involved and their recruitment pattern, and the training status of the individual in relation to the intensity of the exercise. According to Donovan and Pagliassotti(2000),all fiber types in their rabbit muscle preparations released lactate when perfused with 1 mM lactate, which is the resting lactate concentration. As the lactate concentration in their perfusate was increased ,all muscle fiber types showed a transition from net lactate release to net lactate uptake ,but this transition took place at lower lactate concentrations in type I muscle fibers than in type II. In type I muscle fibers ,lactate is disposed of primarily by oxidative degradation, whereas in type II fibers glyconeogenesis seems to be more important. The exact pathway for this glyconeogenesis has not yet been settled, but there are indications that it is via an extramitochondrial path

34. （4）How Does Continued Light Exercise Influence the lactate removal? • E.V.Nweman et al.(1937)noticed that the removal of lactate after exhausting exercise was enhanced if the subject continued to exercise, but at a lower intensity that normally did not produce any lactate. Hermansen and Stensvold(1972)reported that the optimal removal rate of lactate occurred when the intensity of the active recovery exercise was around 60% of maximal oxygen uptake. Other investigators have recommended exercise intensities that vary between 30% and 50% of VO2max. • Because of the increased oxidative capacity of skeletal muscle observed with endurance training, it has been thought that trained subjects exhibit a faster decline in blood lactic acid after a maximal exercise bout. However,both B.W.Evans and Cureton(1983)and D.R.Bassett et al.(1991)reported no differences in blood lactic acid disappearance between trained and untrained individuals during resting recovery from intense exercise.

35. （5）Effects fo Metabolism on Tissue and Blood pH • The hydrolysis of one ATP produces about one proton at the muscle cell pH. Hpwever,during the oxidative phosphorylation, all the products of ATP gydrolysis-adenosine diphosphate(ADP), inorganic phosphate (pi) and H+--are reutilized. This means that there is no net accumulation of H+ in the aerobic metabolism. • From their review, Busa an Nuccitelli(1984)concluded that lactic acid accumulation is not the source of the intracellular pH decrease during anaerobic glycolysis. This is interesting and important from a theoretical point of view. However, the result of the sequence ATP hydrolysis plus rephosphorylation by energy from the breakdown of glycogen is a constant production of 2 mol H+ for each mole of glucosy1(because of the opposite PH dependencies of H+ production by glycolysis and by ATP hydrolysis). In a way, the net effect is what the traditional formula reveals: • glycogen or glucose=2 lactate+2 H+(1)

36. （5）Effects fo Metabolism on Tissue and Blood pH • It is not surprising that the muscle pH is reduced during anaerobic exercise, from about 7.0 to 6.5 or even lower. Secondly, the arterial blood pH can decrease from 7.4 to below 7.0.As discussed previously, the rate of the glycolysis is determined by the need to resynthesize ATP. Actually, the breakdown products of ATP-ADP, adenosine monophosphate,and Pi-are potent stimulators of key glycolytic enzymes, whereas ATP itself is inhibitory. In this way, the rates of ATP hydrolysis and lactate formation are coupled. It is not surprising that there is a high correlation between lactate concentration and pH values in blood samples taken at rest as well as during and after exercise. These authors pointed out that because of the buffer systems of the blood, a 10-fold increase in lactate concentration causes only a 1.42-fold increase in H+ concentration.

37. 3 Evaluation of anaerobic power • An athletes physical fitness cannot be assessed by maximal oxygen uptake alone. Anaerobic metabolism, speed, strength, and maximal power are also determining factors in many types of athletic performance. • Theoretical as well as practical aspects of the anaerobic energy yield during exercise at various work rates are discussed in chapter 8.unfortunately ,at present we do not have any satisfactory methods to measure anaerobic power with a desirable degree of accuracy .it is true that if the mechanical efficiency in cycle ergometer exercise is constant, the energy requirement during exhausting exercise can be predicted by extrapolation .by measuring the oxygen uptake continuously during the entire exercise period, the investigator can calculate oxygen deficit and use it as a measure of anaerobic energy yield . the problem is ,however ,that is most events or types of exercise, one cannot estimate the total energy demand with sufficient accuracy when dealing with maximal or near maximal effort. Consequently ,anaerobic power cannot be determined an increase in lactate concentration in the muscle or in the blood will not give a quantitative measurement of the total lactate production, because we do not know the total volume of body fluid into which the lactate is dissolved. This is handicap when considering how to train anaerobic power most effectively , because we are unable to measure anaerobic power objectively.

38. 3 Evaluation of anaerobic power • When we discussed the force-velocity curve for a maximally contracting muscle (in connection with figure 3.34),we emphasized that the maximal potential was critical .actually ,to achieve optimal human power output ,cycling force and velocity should be equal and close to one third of their maximal values. Sergeant, hoinville, and young (1991) noticed that the velocity for the greatest mechanical power output was 110rev·min-1. Bergh(1985) suggested a braking force of 10% of the subjects body weight ,which is very close to the optimum reported by Nadeau and Brassard (1983),50N for their female and 70N for their male subjects. usually ,the maximal power when tested on a cycle ergometer is attained during the first 2 to 3s of the exercise. Without a sophisiticated apparatus ,it is difficult to measure the total force, that is ,the force exerted to accelerate the mass of the wheel and to overcome the braking force. However, Bergh(1985) found a close relation between this total force per second and the peak velocity of the wheel or pedals. the latter is much easier to measure.

39. 3 Evaluation of anaerobic power • The method of measuring maximal power output during a 30s cycle ergometer test is assumed to reflect the maximal muscular strength of the engaged muscle groups and the power of the high energy phosphate compounds. The average power reflects the anaerobic capacity but it is not a measure of the capacity . the decline in power during the test provides a fatigue curve under these standardize conditions.

40. 4 Interaction Between Aerobic and Anaerobic Energy Yield • This is an attempt to summarize parts of the preceding discussion. Table 8.1 present the contribution to energy output from aerobic and anaerobic processes in maximal efforts in exercise involving large muscle groups. The individual’s maximal aerobic power is set to 5 L·min-1, equivalent to about 100 KJ·min-1 and maximal anaerobic capacity to 200 KJ ·min-1 ,EQUIVALENT TO 9 L of oxygen uptake in aerobic exercise. It is assumed that 100% of the maximal oxygen uptake can be maintained for 10 min,95% for 30 min,85% for 60,and 80% for 120 min. For nonathletes, the figures are roughly 50% of the values listed.

41. 4 Interaction Between Aerobic and Anaerobic Energy Yield • For exercise periods up to 2min,the anaerobic power is more important than the aerobic contribution;at about 2min there is a 50:50 ratio,and with prolonged exercise the aerobic power becomes gradually more dominating.This is illustrated in figure 8.10. • An analysis of the energetic demands of different sporting events and the athlete’s capabilities to fulfill these requirements may help him or her both in training and in selecting suitable events.One factor to consider is that endurance athletes have skeletal muscles with a high proportion of slow-twitch fibers,and sprinters are characterized by a dominance of fast-twitch fibers.However,in many events there is not such a strict pattern in fiber composition(Costill et al.1976;Saltin and Gollnick 1983).So far,muscle fiber typing is not a good instrument for selecting potential athletes.

42. figure 8.10

43. (1) 5 Anaerobic Threshold • The Anaerobic Threshold Concept (2) Problems in Determining Anaerobic Threshold

44. 5 Anaerobic Threshold • The concept of anaerobic threshold (lactate threshold) or OBLA is based on an exponential increase in blood lactate concentration when a person exceeds a certain rate of exercise\oxygen uptake. Anaerobic threshold usually is determined during incremental exercise to establish the point mentioned. Indirectly, a similar breaking point of pulmonary ventilation versus oxygen uptake has been applied, under the assumption that these two points are highly correlated. In many laboratories, testing has been standardized with the goal of finding the rate of exercise or oxygen uptake at which the blood lactate concentration reaches a value between 2.5 and 4mM. • It is evident that the theoretical considerations behind this concept need further clarification, to say the least. It is difficult to establish a well-defined “point”, even for one individual, mainly because the balance between the production and removal of pyruvate differs both between muscle and between muscle fiber types in the same muscle.

45. 5 Anaerobic Threshold • These critical notes do not mean that it is of no interest to study, in normal subjects as well as in patients, how intensity they can exercise without an accumulation of lactate, or to follow the lactate response in subjects submitted to a five rate of exercise or oxygen uptake. On the contrary, this measurement provides important information about the individual’s aerobic potential and about the effect of training. The threshold concept, as such, however, rests on an unstable scientific foundation. At any rate, experienced endurance athletes know quite well themselves what rate of speed they can tolerate without fatigue caused by lactate accumulations. Thus, there is hardly any need for the coach to tell them on the basis of blood lactate analyses.

46. （1）The Anaerobic Threshold Concept • A anaerobic threshold concept was introduced to define the point when metabolic acidosis and associated changes in gas exchange in the lungs occur during graded exercise. Already in 1936,Bang had pointed out that there was a metabolic phase in which the exercising person would encounter an accumulation of lactate in the blood as the exercise proceeded. Since then, considerable efforts have been made to establish the oxygen uptake in relation to the person’s maximal aerobic power when the blood lactate concentration gradually starts too increase during continuous exercise .The work rate at this “breaking point” has been named anaerobic threshold, lactate threshold, or OBLA .

47. （1）The Anaerobic Threshold Concept • Definitely, some muscle fibers use an anaerobic metabolism for the ATP resynthesis even before the muscle, as a whole, has reached its maximal oxygen uptake .In fact, lactate concentration may be higher in the white part of a muscle than in the red part, with the arterial concentration somewhere in between .The capillary density varies within the muscle and so do the myoglobin concentration and the amount of mitochondria. In particular, the type IIX fibers are at a disadvantage .An increased sympathetic activity accompanying intense exercise can induce a lactate formation even in resting muscles. There is a work rate at which the lactate uptake in the blood exceeds the removal so that the lactate concentration increases gradually. From this point, only a relatively small increase in the intensity of exercise can reduce the time to exhaustion from ,say,1h to 15 min. A threshold value often used is an arterial lactate concentration of 4 mM. However,there are marked individual variations in this threshold value.

48. （2）Problems in Determining Anaerobic Threshold • There are different patterns in the kinetics of lactate production and disappearance, between individuals, between muscles within an individual, and even between different muscle fiber types within a muscle. It is therefore not surprising that the increase in blood lactate concentration with a stepwise or ramp-wise increasing work rate is rather smooth, making it difficult to define a threshold, and that the variability of the threshold value for a given subject is large. The threshold value found also is modified by such factors as the athlete’s nutritional state and speed of movement. • In some laboratories,2.5 mM is used as a threshold value, whereas others use something in between this value and 4 mM. Different protocols are used to determine the threshold. Some use a stepwise increase in work rate, whereas others use a continuous increase and with different rates of increase in metabolic demands. Such variations make it difficult to interpret and compare data from different laboratories.

49. Section 3 Genetics of Physical Performance • To attain top performance in a given event, one has to have the basic physiological endowment. In addition,one has to have the mental strength to endure the training involved and the determination to mobilize all of one’s resources to win. The question is whether, or to what extent, the basic requirements that determine performance in a given event are based on genetic endowment. • Bouchard,Malina,and Perusse(1997)reviewed this question extensively. They predicted that the exercise sciences will be strongly influenced by advances in human genetics and molecular biology. So far, the fairly extensive studies of the genotypic contribution to performance phenotypes are mainly of the genetic epidemiology type and are limited largely to comparisons of tweins,siblings,and parent-offspring pairs ,and they are of limited use in determining the genetic contribution to performance phenotypes.

50. Section 3 Genetics of Physical Performance • Because lean body mass and muscle strength are both associated with bone mineral density, which is known to be under genetic, in a classic twin study, examined the size of the genetic component of bone mineral density. The authors concluded that grip strength, leg strength, and lean body mass have a moderate genetic component, and that the genetic component to muscle bulk and strength accounts for little of the genetic component to bone mineral density. • In the case of cardio respiratory fitness phenotypes, genetic factors play a significant role in explaining interindividual differences. • In a study of parent-offspring similarity in motor performance,Cratty(1960) compared the performances in running long jump and 100-yd dash of 24 college-age men with the performances of their fathers when the latter were of college age 34 years earlier. Father-son correlations were 0.86 for the running long jump and 0.59 for the 100-yd dash. This shows that fathers and sons attained fairly similar performances in these speed and power tasks when they were about the same age.