REVIEW ARTICLE

Sports Medicine 12 (3): 161-183. 1991 0112-1642/91/0009-0161/$01.50/0 © Adis International Limited. All rights reserved. SP01054

Quantification of Training in Competitive Sports Methods and Applications William G. Hopkins Department of Physiology and School of Physical Education, University of Otago, Dunedin, New Zealand

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Summary

Summary I. Methods for Quantifying Training 1.1 Retrospective Questionnaires 1.1.1 Question Construction 1.1.2 Time Frame 1.1.3 Method of Administration 1.1.4 Pilot Studies 1.1.5 Reliability and Validity 1.1.6 Compliance 1.2 Diaries 1.3 Physiological Monitoring 1.3.1 Oxygen Consumption 1.3.2 Heart Rate 1.3.3 Blood Lactate 1.4 Direct Observation 2. Applications for Training Data 2.1 Motivation and Systematisation 2.2 Training Prescription 2.3 Sport Science 2.3.1 Characterisation of Training 2.3.2 Performance Prediction and Enhancement 2.3.3 Overtraining 2.3.4 Reproductive Dysfunction 2.3.5 Injury and Illness 2.3.6 Nutrition 3. Conclusions and Future Research

The training of competitive athletes can be assessed by retrospective questionnaires, diaries, physiological monitoring and direct observation of training behaviour. Questionnaires represent the most economical, most comprehensive and least accurate method. Diaries are more valid, but their drawbacks for long term quantitative studies are poor compliance and difficulties in processing the data they generate. Physiological monitoring (of oxygen consumption, heart rate or blood lactate concentration) provides objective measures of training intensity, and direct observation gives valid measures of most aspects of training; however, these methods are impractical for continuous, long term use.

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Coaches and athletes quantify training for purposes of motivation, systematisation of training and training prescription, but there has been little study of the use of training quantification by these practitioners. Motivation and systematisation are probably achieved best with diaries. Direct observation appears to be the best method of ensuring compliance with a training prescription, although heart rate monitoring is also a promising method for prescribing endurance training intensity. Sport scientists quantify training to study its effects on the performance and health status of competitive athletes. Most studies have been descriptive rather than experimental, and unvalidated questionnaires have been the predominant method of assaying training. The main areas of research include performance prediction and enhancement, overtraining, reproductive dysfunction, injury, illness, and nutritional status. Training has substantial effects in all of these areas. There is a need for more experimental studies that utilise validated measures of training to investigate how to reduce sports injuries and enhance competitive sports performance. More attention could also be given to methodological issues of training quantification.

The accumulation of evidence for a link between habitual physical activity and health has stimulated considerable interest in the methodology of measurement of physical activity in populations (Baranowski 1988; Caspersen 1989; LaPorte et al. 1985; Montoye & Taylor 1984). In competitive sports there may be much stronger links between habitual activity (training) and outcomes such as performance and injury. It is therefore surprising that the methodology of measurement of training has not been a focus of attention in the sport science literature. Indeed, this is such a blind spot that some papers reporting on the effects of training neglect to describe or state the method by which their measures of training were obtained. The first section of the present article attempts to review the methods for quantifying training in competitive sports, with an emphasis on practicalities. A reasonable number of methods-based publications on physiological monitoring was available for review, but research on the design and use of questionnaires and diaries for training is virtually nonexistent. Part of this section has therefore been written as unreferenced general advice. The second section reviews the ways athletes, coaches and sport scientists use training data. It includes an epidemiological perspective on the kinds of study that are reported and a brief summary of some of the findings. More detailed reviews of epidemiological issues in sport science

have appeared recently, although these have been restricted to the study of sports injuries (Noyes & Albright 1988; Walter & Hart 1990). Readers should note that the present review does not deal with training programmes, which are another neglected topic in the sport science review literature. Tests of fitness and performance are also outside the scope of the present article (for recent reviews see Foster 1989; Noakes 1988).

1. Methods for Quantifying Training Training data are obtained currently by 4 methods: retrospective questionnaires, diaries, physiological monitoring and direct observation. Retrospective questionnaires and diaries are closely related instruments: both obtain data recalled from the athlete's memory after the training activity has ceased, and both can yield information on any aspect of training. They differ in the frequency and method of administration: questionnaires are completed either on one occasion or infrequently, and may be interviewer- or self-administered; diaries are self-administered at frequent intervals with the aim of obtaining an uninterrupted stream of training data. There are 3 methods of physiological monitoring in general use: measurement of oxygen consumption, heart rate and concentration of blood lactate. These methods yield information about the intensity of training activity. Finally, direct observation, which is carried out by the coach or sport

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scientist as the training session proceeds, can provide data on most aspects of training. 1.1 Retrospective Questionnaires Questionnaires have several clear advantages over other methods of quantifying training: they are by far the easiest and cheapest to administer; they can be constructed to yield information on every aspect of training over any time period; they have the least problems with athlete and coach compliance; finally, they do not interfere with the training programme. However, their great drawback is the SUbjective nature of the measures they provide: questions may be misunderstood, responses may be distorted intentionally or unintentionally, or the required information may be forgotten. The performance of questionnaires can be enhanced if due attention is given to methodological issues of question construction, time frame, method of administration, pilot studies, validity and reliability, and compliance. These issues will be discussed briefly. For further advice on questionnaire design and use, see Cummings et al. (1988) Kelsey et al. (1986) and Thomas and Nelson (1990). 1.1.1 Question Construction Questions should be worded to accommodate any subjects who might have poor reading ability. Compound sentences, double negatives, and words with 3 or more syllables should be avoided. Uniformity in the style of questions and required responses will improve comprehension and ease of responding. It is usually better to provide structured responses for selection rather than space for open-ended responses, even if the questionnaire is administered by interviewer. Self-administered questionnaires should be constructed with a flexible word-processing and drawing package. Most wording should be in a large, easily-read font. Items and responses in multi-item inventories can be delineated with alternate strips of background shading to reduce the possibility of responses being recorded against the wrong items. At the end of the questionnaire an instruction to

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the athlete to check back for errors and questions that may have been missed should be provided. Most questionnaires about training focus on volume, which for sports like running, cycling and swimming is often asked as distance travelled each week (or each microcycle, if the athlete's training microcycle is not 7 days in duration). A more valid measure of volume may be obtained by asking instead for weekly training duration: duration allows for more useful comparison between athletes differing in ability, and it may be recalled more accurately than distance. Weekly duration can also be obtained by asking about the frequency and duration of individual training sessions. Questions about intensity should be included routinely, either by asking about training pace as a speed or as a percentage of maximum or competition effort, or by providing a Likert scale of intensity. The Borg scales are often used for obtaining measures of perceived intensity (reviewed by Williams & Eston 1989), but condensed scales or scales with simpler numbering may be less confusing to athletes and therefore more effective. If athletes train at a variety of intensities within or between sessions, it may be necessary to ask for the time spent in broad categories of intensity, such as hard, moderate and easy. 1.1.2 Time Frame There are no theoretical limits on the time frame that a questionnaire can attempt to assay: for a coach questions about recent training sessions might be most useful, while for someone studying injury the training period of interest might be months or years. It is obvious that questions about training in a recent, short time period are more likely to yield accuracy of detail than those about training in long-past or extended time periods. However, recent training is not necessarily representative of an athlete's general training, because recent training can be determined by the particular phase of the training programme, or by illness, injury or other unusual circumstances. Therefore, in studies where the main focus is the pattern or cumulative effect of training over an extended period, general questions about typical or usual train-

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ing in that period are likely to be more valid than detailed questions about recent training. Baranowski (1988) has presented a discussion of this issue as it relates to physical activity questionnaires for populations generally.

1.1.3 Method of Administration It is generally held that a questionnaire has more validity when it is administered by a trained interviewer than when it is self-administered (e.g. O'Toole et al. 1986). Questionnaires should therefore be administered by interviewer whenever time and resources permit. However, to minimise misinterpretations and transcription errors by the interviewer, it is advisable to construct the questionnaire as if it were to be self-administered. This will reduce errors by the interviewer, and it will also reduce biases that could be introduced if the interviewer has to explain items or make arbitrary decisions in recording responses. 1.1.4 Pilot Studies Draft versions of the questionnaire should be trialled initially on colleagues and, after revision, on a small sample of the athletes for whom it is intended (e.g. Walter et al. 1988). After further revision serious consideration should be given to a larger-scale pilot study to determine test-retest reliability and/or some objective measure of validity. Minor revisions can then be made without further pilot work. If major revision of key questions is indicated, a further large-scale reliability or validity study will be necessary. 1.1.5 Reliability and Validity The limitations of human understanding, memory and honesty produce errors in measures obtained from questionnaires. It is important to have some estimate of the magnitude of these errors, because they degrade the apparent strength of relationships between measures. The extent of error in a measure can be expressed formally in terms of reliability and validity. Estimates of reliability and validity are commonplace in the psychological literature, and they are also reported frequently for measures of physical activity in population studies.

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However, estimates for the reliability or validity of measures of athlete training derived from questionnaires have yet to be reported. Reliability refers to the consistency or reproducibility of a measure, while validity refers to the relationship between the measure and its underlying true value. Reliability is easily determined by repeat administration of the questionnaire to a random subsample of subjects, and this should be done routinely in questionnaire-based studies. Validity is more important than reliability, because a measure can be reliable but invalid. To determine validity, an objective measure of training would be correlated with the subjective measure derived from the questionnaire. Physiological monitoring or direct observation of training sessions could be used to obtain the objective measure, but these methods might be impractical for validation of measures that represent aspects of training with a time frame of more than a week or so. There is also a fundamental statistical problem with determining validity when, as is often the case, the number of the subjects in a study is less than about 30: all subjects would have to take part in the validity study for validity to be estimated with acceptable confidence limits, but this would make the subjective measures from the questionnaire redundant. These problems may help explain why validity has been neglected in questionnaire studies of training.

1.1.6 Compliance If the sample selected for a study is not representative of the population of interest, then the findings of the study may also be unrepresentative or biased. Samples should therefore be chosen randomly. Bias can also arise if there are substantial differences between subjects who agree to fill in a questionnaire and those who do not. For this reason, a study must report the compliance (response) rate. It may be difficult to publish findings in good journals if the rate is less than 70%, so it is vital to do everything possible to enhance compliance. If athletes are contacted by mail, great care should be taken with the accompanying explanatory letter: it must be short, simple, informative

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and persuasive. An offer of a summary of the results of the study may be a helpful inducement. Several reminder notices will need to be sent to some subjects. Length of the questionnaire or interview session may be a deterrent for some athletes: 30 minutes is probably an upper limit for completion time. Lack of confidentiality is another potential deterrent, so all questionnaires should be identified only by a code number. If compliance rates are low, a study can gain credibility by showing that nonrespondents do not differ markedly from respondents on the major variables being surveyed. To determine this would necessitate a different approach to the nonrespondents, for example a personal visit or a phone call if the original contact was attempted by mail (e.g. Koplan et al. 1982).

1.2 Diaries From the point of view of sport research, diaries have one substantial advantage over questionnaires: diary data are likely to be more valid, because they are recorded not only in close temporal proximity to the training sessions, but also for all training sessions over an extended period. In other respects diaries present more problems than questionnaires. The greatest difficulty is with compliance, which may be acceptable at the start of a study but which may drop to an unacceptable rate as athletes lose interest. Regular collection of diary forms or regular encouragement will lessen the drop-out rate, as will keeping the diaries short and simple. Another major problem with diaries is the huge volume of data that they can generate, so where possible the diary sheet should be designed to allow athletes to record their responses directly into boxes ready for entry into a computer (e.g. Poehlitz 1988). When the data have been captured, there is the problem of how best to produce overall measures of training from the individual training sessions. Simple measures of total exposure to training or to the various modes of training may be appropriate for seeking relationships with rates of illness or in-

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jury, but it is less clear how to derive training measures for investigating relationships between training and performance. Banister and his colleagues have suggested a method that takes into account the contribution that each training session might make to an athlete's ongoing fitness and fatigue (Morton et al. 1990). Pilot studies are as necessary for a newly-devised diary form as they are for a questionnaire. However, there is a different emphasis on reliability and validity for a diary compared with that for a questionnaire. There is little point in determining test-retest reliability if the athlete updates the diary every day, because the necessary close proximity of the test and retest will make very high correlations inevitable. On the other hand, determination of validity is much more feasible for a diary than for a questionnaire, because the short time interval represented by a diary entry can be observed or monitored relatively easily. There appears to be only one report in the literature containing data that validate a diary-derived training measure: Robinson et al. (1991) found a modest correlation (0.75) between perceived intensity and mean heart rate for training sessions of individual distance runners. 1.3 Physiological Monitoring Methods of physiological monitoring fall into two groups: those that produce an integrated or average measure of training over a period of time, and those that monitor a training session while it is in progress. None of the techniques in the first group provides sufficiently detailed data about training to earn more than a brief mention here. The only widely-used technique in this group is the fitness test, which provides physiological and sportspecific performance measures such as the maximum oxygen uptake, anaerobic threshold and maximum attainable pace. To the extent that fitness improves with training, a change in a performance measure assesses whether training has been effective; however, a fitness test says nothing about the mode, frequency, duration, intensity or skill components of the training. Two other tech-

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niques in this group are assay of muscle glycogen and assay of total energy consumption. Glycogen assays might be useful for ensuring that training energy expenditure does not exceed the regenerative capaoity of the energy store in muscle (Costill et al. 1988), but the necessary muscle biopsy is too traumatic for continual use on the same athlete. Total exercise energy consumption can be measured using doubly-labelled water (Westerterp et al. 1986; Groves 1988), but the method is far too expensive for routine use and does not distinguish between the contributions of intensity and duration to the total energy expenditure. A large number of physiological variables change during exercise, but only oxygen consumption, heart rate and blood lactate concentration have been used to monitor training sessions in progress. All three are used to determine the intensity of exercise.

1.3.1 Oxygen Consumption Training that can be sustained at a constant pace for more than a few minutes is performed with energy supplied almost entirely from the aerobic energy system. Furthermore, the relationship between oxygen consumption (V02) and output power is close to linear over the range of intensity from rest to maximum steady-state (Astrand & Rodahl 1986). The steady-state V02 is therefore a good measure of the intensity of steady-state training. The intensity of short bursts of activity, such as occur in repetition or interval workouts, cannot be measured directly as oxygen consumption, because the response time of the aerobic system is too slow (e.g. Hagberg et al. 1980) and because such workouts are often supramaximal. It is useful to express the training V02 relative to (as a percentage of) the peak V02, which is usually determined in an incremental test to maximum effort using the same mode of exercise as the training activity. The relative V02 allows more meaningful comparison of the training intensities of athletes who differ in body mass, performing ability or exercise efficiency. Measurement of oxygen consumption requires athletes to breathe into special apparatus to allow expired gas to be collected or analysed. The train-

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ing activIty is therefore most conveniently performed in a laboratory using a sport-specific ergometer. Analysis can be performed as the activity proceeds with one of several commercially-available metabolic carts or with a similar computerised system of analysers of gas volume and composition; alternatively, Douglas bags can be used to store the gas for later analysis. If analysing or collecting gas is too difficult during the training activity, it is possible to analyse or collect gas for several minutes immediately after cessation of activity, and then to calculate the oxygen consumption during the activity by back-extrapolation (e.g. Ricci & Leger 1983). Oxygen consumption appears to be a very stable measure of training intensity: the coefficient of variation over a 6-month period for trained runners running on a treadmill at a constant speed was only 3% (Daniels et al. 1984). An error in peak V02 of about 5% (Rowell 1974) will compound with this error if intensity is expressed as relative V02. Another potential source of error is an upward drift in the V02 of up to 5% per hour during high-intensity constant-load exercise (Rowell 1974).

1.3.2 Heart Rate Heart rate shows a response to exercise similar to that of oxygen consumption, so it can be used in a similar fashion to measure intensity when work load is maintained reasonably constant for several minutes or more. It has the advantage over oxygen consumption of being far easier to assay. Use of the heart rate has also been suggested for gauging times for recovery between intervals (Dare 1979), although this has not been investigated scientifically. In the laboratory heart rates are usually measured with an electrocardiograph. Accurate measurement of heart rate in the field used to be achieved with expensive telemetry or Holter monitoring, but the advent of reliable miniaturised cardiotachometers has brought objective monitoring of training intensity within reach of the average athlete. A variety ofthese devices is now available, and several studies have reviewed their validity and ease of use (Burke & Whelan 1987; Leger & Thi-

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vierge 1988; Macfarlane et al. 1989). One of the best devices is of Finnish origin: the Polar Electro Sport Tester (marketed in the US by Vantage). It consists of a sensing unit that straps around the chest and transmits a signal derived from the electrocardiogram to a wrist-watch unit that calculates and displays the heart rate. A model that stores heart rates also allows the coach and sport scientist to make use of the data, which is either replayed on the watch or downloaded into a computer or special portable analysing unit (which also provides objective evidence of the time spent training). A waterproof version can be used to monitor aquatic training. There are several ways that heart rate can be used to express intensity. The absolute heart rate is useful for the individual athlete monitoring intensity on a day-to-day basis. Heart rate expressed as a percentage of maximum controls for differences in the maximum heart rate between athletes. Differences in the resting heart rate can be taken into account if intensity is expressed as a percent of heart rate reserve: (training heart rate - resting heart rate)/(maximum heart rate - resting heart rate) x 100 (e.g. Karvonen & Vuorimaa 1988). A very practical and apparently very effective method of specifying intensity is to express training heart rates as a percentage of race-pace heart rate (Spangler & Hooker 1990). Finally, the heart rate recorded in the field can be converted to an oxygen consumption or other measure of training pace or power using relationships between heart rate and pace derived for each athlete from a series of steadystate exercise tests (Robinson et al. 1991). A potential source of error in the use of heart rate as a measure of intensity is the increase in heart rate of up to 20 beats/min that occurs during long workouts at constant high work load (Rowell 1974). The V02 during such long workouts increases to a much lesser extent, and would therefore better reflect the constant workload; on the other hand, the increase in heart rate may better reflect the increase in perceived intensity or psychophysical workload that occurs during a long workout at constant pace (Ariyoshi et al. 1979). The day-to-day variation in steady-state exer-

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cise heart rate under controlled laboratory conditions is probably about 3 beats/min (Astrand 1976). A recent study has shown that for elite runners performing continuous running sessions in the field, between-session variation in environmental conditions such as temperature and wind modify the mean heart rate for each session by only a few beats/ minute (Robinson et al. 1991). It would appear, therefore, that the heart rate can provide a precise measure of training intensity. 1.3.3 Blood Lactate The concentration of lactate in the blood rises above its resting value of 1 to 2 mmol/L only when the intensity of exercise is greater than ~60% of maximum. To a first approximation, the lactate concentration reaches a steady-state about 10 minutes after the initiation of constant-load exercise, provided the exercise is not too intense (Shephard 1982). Moreover, the relationship between steadystate lactate concentration and work load, although curvilinear, is reproducible. It is therefore possible to express the intensity of training held at a constant workload for 10 or more minutes as a lactate concentration. Exercise intensities that evoke specific concentrations of blood lactate in the range of 2 to 4 mmol/ L correlate remarkably well with the intensities of endurance rates (Jacobs 1986). A concentration of 4 mmol/L, which corresponds to the pace of an endurance race of about 30 minutes duration (01brecht et al. 1985; Tanaka & Matsuura 1984), is usually termed the anaerobic threshold (Kindermann et al. 1979). At exercise intensities above the anaerobic threshold blood lactate concentration generally rises sharply and does not reach a steady level before the subject is exhausted, so blood lactate concentration is not a well-defined measure of intensity above the anaerobic threshold. However, the peak concentration of blood lactate reached following short, high-intensity exercise does depend on the intensity of such exercise, and the possibility of prescribing sprint training using peak lactates is being investigated (Hellwig et al. 1988). Until recently, blood lactate concentrations had to be determined from venous or arterial blood

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samples with a time-consuming enzymatic assay. The recent upsurge of interest in lactates in training and sport science coincides with the introduction of compact instruments that permit rapid analysis (a few minutes) of a droplet of blood obtained by pricking the finger or earlobe. A portable instrument, suitable for use in the field without mains power, is also available. Blood lactate concentrations can be measured during normal, constant-pace training sessions, when the aim is to characterise or set training intensity directly in terms of a specific lactate concentration. It is impractical to monitor the intensity of every training session; instead, the approach is to measure lactates evoked by a range of paces, then set further workouts at a pace equivalent to the target lactate concentration. Athletes train to the set pace either by direct measurement of pace or by perceived intensity (the 'feel' of the pace that evoked lactate closest to the target lactate); 'spot checks' of lactate concentration can be made from time to time (Skinner 1987). Setting the pace by perceived intensity rather than by direct measurement may be less accurate initially, but it is more likely to keep the athlete training at the chosen intensity if fitness changes between lactate tests; it is also the only way to train at a prescribed intensity over unmarked courses. A less direct but more convenient method of monitoring session intensities can also be used. The athlete performs an incremental exercise test in which pace (or workload) is increased at regular intervals, typically 3 or 4 minutes. Blood lactate concentration is determined at the end of each interval and plotted against the pace for that interval, to produce a so-called lactate profile. The pace corresponding to the anaerobic threshold, say 4 mmolj L, is determined from the profile by interpolation. The intensity of workouts can then be described in relation to the anaerobic threshold pace. The anaerobic threshold determined from such an exercise test shows surprisingly high correlations with the pace of endurance races (Jacobs 1986); it also correlates highly with the threshold determined from a much more time-consuming series of 10to 15-minute constant-pace workouts, and the ab-

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solute values of the pace determined by both methods are very similar (Weltman et al. 1990). Difficulties may arise with lactate monitoring through differences between athletes in the concentration oflactate that represents 3D-minute race pace (e.g. Stegmann & Kindermann 1982), not~ withstanding the reported high validity of the anaerobic threshold. The value of 4 mmol/L that is often advocated for defining anaerobic threshold in a fitness test is therefore not appropriate for defining endurance race pace training for all athletes. A test that purports to define the 'individual anaerobic threshold' (Stegmann et al. 1981) may overcome this difficulty. Even within the same athlete, however, exercise that would produce exhaustion in 30 minutes does not always evoke the same concentration of blood lactate: depletion of muscle glycogen (for example by recent heavy training) may reduce the concentration (Gollnick et al. 1986; Yoshida 1986). Care should therefore be taken to standardise training for the few days before a lactate test is performed. The week-to-week variation in anaerobic threshold pace under ideal laboratory conditions is nevertheless small, about 3% (Weltman et al. 1990). 1.4 Direct Observation Virtually all aspects of training are accessible to quantification by direct observation. The measures usually obtained are the mode, duration and intensity of individual training sessions, but more subjective measures (for example a coach's global impression of whether an athlete is overtrained) are also possible. Direct observation introduces a subjective error for each observer, but eliminates any subjective error associated with each athlete. For studies in which athletes are compared, and in which there is only one observer, measures obtained by direct observation are therefore likely to be more valid than those obtained by questionnaire or diary. The measurement of training intensity by direct observation of training speed or pace can, under ideal circumstances, be more accurate than that obtained by physiological monitoring. This is be-

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cause the error associated with measuring speed derives from measuring time and distance, which can be performed very accurately over a well-defined course at a swimming pool or race track. Directly observed speed can be expressed either as an absolute intensity (e.g. metres per minute) or as a relative intensity (e.g. percentage of the athlete's recent or personal best race pace). For training over hilly terrain or unmarked courses, speed is likely to be less accurate than measures derived from physiological monitoring or perceived exertion. Practical considerations severely limit the amount of data that can be obtained by observation. The main problem arises where there is a need to have an observer present throughout every training session for every athlete: it is time-consuming for the coach or scientist to perform themselves, and expensive if observers are employed. It is also likely that many athletes would refuse to train in the continual presence of an observer. Direct observation may therefore have to be limited to a sample of training sessions, which may make it unsuitable for long term quantification of highly variable training.

2. Applications for Training Data Training data are of interest primarily to athletes, coaches and sport scientists. For athletes and coaches, the main applications for the data are to motivate the athlete, make training systematic, and prescribe training, the aim being to enhance competitive performance. These applications are discussed further below. The relevant publications, which are found almost exclusively in the popular sport literature, are listed in table I. Sport scientists are interested in training data for purposes of publishing scientific studies in learned journals, the ultimate justification for this endeavour being enhancement of athletes' performance or health status. Scientific studies that deal with training data are listed in table II. A discussion of the ditTerent designs and of the main findings of these studies completes this section.

2.1 Motivation and Systematisation Training data obtained by any method have the potential to enhance motivation. If the data are obtained by the coach or are otherwise available for the coach's inspection, the athlete may be less likely to depart from the prescribed training programme. Even if the coach is not involved, an ongoing record of training should heighten the athlete's awareness of the investment of time and etTort that has been made; hopefully, this will promote a pride in achievement that will help carry the athlete through the difficult periods when motivation flags. A record of training data presumably also encourages the athlete and coach to be more systematic and goal-directed in their approach to training, because recording and reviewing a record of training data should stimulate questions about the purpose of mode, frequency, duration, intensity and skill components of specific training sessions. The potential for retrospective questionnaires to stimulate motivation and systematisation is limited, because a questionnaire is administered only once or infrequently. Diaries, on the other hand, are probably the best method to promote organisation in training behaviour, through their ability to produce a continuous record of training and to assay every important aspect of training. Advice on keeping a diary or training log has been provided in the popular literature for a number of sports (table I). It is generally claimed that keeping a diary can benefit attitudes and adherence to training, produce beneficial changes in the training programme itself, and improve subsequent performance in competition. However, objective support for these assertions is lacking. The most important benefit to derive currently from physiological monitoring is probably the motivation that derives from the feeling of being part of a select group receiving the best that sport science has to otTer. Laboratory measurement of oxygen consumption is an awe-inspiring experience for the athlete, and measurement of blood lactate, an invasive and sometimes painful procedure, is probably more impressive than heart rate monitoring. The latest cardiotachometers do excel in

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Table I. References for use of diaries, heart rate monitoring and blood lactate monitoring for purposes of motivation, systematisation or prescription of training in different competitive sports Sport

Reference8

Diaries Cycling Discus Powerlifting Running Rowing Shooting Tennis Track and field Yachting

[Kita 1989; Matheny 1981 J; Singleton (1984); Weaver (1980) Grigalka (1986) [Fodor 1980J Bowerman (1979); Dixon (1982); Henderson (1979); Poehlitz (1988) Nolte (1986); [Ozolin 1983J [Domey 1986J; Kelly (1982); [Stewart & Edwards 1987J [Schuessler 1979J McClements (1983) Miller (1979)

Heart rate monitoring Cycling Running Skiing Swimming Triathlons

Spangler & Hooker (1990) Dare (1979) [Gaskill 1984J Pyne & Telford (1988) Silverman (1987)

Blood lactate monitoring Orienteering Rowing Running Skiing Swimming Various

Seiler (1987) Urhausen et al. (1986) Bueno (1982, 1990); F6hrenbach (1981); Gaisl et al. (1986); Winter (1986); Zalesky (1983) von Duvillard (1988) Costill & King (1983); Councilman (1985); Madsen & Lohberg (1987); Maglischo (1985); Prins (1988); Pyne (1989); Pyne & Telford (1988); Skinner (1987); Troup (1986) Liesen et al. (1985)

a References in brackets (from the Sport Discus database) have not been viewed by the author.

their 'high tech' appeal, and the immediate and continuous feedback of data from a cardiotachometer also ought to be a powerful motivating force to maintain a target training intensity. The perception that others are taking an interest or standing in judgement is the way that direct observation provides motivation to the athlete. Optimising the quality and quantity of direct observation has to be done by trial and error: some athletes may respond best to being observed several times a week, while highly-organised self-motivators may need only a brief infrequent session with the coach. 2.2 Training Prescription Quantification of training is essential if the coach wants to determine whether the athlete is complying with a prescribed training programme or if the

self-coached athlete wants to be sure that self-imposed training targets are being met. Questionnaires are obviously not appropriate for this application, because the need is for ongoing assessment of training behaviour, but diaries, physiological monitoring and direct observation each have their uses. Diaries are the simplest and most flexible method of checking whether prescribed training has been performed. For this purpose the diary can be an unstructured document in which are recorded only those data of interest to the coach and athlete. The problem with a diary, from the coach's point of view, is whether the athlete is being honest or accurate with the entries. Prescribed targets of training intensity can be set and checked with heart rate monitoring. Use of miniaturised cardiotachometers appears to be the

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method of choice, but there has been surprisingly little reaction to these devices in the popular sport literature. The extent of their use is also unknown. It is impractical to use oxygen consumption to prescribe training intensities in all but specialised research settings, but blood lactate assays could now be performed regularly for this purpose by coaches of endurance athletes. Lactate monitoring has received frequent attention in the popular sport literature (table I), but very few coaches may be using it (e.g. Councilman 1985). Indeed, serious reservations have been expressed recently about the utility of blood lactate monitoring for training prescription (Bueno 1990; Busse et al. 1989; Prins 1988). The main complaints are that the assay does not give a dependable assessment of training intensity or current performing ability, and that it is too time-consuming. Direct observation would appear to be the best method of ensuring compliance with all aspects of a prescribed training programme. However, it is only in exceptional circumstances that an observer can be present for every training session. Direct observation therefore has to be supplemented with diaries or heart rate monitoring if a more complete audit of an athlete's programme is wanted. 2.3 Sport Science Studies of human behaviour, including the training of athletes, are of two kinds: descriptive and experimental. In a descriptive study no attempt is made to change behaviour or conditions, whereas in an experimental study the scientist investigates the effects of an imposed change. Descriptive studies of training either characterise training or examine relationships between measures of training and variables related directly or indirectly to performance and health, for example race times, maximum oxygen uptake, bone density, injury rates or psychological state. Descriptive studies can be cross-sectional, longitudinal and case-control. In cross-sectional studies training and other variables of interest in a sample of athletes are assayed once and analysed, whereas in longitudinal studies variables are assayed re-

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peatedly over a period of time. Other labels for longitudinal studies are prospective and cohort, because the studies look for future outcomes in a particular group of athletes. Case-control studies compare the prior training of cases (athletes with a particular attribute, such as an injury or ability) with controls (athletes without the attribute). Casecontrol studies are also called retrospective, because of their focus on past training, but cross-sectional studies can also be called retrospective if the training assayed is anything but current. Experimental studies of training also have several designs. In the simplest, the success of an imposed change in training is judged by comparing attributes of the athletes before and after the change. A better design compares outcomes in an experimental group with those in a control group, who do not modify their training; if subjects are assigned at random to experimental and control groups, the design is known as a randomised controlled trial. Best of all designs is the cross-over, in which the experiment is repeated with the roles of experimental and control subjects reversed. The various designs differ in the quality of evidence they provide for a cause-and-effect relationship between training and performance or health outcomes. Well-designed cross-sectional and casecontrol studies can provide good evidence for the absence of a relationship, but if the studies do reveal a statistically significant relationship, this generally represents only suggestive evidence of a causal connection between training and the outcome. A cross-sectional or case-control study is therefore a good starting point to decide whether it is worth proceeding to the other designs. Longitudinal studies are more difficult and time-consuming, but they produce more convincing conclusions about cause and effect. Experimental studies provide definitive answers to hypotheses suggested by descriptive studies, but lack of resources, lack of compliance by athletes and coaches, or ethical considerations can make experiments difficult to perform. Publications that include data on training of competitive athletes have been grouped for this review under several major topic headings: charac-

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Table II. Descriptive and experimental studies of training 8 grouped by main topic, sport, method of collection of training data and study design Sport

Method b

DesignC

Reference

Characteristation of training Cycling Orienteering

Heart

x-sect

Hopkins & Hawley (1989)

Heart, lactate

x-sect

Lenz (1987)

Rowing

Lactate

Pre-post

Urhausen et al. (1986)

Running

Heart

x-sect x-sect

Robinson et al. (1991)

Long

Heart, oxygen

Skiing Soccer Speed-skating

Ritchie & Hopkins (1991)

Lactate Quest

x-sect

Buhl & Loffler (1988) Pollock (1977); Rowland & Walsh (1985); Siovic (1977);

Heart

x-sect

Sparling et al. (1987); Walter et al. (1988) Kluibenschedl (1980)

Heart, lactate Heart, lactate

x-sect

Karvonen et al. (1985); Simon et al. (1979) Chamoux et al. (1988); Rohde & Espersen (1988)

Heart, lactate

x-sect x-sect

Smith & Roberts (1990)

Lactate

x-sect

Gasiewska et al. (1988) Davie & Newton (1990)

Surf-skiing

Heart

x-sect

Swimming

Lactate

x-sect

Lavoie et al. (1983)

Triathlons

Quest

x-sect

Taekwando Water polo

Heart Heart, oxygen

x-sect x-sect

Ireland & Micheli (1987); O'Toole (1989) Pieter et al. (1990) Pinnington et al. (1990)

Performance prediction and enhancement Cycling Netball Rowing Running

Skiing Soccer Triathlons Swimming

Weightlifting

Observe Quest Quest Lactate Diary

Review Exp-con x-sect x-sect Pre-post Long x-over x-sect

Diary/quest Lactate Lactate/heart Observe/diary Observe/heart Observe? Quest

Pre-post Pre-post Pre-post Pre-post Pre-post Pre-post Long x-sect

? Heart Observe Quest Quest? Observe Quest

x-over

?

Pre-post Long x-sect Long Pre-post Long Long

Diary

Pre-post Long

Jackson & Sharkey (1988); Neufer (1989) Terrados et al. (1988) Krebs et al. 1986) Bale & Hunt (1986) Urhausen et al. (1986) Foster et al. (1977) Adams et al. (1975) Foster (1983); Hagan et al. (1981); Linetz et al. (1981); Scrimgeour et al. (1986) Houmard et al. (1990b); Wittig et al. (1989) SjOdin et al. (1982) Gaisl et al. (1986) Priest & Hagan (1987) Mikesell & Dudley (1984) Acevedo & Goldfarb (1989) Svedenhag & Sjodin (1985) Bale et al. (1985, 1986); Campbell (1985); Dotan et al. (1983); Marti et al. (1988); McKelvie et al. (1985); Siovic (1977) Shepley et al. (1990) Mizuno et al. (1990) Ekstrand et al. (1983b) O'Toole (1989); Zinkgraf et al. (1986) Kohrt et al. (1989) Beckett (1986) Pollock et al. (1987) Ryan et al. (1990) Costill et al. (1985) Hakkinen et al. (1987)

Quantification of Training in Sports

173

Table II. Contd Methodb

Design C

Review

Kuipers & Keizer (1988)

Observe

Pre-post x-over

Dressendorfer et al. (1985); Lehmann et a!. (1990) Kirwan et a!. (1990)

Case-con/long Pre-post

Barron et a!. (1985) Stray-Gundersen et al. (1986)

Pre-post Long Long/exp-con

Costill et al. (1988); Kirwan et al. (1988); Morgan et a!. (1988) Morgan et a!. (1987) O'Connor et a!. (1989)

Review

Cumming et a!. (1989); Hackney (1989); Highet (1989); Keizer &

Pre-post Case-con

Houmard et a!. (1990a) Kaiserauer et a!. (1989); Myerson et a!. (1991)

x-sect

Ayers et a!. (1985); Baker et a!. (1981); Dale et a!. (1979); Drinkwater et a!. (1984); Feicht et a!. (1978); Glass et al. (1987); Gray & Dale (1983); Lutter & Cushman (1982); Sanborn et a!. (1987); Wakat et al. (1982); Wheeler et a!. (1986)

Diary Quest

Long x-sect

Hakkinen et al. (1987. 1989) Carlberg et al. (1983); Sanborn et al. (1982)

Review

Fitzgerald (1988); Taimela et a!. (1990); Taunton et al. (1988)

Archery

Quest

x-sect

Mann & Littke (1989)

Athletics

Quest

x-sect

Kubler (1986)

Boardsailing Figure-skating Football

Quest Quest

x-sect x-sect Review Long Review Long

Allen & Locke (1989) Brock & Striowski (1986) Halpern et al. (1987); Thompson et a!. (1987) Cahill & Griffith (1979) McAuley et a!. (1987) Garrick & Requa (1980); Pettrone & Ricciardelli (1987); Weiker (1985) Sim et a!. (1987) Sutherland (1976) Johansson (1986. 1988) Lysholm & Wiklander (1987) Peters & Bateman (1983) Brunet et a!. (1990); Clement et a!. (1981); Diekhoff (1984);

Sport

Reference

Overtraining Running

Observe/heart Quest

? Swimming

Observe Quest

? Reproductive dysfunction

Rogol (1990); Loucks (1990); Schoutens et a!. (1989) Running

Weightlifting Various

Diary/quest Quest

Injury and Illness

Quest Gymnastics Quest Ice hockey Orienteering Running

Quest Diary Diary Quest

Review Long Long Long Long x-sect

Swimming Triathlons

Quest Quest

x-sect/long Review Exp-con Long x-sect x-sect

Various

Quest

Case-con

Soccer Observe

Jacobs & Berson (1986); James et a!. (1978); Koplan et al. (1982); Marti (1988); McKelvie et a!. (1985); Messier & Pittala (1988); Rowland & Walsh (1985); Walter et a!. (1988) Hoelmich et a!. (1988) Keller et a!. (1987) Ekstrand et a!. (1983a) Ekstrand et a!. (1983b); Nielsen & Yde (1989) McMaster et a!. (1989) Collins et al. (1989); Ireland & Mitchell (1987); O'Toole et a!. (1989) Myburgh et a!. (1988)

continued over

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Sports Medicine 12 (3) 1991

Table II. Contd Sport

Methodb

Design C

Reference

Review

Burke & Read (1989); Campbell & Anderson (1987); Newhouse & Clement (1988) Fogelholm (1989) Haymes & Spillman (1989) Dressendorfer & Sockolov (1980); Manore et al. (1989)

Nutrition

Running

a b c

Quest Quest

x-sect Case-con x-sect

To qualify for inclusion, a study must have assayed training of at least several days' duration in competitive athletes, or be a review that includes training in competitive athletes. Abbreviations for data col/ection method: diary = athletes' diaries; heart = heartrate monitoring; lactate = lactate monitoring; observe = direct observation; oxygen = monitoring of oxygen consumption; quest = questionnaires. Abbreviations for study design: case-con = cases compared with controls; exp-con = experimental study with outcome in experimental group compared with that in matched controls; pre-post = experimental study with pre- and post-experiment data compared in same subjects without controls; long = longitudinal; x-over = experimental study with cross-over design; x-sect = cross-sectional.

terisation of training, performance prediction and enhancement, overtraining, reproductive dysfunction, injuries and illness, and nutrition. A summary of the publications is presented below and in table II. Not included in the table are studies that have compared athletes and nonathletes without analysing training. 2.3.1 Characterisation of Training Studies in this area describe the training behaviour of athletes in a given sport, and they may also compare behaviour during training with that during competition. The aim of such studies is to determine whether training is appropriate for competition, and to set the stage for further studies. As can be seen from table II, the main focus has been on the intensity of training as determined by physiological monitoring. In general, the intensity of training is substantially below the intensity experienced during competition. 2.3.2 Performance Prediction and Enhancement The descriptive studies in this group try to identify those training behaviours that correlate significantly with competitive performance or other indices of fitness. Not surprisingly, better perform-

ance is associated with higher training volume, correlations generally being in the range 0.5 to 0.8 (Bale et al. 1985, 1986; Dotan et al. 1983; Ekstrand et al. 1983b; Foster 1983; Foster et al. 1977; Hagan et al. 1981; Krebs et al.1986; Marti et al. 1988). Better performance is also associated with higher relative training intensity (percentage of maximum), with correlations of less than 0.4 (Bale et al. 1985; Foster 1983; Krebs et al. 1986; O'Toole 1989). Correlations in cross-sectional studies of training probably overestimate the effect of training on performance, because genetically well-endowed athletes may choose to train more or harder. Nevertheless, even if the true effect of training on performance is represented by a low correlation, an improvement in training can substantially improve an athlete's ranking (unpublished computations). Studies should therefore have sufficient numbers of subjects to detect weak but significant associations between training and performance, and should follow up any significant findings with experimental studies. Experimental studies of performance enhancement avoid the pitfalls of cause and effect that are inherent in descriptive studies. Thus far the experimental studies have been confined mainly to endurance sports, where the effects of increasing

Quantification of Training in Sports

and decreasing the training load have been investigated. Training load has been increased by increasing the intensity to bring it more into line with the intensity of competition; after a period of weeks to months at the increased intensity, athletes show an improvement in performance times typically of the order of 5% (Acevedo & Goldfarb 1989; Beckett 1986; Gaisl et al. 1986; Mikesell & Dudley 1984; Priest & Hagan 1987; Sjodin et al. 1982; Urhausen et al. 1986). Decreasing the training load immediately before competition is being studied in attempts to optimise the 'taper' period. Here, reductions in volume for a period of several weeks are accompanied by either a slight improvement (Costill et al. 1985) or no change in performance (Houmard et al. 1990b). A 7-day taper period of high intensity and reduced volume appears to be more effective than complete rest or a low-intensity taper (Shepley et al. 1990). There has been a steady research interest in the possibility of enhancing performance at sea-level by training at altitude. The studies compare sealevel performance before and after a period of training at altitudes of 2000 to 3000m. It is vital to ensure that the intensity and weekly volume of the altitude and sea-level training are comparable if meaningful conclusions are to be drawn, but surprisingly few studies have achieved this. In one, there was no effect of altitude training on aerobic performance (Adams et al. 1975); in another, simulated altitude training produced a substantial but statistically nonsignificant enhancement of work capacity (Terrados et al. 1988); in a third, altitude training enhanced short-distance running performance (Mizuno et al. 1990). In general, the studies suffer from using too few subjects, and none has investigated the effect of altitude training for more than a few weeks. 2.3.3 Overtraining Anecdotal reports have identified various symptoms of overtraining, including impaired performance, inability to meet previously achieved training targets, negative mood states, disturbed sleep, chronic muscle soreness and elevated resting heart rate (e.g. Brown et al. 1983). There appear to

175

have been no cross-sectional studies of the phenomenon. The few published studies have regarded reduced performance and inability to meet previously achieved training targets as defining the overtrained state, and have attempted to identify changes in objective and SUbjective measures that accompany it. These changes include an alteration in hormonal regulation at the level of the hypothalamic-pituitary axis (Barron et al. 1985), an elevation in plasma cortisol (Barron et al. 1985; O'Connor et al. 1989), a reduction in muscle glycogen content (Costill et al. 1988), and a deterioration in specific and general mood states (Morgan et al. 1987, 1988; O'Connor et al. 1989). Whether resting heart rate is a predictor of overtraining is unclear: after a rapid increase in training load, the resting heart rate has been reported to increase (Dressendorfer et al. 1985; Stray-Gundersen et al. 1986), decrease (Lehmann et al. 1990) or remain unchanged (Kirwan et al. 1988). It has been suggested that overtraining might occur when there is insufficient glycogen in muscles to sustain training (Costill et al. 1988). However, an attempt to produce signs and symptoms of overtraining in runners by restricting carbohydrate intake during intense training was largely unsuccessful (Kirwan et al. 1990), possibly because the 5-day period of the experiment was too short. 2.3.4 Reproductive Dysfunction The first substantial evidence that training might. influence reproductive function was provided by cross-sectional studies showing higher rates of menstrual irregularity in athletes than in nonathletes, especially when the athletes were distance runners. It seems obvious that the irregularity is a direct consequence of hard training, but the evidence from studies where training has been assayed and analysed is equivocal: some show significant relationships between training volume and menstrual irregularity (Carlberg et al. 1983; Dale et al. 1979; Drinkwater et al. 1984; Feicht et al. 1978; Sanborn et al. 1982); others do not (Baker et al. 1981; Glass et al. 1987; Gray & Dale 1983; Kaiserauer et al. 1989; Lutter & Cushman 1982; Myerson et al. 1991; Sanborn et al. 1987; Wakat et al.

176

1982), and it is not always a matter of poor design or too few subjects. The roles of dietary and anthropometric factors are also unclear. One factor that does appear to be important is a sudden increase in training load, as shown by experimental studies on previously untrained women (reviewed by Keizer & Rogol 1990). Menstrual irregularity has benefits and problems for the athlete. Retrospective cross-sectional studies of women graduates showed that those who were athletes in their youth have lower rates of cancer later in life than women who were not athletes; the reason for this difference is still not resolved, but it may be partly a result of low oestrogen levels associated with physical training (Frisch et al. 1985, 1989). Unfortunately the low oestrogen levels are accompanied by loss of calcium from bones (osteoporosis), even though cross-sectional studies comparing athletes with nonathletes, and training studies in nonathletes, have demonstrated clearly that physical exercise improves the state of bones (reviewed by Schoutens et al. 1989). Apparently, if the level of training is such that menstrual irregularity develops, the harmful effect of lower oestrogen levels on bone more than offsets the beneficial effect of the physical activity. Menstrual irregularity in athletes is accompanied by alterations in the pattern of release of luteinising hormone from the pituitary, and this appears to be a result of dysfunction in the control of gonadotrophins by the hypothalamus (reviewed by Keizer & Rogol 1990). Dysfunction in the control of the other hormones of the hypothalamicpituitary axis is a sign of overtraining (see section 2.3.3), so it is possible that menstrual irregularity is a signal to the female athlete that she is close to overtraining. Reproductive function in the male athlete has received much less attention than that in the female. Studies comparing sedentary males with endurance athletes have shown reduced levels of testosterone in the athletes and alterations in the hypothalamic-pituitary-gonadal hormone control system similar to those seen in female athletes (reviewed by Cumming et al. 1989; Hackney 1989; see also Hackney et al. 1990). Testosterone levels

Sports Medicine 12 (3) 1991

are lower in runners with higher weekly mileage (Wheeler et al. 1986), and in longitudinal studies reductions in testosterone levels coincide with periods of increased training (Hiikkinen et al. 1987, 1989). The result for some athlete-s, particularly if they are overtrained, may be reduced fertility (Ayers et al. 1985) and reduced libido (Griffith et al. 1990). Reduced training for 3 weeks did not result in improvement in the hormone status in a recent study (Houmard et al. 1990a). 2.3.5 Injury and Illness In the study of sport-related injuries it is usual to distinguish between acute or traumatic injuries, which occur in a brief moment of time in an accident, and chronic, stress or overuse injuries, which result from the gradual accumulation of physical stress during training. The majority of injuries in team and contact sports are acute, whereas overuse injuries predominate in the high-intensity endurance sports such as running and swimming. Much of the data relevant to the cause, treatment and prevention of acute injuries comes from analysis of case reports. The important data do not concern training as such, but rather specific details surrounding the accident, such as behaviour of the injured athlete or of team mates, environmental conditions and equipment. The relevant literature is outside the scope of this review (for recent reviews see table II). Where the cause of a particular kind of injury is clear, an intervention can be implemented on a national scale in the form of rule changes; in the case of cervical injuries in American football, the dramatic decline in injury rates has been assumed to result from changes in training and competition behaviour (e.g. Torg et al. 1990), which are too obvious to need substantiating. Training measures do become important in identification of the causes of overuse injuries. In running, injury rates generally increase with training volume, and more than half of the injuries are attributed either to excessive training or to an increase in training that does not give the body time to adapt (James et al. 1978; Taunton et al. 1988). In other sports lack of an association between

Quantification of Training in Sports

training volume and injury (e.g. Collins et al. 1989; Johansson 1986, 1988; O'Toole et al. 1989) may arise because the athletes doing more training are also more experienced or adapted and therefore less likely to suffer injury per unit of training time; indeed, Ekstrand et al. (1983b) observed an inverted V-shaped relationship between a season's training volume and injuries in soccer. It is common practice to normalise injury rates to hours of training: for example, orienteers, runners and soccer players experience 3 to 8 injuries every 1000 training hours (Ekstrand et al. 1983b; Johansson 1986; Lysholm & Wiklander 1987; Nielsen & Yde 1989). Where there is no correlation between seasonal training volume and injuries, it would seem more sensible to express injury rates as injuries per season or per year. Surprisingly, descriptive and experimental studies have yet to show that lower rates of injury are associated with stretching or warm-up exercise (Safran et al. 1989). One study that used a comprehensive intervention of warm-up, stretching, protective equipment and ankle taping reduced soccer injuries in an experimental group to one quarter of those in a control group (Ekstrand et al. 1983a), but the contributions of warm-up and stretching to the success of the intervention are not clear. Training impinges on two other aspects of the health of athletes. Moderate exercise may stimulate the immune system, but there is now considerable evidence that the hard training experienced by endurance athletes suppresses the immune system and increases the risk of infection (Fitzgerald 1988). However, only one paper has related the risk of infection to a measure of training (Peters & Bateman 1983). Finally, studies of populations reveal lower rates of cardiovascular disease and greater longevity amongst physically active subjects, but do athletes therefore live longer, healthier lives? Most studies of this question have compared former athletes with nonathletes, and none has related mortality, morbidity or disease risk factors specifically to past or present measures of training. The evidence suggests that the protective effect of

177

physical activity is lost if the athlete becomes sedentary (e.g. Paffenbarger et al. 1984). 2.3.6 Nutrition A considerable number of studies have reported significantly lower iron stores in athletes than in nonathletes (reviewed by Newhouse & Clement 1988). Running appears to be a common element in all sports in which poor iron status has been reported, and women are more at risk than men. Few studies have investigated directly the effect of training on iron status: Haymes and Spillman (1989) reported significant differences in serum ferritin of women sprinters and distance runners, who differed in weekly training mileage by a factor of 10; Manore et al. (1989) reported a significant correlation between serum ferritin and weekly mileage in female distance runners, but Fogelholm (1989) did not find a significant correlation between weekly energy expenditure and serum ferritin in 59 male endurance athletes. The serum concentration of the trace element zinc is lower in athletes than sedentary people, and runners who train more tend to have lower levels (Dressendorfer & Sockolov 1980). Chromium stores may be lower as a result of training, and copper may also be affected (reviewed by Campbell & Anderson 1987).

3. Conclusions and Future Research Training is obviously a major part of the lives of competitive athletes and their coaches. Furthermore, the studies summarised in this review show that training has strong effects on the performance and health of the athletes. The measurement of training therefore deserves more attention than it has previously received~ Little is known about the use by sportspeople of the different methods of quantifYing training. Diaries have been advocated in many sports, but how they are being used and by whom are unanswered questions. The few reports that are available on the use of lactate monitoring indicate that it has been tried only by a small fraction of practitioners, and that among these it has been found

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wanting. Monitoring of heart rate appears to be a viable physiological method for prescribing training intensity, but currently it appears to have a low profile among coaches and athletes. Further research in this area would help to establish the real and perceived benefits of these methods and the barriers to their use. Sport scientists monitor oxygen consumption, heart rate or blood lactate to obtain accurate, objective data on training intensity for short term studies. Direct observation is also used to obtain various measures of training. If the time frame of the study is longer than a week or two, diaries and questionnaires are generally the only practical methods of assaying training. Questionnaires are used more than any other method, because they provide a wide range of training measures simply and cheaply. However, insufficient attention has been paid to the errors associated with measures of training derived from questionnaires. It would be desirable if researchers who devise a new questionnaire also determine the reliability of their training measures. Estimates of validity are also needed, but are much more difficult to obtain. A valuable addition to the literature would therefore be a study investigating the validity of typical questionnaires for athletes of various abilities and sports. Experimental studies provide definitive evidence for the effects of training on performance, injury and health, but such studies are rare. This probably reflects greater difficulty in mounting an experimental study in comparison with a descriptive study, but athletes and coaches may also be unwilling to modify training programmes. Studies on attitudes of sportspeople to research might reveal whether cooperation between scientists and sportspeople is a problem, and if so, how it might be addressed. When experiments can be performed, outstanding questions that need attention include: how to reduce the incidence of overuse injuries and osteoporosis without reducing training loads; how to optimise buildup and taper; and how to detect and correct overtraining before it compromises performance.

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Quantification of Training in Sports

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Correspondence and reprints: Dr Will G. Hopkins, Department of Physiology, University of Otago, Box 913, Dunedin, New Zealand.

Quantification of training in competitive sports. Methods and applications.

The training of competitive athletes can be assessed by retrospective questionnaires, diaries, physiological monitoring and direct observation of trai...
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