MEASUREMENT OF TRAINING IN COMPETITIVE SPORTS
Will G Hopkins PhD
Schools of Medicine and Physical Education, University of Otago, Dunedin 9001, New Zealand.
Sportscience 2(4), sportsci.org/jour/9804/wgh.html, 1998 (5463 words)
Reviewed by John A Hawley, Department of Human Biology and Movement Science, RMIT University, Victoria 3083, Australia
For most sports, training probably has a greater effect on performance than nutrition, equipment, psychological state, or any other modifiable factor. Training can also cause injuries, and overtraining can lead to illness. The quantification or measurement of training is therefore an important issue for athletes, coaches, and sport scientists. In this article I describe the characteristics of training, outline methods used to measure and analyze training, give examples of recent applications of the methods, and make suggestions for future applications. I also include examples of forms for gathering data: two questionnaires, a diary, and a recording sheet for direct observation of training. Researchers can download and modify these forms for their own studies.
Training is a complex behavior, mainly because it is performed in a time frame that ranges from seconds to years. Sports people use numerous terms to describe the characteristics of this temporal dimension of training. Single human movements, which occur in a second or two, are combined and repeated to make a training bout or workout, a period of more-or-less uninterrupted physical activity. Workouts may occupy a few minutes or hours, and may be continuous exercise, a set of reps or repeated movements, or a set of sets. A complete training session usually lasts an hour or two and consists of one or more workouts. The nature of each session may vary, but after a week or so a repeated pattern of sessions known as a microcycle usually emerges. A series of microcycles may constitute a phase of training, for example a build-up or speciality phase. A repeated pattern of phases or microcycles makes up a mesocycle, and a season or macrocycle of training may consist of a repeated set of mesocycles. Finally, over a period of years a training history develops.
Studies involving quantification of training focus invariably on only a small part of the training time frame. In some biomechanical applications, the focus of interest is a single movement or limited set of movements, such as a high jump or a javelin throw. In most other applications, particularly those involving investigation of the physiological effects of training, the fundamental unit of training is the workout. Even in studies of injury and illness that focus on a season or history of training, data on typical workouts during one or more phases of training usually provide the key training variables.
Workouts vary between sports, but most can be classified as either endurance, interval, strength or skill. For example, in competitive track running a workout of continuous running is classified as endurance; repetition running (short periods of high-speed running separated by rests or slow-speed running) is an example of an interval workout; short sprints with a weight in tow qualifies as a strength workout; and practicing of starts is a skill workout. This classification reflects common usage by sportspeople, but it also has an underlying theoretical basis: in general, endurance workouts train the aerobic power system, interval workouts train the anaerobic glycolytic system, strength workouts train the phosphagen system, and skill workouts train the central nervous system.
Duration and intensity are important characteristics of a training workout, because they contribute to the short- and long-term effects of the workout on the health and fitness of the athlete. In the case of an endurance workout performed at a reasonably steady pace, only one estimate of duration and intensity may be required. Interval and strength workouts involve multiple periods of work and rest, each of which may need an estimate of intensity and duration. The intensity and duration of skill workouts also need to be characterized, especially if the movements are practiced at sufficiently high intensity and for a sufficient duration to produce a training effect on the body's power systems.
The aims of a study will dictate whether other aspects of training workouts need to be assayed. For example, it may be important to determine details of clothing, equipment, training surface or medium, venue, time of day, weather, consumption of food or drink, psychological state, supervision, or perhaps even the number and caliber of training companions.
There are three groups of methods:: observational (taking measurements in real time or from video recordings), physiological (monitoring heart rate, blood lactate concentration or oxygen consumption), and subjective (use of questionnaires or diaries). The methods in each group are similar in their suitability for assaying training, but there are substantial differences between groups.
Table 1 summarizes the suitability of each method for assaying training in different time frames. Training in the shortest periods of time can be assayed only with observational methods, whereas the longest time frames require subjective methods. All methods, including those in the physiological group, can quantify training at the level of a workout, but the physiological methods are useful only for assaying the intensity of training of steady-state workouts.
Quantification of periods of training from a few seconds to a few weeks can be achieved simply by observing the training either in real time or on video. Practical considerations set the upper limit of the time frame: it is time-consuming for the coach or scientist to be present at every training session, and expensive if observers or video operators are employed. Observation may also cause the athletes to train more intensely or closer to their prescription than they would otherwise do, but in general the measures obtained by observation are probably more valid than those obtained by physiological or subjective means.
The measures usually recorded in real time are the type and duration of the workout, along with relevant split times, distances, weights or workloads that produce measures of intensity. Special stopwatches facilitate recording of multiple times if the workout is a set of intervals. Information on other dimensions such as weather and equipment is also recorded if relevant. It is worth making a recording form with coded columns for all the necessary data. Such forms reduce the rates of error and loss of data and can be sent directly to a data-capture service.
Measures of intensity derived from observation can be expressed either in absolute terms (e.g., pace in minutes per mile) or in relative terms (e.g., pace as a percent of the athlete's personal best pace for the distance). For athletes doing resistance training with weights, an important measure of relative intensity is the repetitions maximum (RM); for example, 80% of 1 RM is 80% of the weight that an athlete can only just lift once. The use of relative intensity simplifies description or prescription of intensity for athletes who differ in ability.
Video is a tool primarily for the coach or biomechanist interested in improving the athlete's skill. It is ideal for the analysis of single movements or intervals of exercise lasting up to a minute or two. The most cost-effective method is qualitative analysis, in which the athlete, coach or sport scientist simply view the video together and decide immediately how technique could be improved. The athlete can then attempt any recommended changes and be filmed for a further round of analysis. Quantitative analysis involves digitization of the video images to permit calculation of spatial and temporal relationships in the movement. Several proprietary hardware-software packages are available for the purpose. Simple but effective digitizing is also possible with minimal extra hardware and software (Allinger, 1998). The procedure is time-consuming and loses the benefit of immediate feedback to the athlete, but it allows detailed comparisons of one athlete with another or of one athlete before and after an intervention.
Video has also been used for time-motion or notational analysis, in which the times spent in various modes of activity or in moving at various speeds are estimated from time and distance measurements taken from the video. As yet the method has been employed only for quantification of the energy demands of competition rather than of training.
Training produces many effects on the body, ranging from acute responses (e.g., increase in breathing frequency during exercise) to chronic adaptations (e.g., increase in blood volume and maximum oxygen consumption after a few weeks of endurance training). Some chronic adaptations find application in studies of the training of non-athletes, where they can provide objective evidence of an increase in physical activity. With athletes, only the acute responses are used to quantify training, and of these responses only three have any practical significance: oxygen consumption, heart rate, and blood lactate concentration. All three provide information only on the intensity of steady-state exercise.
The need for special apparatus to monitor physiological responses sets the upper limits on the useful time frame for these methods. Devices are now available that will allow athletes to monitor their own heart rates indefinitely, but if the data are to be collected by a researcher, several months of monitoring is difficult to achieve. Measurement of lactate concentration is also difficult to sustain for more than a few months, while oxygen consumption requires equipment that can be used realistically only for a few training sessions.
The shortest duration of training that can be monitored is set by the response time of the physiological variables to changes in exercise intensity. Oxygen consumption and heart rate take 3-4 min to reach a steady state, and blood lactate concentration takes even longer, so these variables are unable to provide readily interpretable information on the intensity of reps/intervals.
In theory this is a good measure of the intensity of steady-state exercise, for a number of reasons. First, training that can be sustained at a constant pace for more than a few minutes is performed with energy supplied almost entirely from consumption of oxygen. Secondly, the relationship between steady-state oxygen consumption and power output or speed is linear over the range of intensity from rest to maximum steady state. Thirdly, oxygen consumption drifts upwards by only a few percent in prolonged exercise performed at a constant high workload. Finally, oxygen consumption at a given workload is stable over a period of months of training, in part because exercise efficiency changes little in trained athletes.
In practice, measurement of oxygen consumption requires athletes to breathe into special apparatus to allow expired gas to be collected or analyzed. This requirement limits the monitoring of training activities in the field, although several portable devices weighing only a few kilograms are now available. It is more convenient (but less representative of real training) if the activity can be performed in a laboratory on a sport-specific ergometer. Analysis of oxygen consumption is possible in real time with one of a range of available metabolic carts or with a similar computerized system of analyzers of gas volume and composition; alternatively, Douglas bags can be used to store the gas for later analysis. If analyzing or collecting gas is too difficult during the training activity, it is possible to analyze or collect gas for several minutes immediately after the activity, then to calculate the oxygen consumption that occurred during the activity by back-extrapolation.
Several measures of intensity can be derived from oxygen consumption. Of the absolute measures, milliliters of oxygen per minute per kilogram of body mass (ml.min-1.kg-1) is appropriate for comparing training that involves continual changes in direction or speed, or continuous work against gravity (examples: running, off-road cycling, most team sports). Liters of oxygen per minute (L.min-1) is better for sports like road cycling and swimming. A relative measure that is rarely, if ever, used with athletes is the met (multiple of the resting metabolic rate). The most common relative measure is oxygen consumption expressed as a percent of maximum oxygen consumption, which is usually determined in an incremental test to maximum effort with the same mode of exercise as the training activity. The relative oxygen consumption allows more meaningful comparison of the training intensities of athletes who differ in body mass, performing ability, and exercise efficiency.
For reasons already stated, it is not possible to measure the intensity of short intervals of high-intensity training directly as an oxygen consumption. It is nevertheless possible to exploit the linear relationship between workload (or pace) and oxygen consumption to express the intensity of such workouts as a percent of maximum oxygen consumption. For this purpose the oxygen consumption of several steady-state workouts is determined and plotted against workload, the line through the points is extrapolated to the higher workloads of the interval training, and the "corresponding" oxygen consumption is read off the graph.
This variable 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 more than a few minutes. Heart rate is higher if the same exercise is performed in a hotter environment. It also drifts upward more than oxygen consumption as the athlete heats up in prolonged exercise. It has the advantage over oxygen consumption of being far easier to assay.
In the laboratory heart rates are usually measured with an electrocardiograph, but for field work a range of miniaturized cardiotachometers is available. The most reliable of these detect the electrical activity of the heart and use it to calculate heart rate. Models that store the heart rate allow the coach and sport scientist to make use of the data, which are either replayed on the watch or downloaded into a computer or special portable analyzing unit. Waterproof versions can be used to monitor steady-state aquatic training. The athlete can also measure heart rate directly by palpation of an artery in the wrist or neck, but exercise has to be stopped briefly to perform the measurement and the resulting estimate is not accurate.
Heart rate can be used to express intensity in several ways. The absolute heart rate is useful for the individual athlete monitoring intensity on a day-to-day basis. Heart rate expressed as a percent 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: 100(training heart rate - resting heart rate)/(maximum heart rate - resting heart rate). A practical method of specifying intensity is to express training heart rates as a percent of race-pace heart rate. Heart rate recorded in the field can also be converted to 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 steady-state exercise tests.
During intense exercise lactate produced in muscle by the anaerobic glycolytic pathway diffuses into the blood and causes the blood lactate concentration to rise above the resting value 1-2 mmol.L-1. If the intensity is not too high, blood lactate reaches a steady level after 10-20 min of steady exercise. The relationship between the steady level of lactate and workload is curvilinear but reproducible, which means that lactate can be used to define training intensity. The range of intensities over which this method works is narrow: moderate intensities do not evoke increases in blood lactate, and at high intensities lactate does not reach a steady value before the athlete fatigues.
The highest intensity at which lactate stabilizes is one definition of the anaerobic threshold, and it corresponds to a blood lactate concentration of about 4 mmol.L-1. Exercise at this intensity can be sustained for 30-60 min before fatigue occurs. Blood lactates are measured during training mostly for determination of the anaerobic threshold, then for prescription of intensity of training relative to the threshold. The peak value of lactate concentration reached during or following short high-intensity workouts is sometimes measured by enthusiastic sportspeople, but this practice is not useful.
Compact lactate analyzers are available for determination of blood lactate concentration in a droplet of blood taken from a finger or earlobe. A portable instrument, suitable for use in the field, is also available. The analysis is rapid (1-2 min) and reliable, although technically demanding for the non-scientist. Problems with the technique arise not from the lactate analysis itself but from variability between athletes: the intensity corresponding to a blood lactate concentration of 4 mmol.L-1 is perceived as moderate by some athletes and too hard to sustain by others. Even within the same athlete, variations in muscle glycogen content caused by recent training or diet can alter the lactate concentration corresponding to the anaerobic threshold. Care should therefore be taken to standardize training and diet for the few days before blood lactate is monitored.
Questionnaires and diaries are closely related instruments: a diary is effectively a series of self-administered questionnaires. Both instruments obtain data recalled from memory, and both can be used to assay training over all but the shortest time frames.
In most respects, questionnaires are the best method for assaying training. They are quick and inexpensive to administer and they can provide data on most dimensions of training. Unfortunately no compendium of athlete questionnaires is available, few studies provide useful detail about the wording of their questionnaires, and few studies have reported on the precision of measurement of the items in a questionnaire. The researcher may therefore have to spend a considerable amount of time devising and trialing a questionnaire before using it in a study.
Questions about duration of training can be asked in terms of time spent or distance covered, depending on the sport. Duration of strength and interval training may be better defined in terms of the numbers of reps and sets rather than time spent, because the duration of the work and rest intervals is usually hard to remember or estimate. Intensity can be assayed as estimated pace or workload and expressed subsequently as relative intensity, if the athlete's personal best performance is also recorded. For some workouts it may be preferable or necessary to assay intensity as perceived effort, usually in several broad categories. A two-point scale of intensity or effort could be simply high and moderate-low; a four-point scale could be race-pace, hard, moderate and easy).
For construction of a training questionnaire, it is important to get the help of a few good coaches or athletes who know how training sessions are organized and what terminology is used in their sport. Their advice will help make the decisions on how best to ask about duration and intensity, and whether other dimensions of training are important for the study.
The main drawback with questionnaires is errors in the responses of athletes, who may misinterpret the questions, exaggerate their training, or be unable to remember details. Measures of training derived from questionnaires are therefore usually less precise than those derived from observation or physiological monitoring. Lack of precision results in weakening of the apparent relationship between training and outcomes such as performance or injury, so it is important to estimate the precision of measures derived from questionnaires.
The precision of a measure is expressed formally as reliability and validity (Hopkins, 1998). Reliability of a training measure is the consistency of the measure obtained from repeated measurement of training in a sample of athletes. In the case of questionnaires, reliability is obtained simply by administering the questionnaire on two occasions. Validity describes the relationship between true training and the training obtained concurrently from the questionnaire or other instrument. True training can never be measured perfectly, so in practice validation is a matter of comparing your measure with something better that is more difficult or costly to obtain. For example, direct observation or physiological monitoring can validate a diary (Hewson and Hopkins, 1996). In one study a phone interview was considered to give better measures of training for validating a self-administered questionnaire (Liow and Hopkins, 1996). Validation of training over a season is difficult, because it is usually unrealistic to observe or monitor athletes for more than a few training sessions. One approach is to use a retrospective questionnaire, but to validate the questionnaire against measures from a diary, then to validate a short period of diary data against objective measures taken concurrently (Hewson and Hopkins, 1996).
The quality of data obtained from a questionnaire is determined partly by the method of administration. The worst data are obtained from self-administered questionnaires, especially those sent by mail: misinterpretation or complete omission of questions is frequent, and an acceptable compliance (rate of return, preferably at least 70%) may not be achieved even after repeated reminder notices have been sent. Better data can be obtained if the athlete completes the questionnaire in the presence of an interviewer, who can answer queries and check the completed questionnaire immediately. This technique can also be extended to a small group of athletes. The best data are obtained when one person, preferably one of the principal researchers, administers the questionnaire to each athlete, in person or by phone. In large-scale studies with several interviewers, it is important standardize procedures for recording each item. Misinterpretations and transcription errors by the interviewers will be further minimized if the questionnaire is constructed as if it were to be self-administered.
Draft versions of the questionnaire should be trialed initially on colleagues and, after revision, on a small sample of the athletes for whom it is intended. Analyze the data from this sample, because some problems become apparent only when you extract data from the questionnaires. After further revision give serious consideration to a reliability or validity study: it will make your main study more publishable. Make any minor revisions thereafter without further pilot work, but if major revision of key questions is indicated, further investigation of reliability or validity may be necessary. Now at last you are ready to use the questionnaire!
Data from diaries are likely to be more valid than data from questionnaires, because diary entries are recorded soon after the training sessions, and an uninterrupted record of training over an extended period can be achieved. 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. The problem of coding a large amount of diary data can be avoided if athletes are provided with a diary sheet designed to permit direct recording of responses into numbered columns ready for data capture.
Pilot studies are as necessary for a newly-devised diary as they are for a questionnaire. Reliability is not worth determining for a daily diary, because the necessary close proximity of the test and retest will make high correlations inevitable. On the other hand, investigation 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.
Click on this link to download a zip-compressed set of forms: two questionnaires, a diary, a sheet for recording direct observations, and a guide to the use of the forms. Once unzipped, these files will open with PowerPoint 4, or any later version of PowerPoint. (Click here for help if you have problems with downloading and unzipping.) Modify these forms to suit your requirements, but please cite this article and the associated journal article in any publication arising from their use.
Here is a brief description of the forms:
Quantification of a behavior as complex as training is an exercise in simplification, which occurs at several stages. The most crucial simplification occurs when data are first recorded: if too much detail is sought, the athletes or the researcher will be overwhelmed; on the other hand, details lost at this stage may be important determinants of performance or health. Further simplification occurs at the stage of data analysis, when variables representing the raw training data are combined into one or more global measures of training to permit modeling of relationships between training and performance or health. Statistics should also be simplified and presented with as little jargon as possible, especially if the audience is athletes, coaches, or other lay people.
Statistical analysis of training data poses several challenges. Variables representing training duration or volume are usually not normally distributed, so they need to be transformed if they are the outcome variables in an analysis (Hopkins, 1998). Log transformation usually works well and has the bonus that outcomes can be represented as percent changes or percent differences in training. Rank transformation (resulting in non-parametric analysis) is a second-best choice. As discussed earlier, variables representing training intensity or quality can be expressed in absolute units or relative units.
Training affects the health and fitness of the athlete through duration and intensity, but combining these two variables into a single global measure of training is fraught with difficulty. The simplest and probably best approach is to multiply them together and add them up over all intensities. The resulting variable has the dimensions of work done or energy consumed in performing the exercise. It is sometimes known as a TRIMP (TRaining IMPulse). A problem with this variable is that training performed at a particular intensity for a particular duration produces the same TRIMP as training performed at twice the intensity for half the duration, yet training at the higher intensity usually has disproportionately greater effects on the body. Attempts to introduce a non-linear factor to make higher intensity training contribute more to the total TRIMP score should be avoided, because the value of the factor is arbitrary.
The two groups of sports professionals who make use of methods to quantify training are practitioners (athletes and coaches) and scientists. For practitioners, the main applications are to motivate the athlete, make training systematic, and prescribe training. Sport scientists are interested in the relationships between training and performance, or between training and various aspects of the health of the athlete.
Use by Sports Practitioners
Motivation to adhere to training regimes is likely to be enhanced by any interest shown in the athlete's training, but the high-tech appeal of physiological monitoring and video recording probably succeeds more in this respect than other methods. Diaries appear to be the best way to promote systemization of training behavior, through their ability to produce a continuous record of training; the process of reviewing the training data in a diary should also stimulate a critical approach to the purpose of duration, intensity and skill components of specific workouts and to the purpose of the periodized structure in the training program. Diaries are the most effective method for checking whether most aspects of a training prescription are being followed, provided the coach can be confident about the athlete's honesty or accuracy. Prescribed targets of training intensity for steady-state exercise can be set and checked with heart rate monitoring; lactate monitoring has also been promoted for this purpose, but it is probably not reliable or practical enough for the coach or athlete. [The reviewer of this article noted the lack of convincing evidence that training at a specified target heart rate or lactate concentration results in better performance than less regimented training, for example of higher or more variable intensity.]
Use by Sport Scientists
The research interests of sport scientists fall into two groups: performance and health. The majority of researchers in both groups have used questionnaires as the main method of quantifying training, especially for descriptive studies. Experimental studies, in which the effects of an imposed change in training have been investigated, have been conducted mainly over short periods of time and have used mainly real-time observation to verify compliance with the training program.
Past and present topics of interest in studies of training and performance have included the training behaviors of better performers, the effect of increasing the intensity of training, the effect of training or living at altitude on sea-level performance, and effect of a taper phase of training before a competition. Studies of the relationship between training and health of athletes have dealt with aspects of overtraining, injury, illness, wellness, immune function, psychological state, reproductive function and nutrition.
The methodology of training quantification needs more research. The following projects would provide useful publishable information: comparison of the effectiveness of different methods of prescribing intensity; development and validation of a questionnaire for assaying training in team sports; relationships between coaches' prescriptions and athletes' training behaviors; and surveys of the use and perceived effectiveness of different methods of quantification by coaches and athletes. In addition, all research projects that use a questionnaire or diary to investigate the effects of training on performance or health should address questions about the reliability and validity of the measures of training.
Outstanding research topics to which the appropriate methodologies could be applied in various sports include: optimization of periodization in relation to training phases other than the taper; detection of incipient overtraining; interaction of the effects of nutrition and training on performance; and reduction of rates of injury and illness without reduction of performance.
Allinger, T. (1998). Coaches learn to use video analysis. Sportscience News (July-August) http://sportsci.org/news/biomech/video/video.html.
Hopkins, W.G. (1998). A new view of statistics. Internet Society for Sport Science: http://sportsci.org/stats/.