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HARTMANN, U., and J. MESTER. Training and overtraining markers in selected sport events. Med. Sci. Sports Exerc., Vol. 32, No. 1, pp. 209–215, 2000.Varieties of symptoms are supposed to detect overtraining (OT). Besides the problems of diagnosis and analysis in elite athletes, a daily monitoring of training status takes place with measurement of the parameters serum urea (SU) and serum creatine kinase (CK); therefore, their meaningfulness will be examined, with special respect inter- and intra-individually.Data were obtained from determinations during training from athletes in rowing and athletes of international level.For 6981 SU determinations (male, N = 717; female, N = 285), a slightly asymmetric normal distribution was found (male, 80%, 5–7 mmol·L−1; female, 75%, 4–6 mmol·L−1). Values for women were approximately 1.5 mmol·L−1 lower. Individual variability was enormous; there seems little point in setting fixed value as 8.3 mmol·L−1 for men and 7.0 mmol·L−1 for women as a critical limit for OT. CK has also been measured and evaluated in sports as an essential parameter for determination of muscular stress. Frequency distributions of CK in 2790 samples (male, N = 497; female, N = 350) presented an asymmetric normal distribution with distinct trend toward higher values being evident for the range between 100 and 250 U·L−1. Conspicuously elevated values occurred in the ranges 250–350 U·L−1 and 1000–2000 U·L−1. Men’s maximal values were 3000 U·L−1 and 1150 U·L−1 for women. Individual variability was enormous. Athletes with chronically low CK exhibited mainly low variability; those with chronically higher values exhibited considerable variability.Establishment of both parameters should be useful to determine individual baselines from a large number of samples. Determinations should be made at least every 3 d in standardized conditions. If a large increase is observed in combination with reduced exercise tolerance after a phase of exertion (2–4 d), then the possibility of a catabolic/metabolic activity or insufficient exercise tolerance becomes much more likely.