Considerations in endurance training

The athlete who is physically ill-prepared for endurance activities is at least as likely to suffer adversely in participation as his counterpart in power events. Analysis of time of injuries in major team games indicates that injuries predominate towards the end of the contest. At this time, fatigue prevails in the poorly conditioned athlete with errors creeping increasingly into play which in turn promote injury. Lack of fitness also shows after competition in that recovery takes longer.

Endurance fitness or stamina has local and general aspects. Local or muscular endurance expresses the ability of a muscle group to continue working over a prolonged period without performance impairment. Activity may be cyclical as in the repetitive stride of the distance runner or pedalling of the stage cyclist; it is acyclical in the arm and shoulder muscle involvement of the tennis player over five sets or the basketballer’s jump endurance requirement. These are specific in that local endurance is needed in the muscle group emphasised and training sessions must be designed accordingly. Endurance is promoted by many repetitions at moderate intensity and does not result in muscle hypertrophy. General endurance is manifested in an efficient oxygen transport system by means of which inhaled oxygen is carried in the blood for tissue respiration. In exercise the oxygen required for sustained contractions is offered to working muscles by the cardiovascular system, the portion extracted as it passes through the muscle being indicated by the arterio-venous o2 difference. Endurance exercise elicits both central and peripheral adaptive responses which will to a large degree be specific to the training mode.

PHYSIOLOGICAL BACKGROUND

Energetics

Contraction results from the splitting of adenosine triphosphate (ATP), the only molecule the muscle can use directly. This is supplied by alactacid, lactacid and oxidative mechanisms. As exercise commences, energy is immediately furnishable from intramuscular ATP and creatine phosphate (CP) collectively known as the phosphagens. This constitutes the powerful alactacid mechanism whose capacity is limited to 20 to 30 kj (5 to 7 kcal). Glycogen stored within muscle may be broken down anaerobically (without oxygen) with resultant lactate formation. This lactacid mechanism extends maximal performance for about 30 seconds. In aerobic glycolysis pyruvic acid, the precursor of lactate, is diverted into the aerobic pathway after ATP formation. Here glucose is further broken down to co2 and water with additional ATP simultaneously produced. The lactacid mechanism uses only carbohydrates as its fuel and produces relatively few ATP molecules whereas the aerobic system can use fats, proteins and carbohydrates and yields relatively large amounts of ATP.

Apart from the oxygen bound to myoglobin within the muscle, which may provide limited energy in the acute response to exercise, the aerobic mechanism depends on o2 supply and co2 removal through the ventilatory and cardiovascular systems. In the short term an oxygen deficit develops because of the lag in the system’s responses while anaerobic metabolism is utilised in the meantime before a steady state is attained. The fitter the athlete the sooner this is reached for a given work intensity, allowing the more highly trained to settle earlier to the competitive pace. The more prolonged the work period the smaller is the proportionate involvement of anaerobic processes until it is almost insubstantial in long-term contests. This provides a key for determining the relative emphasis in training for continuous exercise competitions such as running or swimming. These mechanisms obviously interact in a number of endurance sports, many games requiring intermittent acyclical short bursts of intense action depending on lactate producing anaerobic metabolism superimposed on the continuous endurance need. In the intervening periods of cruising, the oxygen debt is mostly repaid and the majority of the lactate removed and recycled or oxidised directly. The ability to tolerate high metabolite levels and quickly recover from anaerobiosis during ongoing performance needs to be developed in training for these events.

Energy sources

Foodstuffs provide fuel sources in the form of protein, fat and carbohydrates. Normal fat and protein stores in a well-fed adult are relatively inexhaustible while survival time is limited if dependent on carbohydrate reserves. Protein is, however, not concerned with energy production during exercise. Normally, fat depots exceed 200MJ (50000kcal) and carbohydrate stores approximate 7.5MJ (1800kcal).

Carbohydrates are stored in the muscles or liver as glycogen. The total glycogen stored by a 70 kg sportsman is about 460 g, 15 per cent held in the liver of which only half is made available. Liver glycogen is mobilised as blood glucose: blood sugar normally totals less than 6 g, 60 per cent of which serves the brain. If blood glucose levels fall appreciably hypoglycaemia develops and both mental concentration and continuing hard exercise are soon impossible. Ingestion of liquid glucose can prevent this condition or provide relief. Fats mobilised from adipose tissue depots provide an alternative substrate to glucose and ensure that glucose supply to the central nervous system is not compromised.

Individuals with diabetes mellitus, a condition that involves fluctuating blood sugar levels, need not be excluded from endurance events where good control of the condition is maintained by medication and preparation made to treat hypoglycaemic shock if necessary. Adequate feeding before training or competition is advised while symptoms including difficulties in concentration, focusing and coordination should be taken as warnings.

Much attention has been focused on the significance of initial muscle glycogen stores for endurance performance, particularly as the development of the muscle biopsy technique made successive sampling of muscle tissue during prolonged exertion possible. Sal-tin (1973) reported a correlation between starting muscle glycogen stores and ability to maintain working at 75 per cent of maximal oxygen uptake (vo2 max). Besides, Swedish soccer players with the lowest glycogen content in their thigh muscle before play were found to cover 25 per cent less distance in the second half of the game than the others. An even more marked difference was observed for running speed. Clearly where muscle glycogen stores are near depletion the pace of work must be reduced or exhaustion follows. The maximal work load at which an individual can perform sustained exercise is determined by the local capacity to oxidise pyruvate in the working muscles. Local glycogen stores are critical for performance between 65 to 89% vo2 max (Hultman, 1971). These stores can be dramatically augmented by an astute combination of training and diet. After glycogen depletion by exhaustive training re-synthesis overshoots to double initial concentrations. The final levels can be boosted further if carbohydrates are avoided for a few days after glycogen depletion. The optimal routine first described by Saltin and Hermansen (1967) is undertaken throughout the week before competition starting with an exhaustive training session. This is followed by three days on a carbohydrate-free diet during which training continues. Then follow a further three days on a carbohydrate enriched diet, in the last two of which training is very light to avoid any reduction of the replenished stores. This procedure is commonly used by marathon runners in the week before racing but is impractical for many sports because of the greater frequency of competition. It is unlikely to be of benefit where competitions are less than one hour in duration.

The relative contribution of fats and carbohydrates depends on the exercise intensity and is modified according to the duration of activity while the type of work, fitness and prior diet affect the proportions of each source used. Carbohydrate metabolism increases with work intensity while fat involvement is greater as exercise is prolonged. Indeed one advantage of prolonged training is the improvement produced in fat mobilisation and utilisation. At the same relative work load, endurance trained athletes derive a greater percentage of their energy from oxidation of fatty acids and less from carbohydrates than do untrained subjects. Though mechanical efficiency is lower when fat is the source of fuel, when the individual case is considered, the greater fat involvement ensures that glycogen is spared so that depletion occurs later, if at all. As caffeine stimulates free fatty acid mobilisation and subsequent oxidation, its ingestion in the hour before endurance work has been advocated by Costill et al (1978). A practical disadvantage is its diuretic effect. The influence of the type of work on choice of substrate is seen in the higher carbohydrate participation during arm work than during leg work at a given level of oxygen uptake. Additionally intermittent work or changes of pace make disproportionate demands on carbohydrate reserves. An inconsistent pace at the commencement of a distance race may contribute towards an increasingly early decrement in performance.

The benefits of a carbohydrate-rich diet for athletic performance are well established. Bergstrom and colleagues (1967) showed that subjects on a diet heavily loaded with carbohydrates could continue at a fixed work load for 189 minutes compared with 126 minutes for subjects on a normal mixed diet and 59 minutes for those on a fat plus protein diet. Broader aspects of diet and nutrition are now considered.

Nutrition

Endurance athletes in hard training tend to expend supra-normal amounts of energy. Finnish distance runners, for example, increased daily energy transformations from 12.56 to 14.65MJ (3 000 to 4000kcal) to 20.93 to 25.12MJ (5 000 to 6000kcal) between 1968 and 1972 with an increase in training distance covered from 70 to 300 km/week (Kvanta, 1972). The balance of dietary foodstuffs is normally 10 to 15 per cent protein, 35 to 40 per cent fat and 50 per cent carbohydrate. This balance can be retained during hard training simply by eating more of the same, though a further bias towards carbohydrate rather than protein more readily provides the energy for arduous physical effort. A large protein intake does not improve endurance performance and is disproportionate to the athlete’s needs.

With athletes training twice or three times and consuming over 21MJ (5 000kcal) daily, eating is best distributed over five to six separate meals rather than the conventional three. This could involve three major meals and three snacks conveniently placed according to the timing of training sessions. This would avoid overloading the digestive system and permit adequate pre-activity nourishment. Meals before competition should be light, preferably mainly carbohydrate and at least three hours beforehand to allow time for digestion. In many sports a liquid pre-game meal has proved effective. Eating too near vigorous exercise may be a cause of stitch, usually felt as a sharp pain in the upper abdomen. Stopping briefly may relieve the condition as can abdominal breathing with exhalation against resistance, while modifying pre-start eating can help prevent it.

Endurance athletes are extremely susceptible to suggestions of magical diets. Vitamin and mineral supplements tend to be readily accepted on presentation of flimsy evidence of any benefit. In the vast majority of cases a well balanced diet is all that is necessary. Fat soluble vitamins – A, D, E, and K – are stored in the body and can be toxic in excess. Water soluble vitamins are rapidly excreted in excess and supplementation leaves the athlete with the doubtful privilege of producing expensive urine. Physical performance is however decreased with deficiencies in B-complex or c vitamins, both involved in energy metabolism, while vitamin E deficiency causes muscle degeneration. Deficiency in B-complex and E vitamins is rare since they are widely distributed in foods. Much vitamin c is lost in processing and cooking foods so some fresh fruit can be a desirable inclusion in the athlete’s diet.

Minerals, like vitamins, are important dietary substances being needed for cell structure and metabolism. Mineral deficiencies can reduce performance proficiency especially in hot conditions where sweating reduces sodium and chloride stores. Exercise can also alter the body’s balance for potassium, calcium, magnesium and phosphorus. A generous salting of food or the taking of a commercially available electrolyte solution should adequately maintain sodium and chloride levels in hard training sessions. Excessive salt intake can however lead to unwanted potassium loss and water retention. Potassium deficiency is inimical to efficient muscle function as well as to storage and synthesis of glycogen and can develop during training in very hot conditions (Knochel, 1977). In stressful training in hot climates limited potassium supplementation may be desirable. Many of the foods rich in potassium also contain magnesium which, too, is lost in sweat: these include fruit juices, cabbage, carrots and nuts. Milk, cheese and fish in the diet ensure against any possible calcium and phosphate lack. Iron which is the active constituent of haemoglobin is the most common of mineral deficiencies particularly in females. Anaemic individuals may also contract zinc shortage, a mineral constituent of some enzymes involved in muscle metabolism. Other trace elements essential for prevention of anaemia include copper and cobalt, a constituent of vitamin B12. The general symptoms of fatigue associated with anaemia should be heeded by undergoing a blood test and can be prevented by the inclusion of meat, liver and greens in the diet.

Whatever conclusions are drawn by the scientific community about diet for endurance specialists they are unlikely to be hailed universally by sports practitioners. Scientific knowledge is probably insufficient at present to set out guidelines in detail for optimal nutrition during hard training. Authorities agree that the secret to successful attainment of potential lies in training rather than elusively in the contents of a pill or bottle. A varied natural diet consisting of grains, fresh vegetables, fruits, berries, milk and eggs, supplemented if so desired by fish and lean meat provides all the fats, carbohydrates, essential proteins, minerals and vitamins needed.

ENDURANCE CAPACITY

Aerobic capacity

The maximal oxygen uptake (vo2 max) of the individual is generally accepted to be the best overall physiological measure of aerobic power and hence endurance capacity. It indicates the maximal rate at which oxygen can be consumed per minute or the power of the aerobic system. In sports without weight categories where body mass is not repetitively lifted against gravity, the absolute value is important. In long-distance running the relative value expressed per kg bodyweight is more crucial. Both absolute and relative values may be relevant as, for example, in crosscountry skiing where the mass on the skis is helpful going downhill and the relative value significant in level or uphill work. The most arduous sports include cross-country skiing, distance running and rowing, while elite competitors in these sports have high values for vo2 max.

Measurement of vo2 max requires laboratory facilities for collection of expired air and analysis of its volume, o2 and co2 content . Repeated measurements allow monitoring of individual response to endurance training as well as evaluation of the regime employed. The vo2 max does not provide the complete answer to the determination of endurance performance though it is highly correlated with proficiency in stamina events, including for example crosscountry running (Costill, 1967) and work-rate in soccer (Thomas and Reilly, 1976). An important consideration is the percentage of the aerobic power that can be utilised throughout the contest. Costill (1972) showed that top marathon runners were not necessarily those with the highest vo2 max figures but rather those that could work at a high fraction of it for the complete race.

The vo2 max presents an overall picture of the functional integration of the lungs, heart, blood and active muscles in aerobic work. Ventilatory capacity does not normally limit endurance performance except at altitude though pulmonary dimensions may show chronic adaptive changes, especially if hard training is undertaken in adolescence. In swimming events, apart from the backstroke, the respiratory rate is tied to the stroke rhythm and must be entrained to it. The ability of the heart to cope with the needs of working muscles for a greater supply of oxygenated blood is normally a more likely limitation of performance.

The volume of blood pumped from the heart per minute is known as the cardiac output. Its increase is much more pronounced than that in arterio-venous o2 difference in the acute response to exercise. Although considerable variability in chronic response exists among individuals, on average the maximum cardiac output and the extraction of o2 by the active muscles appear to account equally for the rise in vo2 max with training (Holloszy, 1978). The determinants of the oxidative capacity of the muscles are probably more important during prolonged sub-maximal work when a relatively small muscle mass is involved (Rusko, 1976). The greater cardiac output with training is attributable to a larger stroke volume or amount pumped out per heart beat. This itself is the result of cardiac muscle hypertrophy, a more powerful pumping action and an enlarged chamber size. The low resting pulse rates of endurance athletes are an obvious training effect. Those changes have long been known but were once thought to be pathological. There is no evidence that the normal healthy heart can be damaged by hard exercise. Myocarditis or inflammation of the heart muscle is possible if exercising severely while suffering viral illness. Caution is needed in returning to hard training or competition after influenzal infection.

The blood pumped from the left ventricle of the heart carries oxygen bound to haemoglobin for distribution to the various regions of the body. The total body haemoglobin (TBH) is higher than normal in top athletes and is significantly correlated with vo2 max.

The high TBH values are explained by a greater blood volume so that haemoglobin concentrations may be normal. Brotherhood et al (1975) found that athletes taking iron and folate supplements were no different in haematological status than others: this observation casts doubt on a widespread practice among endurance athletes, with the exception of females and cases of anaemia. Additionally, 2, 3-diphosphoglycerate (2-3 DPG), an intermediate involved in red blood cell metabolism, was found to be higher in athletes than non-athletes, which would provide them with an advantage in liberating 02 to the tissues. Athletes who donate blood are likely to have reduced endurance performance for two to three weeks afterwards due to the lowered oxygen carrying capacity until the red cell production in bone marrow compensates for the loss. Altruistic athletes feeling an obligation to donate blood will suffer only minimal disruption if they do so during the off-season.

Substantial improvements in oxygen transport capacity and endurance performance have been reported by Ekblom et al (1972) for blood doping. This refers to acutely expanding blood volume (hypervolemia) and the number of red cells (polycythaemia). Elsewhere, Williams (1978) cast doubt on the effects of blood withdrawal and re-infusion as an ergogenic aid, whether it be whole blood, plasma or packed red cells.

It is likely that the quality of storage of blood withdrawn, the timing of the injection and the quantity involved may be critical for achieving any effects. Though banning blood doping is futile because of difficulties of detection, its practice contravenes normal medical and sporting ethics.

At tissue level highly trained athletes are capable of extracting a greater proportion of the oxygen offered for a number of reasons. Oxidative enzymes, which provide for the conversion of fuel into energy through the aerobic resynthesis of ATP, increase with training thereby facilitating aerobic metabolism. Proteins, particularly cytochrome C, involved in aerobic metabolism and located in the mitochondria, increase. Secondly, the number and size of mitochondria, the sites of aerobic metabolism, increase providing a greater surface area for oxygen utilisation. Thirdly, endurance training provokes increased capillarisation within muscle which assists in oxygen supply. Myoglobin content in skeletal muscle increases following training, aiding the diffusion of oxygen from the cell membrane to the mitochondria where it is consumed.

A long-term effect of endurance training is the better mechanical efficiency that is achieved. This means that greater external work is possible for a similar outlay of oxygen consumption. The improvements reflect the more skilful execution of performance, a better co- ordination of muscles for the task in hand and optimal use of the oxygen delivered to them. The degree of improvement is variable being greater for running than cycling and greater still for swimming with its larger muscle mass involvement.

Heritability and trainability

Inevitably the question arises as to the relative contributions of nature and nurture in the emergence of an endurance athlete. It is generally considered that champions are born more so than made and Astrand (1967) concluded ‘I am convinced that anyone interested in winning Olympic gold medals must select his or her parents very carefully’. Other authorities might even extend the choice to include grandparents. The variance between individuals in voa max is considerably greater than the 20 to 25 per cent generally regarded as a good training effect. However, improvements approaching 45 per cent have been found when intensive training programmes are conducted for longer than the customary experimental periods of investigation (Hickson et al, 1977; Holloszy, 1973). The predominance of endowment over environment in determining the maximal aerobic power was substantiated by Klissouras (1971) in investigations of intra-pair differences in identical and non-identical twins. In his study the variation observed in maximal aerobic power was 93 per cent genetically determined. However, it should be realised that such figures might be misleading when considering top athletes since nature and nurture are intertwined so that an organic attribute cannot develop without both a hereditary basis and an appropriate environment.

Genetic factors may also be exemplified in the distribution of different types of skeletal muscle fibres. Two contrasting general fibre types have been distinguished, fast twitch (FT) or white, and slow twitch (ST) or red. Each type is selectively recruited according to the task required: one type cannot be altered to the other except by transplanting their nerve supply. A subdivision of FT fibres is described as fast red or fast oxidative glycolytic (FOG). This has a rich vascularisation, high myoglobin and mitochondrial content and so a high capacity for oxidative as well as anaerobic metabolism. Though the muscle machinery is the same for the different fibre types, the myosin in FT and FOG contains a high level of myosin ATPase, the specialised section of the muscle protein controlling the rate at which ATP is split, compared with lower levels in ST fibres. These levels are increased in ST fibres and decreased in FOG fibres with no changes in the fast white type since they are not recruited in endurance training except intermittently during games. It seems the fast red type tends to take on more characteristics of the ST fibres. Efforts such as repeated 400m runs increase the capacity of the anaerobic system in ST fibres but have no effect on the fast-contracting types. Ingjer (1979), using a refined ATPase method for subdividing FT fibres into four groups, found evidence of changes in these subtypes with endurance training. All fibre types showed a transition towards more mitochondria-rich fibres in the training period. Consequently it seems the biochemical characteristics of muscle fibres can be selectively manipulated to an extent by training though the distribution of fibre types between ST and FT is completely determined by genotype.

Body build is also largely the result of endowment and can be a significant factor in determining athletic success. There is a tendency at top level sport for individuals to gravitate towards the task they are an-thropometrically best suited to. This is manifested in terms of body size, proportions, shape and composition. Runners, for example, are on average smaller, leaner and less muscular as the competitive distance increases. The greater surface area relative to mass gives the smaller individual an advantage in heat dissipation. However, this can obviously be outweighed by compensating factors since some very good marathon runners are tall. Walkers tend to have more body fat than runners of corresponding distances and since body mass is not lifted vertically to the same extent they are not appreciably disadvantaged by the excess dead weight (Reilly et al, 1979). Apart from diet the total energy expended in training is the predominant factor in assisting weight control so that once the training severity exceeds the stimulus threshold, prolonged work periods are recommended for losing weight.

Distance runners also have less muscle mass than their middle-distance counterparts and, since strength tends to be correlated with muscular endurance, could benefit from greater attention to strength training. This conceivably would provide some protection against injury, especially if the tibial, quadriceps and abdominal groups are developed to counter-balance the anticipated training in the calf, hamstrings and iliopsoas from repetitive locomotion. Games players tend to have impressive muscular development to fit them for the rigours of match play.

Somatotype describes physique in the three dimensions of endomorphy (fatness), mesomorphy (muscularity) and ectomorphy (linearty). The somatotype is mainly inherited but is to a much lesser degree affected by environmental factors including nutrition and training. The method has been used widely in describing the physiques of athletes. The majority of Olympic champions appear in the northern section of the somatochart while participants in particular sports tend to cluster together with minor ethnic variations. Endurance athletes are easily separated from specialists in anaerobic power events while specific requirements of the various endurance games are also implicated. It is possible that individuals could flounder indefinitely in an activity for which they are physically ill-equipped by nature, though it is likely that a subtle process of self-selection usually applies.

TYPES OF TRAINING

Long slow distance (LSD)

Long slow distance (LSD) training implies continuous low-intensity activity of an extended duration. This approach has been attributed to the German coach and physician Van Aaken in the 1960s. It was also included about the same time in the background preparation of New Zealand runners coached by Lydiard who advocated high mileage easy runs in the off-season. Applied to other sports it places emphasis on prolonged uninterrupted work-outs eliciting heart rates 60 to 80 per cent of maximal. This roughly corresponds to running speeds of 16 to 14kmh-1. Indeed it is probably effective once the training stimulus threshold is exceeded. This can be calculated according to Karvonen’s (1957) formula using the heart rate (fH):

Training fH = 0.60 (fH,^ – fH rest) + fH rest

An individual with a maximal heart rate of 180 beats min’1 and a resting heart rate of 60 beats min-1, will have a training target heart rate of 132 beats min’l. The formula is frequently used in evaluation of jogging regimes.

The extreme durations in LSD work can lead to significant muscle and joint discomfort and real injury. Training sessions should be progressively lengthened as fitness develops and long work-outs should not be attempted without a gradual build-up.

As the cardiovascular and respiratory systems are not distressed by LSD the more pronounced effects are likely to be peripheral. The respiratory capacity of muscle fibres is related to their habitual contractile activity so that in broad generalisation the greater the number of contractions, the greater the improvement (Holloszy et al, 1977). Considerable increases are found in muscle mitochondrial content and oxidation of fats and carbohydrates improves. Enhanced mechanical efficiency represents an overall training effect.

Tempolauf

Tempo training emphasises high intensity efforts equalling or approaching competitive stress. Its basis is to accustom the performer to the tempo of competition. It may take the form of continuous or intermittent work as in time trials or brief repetitions of the competitive distance with adequate intervening rest periods. It should be used guardedly for time-trial purposes.

The demands of this type of training are harsh, especially if frequently employed. Slower-paced variations should be used in conjunction with tempolauf to allow days of relative relief from the exhaustive high intensity work. Apart from its physiological effects it is likely to assist pace judgement and condition the athlete to the pain of competition.

Fartlek

Fartlek or speed-play is a form of continuous exercise fluctuating in intensity providing welcome variety to the normal routine. It originated in Sweden during the 1940s, being particularly suited to the Scandinavian forest paths but is also compatible with parklands or hilly countryside. Work intensity is varied spontaneously from fast bursts to jogging according to the terrain and the athlete’s current disposition. The relative freedom from time and distance considerations make it immensely enjoyable. It is claimed to develop aerobic and anaerobic endurance equally with some effect also on speed (Wilt, 1968). Though originally devised for runners it is immediately applicable in principle to the training of other sports such as cross-country skiing, cycling, orienteering and race-walking.

Pyramid training

Pyramid training provides a formal method of varying the duration and intensity of work bouts and the recovery intervals. It was incorporated in training programmes of the Russian distance runners Bolotnikov and Kuts. Sessions may involve, for example, precise interval accelerations of 100,200,400,800 and 1200m. This approach is appropriate also to water sports such as canoeing and swimming. It ensures that speed and speed-endurance are not neglected in the quest for greater endurance.

Interval training

Classical interval training was developed in Germany in the 1930s and in its various forms has been the basis of training of numerous world and Olympic champions in running, cycling, rowing, swimming and other sports. It involves alternating short periods of hard work with brief periods of rest or reduced activity. The work periods may vary from 0.5 to 5 minutes while recovery varies in duration from that of the work bout to approximately double it. The complete work-out is fairly tightly structured and monitored by stop-watch.

The variables associated with interval training include the number of repetitions, the duration of effort, work intensity and duration of recovery. Altering the duration of effort between days introduces variety into the programme. The number of repetitions can be systematically increased as conditioning develops, while the pace can then be accelerated. Finally, the recovery periods can be shortened: where these are inadequate to allow recovery, anaerobic endurance is also stressed. Light activity rather than complete rest in the intermission speeds lactate removal from the active muscles.

In the original form pioneered by Gerschler and Reindall the optimum work intensity was considered to be that which elicited heart rates of about 180 beats min-1 while recovery was terminated when the rate dropped to around 120 beats min-1. These rates were considered to provide the optimum stimulus for the heart to expand and pronounced hypertrophy was found to result. The work speed can however be varied to put more or less emphasis on anaerobic endurance as peripheral, as well as central factors, respond to this type of training.

Parlauf

Parlauf or continuous relays can be introduced periodically into training routines especially for stimulation of club morale. It can employ two, three or four members per team for a period pre-determined by the coach. In the two-per-team format, rest periods do not allow complete recovery so that performance inevitably drops off. This type of regime is particularly suited for swimming and middle-distance running but can also be incorporated into the fitness training of games players.

Circuit training

Circuit training provides a good method of general conditioning. The individual rotates around a series of exercises laid out in a circle, usually 8 to 12 separate exercises being involved. Muscle groups are varied between work stations so that local fatigue is avoided while stress is maintained on the cardiovascular system. This method lends itself to group involvement and so is frequently used for squad training.

As fitness develops the number of sets can be increased and the pace accelerated. As progress is readily apparent the athlete is easily motivated by this form of training. It is particularly popular in pre-season conditioning of games players.

Combination methods

It might be thought that the ideal endurance training programme is a combination of the best features of various specific methods so as to secure the best of all possible worlds. However, there is no guarantee that the benefits are. in any way additive and indeed the different regimes overlap to a great degree in their physiological effects. Besides there is unlikely to be one perfect schedule which will be applicable to all as each individual athlete is unique with special strengths and weaknesses. Experience indicates that athletes do employ admixtures of different approaches according to what seems to work for them.

Experimentally it is difficult to unravel the complex ways in which the different elements of fitness in a combined programme interact. It is known that aerobic training leads to a fall in muscle glycolytic enzymes (Sjodin et al, 1976). This has been substantiated in the fall in strength and anaerobic power of soccer players after a pre-season programme of aerobic conditioning (Reilly and Thomas, 1978). For this reason some speed-endurance work should be included in endurance training programmes. Conditioning the cardiovascular system should be given priority in the early build-up to the competitive season. Specificity of training ensures that local effects are achieved. During the competitive season more emphasis may be placed on the speed of work. Competitive performance will provide invaluable feedback as to ongoing modifications. These subde adjustments in programming training are, however, currently as much an art as a science.

Training and competing in endurance sports make enormous claims on personal time and effort. It is important for individual peace of mind that work-outs be organised so that a regular habitual pattern is established: soon training sessions are felt to be an integral pan of the daily routine. Rapid results should not be expected as improvement tends to be gradual. The training load should be elevated in sensible increments to avoid injury from excessive overload. It is also sound to intersperse easy and hard days work particularly during periods of heavy competition. A circumspect approach to conditioning should enable the body’s tremendous adaptive potential to be realised without interruption from trauma.

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