Koutedakis, Y. (1995). Seasonal variation in fitness parameters in competitive athletes. Sports Medicine, 19, 373-392.

This review generalizes from all research. It is easy to find specific instances and even a minority of studies which contradict the generalizations proffered. However, given the exceptionally large bibliography of the article, the strength and directions of its conclusions are justifiable.

Specific Notations

Although there are great variations among sports, physical fitness is a composite which is principally dependent on the aerobic and anaerobic efficiency of muscle, on muscle speed and strength, and on body composition. (p. 374)

Anthropometric measures do not appear to be consistently sensitive to sport participation and therefore, are of limited usefulness in understanding the response to challenging exercise stimulation.

Aerobic fitness. Novice athletes or competitors with relatively low aerobic capacities, usually demonstrate noticeable fluctuations in aerobic fitness variables between seasons of training and non-participation.

When young athletes train seasonally (3-6 months of non-participation) fitness gains from training and participation are lost in inactive periods. However, when athletes spend an extensive amount of time training, particularly over 12-months, a resistance to losing certain VO2max determinants, such as muscle mitochondrial and capillary density, is evidenced when compared to those who train less. This supports the principle that the more one trains, the longer it takes to detrain and to lose at least some training adaptations. [A reference for this observation is: Coyle, E. F., Martin, W. H., Sinacore, D. R., et al. (1984). Time course of loss of adaptations after stopping prolonged intense endurance training. Journal of Applied Physiology, 57, 1857-64.]

Athletes with adequately developed aerobic capacities generally show no seasonal variations in respiratory parameters, despite the fact that performances very often continue to improve.

A tentative explanation for the observed lack of seasonal variation in respiratory parameters may be that athletes begin training at a level of fitness suitable for the structural and functional demands of their respective sports, and maintain rather than change their aerobic fitness over seasons. It is unclear whether the athletes had developed an efficient respiratory system after several years of practice, whether the training stimulus was not high enough to bring about measurable changes, or whether there was an inability in the testing methods to detect changes resulting from training and competition. (p. 379)

In sports where performance is principally determined by skill ("technical" sports), conditioning normally takes place during preparatory periods, aiming to bring competitors to their peak condition just before the competitive season. During that season, training concentrates on skills and tactics and aerobic fitness either remains stable or declines.

Athletes in physically demanding sports show a different response to that of technical athletes. In-season training and competition may result in either increased or unchanged maximal respiratory parameters. Reductions are rarely, if ever, found.

Aerobic fitness is only maintained or stimulated by activity. If that activity declines or ceases, then fitness will regress.

Anaerobic threshold. Anaerobic threshold (ANThreshold) may be defined as the work load just below which steady-state exercise can continue for a prolonged time. It is used extensively for predicting aerobic performance. ANThreshold adaptation is stimulated by a certain amount of work. Extra work above that level will not result in any further adaptation and may even be harmful.

After periods of detraining, whether intentional or unintentional (e.g., injury), aerobic fitness and the ANThreshold level are quickly regained in athletes who perform training for most of the year.

Anaerobic fitness. To assess aspects of anaerobic fitness, all-out cycle ergometer tests, standing broad jumps and vertical jumps are examples of evaluation tools commonly used. Components of anaerobic fitness show little seasonal variation in men and women of different competitive abilities. It is suspected that most tests currently used to evaluate anaerobic fitness do not appear to be sensitive enough to detect seasonal variations. More sophisticated tests are usually able to detect changes from untrained to moderately trained states but are not sensitive to changes in higher levels of fitness.

Muscle strength. With lower level athletes, off-season training that includes a considerable amount of strength training usually provokes an increase in muscular strength. However, when the competitive season commences and strength training is de-emphasized, there is usually a decrease in the off-season gains. Other training features, particularly technique and tactics, are given priority over strength and conditioning activities which, at least, partly detrain.

Even in elite competitors, the trend to fail to maintain the gains made in off-season strength work during the competitive season is evident. The duration and intensity of the off-season work and the change of mode of in-season training could account for this phenomenon.

If off-season gains in strength are not maintained in the competitive season, it is possible that the gains were excessive for the level required for satisfactory participation in in-season training and competitions. On the other hand, in many sports major championships are held mid-season, with competitors aiming to peak at that time. After them, training might be more relaxed (less stimulating) and so end-of-season testing may reflect this reduction in training intensity and could also account for declines.

Flexibility. Sport training and competition do not enhance muscle flexibility. Specific programs are required to produce increases in movement ranges that exceed those which occur naturally in a sport. Some sports, for example, gymnastics and wrestling, emphasize specific flexibility programs and their performers display greater than normal movement ranges. That greater-than-natural range could serve as an injury prevention measure as well as facilitating some extreme movements.

Cardiac parameters. Resting and exercise heart rates are generally not affected by seasonal training or detraining. This could be due to either of two reasons. First, there may be insufficient stimulation to alter cardiovascular fitness in most athletes and so serious questions should be raised about training practices. Second, the heart rate criterion may not be sensitive enough to detect seasonal changes in fitness and, therefore, may not be particularly useful as a training tool. Measurement procedures and timing of testing sessions may also account for some research inconsistencies.

Cardiac dimensions usually do not change in elite athletes but do in individuals who go from inactivity to regular serious activity. Improvements in fitness parameters, such as VO2max and respiratory factors, may occur with or without cardiac changes. Research evidence on this feature is not clear and is often limited.

Blood tests. Maximal lactate measurements have been introduced on the justification that during exercise to exhaustion, the majority of energy supply is provided by anaerobic glycolysis. Increases in blood lactate are assumed, among other things, to represent the capability of muscle to operate in a highly acidic medium. However, maximal lactate measurements give no information on lactate turnover, which may be higher in better trained individuals. That limits their utility as a fitness monitoring tool in sporting environments. Research includes varied results and because of the lack of control of possible causal variables in natural sport settings, a true understanding of why lactates do not change in some individuals and studies but do in others is obscured. This variable is probably best left for use in controlled research laboratories.

Hemoglobin (Hb) normally is measured to determine if there is a reduced concentration of Hb in the blood from physiological hypervolemia. Reduction in circulating Hb during training appears to be unfavorable for aerobic performance and resistance to fatigue. Inadequate diet, rather than seasonal exercise, may be the more likely cause of this decrease. Generally, in elite athletes, there is little seasonal change in Hb concentration due to exercise stress.

Children and adolescents. In children and adolescents, discriminating between the processes of conditioning and growth is a challenging task. Certain physiological changes often attributed to exercise are an inherent part of normal growth. For example, in pre-adolescent male swimmers, physiological changes occurred despite seasonal changes in training cycles to allow for competition and resting. In young runners significant increases in VO2max and running performance occurred despite the training stimulus being primarily anaerobic.

Changes in physiological variables in young performances are more likely to be caused by growth than training stimulation.

Implications. In elite competitors, anaerobic parameters, heart rates, subcutaneous fat, flexibility, and hemoglobin levels remain relatively unchanged through 12-month periods of training. Aerobic metabolism and muscular strength may demonstrate noticeable (mostly unfavorable) changes, and plasma hormonal levels normally follow changes in training intensities. What changes do occur could be the result of methodological problems in testing. Observed alterations may purely reflect incidental fatigue produced by a previous training session rather than a longer-term effect. As well, aspects of genetics, long-term fatigue, and the appropriateness of training are other possible explanations for measurement variations.

It is not known whether greater fitness gains attainable with longer off-season training programs can be successfully maintained over the duration of a competitive season. A tentative consensus would seem to be that specialized training (based mostly on technique and competition tactics) and competitions themselves are inadequate for fitness maintenance and/or improvements.

In novices and athletes at low competitive levels, a training season may lead to considerable functional improvements in the cardiorespiratory system, occasional increases in muscular strength, decreases in body fat, but no changes in flexibility. Exposure to training stimuli associated with definite periods of training and non-training mostly account for these fluctuations.

Changes similar to novices and seasonal participants are seen in children and adolescents although they are largely associated with normal patterns of growth and development rather than exercise stimulation. Response differences between males and females at all levels of participation have not been identified.

In any field testing of athletes, physiological changes which are observed cannot be reliably attributed to training effects. Growth, seasonality, and assessment designs are just as valid explanations for observed variations.

Measurement for measurement sake, convenience, and/or program justification, is particularly misleading since most physiological indices are affected by the state of fatigue or rest in an individual. This is a principal concern with taking physiological measures at select sports camps or non-major competitions when the entry status of athletes is neither known nor controlled.

The value of fitness measures for generating information that can be used to enhance coaching decisions is undermined by the content of this review. It would be desirable to be able to accurately report changes due to training through objective measures to validate training objectives. However, the diversity of sports, types of participation, and coaching programs, which, in turn, interact with the individual characteristics of each performer make inferences from common physiological measures particularly suspect. This concern is heightened even further with elite athletes.

A number of fitness tests are sensitive to changes from untrained to moderately trained states. However, it is incorrect to infer that those same tests will be valid for detecting changes from moderate or general fitness states to high levels of sport-specific fitness. Few tests, if any, are available for assessing maximum beneficial fitness.

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